Desert Intro: 1 of 4

Added: 2026-05-09

[00:00:00]Hello geographers, we're off to our desert landscapes now, and we're going to see the work of wind. And we'll, as we get into this, we'll see why we look at wind in this particular environment, even though it's windy in lots of places. But here's where we can actually see the effects of wind.

[00:00:16]And of course, going back to our climate, these are our B climates where the rainfall does not exceed the evaporation rate. And so, what would we expect to see in those?

[00:00:29]We'd see sparse vegetation, but we're also going to see how other things are going on in our arid areas. That running water is actually— even though there's not a lot of it—it's very important to the processes that we see.

[00:00:42]And then we'll get to look at wind, sand dunes, that kind of stuff, and then we'll look at some unusual desert landscapes as we go through. So I'll come back to all these, so if I'm going kind of quickly past this particular slide, don't worry. The Christmas camel wants us to move on.

[00:00:56]So, sparse vegetation. Obviously, without a lot of rainfall, you're not going to support large plant communities. And notice too that it's pretty discontinuous; that you've got exposed dirt and rock in the area. And this is why wind can do something here, because wind can transport that loose material at the surface.

[00:01:14]So, this is taken just off of I-15. I have no idea why I stopped here. It's an older picture that I have.

[00:01:20]But this is off I-15 on the way to Las Vegas. Same thing here: sparse vegetation.

[00:01:25]We don't get large, towering trees, and if we do get anything tall, it's typically some type of cactus or related species.

[00:01:33]All right, but why is water so important?

[00:01:36]Remember fluvial, stream-related? Why is water so important? So if we think about what the surfaces are like within a desert landscape, because of the lack of vegetation, you often have exposed rocks. Just, that's the bedrock; it's exposed. And when I say impermeable, is that the water doesn't soak into it like it does a soil.

[00:01:56]Or, at the bottom of the slope and at the valley floors, you get that gravel and rocks and sometimes boulders that kind of tumble off the sides of the mountains to the valley floor. Without the water, it doesn't get a lot of weathering, so it kind of stays a rock and gravel. So, what makes that sediments in the valley floor is referred to as alluvium. It makes that sediments very permeable, so the water can pass through it very, very quickly.

[00:02:24]So any rain that falls on this slope is just going to slide down off of it. And as it gets to the valley floor, what's going to happen to it there? It's just simply going to flow through it very quickly. It's the difference between pouring water into a bucket with a hole in the bottom that's full of clay. It's—the clay will soak it up—as opposed to pouring water in a bucket that's full of rocks with a hole in the bottom, where the water will just go right through the bucket very, very quickly. So if the water in the valley, from both the valley sides and the valley floor... Where does water flow to? The lowest point. So all of that water is going to flow to the lowest point in the valley very quickly; much more quickly than it would in a humid environment.

[00:03:08]And so you end up with flash floods.

[00:03:14]So, back to our stream thought, stream lecture.

[00:03:18]The amount of water that ends up in the stream gives it a very, very high discharge.

[00:03:23]Because normally in a humid environment, say you had one square mile and one inch of rain fell in that one square mile. In a humid environment, it would get into the soil; it would soak in. Plants would slow the water from moving down the sides of the slopes, and so by the time the rainfall had finished, some of it made it in the stream channel and a lot of it is trapped in the hillsides. Well, one square mile with one inch of rain in a desert?

[00:03:47]All of that water ends up in the stream channel very quickly.

[00:03:51]So, same amount of rain, just different effects of what we see in the stream channel. And so the flash flood is just the water collects in the stream very, very quickly. These are really dangerous.

[00:04:01]Here's somebody stupid enough to think about crossing the stream. That's asinine.

[00:04:07]The mud makes the surface slick. Water has a... it's actually heavier than you think. And so the water flowing against the vehicle will very easily push it off the side of the road. I'm always amused by people on their great big four-wheel-drive vehicles thinking they can cross this kind of stuff, when the reality is their vehicle is just going to kind of float a little bit. Your tires don't have a lot of friction on the muddy surface. Your tires are full of air, which makes them slightly buoyant.

[00:04:33]Everything works against crossing something like this unless you have a really specialized vehicle.

[00:04:38]Just wait for the water to drop down; it'll get better.

[00:04:42]And again, this happens very, very quickly, so it makes—makes being on the valley floor a very dangerous place to be. That water can build up very, very quickly.

[00:04:53]Let's see... there we go.

[00:04:55]Um... So... when there's thunderstorms around in a desert environment, it's a very dangerous place to be.

[00:05:04]Often you'll see roads in the desert that don't have bridges over these washes. The it just—the cost of building them that could withstand such a high discharge upstream would make it prohibitively expensive. They just assume—and sometimes wrongly so— that people will be smart enough not to try and drive through a flooded road.

[00:05:28]Now, in other places you'll see what they'll do is they'll grate the—or grade—the sediments in this stream bottom, smoothing them out so that often becomes your road. Because again, since it rains infrequently, that's— we don't—you can use that—those sediments for other purposes, such as roads.

[00:05:47]Las Vegas. Oh, poor Las Vegas. It's down in the bottom of a basin, and so it is prone to flooding quite often. And often the new construction that goes in will divert water into culverts that weren't really designed for that much water because they're trying to get the water out of the neighborhoods.

[00:06:03]And so as they build new neighborhoods, they tend to see a shifting in how the flooding occurs.

[00:06:11]Grand Canyon. The center picture here— this is where some campers were killed.

[00:06:16]They set up their camp on some nice, soft sediments because it was a good place to sleep for the night.

[00:06:20]And then there was a storm that they couldn't see up on the mesa above, and then that water just quickly got into that culvert and washed them and their bodies away. And their bodies were found days later downstream.

[00:06:34]Zion National Park: same problem with limited visibility of what's happening on the plateau up above, and you're down in the canyon; and that's where the water is going to end up.

[00:06:45]With that high discharge of the stream... remember, discharge is what's going to transport materials. That's why water's so effective in the desert: because when it does rain—which isn't that often, but when it does—the streams have a high discharge, and they can move a tremendous amount of water in a very short amount of time. And hopefully I can get this video to work.

[00:07:07]Here it comes.

[00:07:09][Music] Oh, shh! Look at that. Look at it.

[00:07:20]Sorry about the sound, but the sound's not as important as the video.

[00:07:42]It slows it down, but there's a lot of water there.

[00:07:47][Music] All right, that's what moves the rocks and boulders in the stream channel.

[00:07:55]I didn't say that this—isn't my... it's not my video. All right, let's move on.

[00:08:03]We'll come back to desert landforms in a little bit.