WEBVTT 00:00:00.000 --> 00:00:01.476 align:middle line:90% [SQUEAKING] 00:00:01.476 --> 00:00:02.940 align:middle line:90% [RUSTLING] 00:00:02.940 --> 00:00:04.404 align:middle line:90% [CLICKING] 00:00:04.404 --> 00:00:16.132 align:middle line:90% 00:00:16.132 --> 00:00:17.840 align:middle line:84% JOHN SOUTHARD: So these are the variables 00:00:17.840 --> 00:00:20.440 align:middle line:84% you'd have to take into account if you're 00:00:20.440 --> 00:00:23.040 align:middle line:84% going to capture the reality of bed 00:00:23.040 --> 00:00:26.620 align:middle line:84% configurations and the usual flow depth, flow velocity, 00:00:26.620 --> 00:00:28.000 align:middle line:90% sediment size. 00:00:28.000 --> 00:00:29.940 align:middle line:90% The fluid density is important. 00:00:29.940 --> 00:00:32.119 align:middle line:84% The fluid viscosity is important. 00:00:32.119 --> 00:00:34.600 align:middle line:84% And then there's sediment density and gravity. 00:00:34.600 --> 00:00:36.960 align:middle line:84% Now, I have to make a few comments about it. 00:00:36.960 --> 00:00:39.200 align:middle line:90% The particles have weight. 00:00:39.200 --> 00:00:42.000 align:middle line:84% And that's a combination from the density and gravity 00:00:42.000 --> 00:00:43.520 align:middle line:90% that makes weight. 00:00:43.520 --> 00:00:47.480 align:middle line:84% But also, density, fluid density-- 00:00:47.480 --> 00:00:50.260 align:middle line:84% sediment density itself is important by itself. 00:00:50.260 --> 00:00:53.820 align:middle line:90% And I want to show you now-- 00:00:53.820 --> 00:00:57.040 align:middle line:90% let's see how lucky I am here. 00:00:57.040 --> 00:00:59.330 align:middle line:90% Yeah. 00:00:59.330 --> 00:01:01.290 align:middle line:90% They act together. 00:01:01.290 --> 00:01:05.550 align:middle line:84% And obviously, weight is important. 00:01:05.550 --> 00:01:08.290 align:middle line:84% That makes the sediment negatively buoyant. 00:01:08.290 --> 00:01:10.610 align:middle line:84% But particle density gives the particle 00:01:10.610 --> 00:01:12.370 align:middle line:90% inertia going through the fluid. 00:01:12.370 --> 00:01:15.090 align:middle line:84% So if you had a turbulent fluid, the particle 00:01:15.090 --> 00:01:19.333 align:middle line:84% tends to go by itself and not be affected by the turbulence. 00:01:19.333 --> 00:01:20.750 align:middle line:84% And here's the thought experiment. 00:01:20.750 --> 00:01:22.810 align:middle line:84% Did I tell you about thought experiments? 00:01:22.810 --> 00:01:26.490 align:middle line:90% I love thought experiments. 00:01:26.490 --> 00:01:30.010 align:middle line:84% Einstein loves thought experiments. 00:01:30.010 --> 00:01:32.130 align:middle line:84% His whole theory of relativity was based 00:01:32.130 --> 00:01:33.690 align:middle line:90% on some thought experiments. 00:01:33.690 --> 00:01:35.227 align:middle line:90% I saw Einstein once. 00:01:35.227 --> 00:01:36.310 align:middle line:90% What do you think of that? 00:01:36.310 --> 00:01:38.078 align:middle line:90% 1952, in Princeton. 00:01:38.078 --> 00:01:39.870 align:middle line:84% He was walking on a sidewalk near his home, 00:01:39.870 --> 00:01:42.453 align:middle line:84% and I was sitting there in the car, and I watched him walk by. 00:01:42.453 --> 00:01:44.610 align:middle line:90% 00:01:44.610 --> 00:01:46.800 align:middle line:84% So look, you're in a zero-gravity spaceship 00:01:46.800 --> 00:01:47.550 align:middle line:90% up there in space. 00:01:47.550 --> 00:01:50.250 align:middle line:84% And you have a big tank of water, closed-in tank of water. 00:01:50.250 --> 00:01:52.930 align:middle line:84% And you have a way of shooting a particle into the tank 00:01:52.930 --> 00:01:54.390 align:middle line:84% and watching what happens with it. 00:01:54.390 --> 00:01:56.890 align:middle line:84% Now, the particle has no weight at all. 00:01:56.890 --> 00:02:00.710 align:middle line:84% But the difference in density still 00:02:00.710 --> 00:02:02.610 align:middle line:84% is important because it has inertia. 00:02:02.610 --> 00:02:05.630 align:middle line:84% And if the flow in there were turbulent, 00:02:05.630 --> 00:02:08.650 align:middle line:84% and you shoot the particle, it would try to take its own path, 00:02:08.650 --> 00:02:12.656 align:middle line:90% not affected by the turbulence. 00:02:12.656 --> 00:02:13.647 align:middle line:90% And I showed you this. 00:02:13.647 --> 00:02:14.730 align:middle line:90% I think I showed you this. 00:02:14.730 --> 00:02:18.110 align:middle line:84% It's to remind you about what buoyancy is in the first place. 00:02:18.110 --> 00:02:23.230 align:middle line:84% And here's one of my all-time heroes, Archimedes. 00:02:23.230 --> 00:02:27.310 align:middle line:84% So rho s And g together account for the motion of the particle. 00:02:27.310 --> 00:02:30.590 align:middle line:84% And we don't need to worry about the weight per unit volume. 00:02:30.590 --> 00:02:33.832 align:middle line:84% Rho s and g take care of the weight per unit volume, 00:02:33.832 --> 00:02:35.290 align:middle line:84% so we don't need to worry about it. 00:02:35.290 --> 00:02:38.150 align:middle line:90% 00:02:38.150 --> 00:02:42.150 align:middle line:84% So what's most important for us are, 00:02:42.150 --> 00:02:45.070 align:middle line:84% I think, depth velocity and sediment size. 00:02:45.070 --> 00:02:47.910 align:middle line:84% And there are various ways of non-dimensionalizing. 00:02:47.910 --> 00:02:49.370 align:middle line:84% And this one, I think, is useful. 00:02:49.370 --> 00:02:53.150 align:middle line:84% This is different from the PowerPoint number three 00:02:53.150 --> 00:02:55.970 align:middle line:90% you had, different in some ways. 00:02:55.970 --> 00:02:59.160 align:middle line:90% But anyway, there it is. 00:02:59.160 --> 00:03:03.640 align:middle line:84% So we can use the three dimensionless variables, 00:03:03.640 --> 00:03:06.080 align:middle line:84% flow depth, flow velocity, and sediment size, 00:03:06.080 --> 00:03:07.743 align:middle line:90% nondimensionalized. 00:03:07.743 --> 00:03:09.160 align:middle line:84% But what I'm going to do-- and you 00:03:09.160 --> 00:03:11.560 align:middle line:84% can make a three-dimensional diagram out of it, 00:03:11.560 --> 00:03:13.995 align:middle line:84% section this way, section this way, section that way, 00:03:13.995 --> 00:03:15.620 align:middle line:84% and I'm going to show you some results. 00:03:15.620 --> 00:03:20.400 align:middle line:90% 00:03:20.400 --> 00:03:21.780 align:middle line:90% It's non-dimensional. 00:03:21.780 --> 00:03:24.560 align:middle line:84% But the graphs that I'm showing you have-- 00:03:24.560 --> 00:03:29.840 align:middle line:84% these variables are normalized to 10-degree water temperature 00:03:29.840 --> 00:03:31.740 align:middle line:84% so that it all comes out nicely on the graph. 00:03:31.740 --> 00:03:35.400 align:middle line:84% And I'm going to make some more comments about that soon. 00:03:35.400 --> 00:03:36.920 align:middle line:90% So here's the sections. 00:03:36.920 --> 00:03:41.440 align:middle line:84% All the diagrams are normalized to 10 degree. 00:03:41.440 --> 00:03:43.260 align:middle line:84% I don't expect you to see a lot of this. 00:03:43.260 --> 00:03:48.120 align:middle line:84% But I'm going to show you the next slide in more detail. 00:03:48.120 --> 00:03:53.440 align:middle line:90% This is a flow depth versus-- 00:03:53.440 --> 00:03:58.190 align:middle line:84% so what you see is for low velocities, there's no movement. 00:03:58.190 --> 00:03:59.310 align:middle line:90% Then you have ripples. 00:03:59.310 --> 00:04:00.630 align:middle line:90% Then you have dunes. 00:04:00.630 --> 00:04:02.170 align:middle line:90% Then you have upper plane bed. 00:04:02.170 --> 00:04:05.390 align:middle line:84% But these lines down here are for equal Froude number, 00:04:05.390 --> 00:04:06.770 align:middle line:90% Froude number about 1. 00:04:06.770 --> 00:04:09.610 align:middle line:84% And beyond that, you get anti-dunes. 00:04:09.610 --> 00:04:11.810 align:middle line:84% And if you made dunes way down here somewhere, 00:04:11.810 --> 00:04:14.490 align:middle line:84% you'd find that the dunes and the anti-dunes 00:04:14.490 --> 00:04:16.490 align:middle line:84% would interact with each other somehow. 00:04:16.490 --> 00:04:17.990 align:middle line:84% And I've never done that in the lab. 00:04:17.990 --> 00:04:19.698 align:middle line:84% I can't tell you what it would look like. 00:04:19.698 --> 00:04:23.170 align:middle line:90% 00:04:23.170 --> 00:04:25.730 align:middle line:84% This is one of my favorite slides. 00:04:25.730 --> 00:04:28.650 align:middle line:84% This is another section, U versus-- 00:04:28.650 --> 00:04:31.450 align:middle line:90% velocity versus sediment size. 00:04:31.450 --> 00:04:35.710 align:middle line:84% This is for a flow depth of about 0.25 to 0.4 meters, 00:04:35.710 --> 00:04:36.990 align:middle line:90% so a lot of data. 00:04:36.990 --> 00:04:39.810 align:middle line:84% Almost all these data come from the laboratory, 00:04:39.810 --> 00:04:42.450 align:middle line:84% my laboratory, a lot of other people's laboratories. 00:04:42.450 --> 00:04:47.090 align:middle line:84% And it plots very nicely, interestingly, I think. 00:04:47.090 --> 00:04:50.170 align:middle line:84% For fine sediments, you find ripples, 00:04:50.170 --> 00:04:52.870 align:middle line:84% and then they change to upper plane bed at a certain point. 00:04:52.870 --> 00:04:55.830 align:middle line:84% I told you that already, I guess. 00:04:55.830 --> 00:04:59.550 align:middle line:84% For another range of sediment sizes about in here, 00:04:59.550 --> 00:05:02.570 align:middle line:84% ripples go into dunes, and the dunes go into plane bed. 00:05:02.570 --> 00:05:05.270 align:middle line:90% 00:05:05.270 --> 00:05:09.687 align:middle line:84% But beyond about half millimeter, 00:05:09.687 --> 00:05:10.770 align:middle line:90% there are no more ripples. 00:05:10.770 --> 00:05:12.250 align:middle line:90% Ripples don't form, only dunes. 00:05:12.250 --> 00:05:15.590 align:middle line:84% As soon as you go from no motion, you develop dunes. 00:05:15.590 --> 00:05:17.850 align:middle line:84% And the anti-dunes would be way up in here somewhere. 00:05:17.850 --> 00:05:20.070 align:middle line:84% This is Froude number 1 right here. 00:05:20.070 --> 00:05:21.310 align:middle line:90% Does that make sense to you? 00:05:21.310 --> 00:05:26.050 align:middle line:84% And I think I have a cartoon of this in your notes, 00:05:26.050 --> 00:05:28.070 align:middle line:90% which shows this. 00:05:28.070 --> 00:05:30.870 align:middle line:90% And let me go back here. 00:05:30.870 --> 00:05:34.550 align:middle line:84% What I like about this is you can fit a curve, a very natural, 00:05:34.550 --> 00:05:36.970 align:middle line:90% normal curve with no scatter. 00:05:36.970 --> 00:05:40.050 align:middle line:84% It really works, which means we're doing something right. 00:05:40.050 --> 00:05:43.710 align:middle line:90% 00:05:43.710 --> 00:05:45.220 align:middle line:84% I have a colleague named Dave Rubin. 00:05:45.220 --> 00:05:46.970 align:middle line:84% We've been together for a long, long time. 00:05:46.970 --> 00:05:48.890 align:middle line:90% And he picked up on this. 00:05:48.890 --> 00:05:54.140 align:middle line:84% And he and Dave McCulloch made-- this is a little complicated. 00:05:54.140 --> 00:05:56.640 align:middle line:84% But this is the three-dimensional graph 00:05:56.640 --> 00:05:58.160 align:middle line:90% that I just told you about. 00:05:58.160 --> 00:06:03.160 align:middle line:84% But it extends up to a considerable depth. 00:06:03.160 --> 00:06:05.320 align:middle line:90% And you get stuff out in here. 00:06:05.320 --> 00:06:07.440 align:middle line:84% These are sections through that graph. 00:06:07.440 --> 00:06:12.920 align:middle line:84% And you have to imagine volumes of existence fields. 00:06:12.920 --> 00:06:16.720 align:middle line:84% And as far as I know, nobody's improved 00:06:16.720 --> 00:06:18.760 align:middle line:84% upon that, which seems strange because it's 00:06:18.760 --> 00:06:22.120 align:middle line:84% really important to think about greater flow depths, not just 00:06:22.120 --> 00:06:25.460 align:middle line:84% the typical flow depth like this in laboratory channels. 00:06:25.460 --> 00:06:27.480 align:middle line:84% It's seldom greater than about a meter 00:06:27.480 --> 00:06:30.400 align:middle line:84% because you have to have an enormous, enormous channel 00:06:30.400 --> 00:06:34.940 align:middle line:90% to make different things. 00:06:34.940 --> 00:06:40.680 align:middle line:84% So now, we're limiting ourselves for water on Earth, gravity, 00:06:40.680 --> 00:06:44.800 align:middle line:84% and sediment particles, quartz density, sediment density, 00:06:44.800 --> 00:06:46.920 align:middle line:90% and water. 00:06:46.920 --> 00:06:52.100 align:middle line:84% But you can easily adjust this for different gravity. 00:06:52.100 --> 00:06:55.760 align:middle line:84% And I'll make a few comments pretty soon about Mars. 00:06:55.760 --> 00:06:58.180 align:middle line:84% But there are zillions of planets out there 00:06:58.180 --> 00:07:02.660 align:middle line:84% in the universe that would have flowing liquids, 00:07:02.660 --> 00:07:05.148 align:middle line:84% moving sediment particles under some gravity. 00:07:05.148 --> 00:07:06.440 align:middle line:90% And there are some constraints. 00:07:06.440 --> 00:07:09.540 align:middle line:84% There aren't too many liquids that have different densities 00:07:09.540 --> 00:07:10.880 align:middle line:90% and viscosities. 00:07:10.880 --> 00:07:12.620 align:middle line:84% You can use motor oil and honey, I 00:07:12.620 --> 00:07:15.060 align:middle line:84% suppose, to have higher viscosities. 00:07:15.060 --> 00:07:18.500 align:middle line:84% But condensed matter liquids don't have 00:07:18.500 --> 00:07:19.840 align:middle line:90% a great range of densities. 00:07:19.840 --> 00:07:22.380 align:middle line:84% But just keep in mind that this is just one little thing 00:07:22.380 --> 00:07:24.860 align:middle line:84% on Earth, and we have a wide range in the universe 00:07:24.860 --> 00:07:27.780 align:middle line:84% that we're not going to know anything about. 00:07:27.780 --> 00:07:29.372 align:middle line:90% Oh, and here's an issue. 00:07:29.372 --> 00:07:31.580 align:middle line:84% I don't know whether you've been thinking about this. 00:07:31.580 --> 00:07:34.105 align:middle line:84% It's the boundary shear stress that moves the sediment. 00:07:34.105 --> 00:07:35.980 align:middle line:84% So why don't we use the boundary shear stress 00:07:35.980 --> 00:07:39.980 align:middle line:84% on that graph instead of depth and velocity? 00:07:39.980 --> 00:07:42.860 align:middle line:90% But there's a problem here. 00:07:42.860 --> 00:07:47.400 align:middle line:84% Now, this is an old, old, old slide that I made in 1975. 00:07:47.400 --> 00:07:51.350 align:middle line:84% And I was calling it flatbed instead of upper plane bed. 00:07:51.350 --> 00:07:55.810 align:middle line:84% And this is a graph of bed shear stress versus mean velocity. 00:07:55.810 --> 00:07:58.318 align:middle line:84% And it doesn't just go up, monotonically upward. 00:07:58.318 --> 00:07:59.610 align:middle line:90% There's that little bump there. 00:07:59.610 --> 00:08:02.790 align:middle line:84% And the next slide explains it more. 00:08:02.790 --> 00:08:05.672 align:middle line:84% So this is the boundary shear stress versus velocity. 00:08:05.672 --> 00:08:07.130 align:middle line:84% And here's that curve I showed you. 00:08:07.130 --> 00:08:09.870 align:middle line:84% And there's a range of boundary shear stresses 00:08:09.870 --> 00:08:14.212 align:middle line:84% for which you can have 1, 2, 3 different flow velocities. 00:08:14.212 --> 00:08:15.170 align:middle line:90% Now, why would that be? 00:08:15.170 --> 00:08:17.710 align:middle line:84% Can you think about why that would be? 00:08:17.710 --> 00:08:20.150 align:middle line:84% Strain your brain a little bit here. 00:08:20.150 --> 00:08:23.650 align:middle line:84% I don't get any responses, so I may go on ahead. 00:08:23.650 --> 00:08:27.830 align:middle line:84% So as you increase the velocity over rugged bed forms, dunes, 00:08:27.830 --> 00:08:30.170 align:middle line:84% and ripples, the boundary shear stress, 00:08:30.170 --> 00:08:33.110 align:middle line:84% the total boundary sheer stress is high because of all that form 00:08:33.110 --> 00:08:33.610 align:middle line:90% drag. 00:08:33.610 --> 00:08:35.070 align:middle line:90% Remember form drag? 00:08:35.070 --> 00:08:37.770 align:middle line:84% But then the dunes wash out to plane bed. 00:08:37.770 --> 00:08:41.030 align:middle line:84% And all of a sudden, there's no form drag, only skin friction. 00:08:41.030 --> 00:08:44.290 align:middle line:84% So you'd expect to have overlap in the graphs. 00:08:44.290 --> 00:08:49.160 align:middle line:90% 00:08:49.160 --> 00:08:50.880 align:middle line:90% This is just to glance at. 00:08:50.880 --> 00:08:52.540 align:middle line:90% And there's a cartoon of it. 00:08:52.540 --> 00:08:54.760 align:middle line:84% There's an area, a couple of areas in here, 00:08:54.760 --> 00:08:57.360 align:middle line:84% for which there is overlap of data. 00:08:57.360 --> 00:08:59.320 align:middle line:90% It gets really messy in here. 00:08:59.320 --> 00:09:01.680 align:middle line:84% And that's just because we're dealing 00:09:01.680 --> 00:09:10.080 align:middle line:84% with a non-monotonically increasing value of the flow 00:09:10.080 --> 00:09:12.280 align:middle line:90% stress, of the stress. 00:09:12.280 --> 00:09:13.578 align:middle line:90% And there it is. 00:09:13.578 --> 00:09:14.620 align:middle line:90% You have to live with it. 00:09:14.620 --> 00:09:17.280 align:middle line:90% 00:09:17.280 --> 00:09:18.960 align:middle line:90% So do you get around it? 00:09:18.960 --> 00:09:19.640 align:middle line:90% So when? 00:09:19.640 --> 00:09:21.440 align:middle line:84% AUDIENCE: From the three-dimensional graph 00:09:21.440 --> 00:09:25.840 align:middle line:84% that you showed, are those just for subaqueous dunes? 00:09:25.840 --> 00:09:27.760 align:middle line:84% Or are they also applied to eolian? 00:09:27.760 --> 00:09:29.960 align:middle line:84% JOHN SOUTHARD: They're for water-- 00:09:29.960 --> 00:09:33.220 align:middle line:84% well, water or they would be good for any other liquid. 00:09:33.220 --> 00:09:35.020 align:middle line:90% But let me point this out. 00:09:35.020 --> 00:09:36.220 align:middle line:90% I forgot to point it out. 00:09:36.220 --> 00:09:38.520 align:middle line:84% These graphs are for a given ratio 00:09:38.520 --> 00:09:41.200 align:middle line:84% of Rho s over Rho, density ratio. 00:09:41.200 --> 00:09:43.300 align:middle line:84% That was one of the dimensionless variables. 00:09:43.300 --> 00:09:49.900 align:middle line:84% There were three, velocity, flow velocity, and water depth 00:09:49.900 --> 00:09:50.720 align:middle line:90% and sediment size. 00:09:50.720 --> 00:09:51.720 align:middle line:90% But there's another one. 00:09:51.720 --> 00:09:54.740 align:middle line:84% This is all for that density ratio, quartz sand and water, 00:09:54.740 --> 00:09:56.780 align:middle line:90% for example. 00:09:56.780 --> 00:09:59.423 align:middle line:84% So you have a whole different diagram 00:09:59.423 --> 00:10:01.340 align:middle line:84% with whole different existence fields, similar 00:10:01.340 --> 00:10:05.860 align:middle line:84% but not the same, if you have a different density ratio. 00:10:05.860 --> 00:10:09.280 align:middle line:84% Now, we made some experiments with tungsten grains. 00:10:09.280 --> 00:10:13.260 align:middle line:84% We bought a ton of tungsten particles. 00:10:13.260 --> 00:10:16.820 align:middle line:84% Tungsten has density almost as high as gold. 00:10:16.820 --> 00:10:19.540 align:middle line:90% And we made bed forms. 00:10:19.540 --> 00:10:21.620 align:middle line:84% This is a project I did in South Africa 00:10:21.620 --> 00:10:23.740 align:middle line:84% with some colleagues in South Africa. 00:10:23.740 --> 00:10:25.860 align:middle line:84% I don't have a copy of the publication. 00:10:25.860 --> 00:10:28.400 align:middle line:84% If I had, I would have tried to put something in here. 00:10:28.400 --> 00:10:32.920 align:middle line:84% But anyway, that's the way you could do it, 00:10:32.920 --> 00:10:36.980 align:middle line:84% is to somehow partition the drag so that you look only 00:10:36.980 --> 00:10:38.680 align:middle line:90% at the skin friction part. 00:10:38.680 --> 00:10:40.860 align:middle line:84% And there are various techniques that 00:10:40.860 --> 00:10:43.750 align:middle line:84% have been developed for drag partitioning, and none of them 00:10:43.750 --> 00:10:44.530 align:middle line:90% works perfectly. 00:10:44.530 --> 00:10:45.830 align:middle line:90% Some of them work OK. 00:10:45.830 --> 00:10:48.492 align:middle line:84% But if you didn't do that, if you didn't do that, 00:10:48.492 --> 00:10:50.450 align:middle line:84% then you can't use total boundary shear stress. 00:10:50.450 --> 00:10:54.193 align:middle line:84% It's just a point that you need to know about. 00:10:54.193 --> 00:10:55.610 align:middle line:84% This has probably occurred to you. 00:10:55.610 --> 00:10:56.943 align:middle line:90% Are ripples and dunes different? 00:10:56.943 --> 00:10:58.247 align:middle line:90% Well, obviously they are. 00:10:58.247 --> 00:10:59.330 align:middle line:90% They're different in size. 00:10:59.330 --> 00:11:00.580 align:middle line:90% They're different in behavior. 00:11:00.580 --> 00:11:02.390 align:middle line:84% And they're different in origin as well. 00:11:02.390 --> 00:11:08.990 align:middle line:84% And there's something called a spectral gap. 00:11:08.990 --> 00:11:11.910 align:middle line:84% Current ripples in water on Earth 00:11:11.910 --> 00:11:14.270 align:middle line:84% are seldom bigger than about a decimeter. 00:11:14.270 --> 00:11:19.190 align:middle line:84% Dunes, however, are seldom less than about a half meter, 00:11:19.190 --> 00:11:20.790 align:middle line:90% even in shallow flows. 00:11:20.790 --> 00:11:26.490 align:middle line:84% So there's a gap, a spectral gap, in sizes there. 00:11:26.490 --> 00:11:30.250 align:middle line:84% Ripple spacing is almost independent of flow depth. 00:11:30.250 --> 00:11:32.510 align:middle line:84% You can have flows that are half meter deep, 00:11:32.510 --> 00:11:33.530 align:middle line:90% and you make ripples. 00:11:33.530 --> 00:11:34.910 align:middle line:84% You can have flows that are 10 meters deep, 00:11:34.910 --> 00:11:36.618 align:middle line:84% and you have the same ripples down there, 00:11:36.618 --> 00:11:38.750 align:middle line:84% if you have the same near bed flow velocity. 00:11:38.750 --> 00:11:40.790 align:middle line:84% Dunes, on the other hand, the dune spacing 00:11:40.790 --> 00:11:42.520 align:middle line:84% goes as the water depth by something 00:11:42.520 --> 00:11:44.200 align:middle line:90% like a factor of 5 to 10. 00:11:44.200 --> 00:11:46.640 align:middle line:84% So they really do change with water depth 00:11:46.640 --> 00:11:48.680 align:middle line:84% considerably, which is good for interpretation 00:11:48.680 --> 00:11:53.600 align:middle line:84% because if you can back out dune size from your outcrop, 00:11:53.600 --> 00:11:57.300 align:middle line:84% then you'd have something to say about the water depth. 00:11:57.300 --> 00:12:00.640 align:middle line:90% 00:12:00.640 --> 00:12:02.390 align:middle line:84% This is something I'd like to address. 00:12:02.390 --> 00:12:04.140 align:middle line:84% And I've been thinking about it for years. 00:12:04.140 --> 00:12:07.320 align:middle line:84% There have been various papers written by various people 00:12:07.320 --> 00:12:14.440 align:middle line:84% on making stability analyses to explain the dynamics of ripples 00:12:14.440 --> 00:12:15.600 align:middle line:90% and dunes. 00:12:15.600 --> 00:12:19.580 align:middle line:84% You start with a planar bed, and you have a flow over it, 00:12:19.580 --> 00:12:21.400 align:middle line:84% and you make a little disturbance. 00:12:21.400 --> 00:12:24.700 align:middle line:84% And sometimes that disturbance generates bedforms. 00:12:24.700 --> 00:12:26.160 align:middle line:84% And you saw that when I was talking 00:12:26.160 --> 00:12:30.640 align:middle line:84% about the incipient ripples earlier, last time. 00:12:30.640 --> 00:12:34.780 align:middle line:84% But sometimes it gets washed out again, and it's unstable. 00:12:34.780 --> 00:12:38.760 align:middle line:84% And so you have to do that kind of thinking 00:12:38.760 --> 00:12:41.400 align:middle line:84% to try to account for why there are ripples in the first place 00:12:41.400 --> 00:12:42.600 align:middle line:84% and why there are dunes in the first place. 00:12:42.600 --> 00:12:44.000 align:middle line:90% And I'm not addressing that. 00:12:44.000 --> 00:12:46.780 align:middle line:84% But you should be aware that's a problem. 00:12:46.780 --> 00:12:47.477 align:middle line:90% How about Mars? 00:12:47.477 --> 00:12:49.060 align:middle line:84% I'm going to come back to Mars because 00:12:49.060 --> 00:12:51.940 align:middle line:84% these planetary sedimentologists have 00:12:51.940 --> 00:12:53.700 align:middle line:90% to worry about things on Mars. 00:12:53.700 --> 00:12:58.660 align:middle line:84% And so you could redo this diagram just the way 00:12:58.660 --> 00:13:02.500 align:middle line:84% it was, but plug in different gravity, which you can do. 00:13:02.500 --> 00:13:05.620 align:middle line:84% And here are the results that I figured out a long time ago. 00:13:05.620 --> 00:13:07.440 align:middle line:84% From one kind of bed form to another 00:13:07.440 --> 00:13:12.460 align:middle line:84% takes place at lower velocity on Mars by a factor of about 0.74. 00:13:12.460 --> 00:13:19.540 align:middle line:84% And if you look at the change from one kind of bed form 00:13:19.540 --> 00:13:24.660 align:middle line:84% to another takes place larger by a factor of about 1.36. 00:13:24.660 --> 00:13:28.180 align:middle line:84% That's, I think, my almost total contribution 00:13:28.180 --> 00:13:31.618 align:middle line:90% to planetary sedimentology. 00:13:31.618 --> 00:13:33.660 align:middle line:84% No, there's going to be another one coming along, 00:13:33.660 --> 00:13:36.300 align:middle line:90% too, that I'll mention later. 00:13:36.300 --> 00:13:39.210 align:middle line:84% So now we're on to oscillatory flow bed forms, 00:13:39.210 --> 00:13:40.750 align:middle line:90% which are just as important. 00:13:40.750 --> 00:13:43.790 align:middle line:84% How do you make oscillatory bed forms in the laboratory? 00:13:43.790 --> 00:13:45.390 align:middle line:90% We've done this. 00:13:45.390 --> 00:13:48.330 align:middle line:84% It's a tank, a horizontal tank, sediment bed. 00:13:48.330 --> 00:13:51.410 align:middle line:84% And you have a wave generator, either paddle back and forth, 00:13:51.410 --> 00:13:53.610 align:middle line:84% or you could have a piston going up and down, 00:13:53.610 --> 00:13:55.930 align:middle line:84% and the waves go down to the other end. 00:13:55.930 --> 00:13:57.878 align:middle line:84% And what you have to do is put in a total wave 00:13:57.878 --> 00:13:59.670 align:middle line:84% absorber at the other end, so you don't get 00:13:59.670 --> 00:14:02.003 align:middle line:84% reflected waves, because then you'd have standing waves. 00:14:02.003 --> 00:14:03.670 align:middle line:90% And we don't want that. 00:14:03.670 --> 00:14:04.770 align:middle line:90% But you can also do this. 00:14:04.770 --> 00:14:06.670 align:middle line:84% And we did this big time in building 00:14:06.670 --> 00:14:09.370 align:middle line:84% N9, back about 20 years ago with Bill Arnold 00:14:09.370 --> 00:14:10.370 align:middle line:90% and one of his students. 00:14:10.370 --> 00:14:12.162 align:middle line:84% You can have a liquid pendulum in which you 00:14:12.162 --> 00:14:20.990 align:middle line:84% take a tank with reservoirs, and you move the level of water 00:14:20.990 --> 00:14:23.810 align:middle line:84% in the reservoirs back and forth with some sort of piston. 00:14:23.810 --> 00:14:24.450 align:middle line:90% And it works. 00:14:24.450 --> 00:14:26.630 align:middle line:84% And you can make nice bed forms that way. 00:14:26.630 --> 00:14:28.030 align:middle line:90% This looks very clever. 00:14:28.030 --> 00:14:31.530 align:middle line:84% You have still water and a thing that moves back, 00:14:31.530 --> 00:14:34.050 align:middle line:84% oscillates back and forth, and you can make ripples with it. 00:14:34.050 --> 00:14:36.170 align:middle line:84% But the ripples aren't the same as the others. 00:14:36.170 --> 00:14:37.892 align:middle line:84% So people have written papers about that. 00:14:37.892 --> 00:14:39.600 align:middle line:84% They have to admit that it doesn't really 00:14:39.600 --> 00:14:42.000 align:middle line:90% work for natural environments. 00:14:42.000 --> 00:14:44.060 align:middle line:90% But they've done it. 00:14:44.060 --> 00:14:45.700 align:middle line:90% So this is the first order here. 00:14:45.700 --> 00:14:50.020 align:middle line:84% This is the big message, if you want to look at it that way. 00:14:50.020 --> 00:14:51.080 align:middle line:90% Details later. 00:14:51.080 --> 00:14:54.880 align:middle line:84% So as you keep increasing the oscillatory velocity-- 00:14:54.880 --> 00:14:56.400 align:middle line:84% there's no current involved here. 00:14:56.400 --> 00:14:59.040 align:middle line:84% You have straight to two-dimensional ripples, 00:14:59.040 --> 00:15:00.500 align:middle line:84% regular straight two-dimensional. 00:15:00.500 --> 00:15:02.360 align:middle line:84% And then at a certain point-- and I'm 00:15:02.360 --> 00:15:06.520 align:middle line:84% going to get into this more in a couple of slides. 00:15:06.520 --> 00:15:09.102 align:middle line:84% They're small, but they get three-dimensional. 00:15:09.102 --> 00:15:10.560 align:middle line:84% And then they get larger and larger 00:15:10.560 --> 00:15:11.768 align:middle line:90% into large three-dimensional. 00:15:11.768 --> 00:15:13.680 align:middle line:84% And finally, at the highest velocities, 00:15:13.680 --> 00:15:15.060 align:middle line:90% you get a plane bed again. 00:15:15.060 --> 00:15:17.580 align:middle line:84% That's the basic message here, what goes on. 00:15:17.580 --> 00:15:19.440 align:middle line:90% But we'll try to go beyond that. 00:15:19.440 --> 00:15:20.820 align:middle line:90% So here we go again. 00:15:20.820 --> 00:15:23.000 align:middle line:84% We're going to make another dimensional analysis. 00:15:23.000 --> 00:15:28.140 align:middle line:84% And so just-- assuming that you're doing it. 00:15:28.140 --> 00:15:33.920 align:middle line:84% And so we're going to use either oscillation period 00:15:33.920 --> 00:15:38.740 align:middle line:84% T, orbital diameter d0, or maximum velocity, 00:15:38.740 --> 00:15:40.300 align:middle line:90% orbital velocity, Um. 00:15:40.300 --> 00:15:42.980 align:middle line:84% And it turns out-- and I'm going to show it in the next slide-- 00:15:42.980 --> 00:15:45.020 align:middle line:84% those three are not independent of one another. 00:15:45.020 --> 00:15:47.980 align:middle line:84% There's a relationship, Um T equals pi d0. 00:15:47.980 --> 00:15:50.720 align:middle line:84% So only two of them can be chosen independently. 00:15:50.720 --> 00:15:55.140 align:middle line:84% And what we're going to do is choose period and velocity 00:15:55.140 --> 00:15:55.640 align:middle line:90% for that. 00:15:55.640 --> 00:15:58.300 align:middle line:84% But I just want you to be aware that those are the only two 00:15:58.300 --> 00:16:01.980 align:middle line:84% you need to account for what waves do on the bottom. 00:16:01.980 --> 00:16:04.760 align:middle line:84% And so you get another three-dimensional graph. 00:16:04.760 --> 00:16:07.500 align:middle line:84% I keep giving you these three-dimensional graphs, 00:16:07.500 --> 00:16:10.620 align:middle line:84% oscillatory velocity Um, oscillation period T, 00:16:10.620 --> 00:16:12.260 align:middle line:90% sediment size d. 00:16:12.260 --> 00:16:14.217 align:middle line:84% And this is what I mentioned here, 00:16:14.217 --> 00:16:16.800 align:middle line:84% that you have this relationship, which I'm not proving to you. 00:16:16.800 --> 00:16:19.900 align:middle line:90% But there it is. 00:16:19.900 --> 00:16:21.360 align:middle line:84% Now, you can section various ways. 00:16:21.360 --> 00:16:22.818 align:middle line:84% There's three ways you can section. 00:16:22.818 --> 00:16:27.860 align:middle line:84% And it gets a little complicated. 00:16:27.860 --> 00:16:34.630 align:middle line:84% But I have to point out that in a laboratory tank 00:16:34.630 --> 00:16:38.150 align:middle line:90% or channel with waves-- 00:16:38.150 --> 00:16:38.650 align:middle line:90% I'm sorry. 00:16:38.650 --> 00:16:39.442 align:middle line:90% Let me start again. 00:16:39.442 --> 00:16:42.590 align:middle line:84% If you had an oscillatory flow duct, like that liquid pendulum 00:16:42.590 --> 00:16:45.590 align:middle line:84% thing, you're at liberty to specify 00:16:45.590 --> 00:16:48.110 align:middle line:84% any orbital diameter, any orbital velocity, 00:16:48.110 --> 00:16:49.370 align:middle line:90% any wave period you want. 00:16:49.370 --> 00:16:52.870 align:middle line:84% But real waves don't work that way because the way waves work, 00:16:52.870 --> 00:16:54.450 align:middle line:90% there's a certain range. 00:16:54.450 --> 00:16:56.950 align:middle line:84% There's only a certain range of those variables 00:16:56.950 --> 00:17:00.150 align:middle line:84% that are actually produced at the bed 00:17:00.150 --> 00:17:02.830 align:middle line:90% under shoaling water waves. 00:17:02.830 --> 00:17:07.510 align:middle line:84% So if you think of that three-dimensional graph, 00:17:07.510 --> 00:17:11.990 align:middle line:84% there's some volume in there, which is realistic for waves. 00:17:11.990 --> 00:17:15.150 align:middle line:84% And the other areas are not realistic for waves, 00:17:15.150 --> 00:17:18.270 align:middle line:84% even though you can make them in a laboratory. 00:17:18.270 --> 00:17:20.390 align:middle line:84% That's how we have to live with that. 00:17:20.390 --> 00:17:23.750 align:middle line:84% But in this permissible volume, if I can call it 00:17:23.750 --> 00:17:26.050 align:middle line:84% that, there are existence fields, 00:17:26.050 --> 00:17:27.690 align:middle line:84% three-dimensional existence fields, 00:17:27.690 --> 00:17:30.203 align:middle line:84% same way there was for unidirectional flow. 00:17:30.203 --> 00:17:31.370 align:middle line:90% Does that make sense to you? 00:17:31.370 --> 00:17:34.160 align:middle line:84% You can picture in the-- there's this volume in there 00:17:34.160 --> 00:17:36.340 align:middle line:84% that things could be happening under waves. 00:17:36.340 --> 00:17:39.440 align:middle line:84% And there's various kinds of small 00:17:39.440 --> 00:17:43.200 align:middle line:84% versus large, straight crested versus three-dimensional are 00:17:43.200 --> 00:17:44.500 align:middle line:90% going to be in there somewhere. 00:17:44.500 --> 00:17:47.760 align:middle line:90% 00:17:47.760 --> 00:17:49.240 align:middle line:84% Every ripple you can possibly make 00:17:49.240 --> 00:17:50.900 align:middle line:84% would be in this three-dimensional diagram. 00:17:50.900 --> 00:17:52.317 align:middle line:84% But the trouble is not every point 00:17:52.317 --> 00:17:55.180 align:middle line:84% in the diagram is occupied by a bed configuration. 00:17:55.180 --> 00:17:58.520 align:middle line:84% That's what I just pointed out to you. 00:17:58.520 --> 00:18:00.220 align:middle line:84% So how do you get data on these things? 00:18:00.220 --> 00:18:04.840 align:middle line:84% Well, experimental tanks and channels have been done often. 00:18:04.840 --> 00:18:06.500 align:middle line:90% There's a size limit. 00:18:06.500 --> 00:18:09.800 align:middle line:84% You can build an enormous, enormous wave channel 00:18:09.800 --> 00:18:11.120 align:middle line:90% and make real waves. 00:18:11.120 --> 00:18:19.160 align:middle line:84% And they had one at the US Army Corps of Engineers Waterways 00:18:19.160 --> 00:18:20.180 align:middle line:90% Experiment Station. 00:18:20.180 --> 00:18:22.500 align:middle line:84% They had one of these enormous tanks. 00:18:22.500 --> 00:18:24.080 align:middle line:90% But you're still limited. 00:18:24.080 --> 00:18:26.860 align:middle line:84% Out in nature, there are plenty of 10 to 15 second wave periods. 00:18:26.860 --> 00:18:28.860 align:middle line:84% And you can't make one of those in a laboratory. 00:18:28.860 --> 00:18:30.720 align:middle line:90% So there's a definite limit. 00:18:30.720 --> 00:18:32.720 align:middle line:84% Or you can make observations of shallow ocean. 00:18:32.720 --> 00:18:35.360 align:middle line:84% And there's been studies to do that. 00:18:35.360 --> 00:18:39.040 align:middle line:84% But it's tough because it has to endure storms. 00:18:39.040 --> 00:18:40.588 align:middle line:84% You have to record the stuff somehow. 00:18:40.588 --> 00:18:42.880 align:middle line:84% You have to wait a long time until a storm comes along. 00:18:42.880 --> 00:18:45.940 align:middle line:84% But people try to do it, and it's a valuable thing to do. 00:18:45.940 --> 00:18:48.700 align:middle line:84% So this is a graph that I took from my notes. 00:18:48.700 --> 00:18:53.300 align:middle line:84% It's just one section, a velocity period section, 00:18:53.300 --> 00:18:59.740 align:middle line:84% for sand size about point 0.01, 0.02 millimeters of fine sand. 00:18:59.740 --> 00:19:02.120 align:middle line:84% And let me tell you some things about this. 00:19:02.120 --> 00:19:05.340 align:middle line:84% These downward sloping lines are contours 00:19:05.340 --> 00:19:09.540 align:middle line:84% of equal d0, which has to be in there because you've 00:19:09.540 --> 00:19:12.820 align:middle line:84% collapsed a three-dimensional down into two dimensions. 00:19:12.820 --> 00:19:18.820 align:middle line:84% And these planes of equal d0 would come out as lines 00:19:18.820 --> 00:19:21.580 align:middle line:90% through the graph. 00:19:21.580 --> 00:19:24.240 align:middle line:84% I'm not showing you all the nature of the data points. 00:19:24.240 --> 00:19:28.750 align:middle line:84% But all of the solid diamonds and the open circles 00:19:28.750 --> 00:19:37.490 align:middle line:84% are relatively low velocities and oscillation periods. 00:19:37.490 --> 00:19:42.210 align:middle line:84% And then the ones up in here the squares, the open squares, 00:19:42.210 --> 00:19:43.910 align:middle line:84% solid squares, and some other things, 00:19:43.910 --> 00:19:48.730 align:middle line:84% are for much larger oscillation ripples that get produced. 00:19:48.730 --> 00:19:50.550 align:middle line:90% And I've tried to contour. 00:19:50.550 --> 00:19:55.310 align:middle line:84% These are-- and I don't think-- did I say this? 00:19:55.310 --> 00:19:56.990 align:middle line:84% Yeah, dashed curves, ripple spacing. 00:19:56.990 --> 00:19:59.050 align:middle line:84% I tried to contour the ripple spacing. 00:19:59.050 --> 00:20:02.910 align:middle line:84% And they increase very regularly up 00:20:02.910 --> 00:20:04.445 align:middle line:90% from lower left to upper right. 00:20:04.445 --> 00:20:06.570 align:middle line:84% But there's another curve in here, the solid curve. 00:20:06.570 --> 00:20:07.820 align:middle line:90% And that's an important curve. 00:20:07.820 --> 00:20:11.250 align:middle line:84% Everything below that curve is two-dimensional bedforms. 00:20:11.250 --> 00:20:13.310 align:middle line:84% And up above that is three-dimensional bedforms. 00:20:13.310 --> 00:20:14.610 align:middle line:90% It's not a definite cutoff. 00:20:14.610 --> 00:20:16.670 align:middle line:84% It's not like one of those boundaries in ripples and dunes 00:20:16.670 --> 00:20:17.810 align:middle line:90% in your directional flow. 00:20:17.810 --> 00:20:18.970 align:middle line:90% There's a gradation. 00:20:18.970 --> 00:20:23.710 align:middle line:84% There's a range in here around that line in which 00:20:23.710 --> 00:20:27.290 align:middle line:84% the ripples start to be three-dimensional and then 00:20:27.290 --> 00:20:30.170 align:middle line:90% become three-dimensional. 00:20:30.170 --> 00:20:31.130 align:middle line:90% I made that long ago. 00:20:31.130 --> 00:20:33.550 align:middle line:84% And I never followed up and made others like it. 00:20:33.550 --> 00:20:34.470 align:middle line:90% But there it is. 00:20:34.470 --> 00:20:38.730 align:middle line:84% Some pictures-- it probably won't surprise you, ripples, 00:20:38.730 --> 00:20:41.250 align:middle line:84% oscillation ripples, small-scale oscillations, 00:20:41.250 --> 00:20:43.110 align:middle line:84% typically straight-crested and regular. 00:20:43.110 --> 00:20:46.330 align:middle line:84% There are tuning forks, often, you see. 00:20:46.330 --> 00:20:49.790 align:middle line:84% This is from the Moenkopi near Vegas. 00:20:49.790 --> 00:20:52.310 align:middle line:84% It's a nice section, a lot of interesting stuff in it. 00:20:52.310 --> 00:20:56.450 align:middle line:84% And there again you have a tuning fork junction and still 00:20:56.450 --> 00:20:59.698 align:middle line:90% another from the same place. 00:20:59.698 --> 00:21:00.990 align:middle line:90% I don't know where that's from. 00:21:00.990 --> 00:21:03.330 align:middle line:84% That's a lens cap up on the top, but again, 00:21:03.330 --> 00:21:04.710 align:middle line:90% straight-crested regular. 00:21:04.710 --> 00:21:06.230 align:middle line:90% They're rounded off at the top. 00:21:06.230 --> 00:21:09.650 align:middle line:90% And I'm not sure why. 00:21:09.650 --> 00:21:13.930 align:middle line:84% This is classic, classic small-scale straight-crested 00:21:13.930 --> 00:21:18.030 align:middle line:84% oscillation ripples from the Ferron sandstone 00:21:18.030 --> 00:21:21.730 align:middle line:84% member of the Mancos and looking straight down on it. 00:21:21.730 --> 00:21:25.180 align:middle line:84% There's a pen or a pencil for scale over there 00:21:25.180 --> 00:21:30.100 align:middle line:84% and a similar kind of thing from the Cardium up in Alberta. 00:21:30.100 --> 00:21:32.980 align:middle line:90% Now, what's going on here? 00:21:32.980 --> 00:21:36.030 align:middle line:90% Explain that to me. 00:21:36.030 --> 00:21:37.780 align:middle line:84% The hint, of course, is that we're dealing 00:21:37.780 --> 00:21:38.822 align:middle line:90% with oscillation ripples. 00:21:38.822 --> 00:21:42.340 align:middle line:90% So what do you make of that? 00:21:42.340 --> 00:21:45.180 align:middle line:84% I have to challenge you guys now and then. 00:21:45.180 --> 00:21:48.860 align:middle line:84% Well, what I should have done is put the next slide in 00:21:48.860 --> 00:21:51.240 align:middle line:84% and turn it upside down because if you did that, 00:21:51.240 --> 00:21:53.120 align:middle line:84% it would just look oscillation ripples. 00:21:53.120 --> 00:21:54.900 align:middle line:84% This is a slab that came off something, 00:21:54.900 --> 00:21:56.380 align:middle line:90% and it fell upside down. 00:21:56.380 --> 00:21:59.280 align:middle line:84% That's what a ripple bed looks like upside down. 00:21:59.280 --> 00:22:02.100 align:middle line:90% 00:22:02.100 --> 00:22:05.440 align:middle line:84% I've never seen that, except just in one place. 00:22:05.440 --> 00:22:06.820 align:middle line:84% And now, on a broader scale, this 00:22:06.820 --> 00:22:13.500 align:middle line:84% is a big flat tidal sandbar off the coast of Eastham 00:22:13.500 --> 00:22:16.580 align:middle line:90% in Cape Cod, in Mass Bay. 00:22:16.580 --> 00:22:20.243 align:middle line:84% And you see, if you looked at just a little area here, 00:22:20.243 --> 00:22:22.160 align:middle line:84% it would look sort of like what we were doing. 00:22:22.160 --> 00:22:24.118 align:middle line:84% But when you look at all the whole field there, 00:22:24.118 --> 00:22:29.430 align:middle line:84% there's a lot of sinuosity and tuning fork junctions and things 00:22:29.430 --> 00:22:30.290 align:middle line:90% like that. 00:22:30.290 --> 00:22:34.170 align:middle line:84% There are a whole series of these bars, one here, one here. 00:22:34.170 --> 00:22:37.290 align:middle line:84% You can count four or five bars at spring low tide 00:22:37.290 --> 00:22:39.410 align:middle line:90% where the water is lowest. 00:22:39.410 --> 00:22:40.650 align:middle line:90% It's an amazing place. 00:22:40.650 --> 00:22:43.770 align:middle line:90% 00:22:43.770 --> 00:22:49.130 align:middle line:84% Some ripples-- you can see, this one looks symmetrical. 00:22:49.130 --> 00:22:51.110 align:middle line:84% This one is asymmetrical, but you 00:22:51.110 --> 00:22:54.810 align:middle line:84% can see the laminae inside the ripples, indicating the ripples. 00:22:54.810 --> 00:22:57.670 align:middle line:84% We're moving in one direction, shifting in one direction. 00:22:57.670 --> 00:23:01.150 align:middle line:90% And that can happen. 00:23:01.150 --> 00:23:04.750 align:middle line:84% That can happen in oscillatory flow, even when it's 00:23:04.750 --> 00:23:07.510 align:middle line:90% purely oscillatory. 00:23:07.510 --> 00:23:09.310 align:middle line:84% And I'll tell you more about that. 00:23:09.310 --> 00:23:10.410 align:middle line:90% They can get really big. 00:23:10.410 --> 00:23:14.150 align:middle line:84% We made this in an oscillatory flow duct with a long period. 00:23:14.150 --> 00:23:15.630 align:middle line:90% And they're big. 00:23:15.630 --> 00:23:17.450 align:middle line:90% These are centimeters here. 00:23:17.450 --> 00:23:21.630 align:middle line:90% 00:23:21.630 --> 00:23:22.910 align:middle line:90% This is an amazing photograph. 00:23:22.910 --> 00:23:24.650 align:middle line:90% I didn't take it. 00:23:24.650 --> 00:23:30.250 align:middle line:84% My long-term colleague and mentor, John Harms, 00:23:30.250 --> 00:23:33.250 align:middle line:84% gave me this slide, copied this slide for me. 00:23:33.250 --> 00:23:38.770 align:middle line:84% And this is a half a meter, I think, half a meter scale. 00:23:38.770 --> 00:23:40.090 align:middle line:90% And these are big. 00:23:40.090 --> 00:23:42.490 align:middle line:90% They're a meter plus scale. 00:23:42.490 --> 00:23:46.160 align:middle line:84% They're probably in coarse sand, I'm guessing. 00:23:46.160 --> 00:23:47.910 align:middle line:84% They're very straight-pressed and regular. 00:23:47.910 --> 00:23:51.830 align:middle line:84% And I've never seen one of those in my doings. 00:23:51.830 --> 00:23:53.610 align:middle line:90% But he showed it. 00:23:53.610 --> 00:23:55.690 align:middle line:90% Now, this my favorite outcrop. 00:23:55.690 --> 00:23:56.490 align:middle line:90% It's a win. 00:23:56.490 --> 00:23:59.210 align:middle line:84% AUDIENCE: Does the spacing between the oscillatory ripples 00:23:59.210 --> 00:24:00.970 align:middle line:84% vary with flow depth the same way you 00:24:00.970 --> 00:24:02.790 align:middle line:90% have with unidirectional flow? 00:24:02.790 --> 00:24:03.992 align:middle line:90% And can you backtrack? 00:24:03.992 --> 00:24:06.450 align:middle line:84% JOHN SOUTHARD: Well, go back to the graph with all the data 00:24:06.450 --> 00:24:07.550 align:middle line:90% points on it, remember. 00:24:07.550 --> 00:24:10.270 align:middle line:90% And we contoured the spacing. 00:24:10.270 --> 00:24:15.310 align:middle line:84% So it varies with both variables, not just one. 00:24:15.310 --> 00:24:18.475 align:middle line:90% 00:24:18.475 --> 00:24:19.350 align:middle line:90% That's a rock hammer. 00:24:19.350 --> 00:24:20.350 align:middle line:90% You see the rock hammer. 00:24:20.350 --> 00:24:22.933 align:middle line:84% And if you look at that, you can recognize there are hummocks, 00:24:22.933 --> 00:24:24.380 align:middle line:90% and there are swales. 00:24:24.380 --> 00:24:26.140 align:middle line:84% And they're isotropic in the sense 00:24:26.140 --> 00:24:28.380 align:middle line:84% that they don't bend one way or bend the other way. 00:24:28.380 --> 00:24:30.678 align:middle line:84% And I remember looking at this outcrop-- it's 00:24:30.678 --> 00:24:32.720 align:middle line:84% a little bigger than what I took the picture of-- 00:24:32.720 --> 00:24:37.220 align:middle line:84% and you can sense that the hummocks are arranged 00:24:37.220 --> 00:24:39.500 align:middle line:90% in a hexagonal pattern. 00:24:39.500 --> 00:24:43.780 align:middle line:84% And in the middle of the hexagon, there's a swale. 00:24:43.780 --> 00:24:47.040 align:middle line:84% And I even, in one place-- and I can't point it out to you-- 00:24:47.040 --> 00:24:48.860 align:middle line:84% there's a place where within the swale, 00:24:48.860 --> 00:24:51.920 align:middle line:84% there's a little miniature hummock right in the swale. 00:24:51.920 --> 00:24:54.100 align:middle line:84% It's amazing, my favorite outcrop. 00:24:54.100 --> 00:25:00.500 align:middle line:84% But I went back here some years afterward, maybe 8 or 10 years. 00:25:00.500 --> 00:25:03.360 align:middle line:84% It had fallen apart, a tragic loss. 00:25:03.360 --> 00:25:04.560 align:middle line:90% It had fallen apart. 00:25:04.560 --> 00:25:06.040 align:middle line:90% And it's not there anymore. 00:25:06.040 --> 00:25:08.620 align:middle line:90% 00:25:08.620 --> 00:25:10.920 align:middle line:84% I don't remember where I took this photo. 00:25:10.920 --> 00:25:12.580 align:middle line:90% There's a rock hammer there. 00:25:12.580 --> 00:25:14.980 align:middle line:84% But it's, again, hummocky swale, although it 00:25:14.980 --> 00:25:18.040 align:middle line:84% has some lineation to it, and it's somewhat asymmetrical. 00:25:18.040 --> 00:25:20.470 align:middle line:84% And this I want you to keep this in mind 00:25:20.470 --> 00:25:22.950 align:middle line:84% when we talk about combined flow bedforms. 00:25:22.950 --> 00:25:26.350 align:middle line:84% It's not that great a picture, but it 00:25:26.350 --> 00:25:27.970 align:middle line:90% shows some interesting things. 00:25:27.970 --> 00:25:30.910 align:middle line:90% 00:25:30.910 --> 00:25:34.030 align:middle line:84% Here's a close-up from straight down on a hummock. 00:25:34.030 --> 00:25:36.990 align:middle line:84% And you can convince yourself that it's 00:25:36.990 --> 00:25:39.910 align:middle line:84% three-armed, one this way, one that way and one that way, 00:25:39.910 --> 00:25:41.830 align:middle line:90% with a peak to it. 00:25:41.830 --> 00:25:45.192 align:middle line:84% And I think this was from somewhere-- 00:25:45.192 --> 00:25:47.650 align:middle line:84% somewhere in Canada, I was looking at it with Roger Walker, 00:25:47.650 --> 00:25:50.670 align:middle line:90% but I can't remember where. 00:25:50.670 --> 00:25:52.450 align:middle line:84% This is another one of my favorite chunks. 00:25:52.450 --> 00:25:54.030 align:middle line:84% I carried this out of the outcrop 00:25:54.030 --> 00:25:56.910 align:middle line:84% from the wood canyon in the Southern Nopah Range. 00:25:56.910 --> 00:26:02.130 align:middle line:84% And here's the scale, a hummock here, a swale, 00:26:02.130 --> 00:26:03.330 align:middle line:90% a hummock over here. 00:26:03.330 --> 00:26:05.990 align:middle line:84% And the whole bed, presumably, was like that hummocky swale, 00:26:05.990 --> 00:26:09.150 align:middle line:84% on a medium scale, a couple of decimeters. 00:26:09.150 --> 00:26:11.223 align:middle line:90% And if you look closely-- 00:26:11.223 --> 00:26:12.890 align:middle line:84% and this is getting ahead of ourselves-- 00:26:12.890 --> 00:26:15.470 align:middle line:84% the stratification here is medium scale 00:26:15.470 --> 00:26:16.768 align:middle line:90% hummocky cross-stratification. 00:26:16.768 --> 00:26:18.810 align:middle line:84% And I'm going to say a lot more about that coming 00:26:18.810 --> 00:26:23.730 align:middle line:90% up soon in the next session. 00:26:23.730 --> 00:26:26.370 align:middle line:84% Now, I'm going to take a shortcut here and show you 00:26:26.370 --> 00:26:30.290 align:middle line:84% a couple of graphs that show that there are things called 00:26:30.290 --> 00:26:33.690 align:middle line:84% orbital ripples, spacing consistently just a little less 00:26:33.690 --> 00:26:37.690 align:middle line:84% than the orbital diameter, through a transition in what 00:26:37.690 --> 00:26:40.930 align:middle line:84% are called suborbital, and orbital ripples, largely 00:26:40.930 --> 00:26:44.770 align:middle line:84% independent of the spacing, but it 00:26:44.770 --> 00:26:47.650 align:middle line:90% is dependent on particle size. 00:26:47.650 --> 00:26:53.350 align:middle line:84% You get, in fine sand, only in fine sands, 00:26:53.350 --> 00:26:55.890 align:middle line:84% and in very long excursion distances, 00:26:55.890 --> 00:27:01.330 align:middle line:84% you get ripples that look like current ripples. 00:27:01.330 --> 00:27:04.090 align:middle line:84% This is from a classic paper written by my colleague, 00:27:04.090 --> 00:27:07.930 align:middle line:84% Ed Clifton, way back-- he died a few years ago-- 00:27:07.930 --> 00:27:09.970 align:middle line:90% in which he plotted-- 00:27:09.970 --> 00:27:17.300 align:middle line:84% and I think I have the axis, lambda-- that's 00:27:17.300 --> 00:27:19.920 align:middle line:84% the spacing-- over the square root of D. 00:27:19.920 --> 00:27:23.100 align:middle line:84% I don't know why he did that because it's not dimensionless. 00:27:23.100 --> 00:27:29.380 align:middle line:84% And the horizontal axis is the d0 over D. Let me go back. 00:27:29.380 --> 00:27:31.500 align:middle line:90% And so there's a trend here. 00:27:31.500 --> 00:27:34.020 align:middle line:84% And those are the orbital ripples. 00:27:34.020 --> 00:27:36.180 align:middle line:84% And then it breaks through some messiness 00:27:36.180 --> 00:27:41.300 align:middle line:84% and comes out to a big group of anorbital ripples. 00:27:41.300 --> 00:27:44.260 align:middle line:84% These are data from both laboratory and field. 00:27:44.260 --> 00:27:45.700 align:middle line:90% It's not the only one. 00:27:45.700 --> 00:27:48.260 align:middle line:90% I can skip that. 00:27:48.260 --> 00:27:51.140 align:middle line:84% In a more recent study-- this is from Pat Wiberg and her 00:27:51.140 --> 00:27:55.700 align:middle line:84% colleague back in the late '90s, the same kind of-- 00:27:55.700 --> 00:28:01.920 align:middle line:84% they plotted spacing over D and d0 over D, 00:28:01.920 --> 00:28:03.200 align:middle line:90% so it's a real dimensionless. 00:28:03.200 --> 00:28:04.700 align:middle line:84% And you can see, there's a whole bunch of points 00:28:04.700 --> 00:28:06.580 align:middle line:84% here, both from field and laboratory 00:28:06.580 --> 00:28:09.780 align:middle line:90% data that are orbital ripples. 00:28:09.780 --> 00:28:10.920 align:middle line:90% They go with the space. 00:28:10.920 --> 00:28:13.160 align:middle line:90% They go with the spacing. 00:28:13.160 --> 00:28:14.690 align:middle line:84% But there's a whole bunch out here, 00:28:14.690 --> 00:28:16.310 align:middle line:90% which are totally separate. 00:28:16.310 --> 00:28:18.170 align:middle line:90% Those only field data. 00:28:18.170 --> 00:28:20.070 align:middle line:84% And those are an anorbital ripples. 00:28:20.070 --> 00:28:21.950 align:middle line:84% So it seems strange, doesn't it, that you 00:28:21.950 --> 00:28:24.630 align:middle line:84% can make both orbital ripples and anorbital ripples 00:28:24.630 --> 00:28:27.750 align:middle line:84% in the lab, but the only ones you see in the field 00:28:27.750 --> 00:28:29.830 align:middle line:90% are anorbital ripples. 00:28:29.830 --> 00:28:32.950 align:middle line:84% There's another example from a paper 00:28:32.950 --> 00:28:37.270 align:middle line:84% we wrote in 2005, in which these are the-- 00:28:37.270 --> 00:28:41.090 align:middle line:84% I won't go into details, but these are the vortex ripples, 00:28:41.090 --> 00:28:43.650 align:middle line:84% and these are the orbital ripples. 00:28:43.650 --> 00:28:48.670 align:middle line:84% And those down in the left-hand corner are anorbital ripples. 00:28:48.670 --> 00:28:51.870 align:middle line:84% So this summarizes what I'm trying to tell you here 00:28:51.870 --> 00:28:53.590 align:middle line:90% without a lot of details. 00:28:53.590 --> 00:28:54.930 align:middle line:90% But somehow they're different. 00:28:54.930 --> 00:28:57.590 align:middle line:84% There's some of instability that makes them different. 00:28:57.590 --> 00:29:00.870 align:middle line:90% 00:29:00.870 --> 00:29:03.012 align:middle line:84% I've wondered for a long time, and my colleagues 00:29:03.012 --> 00:29:04.470 align:middle line:84% have also wondered at the same time 00:29:04.470 --> 00:29:08.230 align:middle line:84% with me, about whether anorbital ripples are really 00:29:08.230 --> 00:29:11.150 align:middle line:84% just reversing current ripples because suppose 00:29:11.150 --> 00:29:15.010 align:middle line:84% you have a very long orbital diameter and a fairly 00:29:15.010 --> 00:29:16.850 align:middle line:84% substantial velocity over the bed. 00:29:16.850 --> 00:29:20.810 align:middle line:84% So for the 10, 15, 20 seconds that the flow flows this way, 00:29:20.810 --> 00:29:22.510 align:middle line:84% current ripples want to try to form. 00:29:22.510 --> 00:29:23.630 align:middle line:90% They're opportunistic. 00:29:23.630 --> 00:29:25.910 align:middle line:84% They form whenever the current velocity is right. 00:29:25.910 --> 00:29:26.947 align:middle line:90% And then it reverses. 00:29:26.947 --> 00:29:28.030 align:middle line:90% You go back the other way. 00:29:28.030 --> 00:29:29.490 align:middle line:90% They're still there. 00:29:29.490 --> 00:29:31.350 align:middle line:84% But they flip over and grow some more. 00:29:31.350 --> 00:29:33.230 align:middle line:84% And you go back and forth and back and forth, 00:29:33.230 --> 00:29:37.650 align:middle line:84% and you end up with anorbital ripples that are basically 00:29:37.650 --> 00:29:40.570 align:middle line:84% current ripples that can't make up their minds which way to go, 00:29:40.570 --> 00:29:42.370 align:middle line:84% if you want to look at it that way. 00:29:42.370 --> 00:29:44.070 align:middle line:84% I'm not sure I'm right about that. 00:29:44.070 --> 00:29:45.778 align:middle line:84% And I've talked with colleagues about it, 00:29:45.778 --> 00:29:49.570 align:middle line:84% and there's some agreement among us that that's the way it works. 00:29:49.570 --> 00:29:51.650 align:middle line:84% Now, there's something called ladder-back ripples 00:29:51.650 --> 00:29:55.710 align:middle line:84% or cross-ripples, which, to me, are mysterious. 00:29:55.710 --> 00:29:56.470 align:middle line:90% Look at that. 00:29:56.470 --> 00:29:57.630 align:middle line:90% I forget where I took that. 00:29:57.630 --> 00:29:58.550 align:middle line:90% That's my scale. 00:29:58.550 --> 00:30:01.770 align:middle line:90% So I took that picture. 00:30:01.770 --> 00:30:05.870 align:middle line:84% And you can see, there's some major oscillation ripples. 00:30:05.870 --> 00:30:09.290 align:middle line:84% And then in the troughs, there are some minor, smaller 00:30:09.290 --> 00:30:10.150 align:middle line:90% oscillation ripples. 00:30:10.150 --> 00:30:12.300 align:middle line:84% They're almost the same size, I guess. 00:30:12.300 --> 00:30:13.820 align:middle line:90% Here's another example. 00:30:13.820 --> 00:30:15.740 align:middle line:84% That's a watch for scale in the middle. 00:30:15.740 --> 00:30:19.640 align:middle line:84% So these are the main oscillation ripples. 00:30:19.640 --> 00:30:22.440 align:middle line:84% But look at all the smaller ones in the-- 00:30:22.440 --> 00:30:24.060 align:middle line:84% now, is that because of something, 00:30:24.060 --> 00:30:26.720 align:middle line:84% how it works under these conditions? 00:30:26.720 --> 00:30:29.420 align:middle line:84% Or is it you made the large ripples first, 00:30:29.420 --> 00:30:31.820 align:middle line:84% and then things changed, and you got oscillation 00:30:31.820 --> 00:30:34.260 align:middle line:84% from the other direction, which seems to me to possibly. 00:30:34.260 --> 00:30:38.060 align:middle line:84% And I don't know how you tell the difference. 00:30:38.060 --> 00:30:41.540 align:middle line:84% So here's the two ways you maybe could 00:30:41.540 --> 00:30:44.780 align:middle line:84% make them, non-parallel oscillations 00:30:44.780 --> 00:30:46.920 align:middle line:84% or a single component under certain conditions. 00:30:46.920 --> 00:30:48.520 align:middle line:84% And that's what I want to get to next. 00:30:48.520 --> 00:30:51.620 align:middle line:90% 00:30:51.620 --> 00:30:56.340 align:middle line:84% Ed Clifton, who I mentioned, organized some data 00:30:56.340 --> 00:30:59.880 align:middle line:84% from various places, shoaling waves, waves coming in, 00:30:59.880 --> 00:31:01.780 align:middle line:84% shoaling, finally breaking on the shore. 00:31:01.780 --> 00:31:04.660 align:middle line:84% And out in the fairly deep water, 00:31:04.660 --> 00:31:09.182 align:middle line:84% you get active, long-crested or oscillation ripples 00:31:09.182 --> 00:31:09.890 align:middle line:90% we're looking at. 00:31:09.890 --> 00:31:11.190 align:middle line:90% Then they get irregular. 00:31:11.190 --> 00:31:14.630 align:middle line:84% Then you get cross-ripples for reasons I have no idea why. 00:31:14.630 --> 00:31:19.330 align:middle line:84% And then when the waves break and run up the beach, 00:31:19.330 --> 00:31:22.190 align:middle line:84% you get what you call lunate megaripples. 00:31:22.190 --> 00:31:24.670 align:middle line:84% They're not oscillation ripples anymore. 00:31:24.670 --> 00:31:27.990 align:middle line:90% 00:31:27.990 --> 00:31:32.470 align:middle line:84% I have no idea how this formed, pentagonal oscillation ripples, 00:31:32.470 --> 00:31:35.550 align:middle line:90% no idea how it formed. 00:31:35.550 --> 00:31:38.750 align:middle line:84% I took that when Palmeiro was just 00:31:38.750 --> 00:31:41.900 align:middle line:84% finishing his doctoral thesis up there in St. Johns, 00:31:41.900 --> 00:31:43.790 align:middle line:84% in Newfoundland, and we went across 00:31:43.790 --> 00:31:46.303 align:middle line:84% to Bell Island and a lot of interesting stuff. 00:31:46.303 --> 00:31:46.970 align:middle line:90% And there it is. 00:31:46.970 --> 00:31:50.670 align:middle line:90% I don't know anything about it. 00:31:50.670 --> 00:31:53.770 align:middle line:84% So now, this may be counterintuitive to you, 00:31:53.770 --> 00:31:58.390 align:middle line:84% but oscillation ripples formed in purely oscillatory flow-- 00:31:58.390 --> 00:32:04.510 align:middle line:84% AUDIENCE: What if one of the orientations of variables was 00:32:04.510 --> 00:32:06.472 align:middle line:90% 3D, and one was 2D? 00:32:06.472 --> 00:32:08.930 align:middle line:84% JOHN SOUTHARD: Are you talking about the pentagonal ripples 00:32:08.930 --> 00:32:10.770 align:middle line:90% now? 00:32:10.770 --> 00:32:13.850 align:middle line:84% Maybe there are three or more different oscillation 00:32:13.850 --> 00:32:16.250 align:middle line:84% components, maybe something like that. 00:32:16.250 --> 00:32:16.932 align:middle line:90% I don't know. 00:32:16.932 --> 00:32:17.890 align:middle line:90% AUDIENCE: It's so cool. 00:32:17.890 --> 00:32:18.210 align:middle line:90% JOHN SOUTHARD: I know. 00:32:18.210 --> 00:32:19.190 align:middle line:90% It's amazing. 00:32:19.190 --> 00:32:22.450 align:middle line:84% So ripples formed under purely oscillatory flow 00:32:22.450 --> 00:32:24.770 align:middle line:90% aren't always symmetrical. 00:32:24.770 --> 00:32:26.810 align:middle line:84% Now, way back in hour one, I told you 00:32:26.810 --> 00:32:29.610 align:middle line:84% about how under shoaling waves, there's 00:32:29.610 --> 00:32:33.570 align:middle line:90% fast and short, slow and long. 00:32:33.570 --> 00:32:36.010 align:middle line:84% The water doesn't go anywhere on a net basis, 00:32:36.010 --> 00:32:39.310 align:middle line:84% but because sediment transport rate is so steeply climbing, 00:32:39.310 --> 00:32:42.210 align:middle line:84% a function of the flow velocity, that you end up 00:32:42.210 --> 00:32:45.330 align:middle line:84% getting net transport towards shore, 00:32:45.330 --> 00:32:48.870 align:middle line:84% and you can get asymmetrical, purely oscillatory flow. 00:32:48.870 --> 00:32:51.050 align:middle line:84% It seems counterintuitive, but it happens. 00:32:51.050 --> 00:32:53.230 align:middle line:84% Now, a little bit on the eolian bed configurations-- 00:32:53.230 --> 00:32:55.730 align:middle line:84% I'm not going to say a lot about it. 00:32:55.730 --> 00:32:59.050 align:middle line:84% I mentioned barchans early on when we talked 00:32:59.050 --> 00:33:01.530 align:middle line:90% about sediment transport. 00:33:01.530 --> 00:33:02.750 align:middle line:90% Those are miniature. 00:33:02.750 --> 00:33:03.510 align:middle line:90% These are major. 00:33:03.510 --> 00:33:05.740 align:middle line:90% These are big, big ones. 00:33:05.740 --> 00:33:07.680 align:middle line:90% I forgot where that is even. 00:33:07.680 --> 00:33:12.020 align:middle line:84% And here's a more distant view from the air of an isolated 00:33:12.020 --> 00:33:13.860 align:middle line:90% barchan. 00:33:13.860 --> 00:33:16.660 align:middle line:84% So I'm not going to say anything more about barchans. 00:33:16.660 --> 00:33:20.500 align:middle line:84% Read Bagnold's book if you want to know about barchans. 00:33:20.500 --> 00:33:23.700 align:middle line:84% So classic wind ripples-- now, at first glance, you look at 00:33:23.700 --> 00:33:26.080 align:middle line:84% and say, oh, they're oscillation ripples underwater. 00:33:26.080 --> 00:33:28.760 align:middle line:84% But they're very distinctive in their shape. 00:33:28.760 --> 00:33:31.757 align:middle line:84% They're asymmetrical, and they have grain-size segregation 00:33:31.757 --> 00:33:34.340 align:middle line:84% that's very different from what you'd find in oscillatory flow 00:33:34.340 --> 00:33:37.420 align:middle line:90% ripples. 00:33:37.420 --> 00:33:39.080 align:middle line:90% They can get fairly good size. 00:33:39.080 --> 00:33:41.180 align:middle line:84% Here are some that are getting up pretty big. 00:33:41.180 --> 00:33:43.460 align:middle line:84% There's not a scale in there, except for the bush, 00:33:43.460 --> 00:33:44.480 align:middle line:90% unfortunately. 00:33:44.480 --> 00:33:46.060 align:middle line:90% I should have put a scale in. 00:33:46.060 --> 00:33:52.440 align:middle line:84% But they're decked with smaller scale wind ripples as well. 00:33:52.440 --> 00:33:53.940 align:middle line:84% Now, if you look at the dunes, there 00:33:53.940 --> 00:33:57.040 align:middle line:84% are a lot of active coastal dunes along the coast of Oregon, 00:33:57.040 --> 00:33:57.840 align:middle line:90% for example. 00:33:57.840 --> 00:34:00.605 align:middle line:84% I'm out there with my colleagues. 00:34:00.605 --> 00:34:02.480 align:middle line:84% They take me out there to show me this stuff. 00:34:02.480 --> 00:34:04.800 align:middle line:84% And you can see the stoss surface 00:34:04.800 --> 00:34:10.239 align:middle line:84% of the dune, strong eolian transport, no ripples, plane bed 00:34:10.239 --> 00:34:13.600 align:middle line:84% transport, reach the crest, and the grains that 00:34:13.600 --> 00:34:16.760 align:middle line:84% are deposited at the crest slide down the crest. 00:34:16.760 --> 00:34:21.280 align:middle line:84% This is a view of the same dune with-- here's a slip face 00:34:21.280 --> 00:34:24.080 align:middle line:84% at angle of repose, and the grains slide 00:34:24.080 --> 00:34:28.400 align:middle line:84% down as little miniature grain flows out onto the-- this 00:34:28.400 --> 00:34:31.380 align:middle line:84% is an earlier dune that this one is overriding. 00:34:31.380 --> 00:34:34.280 align:middle line:90% 00:34:34.280 --> 00:34:37.840 align:middle line:84% Now I have to say some things about combined-flow bedforms, 00:34:37.840 --> 00:34:39.480 align:middle line:84% but I'm not happy with it because I 00:34:39.480 --> 00:34:41.040 align:middle line:90% don't know much about it. 00:34:41.040 --> 00:34:43.100 align:middle line:84% I don't think anybody knows much about it. 00:34:43.100 --> 00:34:45.340 align:middle line:84% It's a jungle, when you think about it. 00:34:45.340 --> 00:34:49.020 align:middle line:84% You have all the things that go on in unidirectional flow, 00:34:49.020 --> 00:34:51.195 align:middle line:84% everything that's going on in oscillatory flow, 00:34:51.195 --> 00:34:53.320 align:middle line:84% and everything in between, when you combine the two 00:34:53.320 --> 00:34:56.560 align:middle line:84% flows in various ways, and you get an enormous variety 00:34:56.560 --> 00:34:58.400 align:middle line:84% of bed configurations, and therefore, 00:34:58.400 --> 00:35:00.760 align:middle line:84% an enormous variety of sedimentary structures. 00:35:00.760 --> 00:35:02.870 align:middle line:90% And it's a jungle. 00:35:02.870 --> 00:35:06.790 align:middle line:84% It's a dog's breakfast, as John Grotzinger likes to say. 00:35:06.790 --> 00:35:09.530 align:middle line:90% 00:35:09.530 --> 00:35:14.030 align:middle line:90% So that's the topic. 00:35:14.030 --> 00:35:16.690 align:middle line:84% How do you make combined-flow bed configurations? 00:35:16.690 --> 00:35:19.250 align:middle line:90% Well, you can do it in the lab. 00:35:19.250 --> 00:35:24.170 align:middle line:84% If you have a unidirectional flow and a parallel oscillation, 00:35:24.170 --> 00:35:25.510 align:middle line:90% it's pretty easy to do. 00:35:25.510 --> 00:35:28.650 align:middle line:84% And we've done it in our laboratory. 00:35:28.650 --> 00:35:33.250 align:middle line:84% But if they're at right angles, it might be doable in the lab. 00:35:33.250 --> 00:35:35.890 align:middle line:84% I once thought about writing a proposal 00:35:35.890 --> 00:35:39.970 align:middle line:84% to build a flow channel with flow and reservoir tanks 00:35:39.970 --> 00:35:40.990 align:middle line:90% on the side. 00:35:40.990 --> 00:35:43.743 align:middle line:84% And you can rock the channel back and forth 00:35:43.743 --> 00:35:45.910 align:middle line:84% to make an oscillation while the current is flowing. 00:35:45.910 --> 00:35:46.630 align:middle line:90% I never did it. 00:35:46.630 --> 00:35:50.250 align:middle line:84% But I thought it would be a cool idea to do. 00:35:50.250 --> 00:35:50.990 align:middle line:90% It didn't do it. 00:35:50.990 --> 00:35:52.365 align:middle line:84% Oh, wait a minute, wait a minute. 00:35:52.365 --> 00:35:54.770 align:middle line:84% And the third would be to-- if you 00:35:54.770 --> 00:35:57.473 align:middle line:84% have more than one oscillatory component 00:35:57.473 --> 00:35:58.890 align:middle line:84% plus the unidirectional flow, this 00:35:58.890 --> 00:36:00.430 align:middle line:90% would be very difficult to do. 00:36:00.430 --> 00:36:02.020 align:middle line:90% And I think it's been done. 00:36:02.020 --> 00:36:03.760 align:middle line:90% And I'm not into the literature. 00:36:03.760 --> 00:36:07.380 align:middle line:84% You'd have to have a big wave tank with wave makers here, 00:36:07.380 --> 00:36:10.000 align:middle line:84% and wave makers over here, and wave makers over here. 00:36:10.000 --> 00:36:12.500 align:middle line:84% Plus, you'd have to pump water from one side of the tank 00:36:12.500 --> 00:36:14.060 align:middle line:84% to the other and produce the current. 00:36:14.060 --> 00:36:16.160 align:middle line:90% And that's a big job. 00:36:16.160 --> 00:36:18.540 align:middle line:84% And I don't think much has been done on it. 00:36:18.540 --> 00:36:22.420 align:middle line:84% So here we go again, another dimensional analysis. 00:36:22.420 --> 00:36:25.740 align:middle line:84% You need not just max orbital velocity, 00:36:25.740 --> 00:36:29.820 align:middle line:84% you need directional flow velocity and period, period 00:36:29.820 --> 00:36:30.720 align:middle line:90% and size. 00:36:30.720 --> 00:36:33.160 align:middle line:84% So here you have four variables instead of three. 00:36:33.160 --> 00:36:35.420 align:middle line:84% Well now, I cannot, and I don't think anybody can, 00:36:35.420 --> 00:36:38.360 align:middle line:84% visualize a four-dimensional diagram. 00:36:38.360 --> 00:36:40.798 align:middle line:84% I think that's beyond our capabilities. 00:36:40.798 --> 00:36:42.340 align:middle line:84% So what you'd have to think about is, 00:36:42.340 --> 00:36:44.340 align:middle line:84% you make one of those three-dimensional graphs 00:36:44.340 --> 00:36:47.860 align:middle line:84% for every value of the fourth variable. 00:36:47.860 --> 00:36:49.040 align:middle line:90% And you could do that. 00:36:49.040 --> 00:36:50.460 align:middle line:84% It's an enormous job, and it would 00:36:50.460 --> 00:36:52.740 align:middle line:84% take a lifetime of experimentation 00:36:52.740 --> 00:36:54.440 align:middle line:90% to fill in a graph like that. 00:36:54.440 --> 00:36:59.480 align:middle line:90% 00:36:59.480 --> 00:37:05.700 align:middle line:84% So this is from before and from earlier. 00:37:05.700 --> 00:37:10.800 align:middle line:84% And now, we're dealing with this oscillatory velocity, 00:37:10.800 --> 00:37:13.780 align:middle line:84% versus oscillation period, versus sediment size. 00:37:13.780 --> 00:37:15.240 align:middle line:84% And you'd have to do one of those 00:37:15.240 --> 00:37:18.200 align:middle line:84% for every value of unidirectional flow added 00:37:18.200 --> 00:37:19.200 align:middle line:90% on to it. 00:37:19.200 --> 00:37:20.460 align:middle line:90% It gets really messy. 00:37:20.460 --> 00:37:23.258 align:middle line:90% 00:37:23.258 --> 00:37:24.300 align:middle line:90% We don't have to do this. 00:37:24.300 --> 00:37:27.282 align:middle line:84% There's another way of-- there's a velocity symmetry value, 00:37:27.282 --> 00:37:28.240 align:middle line:90% but it's not important. 00:37:28.240 --> 00:37:29.260 align:middle line:90% Don't worry about. 00:37:29.260 --> 00:37:30.520 align:middle line:90% I'm not going to say anything. 00:37:30.520 --> 00:37:33.900 align:middle line:84% So we're far from filling these diagrams. 00:37:33.900 --> 00:37:36.760 align:middle line:90% It's just the way it is. 00:37:36.760 --> 00:37:38.580 align:middle line:90% Here's some nice papers. 00:37:38.580 --> 00:37:43.120 align:middle line:84% In case you're interested, you can pursue some of these papers. 00:37:43.120 --> 00:37:45.920 align:middle line:90% Ours is one of them. 00:37:45.920 --> 00:37:49.920 align:middle line:84% There was a student, one of Bill Arnott's students 00:37:49.920 --> 00:37:52.600 align:middle line:84% from University of Ottawa, Simone Dumas, 00:37:52.600 --> 00:37:56.920 align:middle line:84% came down to build and operate a giant flow 00:37:56.920 --> 00:37:59.250 align:middle line:84% channel, oscillatory flow channel, 00:37:59.250 --> 00:38:03.130 align:middle line:84% with unidirectional flow as well. 00:38:03.130 --> 00:38:06.910 align:middle line:84% She and I built this thing with some help from other employees. 00:38:06.910 --> 00:38:10.890 align:middle line:84% She was the person who was the best arc 00:38:10.890 --> 00:38:13.850 align:middle line:84% welder of any of the employees and students I've ever had. 00:38:13.850 --> 00:38:16.610 align:middle line:84% Now, I teach these people how to do that because we build things. 00:38:16.610 --> 00:38:20.610 align:middle line:90% And she was really good at it. 00:38:20.610 --> 00:38:24.850 align:middle line:84% So here are some of the ripples that she got. 00:38:24.850 --> 00:38:27.950 align:middle line:84% This is for-- small-scale bed forms range from, 00:38:27.950 --> 00:38:30.970 align:middle line:84% as you might imagine, symmetrical to somewhat 3D 00:38:30.970 --> 00:38:34.550 align:middle line:84% to very 3D and on into basic current ripples. 00:38:34.550 --> 00:38:37.730 align:middle line:84% And you can do the same kind of thing for large ripples, 00:38:37.730 --> 00:38:41.770 align:middle line:84% again, symmetrical for almost purely oscillatory flow. 00:38:41.770 --> 00:38:43.890 align:middle line:84% They get a little three-dimensional, 00:38:43.890 --> 00:38:45.870 align:middle line:84% and they're somewhat asymmetrical. 00:38:45.870 --> 00:38:52.110 align:middle line:84% Then they get to be more three-dimensional, 00:38:52.110 --> 00:38:54.610 align:middle line:84% and then you finally get to dunes and your directional flow. 00:38:54.610 --> 00:38:56.340 align:middle line:84% So that's a way of looking at it. 00:38:56.340 --> 00:38:59.240 align:middle line:84% She made these conclusions based on all the experiments, 00:38:59.240 --> 00:39:01.400 align:middle line:84% all the runs she made in the duct. 00:39:01.400 --> 00:39:04.900 align:middle line:84% And this is her graph, which is a good one, oscillatory flow 00:39:04.900 --> 00:39:07.860 align:middle line:84% velocity versus unidirectional flow velocity. 00:39:07.860 --> 00:39:11.540 align:middle line:84% And this is for a particular size, 0.14 millimeters size, 00:39:11.540 --> 00:39:14.800 align:middle line:84% 8 second period, which is pretty realistic of things in nature. 00:39:14.800 --> 00:39:18.260 align:middle line:84% And you can see, you get no movement, lots 00:39:18.260 --> 00:39:20.900 align:middle line:90% of rugged bedforms, plane bed. 00:39:20.900 --> 00:39:23.140 align:middle line:84% And she has these lines, but she explains 00:39:23.140 --> 00:39:27.220 align:middle line:84% in the text of the paper that those are gradations. 00:39:27.220 --> 00:39:29.760 align:middle line:84% There's a gradation between symmetric large ripples, 00:39:29.760 --> 00:39:32.920 align:middle line:84% asymmetric large ripples, asymmetric small ripples, 00:39:32.920 --> 00:39:36.157 align:middle line:84% and symmetric small ripples with no definite boundaries. 00:39:36.157 --> 00:39:37.740 align:middle line:84% So this is one of these diagrams where 00:39:37.740 --> 00:39:39.657 align:middle line:84% we don't have a lot of nice boundaries the way 00:39:39.657 --> 00:39:44.520 align:middle line:84% we did in unidirectional flow, which we have to live with. 00:39:44.520 --> 00:39:47.240 align:middle line:84% This was one that I did with Bill Arnott. 00:39:47.240 --> 00:39:49.400 align:middle line:84% And we published a paper earlier than that. 00:39:49.400 --> 00:39:52.420 align:middle line:84% And it shows the same kind of thing with data points. 00:39:52.420 --> 00:39:54.280 align:middle line:90% And there's another one-- 00:39:54.280 --> 00:39:55.700 align:middle line:90% oh, there's not another one. 00:39:55.700 --> 00:39:59.800 align:middle line:84% There's one in the addendum, which I didn't include here, 00:39:59.800 --> 00:40:02.940 align:middle line:84% a more recent paper by Perillo et al, 00:40:02.940 --> 00:40:05.040 align:middle line:84% Mauricio Perillo, my young colleague, 00:40:05.040 --> 00:40:09.480 align:middle line:84% and they did a very similar kind of duct and similar experiments. 00:40:09.480 --> 00:40:10.900 align:middle line:90% Look at this. 00:40:10.900 --> 00:40:14.060 align:middle line:84% And they produced just the same kind of graph. 00:40:14.060 --> 00:40:16.900 align:middle line:84% But it's nice to look at because it has colors in it. 00:40:16.900 --> 00:40:18.780 align:middle line:84% And that's in the addendum there. 00:40:18.780 --> 00:40:20.280 align:middle line:84% I'm pretty sure it's in the addendum 00:40:20.280 --> 00:40:23.260 align:middle line:84% if you want to look at it sometime. 00:40:23.260 --> 00:40:26.280 align:middle line:84% Photo to come, but I don't have any photos. 00:40:26.280 --> 00:40:30.240 align:middle line:84% I've never taken a photo of what I think to be or are 00:40:30.240 --> 00:40:33.040 align:middle line:84% know to be a combined-flow bed form. 00:40:33.040 --> 00:40:35.320 align:middle line:90% And that's just the way it is. 00:40:35.320 --> 00:40:38.420 align:middle line:84% There are photographs from the experiments. 00:40:38.420 --> 00:40:40.060 align:middle line:90% And I don't have access to them. 00:40:40.060 --> 00:40:43.020 align:middle line:84% I tried to get them, couldn't get them easily enough. 00:40:43.020 --> 00:40:47.160 align:middle line:90% So now, it is getting late. 00:40:47.160 --> 00:40:49.977 align:middle line:84% And it's time to start on number four. 00:40:49.977 --> 00:40:52.060 align:middle line:84% So now, we're dealing with sedimentary structures. 00:40:52.060 --> 00:40:53.970 align:middle line:84% We're going to look at rocks now and see 00:40:53.970 --> 00:40:56.170 align:middle line:90% what the structures are like. 00:40:56.170 --> 00:40:58.770 align:middle line:84% Now, I don't want to insult your intelligence, but a stratum 00:40:58.770 --> 00:41:02.050 align:middle line:84% or stratum, distinctive layer of deposited sediment. 00:41:02.050 --> 00:41:03.370 align:middle line:90% And it can be tabular. 00:41:03.370 --> 00:41:05.330 align:middle line:90% It can be non-tabular. 00:41:05.330 --> 00:41:13.610 align:middle line:84% And there's a conventional lamina versus bed. 00:41:13.610 --> 00:41:14.830 align:middle line:90% This is a terrible term. 00:41:14.830 --> 00:41:16.890 align:middle line:84% Never used this term, laminations. 00:41:16.890 --> 00:41:19.390 align:middle line:84% It's either lamination or laminae, one or the other, 00:41:19.390 --> 00:41:20.970 align:middle line:90% but not laminations. 00:41:20.970 --> 00:41:22.590 align:middle line:90% This is the editor. 00:41:22.590 --> 00:41:25.090 align:middle line:84% This is the copy editor in me speaking-- no, really, I'm 00:41:25.090 --> 00:41:25.590 align:middle line:90% serious. 00:41:25.590 --> 00:41:26.590 align:middle line:90% A lot of people say that. 00:41:26.590 --> 00:41:28.460 align:middle line:84% And you know the difference between texture and structure, 00:41:28.460 --> 00:41:28.960 align:middle line:90% right? 00:41:28.960 --> 00:41:32.370 align:middle line:84% We're dealing with structures here, not textures. 00:41:32.370 --> 00:41:36.670 align:middle line:84% Modes of deposition-- this is pretty simple to understand. 00:41:36.670 --> 00:41:38.588 align:middle line:84% You can have fallout without traction. 00:41:38.588 --> 00:41:39.630 align:middle line:90% Clearly, you can do that. 00:41:39.630 --> 00:41:41.250 align:middle line:90% And this happens many times. 00:41:41.250 --> 00:41:42.987 align:middle line:84% Or you can have fallout with traction. 00:41:42.987 --> 00:41:45.070 align:middle line:84% Particles are coming down, being added to the bed, 00:41:45.070 --> 00:41:47.400 align:middle line:90% so we get aggradation. 00:41:47.400 --> 00:41:49.150 align:middle line:84% Differential transport is a little tricky. 00:41:49.150 --> 00:41:50.195 align:middle line:90% I want to show you that. 00:41:50.195 --> 00:41:51.820 align:middle line:84% And of course, there's mass deposition, 00:41:51.820 --> 00:41:54.580 align:middle line:84% like debris flows grinding to a halt, which 00:41:54.580 --> 00:41:58.620 align:middle line:84% is outside the scope of this presentation. 00:41:58.620 --> 00:42:01.180 align:middle line:84% So here's the flow, a non-uniform flow. 00:42:01.180 --> 00:42:04.480 align:middle line:84% It's deepening and slowing as it goes downstream. 00:42:04.480 --> 00:42:07.020 align:middle line:84% You have a flow velocity U, a sediment transport 00:42:07.020 --> 00:42:10.040 align:middle line:90% rate Qs at both sections. 00:42:10.040 --> 00:42:12.180 align:middle line:84% But you can see that the sediment transport rate 00:42:12.180 --> 00:42:14.760 align:middle line:90% is greater here than down here. 00:42:14.760 --> 00:42:17.460 align:middle line:84% So sediment must be being stored on the bed. 00:42:17.460 --> 00:42:18.360 align:middle line:90% That make sense? 00:42:18.360 --> 00:42:19.700 align:middle line:90% That's bookkeeping. 00:42:19.700 --> 00:42:24.780 align:middle line:90% And so that's-- well. 00:42:24.780 --> 00:42:26.460 align:middle line:84% Deposition, you have to think of, 00:42:26.460 --> 00:42:30.740 align:middle line:84% it can be one or both of two of those factors. 00:42:30.740 --> 00:42:33.680 align:middle line:84% And we'd like to know how to figure out which is which. 00:42:33.680 --> 00:42:35.160 align:middle line:84% I don't think that's an easy job. 00:42:35.160 --> 00:42:38.380 align:middle line:84% But you have to be aware that's how deposition works. 00:42:38.380 --> 00:42:41.720 align:middle line:84% Mass deposition-- I'm going to not go through this very fast. 00:42:41.720 --> 00:42:43.620 align:middle line:84% I'm going to go through this very fast. 00:42:43.620 --> 00:42:45.280 align:middle line:90% Debris flows are important. 00:42:45.280 --> 00:42:50.840 align:middle line:84% The bouma A, the lowest part of a turbidity current deposit, 00:42:50.840 --> 00:42:52.088 align:middle line:90% here's the bouma sequence. 00:42:52.088 --> 00:42:53.880 align:middle line:84% You probably know about the bouma sequence. 00:42:53.880 --> 00:42:57.200 align:middle line:90% This part down here is massive. 00:42:57.200 --> 00:42:58.500 align:middle line:90% And it involves mass flow. 00:42:58.500 --> 00:43:02.560 align:middle line:84% We did some experiments on that once with a master's student. 00:43:02.560 --> 00:43:04.660 align:middle line:84% So here's another way of looking at it. 00:43:04.660 --> 00:43:09.920 align:middle line:84% If you have flow of a thick mass of sediment, but it's flowing, 00:43:09.920 --> 00:43:14.060 align:middle line:84% the shear stress, the shear, is least up in the top. 00:43:14.060 --> 00:43:16.960 align:middle line:84% So that means it will freeze earlier at the top 00:43:16.960 --> 00:43:20.600 align:middle line:84% and freeze gradually downward, until finally, the whole thing 00:43:20.600 --> 00:43:24.440 align:middle line:84% is a plug of sediment, immobile, which I think 00:43:24.440 --> 00:43:26.320 align:middle line:90% is a nice way of looking at it. 00:43:26.320 --> 00:43:30.280 align:middle line:84% So we can deal with planar lamination. 00:43:30.280 --> 00:43:33.220 align:middle line:84% Sometimes people call planar lamination plane-parallel. 00:43:33.220 --> 00:43:35.080 align:middle line:84% Don't call it horizontal lamination 00:43:35.080 --> 00:43:36.642 align:middle line:90% because it's not horizontal. 00:43:36.642 --> 00:43:38.100 align:middle line:84% It may have started out horizontal. 00:43:38.100 --> 00:43:38.940 align:middle line:90% It may not have. 00:43:38.940 --> 00:43:40.440 align:middle line:84% But when you see it, it's usually 00:43:40.440 --> 00:43:43.680 align:middle line:90% not, so planar lamination. 00:43:43.680 --> 00:43:45.680 align:middle line:90% It's called planar lamination. 00:43:45.680 --> 00:43:50.570 align:middle line:84% Two kinds-- one, obviously, you get a flow dropping sediment 00:43:50.570 --> 00:43:52.710 align:middle line:90% without further traction. 00:43:52.710 --> 00:43:55.570 align:middle line:84% And if the surface is planar, it's 00:43:55.570 --> 00:43:57.810 align:middle line:84% going to be building up a deposit, 00:43:57.810 --> 00:43:59.890 align:middle line:90% planar laminated deposit. 00:43:59.890 --> 00:44:02.690 align:middle line:84% But you can also-- and I think I've made this clear to you 00:44:02.690 --> 00:44:04.290 align:middle line:84% already-- you can have deposition 00:44:04.290 --> 00:44:07.250 align:middle line:84% during traction, active traction, 00:44:07.250 --> 00:44:09.850 align:middle line:90% in the plane bed regime. 00:44:09.850 --> 00:44:15.410 align:middle line:84% And so you build up a planar laminated bed during transport. 00:44:15.410 --> 00:44:17.693 align:middle line:84% I think this is from Bill Arnott's field area. 00:44:17.693 --> 00:44:19.610 align:middle line:84% I was on his thesis committee, and we went out 00:44:19.610 --> 00:44:22.410 align:middle line:84% for a glorious week in Montana at his field area 00:44:22.410 --> 00:44:27.150 align:middle line:84% after he passed his thesis defense, and nice lamination. 00:44:27.150 --> 00:44:28.670 align:middle line:90% That's a 15-centimeter scale. 00:44:28.670 --> 00:44:34.530 align:middle line:84% So these laminae are a fraction of a centimeter thick, 00:44:34.530 --> 00:44:36.530 align:middle line:90% which is very typical. 00:44:36.530 --> 00:44:38.190 align:middle line:84% It gets a little more complicated. 00:44:38.190 --> 00:44:40.990 align:middle line:84% I think this is in the same section we were looking at, 00:44:40.990 --> 00:44:42.870 align:middle line:84% and planar laminated, planar laminated. 00:44:42.870 --> 00:44:46.220 align:middle line:84% But looking here, you can see some vague foresets in here. 00:44:46.220 --> 00:44:49.193 align:middle line:84% So something happened to the current, and it decreased. 00:44:49.193 --> 00:44:50.860 align:middle line:84% And then it started up again, and that's 00:44:50.860 --> 00:44:52.440 align:middle line:90% how I interpret that anyway. 00:44:52.440 --> 00:44:54.700 align:middle line:90% It's a little tricky. 00:44:54.700 --> 00:44:56.660 align:middle line:84% A couple more slides-- you've probably seen 00:44:56.660 --> 00:44:58.320 align:middle line:90% planar lamination in the field. 00:44:58.320 --> 00:45:01.860 align:middle line:90% 00:45:01.860 --> 00:45:05.660 align:middle line:84% So there's an idea floating around, 00:45:05.660 --> 00:45:08.560 align:middle line:84% and one of my grad students, Chris Paolo, 00:45:08.560 --> 00:45:10.540 align:middle line:84% was partly responsible for this-- 00:45:10.540 --> 00:45:14.020 align:middle line:84% the idea that the bed isn't perfectly planar. 00:45:14.020 --> 00:45:16.460 align:middle line:84% There's very low amplitude, very long 00:45:16.460 --> 00:45:21.300 align:middle line:84% spacing features that move along the plane bed surface 00:45:21.300 --> 00:45:23.060 align:middle line:90% in the upper plane bed regime. 00:45:23.060 --> 00:45:25.540 align:middle line:84% And this is what makes the laminae as they go by, 00:45:25.540 --> 00:45:27.860 align:middle line:84% little laminae, about a centimeter, about a couple 00:45:27.860 --> 00:45:30.100 align:middle line:90% of millimeters thick. 00:45:30.100 --> 00:45:34.020 align:middle line:90% I can believe it. 00:45:34.020 --> 00:45:37.460 align:middle line:84% Now, I don't need to tell you this, difference in grain size 00:45:37.460 --> 00:45:38.360 align:middle line:90% within a lamina. 00:45:38.360 --> 00:45:40.980 align:middle line:90% That's how you see them. 00:45:40.980 --> 00:45:42.480 align:middle line:84% Now, here's an interesting question. 00:45:42.480 --> 00:45:44.680 align:middle line:84% I've tried to do this in the field, next time you're 00:45:44.680 --> 00:45:46.860 align:middle line:84% in the field and looking at plane planar lamination. 00:45:46.860 --> 00:45:48.520 align:middle line:84% How far can you trace a given laminate 00:45:48.520 --> 00:45:52.400 align:middle line:84% before it disappears, replaced by another, changes in some way? 00:45:52.400 --> 00:45:56.680 align:middle line:84% And typically, it's something like from well less than a meter 00:45:56.680 --> 00:46:00.720 align:middle line:84% to as much as a few meters, if you have a nice enough outcrop. 00:46:00.720 --> 00:46:04.440 align:middle line:90% It's nice to play around with. 00:46:04.440 --> 00:46:07.440 align:middle line:84% Now, there's something called parting-step lineation. 00:46:07.440 --> 00:46:09.600 align:middle line:84% You may have heard of parting-step lineation. 00:46:09.600 --> 00:46:15.040 align:middle line:84% So you have a lithified plane-bedded succession. 00:46:15.040 --> 00:46:17.820 align:middle line:84% And when it's brings up to the surface, it's weathered. 00:46:17.820 --> 00:46:18.680 align:middle line:90% It splits. 00:46:18.680 --> 00:46:21.300 align:middle line:84% It often splits along bedding planes, 00:46:21.300 --> 00:46:24.680 align:middle line:84% bedding surfaces that happen to be-- during plane bed-- 00:46:24.680 --> 00:46:28.200 align:middle line:84% that are weaker than the surrounding 00:46:28.200 --> 00:46:30.320 align:middle line:90% strata above and below it. 00:46:30.320 --> 00:46:35.720 align:middle line:90% And the nice thing about it-- 00:46:35.720 --> 00:46:41.920 align:middle line:84% this is from the sidewalk going to a tea plantation in Sochi. 00:46:41.920 --> 00:46:46.850 align:middle line:84% And you can see because of the orientation of the grains 00:46:46.850 --> 00:46:49.470 align:middle line:84% as they're being transported under plane bed conditions, 00:46:49.470 --> 00:46:50.990 align:middle line:90% produce an anisotropy. 00:46:50.990 --> 00:46:54.510 align:middle line:84% And then when it parts along a bedding surface, 00:46:54.510 --> 00:46:58.050 align:middle line:84% that anisotropy shows up as these parting steps. 00:46:58.050 --> 00:46:59.678 align:middle line:90% It's pretty understandable. 00:46:59.678 --> 00:47:00.470 align:middle line:90% Here's another one. 00:47:00.470 --> 00:47:01.928 align:middle line:84% I can't remember where that's from. 00:47:01.928 --> 00:47:04.890 align:middle line:90% 00:47:04.890 --> 00:47:10.270 align:middle line:84% So that's all I'm going to say about parting lineation. 00:47:10.270 --> 00:47:15.410 align:middle line:84% But now we get into another major part of the presentation. 00:47:15.410 --> 00:47:17.370 align:middle line:84% How do you interpret the flow conditions 00:47:17.370 --> 00:47:20.330 align:middle line:84% by looking at the cross-stratified bed? 00:47:20.330 --> 00:47:22.890 align:middle line:84% That's a major undertaking, and I need 00:47:22.890 --> 00:47:25.530 align:middle line:90% to make some comments about it. 00:47:25.530 --> 00:47:26.730 align:middle line:90% There's a forward problem. 00:47:26.730 --> 00:47:28.510 align:middle line:84% You know about forward problems and inverse problems, right? 00:47:28.510 --> 00:47:30.990 align:middle line:84% The forward problem is you have a flowover bed. 00:47:30.990 --> 00:47:32.650 align:middle line:90% It forms bed configurations. 00:47:32.650 --> 00:47:35.490 align:middle line:84% During aggradation, sedimentary structures are formed, 00:47:35.490 --> 00:47:36.910 align:middle line:90% and you get stratification. 00:47:36.910 --> 00:47:39.970 align:middle line:84% But the inverse problem is trickier. 00:47:39.970 --> 00:47:41.488 align:middle line:84% You see the stratification, and you 00:47:41.488 --> 00:47:43.530 align:middle line:84% try to figure out what the bed configuration was. 00:47:43.530 --> 00:47:45.030 align:middle line:84% And then from the bed configuration, 00:47:45.030 --> 00:47:47.070 align:middle line:84% you want to know plus aggregation, 00:47:47.070 --> 00:47:48.430 align:middle line:90% what was the flow like? 00:47:48.430 --> 00:47:50.182 align:middle line:84% That's what you want to back out. 00:47:50.182 --> 00:47:52.390 align:middle line:84% That's the whole purpose of doing this kind of thing, 00:47:52.390 --> 00:47:54.590 align:middle line:84% is make interpretations like that. 00:47:54.590 --> 00:47:56.270 align:middle line:90% And it's not easy. 00:47:56.270 --> 00:47:57.030 align:middle line:90% Why? 00:47:57.030 --> 00:47:59.510 align:middle line:84% It can be difficult or impossible 00:47:59.510 --> 00:48:02.510 align:middle line:90% because there's local erosion. 00:48:02.510 --> 00:48:04.730 align:middle line:90% Time gets unrecorded. 00:48:04.730 --> 00:48:08.530 align:middle line:84% And so local deposit geometry, which existed at one time, 00:48:08.530 --> 00:48:09.530 align:middle line:90% isn't there anymore. 00:48:09.530 --> 00:48:13.790 align:middle line:84% So that's a universal problem that we have to deal with. 00:48:13.790 --> 00:48:16.230 align:middle line:84% Anyway, here are a few more thought 00:48:16.230 --> 00:48:18.830 align:middle line:90% experiments coming along. 00:48:18.830 --> 00:48:23.030 align:middle line:84% I got to quit in a few minutes, but let me just go through this. 00:48:23.030 --> 00:48:24.250 align:middle line:90% How could you do this? 00:48:24.250 --> 00:48:28.530 align:middle line:84% You could set up a flow over the bed to make a bed configuration. 00:48:28.530 --> 00:48:30.670 align:middle line:84% And that's been done many, many times. 00:48:30.670 --> 00:48:33.930 align:middle line:84% You can add sediment above, at a constant or varying rate, 00:48:33.930 --> 00:48:36.490 align:middle line:84% while flow velocity is either constant or varying, 00:48:36.490 --> 00:48:40.360 align:middle line:84% and you degrade a bed under varying conditions. 00:48:40.360 --> 00:48:43.305 align:middle line:84% And then you can section the deposit vertically 00:48:43.305 --> 00:48:45.680 align:middle line:84% downstream, cross-stream orientation, parallel to the bed 00:48:45.680 --> 00:48:47.440 align:middle line:84% if you wanted to, and you can see 00:48:47.440 --> 00:48:49.120 align:middle line:90% what the structures look like. 00:48:49.120 --> 00:48:52.600 align:middle line:84% But if this was made by differential transport, 00:48:52.600 --> 00:48:54.580 align:middle line:84% it might be difficult to figure this out. 00:48:54.580 --> 00:48:57.040 align:middle line:84% But anyway, that's the kind of thinking you have to do. 00:48:57.040 --> 00:48:58.680 align:middle line:84% So another thing you could do is what's 00:48:58.680 --> 00:49:00.940 align:middle line:90% called synthetic aggregation. 00:49:00.940 --> 00:49:02.880 align:middle line:84% We've done some of this in the laboratory. 00:49:02.880 --> 00:49:05.360 align:middle line:84% You set up a flow and make a bed configuration. 00:49:05.360 --> 00:49:08.800 align:middle line:84% Then you make time-series maps of the bed, 00:49:08.800 --> 00:49:14.920 align:middle line:84% and you artificially aggrade them in time steps, 00:49:14.920 --> 00:49:17.760 align:middle line:84% and you end up with a cross-stratified deposit. 00:49:17.760 --> 00:49:20.520 align:middle line:84% And it does pretty much mimic what 00:49:20.520 --> 00:49:22.920 align:middle line:84% would happen if you actually degraded 00:49:22.920 --> 00:49:26.080 align:middle line:84% the bed, which of course, is very difficult. 00:49:26.080 --> 00:49:28.000 align:middle line:84% I guess you could stack them by computer. 00:49:28.000 --> 00:49:31.720 align:middle line:84% This is fairly easy in the sidewall, transparent sidewall, 00:49:31.720 --> 00:49:32.660 align:middle line:90% of a channel. 00:49:32.660 --> 00:49:35.060 align:middle line:84% But it's not easy if you're looking at a whole area. 00:49:35.060 --> 00:49:35.893 align:middle line:90% How would you do it? 00:49:35.893 --> 00:49:38.650 align:middle line:84% You'd have to do a sonar profile, sonar profile, sonar 00:49:38.650 --> 00:49:40.210 align:middle line:90% profile, and then stack them up. 00:49:40.210 --> 00:49:41.210 align:middle line:90% It could be done. 00:49:41.210 --> 00:49:43.670 align:middle line:84% And I don't know how much it's been done. 00:49:43.670 --> 00:49:46.370 align:middle line:90% We did some of it. 00:49:46.370 --> 00:49:48.490 align:middle line:84% In the natural flow environment, the obvious thing 00:49:48.490 --> 00:49:51.450 align:middle line:84% is to go out to some station out offshore, 00:49:51.450 --> 00:49:53.730 align:middle line:84% in the shallow offshore, and instrument it 00:49:53.730 --> 00:49:56.550 align:middle line:84% with some of permanent tripod structure, 00:49:56.550 --> 00:50:01.010 align:middle line:84% looking down at the bed, and also measuring the flow. 00:50:01.010 --> 00:50:03.030 align:middle line:84% And there have been some good studies. 00:50:03.030 --> 00:50:05.490 align:middle line:84% But that's really difficult because it 00:50:05.490 --> 00:50:07.230 align:middle line:90% has to resist big storms. 00:50:07.230 --> 00:50:09.690 align:middle line:84% And there are all kinds of technological problems 00:50:09.690 --> 00:50:11.067 align:middle line:90% in actually making it work. 00:50:11.067 --> 00:50:12.150 align:middle line:90% But there is some of that. 00:50:12.150 --> 00:50:15.330 align:middle line:90% And that's very valuable to do. 00:50:15.330 --> 00:50:16.990 align:middle line:84% So I think that's a good place to quit. 00:50:16.990 --> 00:50:18.450 align:middle line:90% It's after 4:00. 00:50:18.450 --> 00:50:21.090 align:middle line:84% I'm going to point out that facies models-- you probably 00:50:21.090 --> 00:50:23.930 align:middle line:84% know about facies models, models for interpreting 00:50:23.930 --> 00:50:25.730 align:middle line:90% sedimentary environments. 00:50:25.730 --> 00:50:29.970 align:middle line:84% This is a nice statement, well worded 00:50:29.970 --> 00:50:35.650 align:middle line:84% in the introduction of the SEPM Special Publication 84 in 2005. 00:50:35.650 --> 00:50:37.830 align:middle line:84% A model is a point of comparison, 00:50:37.830 --> 00:50:39.670 align:middle line:84% a guide for further observations, 00:50:39.670 --> 00:50:42.270 align:middle line:84% serves as a base for hydrodynamic interpretation, 00:50:42.270 --> 00:50:46.650 align:middle line:84% and it acts as a predictor, a predictor for new situations. 00:50:46.650 --> 00:50:48.710 align:middle line:84% That's really valuable to be able to do. 00:50:48.710 --> 00:50:51.790 align:middle line:84% And what we're dealing with here is a kind 00:50:51.790 --> 00:50:55.118 align:middle line:90% of a subset of facies models. 00:50:55.118 --> 00:50:56.410 align:middle line:90% And that's depositional models. 00:50:56.410 --> 00:50:59.010 align:middle line:84% Look at a particular bed in a given facies. 00:50:59.010 --> 00:51:00.990 align:middle line:84% What can you back out of that bed 00:51:00.990 --> 00:51:03.790 align:middle line:84% in terms of making interpretations of flow 00:51:03.790 --> 00:51:05.550 align:middle line:90% conditions and sedimentation? 00:51:05.550 --> 00:51:08.950 align:middle line:84% And I think that that's all I'm going to deal with. 00:51:08.950 --> 00:51:11.810 align:middle line:84% Next time, I'm going to start in with cross-stratification, 00:51:11.810 --> 00:51:14.510 align:middle line:84% which is really the main thing in this presentation. 00:51:14.510 --> 00:51:16.890 align:middle line:84% And so that'll be two weeks from now, 00:51:16.890 --> 00:51:19.930 align:middle line:84% remember, two weeks, same time, same place. 00:51:19.930 --> 00:51:23.070 align:middle line:84% And I'll finish up the presentation 00:51:23.070 --> 00:51:24.590 align:middle line:84% talking about cross-stratification 00:51:24.590 --> 00:51:26.470 align:middle line:84% in various kinds of flow environments 00:51:26.470 --> 00:51:28.270 align:middle line:90% with lots of pictures. 00:51:28.270 --> 00:51:30.140 align:middle line:90% See you then. 00:51:30.140 --> 00:51:36.000 align:middle line:90%