Some of the most spectacular features that were noticed early on, even as early as Mariner 9 on Mars are features that are now called outflow valleys. Let me show you what they look like and you can see for yourself why they're called outflow valleys. You look at them and you say, "There was a big outflow here." If we started on Google Mars and we staring now at Valles Marineris, and we just go a little bit North, we'll first zoom in here, we move a little North of Valles Marineris until we start to see these series of cracks. Something going on here. It's not the best view, Google Mars is not always quite the same as getting a nice view because it's striped and inconsistent, but you can start to navigate around some. You see something that's happened in through here and a series of channels that have come around the corner here into this strange region in through here. Let's look in more detail at that region right in there, zoom in here, and this is called Cassey Valleys. This is a huge, what looks like outflow channels, it looks like flows have gone in through here, flows have gone here, flows have gone along in here, flows have gone along in here, they all empty out in this great plains that's at lower elevation, that's in the Northern part of the planet. Google Earth isn't the greatest way to look at it as I said. So, let's look at some actual images. This one is particularly good because it doesn't just show the image of what it looks like, but it's also color-coded with topography showing you the elevations. Notice that the yellow here are at zero, we call it zero sea-level, Mars doesn't have a sea. So, there has been a sea-level essentially made up for Mars and that's what this sort of yellowish green all throughout here is sea level in through here, sea level in through here, and these regions in through here start out a little bit below that sort of this greenish is all up in here, and notice that it steeply goes down until these blue regions which are much deeper, this is in kilometers. So, you've gone down a couple of kilometers through the course of this channel. What does it look like? Well, it's really hard to look at this and not think some sort of flow. There been arguments ever since these were discovered about exactly what was flowing through there. Perhaps it was ice, perhaps it was lava, but in the end, it is generally agreed that water is the most likely culprit. In fact, water is really the only likely culprit for having formed these sorts of channels. Why water? Well again, just like we've seen before, one of the ways that you understand surface features that you see on Mars is through analogies on Earth. This is done, just look like at a river. This looks like some huge outflow. In fact, maybe some flooding event, maybe some dam breaking and washing a lot of stuff out through there. We have things like that on the Earth that we can look at, and we can look at the specific features, and see if we can match up some of the stuff we see on Earth with some of the stuff we see on Mars. We're going to go back to Earth now and look at the Eastern part of the state of Washington which as we zoom in, looks distinct. These regions in through here, along here's the Columbia River, other rivers up through here, that are generally brown. They are called Scablands. Scablands meaning regions where the soil has been washed away, where nothing is growing which is why they're generally brown. Let's zoom in a little bit more. The green that you see in through here is irrigation coming from the rivers, but everywhere else it's just a brown wasteland. Look closer and closer at this brown wasteland and you realize it's a series of these ridges going in this direction. This is the channel part of the Channeled Scablands. It's not river valleys connecting things, it's not like there are flows in the middle of each one of these things. So, what is it? Well, what it is was debated for many decades until it was finally recognized and finally believed that what you're seeing here in Western Washington is the result of massive flooding. The massive flooding occurred near the ends of the ice ages when glaciers began to melt, water would pull up behind them. Eventually again, the glaciers are continuing to melt and those glacial dams break catastrophically. When the glacial dams break catastrophically, they come streaming down through here and make these Channeled Scablands, in addition to boring out the Columbia River Gorge that goes through there. Those features, those long streamline ridges, they are all typical of what you get in the giant floods, and they are exactly what we see on these outflow channels on Mars. You can see them here in regions like this. You can see them in through here. You can see them in through here, down at the end. They're all over the place on these outflow channels. In fact, if you look at some of the more recent imagery, here is an obscenely detailed close-up of a tiny, tiny region of this outflow channel. You can see everywhere. You see these channels, you see regions that perhaps were never covered like in through here, maybe these didn't get covered over, maybe there are islands that maybe this part of the island is getting covered, but everywhere else it's evidence of channels and braiding, and huge amounts of water flowing in through here. Now, I said huge amounts of water flowing in through here. The obvious question is how much water and how long did it flow? How would you figure out the answer to the question? Well, this is the thing that terrestrial hydrologists had been playing around with for centuries. How do you look at something like a river valley, an ancient river valley? Perhaps, figure out how much water it had in it, how fast that water was flowing, what kind of volume of water went through that valley? One way to do that is with some very simple experiments and looking at flows. The simplest flow that you can imagine that is related to a valley. Imagine taking a channel on an inclined, I'm going to draw it this way. Here's the channel, it's going incline like this and sticking water in the top of it and watching that water flow down the channel and measuring how fast that water goes. Pretty simple experiment, you can guess some of the things that are going to matter for how fast the water flows. Well, the angle of the steep channels are going to flow faster, right? The amount of water? Probably the shape of the channel, maybe. What the channel's made up? If the channel is rough at the bottom or smooth at the bottom, should definitely affect things. So, you do all these experiments, you come up with all the results and you then try to make sense out of it. Well, dealing with the shape of the bottom is a little bit complicated. So, we're going to ignore the shape of the bottom. We're going to take into account things like the shape of the channel itself, the height of the flow, and the slope, and really those are the only things that you could imagine as long as you have the same material in the channel is the only things that you can imagine will make a difference in the flow. So, you take those things, what do we have? We have, let's say, a width, we have a height, and we have an angle here that the flow is making and of course, we have the force of gravity pulling everything down. Let's think about what's going to make a difference. Well, if the channels are at a particular angle, there's a force down the channel, not of g, the force of gravity, but of sine theta times g, g sine theta. Sine theta is this angle here, when sine theta is small, when theta is small, there's very little force, when theta is big you get a very big force of gravity in that direction. The next thing you do is something that seems a little bit like cheating. Maybe it's a little bit like cheating. But to do as little simple dimensional analysis, we're looking for a velocity and hydrolysis. Always use u, you might think you should use v for velocity. You'd apparently be wrong, u is in meters per second. What do we have to deal with? Well, we know that we have g sin Theta, and that is in g, the acceleration due to gravity is in meters per second squared. So, what are we going to do to meters per second squared that has something to do with these quantities over here that's going to make meters per second? Well, obviously if we multiply by time, we're done. We don't have any time. So there is no time dimension in here that we could possible use for our dimensional analysis. In fact, the only thing that we have in our dimensional analysis is the shape of the channel. Basically, the width here and the height here. So we have distances. How are we going to make a distance turn this into this? Well, the only way to do it is going to be to multiply by something that's in meters and then take the square root, I'm going to take it to the 1.5 power. If I do that, I'm going to have something that has the right dimensions. Okay, what do we have this in meters? Well, here's where empirically, you can determine that the correct formula to use is the ratio of the area, which is the width times the height. The area of the flow inside here over the wetted perimeter, not the entire perimeter of the pipe but the wetted part, the wedded part is going to be h h and w is going to be w plus h plus h. This ratio which has dimensions of distance, we'll call it meters. If we multiply it up in here, it gives us the right units. Does it give us right answer? Well, yes it does actually give us the right answer, and this is where you had to empirically show that this is actually correct. But what you find is that the velocity is g sin Theta times this ratio which goes by the variable h, the hydraulic radius. It's called to the one-half power divided by we'll call it c sub f, or perhaps the better term is fudge factor. It's not exactly equal to this. If we just plug these numbers in and thought you'd get a velocity, you'd be wrong. So you have to calibrate it, you have to measure these velocities and channels and you calibrate with c sub f. C sub f is where all of the interesting stuff about the shape, the material that's down here, if this is a rough surface, a smooth surface, all of that comes in this co-efficient and it's all divided over here. But those things can be measured. They've been measured for typical river conditions on Earth. Nobody quite knows what to do about Mars, but you can sort of try to guess what the answers might be, and if you knew the width of the Martian channel, and the height of the Martian channel, and the slope of the Martian channel, you could calculate the velocity that that water was going. Let's go give it a try. So it's pretty obvious how to get a width on a channel like this. You can simply measure how big across it is here, or here, or you can try a larger region in through here. How do you get the height of the channel? Well, this is where you go in and look at those detailed pictures that I showed you last time and try to figure out what should these features have been covered and which of them had been not covered. If everything has been covered, the height is at least that much, and if you can find the first feature that's uncovered, for example, this is clearly uncovered. It's the same height as it is here, but maybe you can find shore lines in through here, maybe you can get the width in this manner. How do you get the slope? Well, that's easy. We have the heights all in through here, so we can measure the average slope across this whole region and we get velocities. Because we don't know what that c f value is the fudge factor, we have to guess a plausible range of what the velocities might be. The velocities that you get by doing this are in the range of 1 to maybe 50 meters per second. It's pretty fast water-flow, and what you really are interested in or what you are at least as interested in is how much water is flowing. Well, you can do that very easily. You know the area because you know the width and the height and you know the velocity. So you can calculate what is usually called Q, the total rate of water discharge and you get between about 0.01 and 2 times 10 to the seventh cubic meters per second. 0.01 to 2 times 10 to the seventh cubic meters per second is a unit that no normal person ever thinks about. So let's compare it to something. What should we compare it to? How about those big floods that made the Eastern Washington channeled scablands? Those are between about 0.1 and 2 times 10 to the seventh meter cube per second. Not the similar rates coming out of these floods has the floods that made the massive channeled scablands in Eastern Washington. One more point comparison is the Mississippi River which drains a significant chunk of the North American continent and it drains 0.003 meter cubed per second. It's not that much smaller than the lowest estimate that we have here, it's only about third smaller, but the higher ends are much bigger and the one maybe scablands are much bigger. This is an interesting result and it's only because of these very nice topological data that we can get these results. Early results that tried to figure out the slopes were giving answers that were maybe in order of magnitude higher than the suggesting that these were monster floods compared to the channeled scablands. Down it seems that they are just typical, I would say, normal terrestrial floods. But there's so much area carved out through here. You can calculate that there must have been not just one but many of these floods over a fairly extended amount of time. Where did they come from? Let's go back and look at Google Mars again and see if we can figure out the source of these floods. I like to do my navigating from landmarks that I recognized. So, again here's Valles mariners. Does it come from Valles mariners? Well, no. In fact, you can look at if there were flows in through here. Where did they go? They go out through here on the eastern end. What we found is that they look like they came from up in here. Remember again, here's the valleys that we were just looking at. Here's where they flow out. That is sort of channeled scablands looking sort of region, and they come from up in here. What's going on up in here? Well, it's unknown. It's perhaps related to this large volcanic province thesis. If we go back out, you'll see that the big volcanoes, the big volcanic bulges here, one of the reasons for this big valley in through here. So, it's possible that things like volcanic magma could have hit a large pockets of ground ice. There could have been aquifer that get heated or broke out for some reason, broke out repeatedly. Something like this had to happen that would have happened multiple times and give moderate floods across this fairly extended area. One of the interesting questions of course, if this did happen, where did all that water go? Well, it goes out into here, to this outflow channel and then you don't see it channeled anymore, and in fact, as we'll see later, this entire northern plains looks like it could have been a nearly global ocean in the distant past. We'll cover that in a later lecture.
