WEBVTT - Sand Dunes: They Are What You Think They Are 0:00:00.440 --> 0:00:04.200 Attention, Chicago and Toronto. We're coming to see you guys soon, 0:00:04.720 --> 0:00:07.000 so we better hurry up and buy your tickets because 0:00:07.040 --> 0:00:09.760 they're going fast. Yeah, man, Chicago at the Hairs Theater July. 0:00:11.320 --> 0:00:13.280 We've actually sold a lot of tickets now, yeah, you 0:00:13.360 --> 0:00:15.920 guys listen, thank you, thanks for stepping up. In Toronto 0:00:16.000 --> 0:00:19.119 at the Danforth Music Hall the next night, July. It 0:00:19.200 --> 0:00:21.439 may be sold out by now. Yeah. Well, there's only 0:00:21.440 --> 0:00:23.400 one way to find out. Go on to s y 0:00:23.520 --> 0:00:25.560 s K live dot com and you'll find links to 0:00:25.720 --> 0:00:27.960 the ticket sites and all the show info you need, 0:00:28.000 --> 0:00:31.560 and we will see you soon. Welcome to Stuff You 0:00:31.600 --> 0:00:40.800 Should Know, a production of I Heart Radios How Stuff Works. Hey, 0:00:40.880 --> 0:00:43.640 and welcome to the podcast. I'm Josh Clark, and there's 0:00:43.720 --> 0:00:46.599 Charles w Chuck Bryant, there's Jerry over there, and this 0:00:46.680 --> 0:00:51.840 is Earth Science Time. Baby. I love this stuff. Yeah, 0:00:51.880 --> 0:00:58.040 this one was a little well, it's about dry. I 0:00:58.200 --> 0:01:00.560 just caught myself at the last second. Thank you. It 0:01:00.600 --> 0:01:03.920 was a little dry though, Uh it was, But I 0:01:03.920 --> 0:01:06.120 mean we're talking sand dudes. There's just so much you 0:01:06.120 --> 0:01:08.520 can do with something, do you know what I mean? Yeah, 0:01:08.520 --> 0:01:10.080 But it's also one of those is kind of neat, 0:01:10.120 --> 0:01:12.080 and that when next time I go to the beach 0:01:12.959 --> 0:01:16.240 or the desert, I will I'm armed with a little 0:01:16.240 --> 0:01:18.440 more knowledge, which is always nice. Are you gonna go 0:01:18.520 --> 0:01:21.440 do some sandboarding? I don't think so, although I did 0:01:21.440 --> 0:01:24.120 look at some videos. It sounds pretty awesome to me. 0:01:24.280 --> 0:01:26.160 It looks like a great way for a forty eight 0:01:26.240 --> 0:01:28.920 year old to break his knee. Did you, oh man, 0:01:29.200 --> 0:01:33.480 breaking your knee? Can you imagine? No? Did you, um 0:01:33.520 --> 0:01:37.640 listen to the sound of dunes singing? Uh? Yeah, and 0:01:37.680 --> 0:01:41.399 I've heard that sound like in person? What kind of 0:01:41.480 --> 0:01:45.120 life have you lived? I mean a life wire been 0:01:45.160 --> 0:01:47.720 around some sand dunes? Wow, that's neat. I think I 0:01:47.720 --> 0:01:51.400 heard the dune singing on a TV commercial shoot out 0:01:51.440 --> 0:01:54.840 in the desert. That's where I heard it. Well, what 0:01:54.960 --> 0:01:58.560 were they singing? Do you remember they were singing? Uh? 0:01:58.960 --> 0:02:05.560 Fresh friends? No, No, these were not European dunes. So 0:02:05.640 --> 0:02:10.240 you've been, um nice, you've been around dunes that were 0:02:10.280 --> 0:02:12.920 not beach dunes, because my only experience has been just 0:02:13.000 --> 0:02:16.040 beach dunes. Standards, stay off the dunes, beach dunes. These 0:02:16.040 --> 0:02:19.520 are desert dunes. That's pretty neat. Yeah, it looked like 0:02:19.560 --> 0:02:23.240 in fact, I believe they had even done some Star 0:02:23.280 --> 0:02:29.520 Wars reshoots in this area of California. Wow, it wasn't Tunisia, 0:02:30.160 --> 0:02:33.760 but it stood in for Tunisia. So I was told, 0:02:34.600 --> 0:02:38.560 just like those hills stood in for Korea and mash 0:02:38.720 --> 0:02:42.079 that's right. But this is a Michael bay Chevy commercial, okay. 0:02:42.120 --> 0:02:44.240 And I got to stand around and watch him scream 0:02:44.280 --> 0:02:49.320 at everybody that's neat man, what a good guy? Um Like, 0:02:49.360 --> 0:02:52.880 I said, I've only been around dunes on the beach, 0:02:52.960 --> 0:02:55.959 coastal dunes, right, coastal dunes. But I was talking to 0:02:56.400 --> 0:02:59.000 you me, and I guess these would constitute coastal dunes. 0:02:59.040 --> 0:03:02.160 But she said she taught in Japan, you know, um 0:03:02.240 --> 0:03:05.760 years and years ago, and a prefecture called to Tori, 0:03:06.520 --> 0:03:10.000 which is the least populated prefecture in Japan, and they 0:03:10.080 --> 0:03:14.920 actually had some amazingly beautiful dunes which look like desert dunes, 0:03:15.480 --> 0:03:18.800 but it's coastal. So I guess they're coastal dunes. But 0:03:18.840 --> 0:03:21.040 they don't look like coastal dunes. They look like desert 0:03:21.120 --> 0:03:25.360 dunes in South Carolina. No, it's definitely not. And I 0:03:25.440 --> 0:03:28.040 was like dunes in Japan that doesn't make any sense. 0:03:28.080 --> 0:03:30.160 But I saw him with my own eyes. And unless 0:03:30.160 --> 0:03:33.560 she photoshopped these pictures they were real, which would have 0:03:33.600 --> 0:03:36.120 really been something because they weren't even her pictures. They 0:03:36.120 --> 0:03:38.520 were posted on the internet. It would be a weird thing. 0:03:39.040 --> 0:03:42.480 I suppose she could have photoshop the pictures, started a 0:03:42.520 --> 0:03:46.760 website with an unrelated name uploaded um and then made 0:03:46.760 --> 0:03:49.640 it look like she was searching just Google images, which 0:03:49.640 --> 0:03:52.520 she was just to fool me. And then she's like, 0:03:52.600 --> 0:03:56.280 I got you on a dune fake burn right, classic 0:03:56.320 --> 0:04:01.280 dune fake fake but she um. She also, by the way, 0:04:01.320 --> 0:04:04.520 she when she taught in Japan, um, she taught with 0:04:04.640 --> 0:04:07.680 our buddy Raymie, who we're going to see in Toronto soon. 0:04:07.920 --> 0:04:10.280 That's great. Which, by the way, if you haven't gotten 0:04:10.320 --> 0:04:13.120 your tickets to Chicago, it's probably too late for Toronto 0:04:13.160 --> 0:04:15.960 by the time this comes out. How about this. If 0:04:16.000 --> 0:04:18.119 you're listening to this and you haven't bought your ticket 0:04:18.200 --> 0:04:22.880 for Portland's Maine, shame on you. Okay, So sand dunes. 0:04:24.279 --> 0:04:28.479 I love this article, by the way by Debbie Ronka yep, 0:04:28.760 --> 0:04:32.719 And she basically says a sand dune needs three things 0:04:32.800 --> 0:04:36.680 to form. You need loose sand because that's the kind 0:04:36.760 --> 0:04:40.680 that can blow around you need wind to blow a 0:04:40.720 --> 0:04:44.880 sand dune around, and then you need an obstacle, which 0:04:44.920 --> 0:04:47.320 can be anything. It can be a bed of pebbles, 0:04:47.360 --> 0:04:49.440 it can be a big rock, can be a tree, 0:04:50.080 --> 0:04:53.160 but it's something for the sand to hit and say, oh, 0:04:53.400 --> 0:04:56.320 I can't go any further. And then as more and 0:04:56.320 --> 0:05:00.000 more sand hits that obstacle, the sand dune starts to build, 0:05:00.200 --> 0:05:04.840 and then the sand dune itself becomes the obstacle. In 0:05:04.960 --> 0:05:08.960 one of the most zen processes around on Earth. It 0:05:09.080 --> 0:05:13.520 really really is. It's a true like uh layering effect 0:05:14.240 --> 0:05:18.320 that if you see sped up with the time lapse camera, yeah, 0:05:18.360 --> 0:05:22.640 it's pretty remarkable. Well, that actually reveals maybe the fact 0:05:22.680 --> 0:05:27.440 of the podcast to me, sand dunes move. I thought 0:05:27.440 --> 0:05:31.360 you're gonna say time lapse photography is possible, right if 0:05:31.720 --> 0:05:34.680 but if you watch the sand dune over a long 0:05:34.800 --> 0:05:38.200 enough exposure, you would see it moving forward. And here's 0:05:38.200 --> 0:05:40.760 the thing. It doesn't just move in that like the 0:05:40.800 --> 0:05:44.200 sand gets blown around and and you know, the sand 0:05:44.240 --> 0:05:47.039 dune takes all these different shapes. It keeps its shape 0:05:47.120 --> 0:05:50.279 and just moves forward depending on the type of dune 0:05:50.560 --> 0:05:53.360 and the type of what's called wind regime in the area. 0:05:53.520 --> 0:05:57.400 That's right. I just think that it is amazing. They're 0:05:57.440 --> 0:06:01.040 clearly alive and can feel pain. So you really shouldn't 0:06:01.040 --> 0:06:03.720 walk on the sand, dude. And the shape is so 0:06:03.839 --> 0:06:06.680 dictated by the fact that, you know, maybe the wind 0:06:06.680 --> 0:06:09.240 always blows in one direction where you are maybe opposed 0:06:09.279 --> 0:06:12.839 in two directions only maybe it blows from many directions, 0:06:13.400 --> 0:06:19.599 and that's all gonna dictate this malleable living, breathing, breathing, feeling, 0:06:19.680 --> 0:06:23.400 emotional beast right, that will kill you if you don't 0:06:23.400 --> 0:06:25.960 treat it right. It has. It's killed a couple of 0:06:26.040 --> 0:06:29.400 people at least. So let's talk about how wind can 0:06:29.480 --> 0:06:33.920 move sand around. Uh. It's generally a few different ways. 0:06:34.040 --> 0:06:41.320 There's uh saltation, which is mostly like of sand. Grains 0:06:41.440 --> 0:06:44.400 move like this and that's just the wind is just 0:06:44.440 --> 0:06:48.560 bouncing them along. Yeah, I thought these percentages were pretty specific. 0:06:49.680 --> 0:06:52.560 Four percent, one percent, Like who who came up with 0:06:52.600 --> 0:06:58.160 those percentages? Okay, all right, well then they probably are accurate. 0:06:58.320 --> 0:07:02.839 There's creep, Yes, creep I'd never witnessed or heard of before, 0:07:02.880 --> 0:07:05.599 of you, I don't think. So that's the four percent 0:07:05.880 --> 0:07:08.320 um of sand moves this way, and this is when 0:07:08.920 --> 0:07:13.120 grains are colliding with other grains um, like you know, 0:07:13.160 --> 0:07:15.800 maybe gravel or something causing them to move. It's like 0:07:15.880 --> 0:07:23.440 sand croquet. Yeah. Um, salmon croquettes, No, those aren't the 0:07:23.480 --> 0:07:26.040 best croquettes if you ask me. Frankly, I'm just gonna 0:07:26.040 --> 0:07:28.280 come out and say it. The only way to eat 0:07:28.320 --> 0:07:32.960 salmon is raw. I'm sorry. Oh I love a grilled 0:07:32.960 --> 0:07:36.960 salmon with that crispy skin. M m mmm. I like 0:07:37.040 --> 0:07:41.320 grilled fish. It's just when salmon is cooked, it undergoes 0:07:41.360 --> 0:07:43.800 a taste conversion that I'm not a fan of. I 0:07:43.880 --> 0:07:46.520 prefer it raw. No, I love raw salmon for sure, 0:07:46.520 --> 0:07:49.040 but I love that crispy skin so much. Hey, i'm 0:07:49.040 --> 0:07:51.520 not yucking your young man. If you like cooked salmon, 0:07:52.040 --> 0:07:54.960 have at it. And I do like fish skin, crispy 0:07:55.000 --> 0:07:56.760 fish skin. I'm with you, but I'm more like a 0:07:56.880 --> 0:08:00.800 cooked trout fish skin kind of guy. Yeah. Uh. When 0:08:00.840 --> 0:08:04.840 I was a kid, a very big seventies meal um 0:08:04.880 --> 0:08:08.440 in my household was the canned salmon croquettes. Oh yeah, 0:08:08.480 --> 0:08:11.240 I've had those. Yeah, it's just the bones, you know, 0:08:11.320 --> 0:08:13.520 Like I don't like there to be bones in my food. 0:08:14.120 --> 0:08:16.640 I'm with you. I'll eat something off the bone. I 0:08:16.680 --> 0:08:19.560 just don't want to be expected to actually eat the bone. 0:08:20.920 --> 0:08:25.160 I guess I don't know at a good butcher or 0:08:25.200 --> 0:08:29.000 a good fisher. Okay, but don't that. But aren't there 0:08:29.040 --> 0:08:35.520 still really really tiny little bones. It depends on the salmon. 0:08:37.040 --> 0:08:41.480 But sure with you. I don't like bones either, so um. 0:08:41.520 --> 0:08:44.240 Obviously we're talking about sand dunes still. Yeah, but the 0:08:44.280 --> 0:08:46.400 suspension is the third way. We gotta finish that up 0:08:46.760 --> 0:08:50.000 right right, Um, that's where that's where the wind blows 0:08:50.280 --> 0:08:55.080 very strongly, um, so strongly and from enough different directions 0:08:55.120 --> 0:08:58.400 at once that it actually lifts the sand into the air. 0:08:59.160 --> 0:09:00.839 And this is what a US storm is, or a 0:09:00.920 --> 0:09:05.400 sandstorm or um any number of Basically, if they're sand 0:09:05.400 --> 0:09:08.559 blowing around in the air, that's this is the suspension 0:09:08.640 --> 0:09:11.679 movement of sand up though in the air. Like when 0:09:11.720 --> 0:09:14.600 you go to the beach. Sometimes you'll see sand in 0:09:14.600 --> 0:09:18.880 the right conditions blowing along the ground that couple inches 0:09:18.920 --> 0:09:21.559 off the ground. That's not the same thing, man, No, 0:09:21.720 --> 0:09:25.280 that's saltation. That hurts. That's really painful. Yeah, I guess 0:09:25.320 --> 0:09:32.120 it can hurt, can it? Oh? It can hurts. So um, 0:09:32.280 --> 0:09:37.679 we've kind of already described like how a sand dune forms, um, 0:09:37.720 --> 0:09:43.400 sort of sort of, but the there's there's a lot 0:09:43.440 --> 0:09:45.400 of different kinds of sand dunes. We're gonna get into it, 0:09:45.440 --> 0:09:50.000 don't worry. But there's a general way that a sand 0:09:50.080 --> 0:09:54.120 dune forms where the sand blows along hits a something 0:09:54.160 --> 0:09:56.680 that stops. It's for momentum, and then it starts to 0:09:56.720 --> 0:10:00.480 pile up. And when this piling up happens, a sand 0:10:00.559 --> 0:10:06.160 dune typically undergoes a fairly predictable um evolution, I guess, 0:10:06.720 --> 0:10:09.960 whereas more and more sand builds up, the sand dune 0:10:10.000 --> 0:10:13.080 gets bigger and bigger, and the sand just kind of 0:10:13.120 --> 0:10:15.920 smacks into the back of the sand dune, and the 0:10:16.040 --> 0:10:19.959 lighter sand will just continue up and over the sand dune. 0:10:20.480 --> 0:10:22.480 And then once it makes it down the other side, 0:10:22.480 --> 0:10:25.400 which is called the slip face, which is the side 0:10:25.400 --> 0:10:29.840 that's protected from the wind, the um the sand dune 0:10:29.880 --> 0:10:32.560 just kind of gets bigger and bigger. But eventually enough 0:10:32.600 --> 0:10:35.319 sand will pile up on the back side that it 0:10:35.720 --> 0:10:40.080 forms a crest where it basically piles up and forms 0:10:40.080 --> 0:10:42.320 a peak or crest or something like that. And then 0:10:42.360 --> 0:10:45.640 this crest can get so so big and so pronounced 0:10:45.840 --> 0:10:49.200 that it will actually crumble under its own weight. Yeah, 0:10:49.240 --> 0:10:53.000 I mean, it's just it's like raw physics before your 0:10:53.080 --> 0:10:57.040 very eyes. These layers, those light sands blowing over and 0:10:57.080 --> 0:11:00.240 it's layer after layer building up. Then that crest gets 0:11:00.240 --> 0:11:02.800 super tall, like you could mess around with it if 0:11:02.800 --> 0:11:04.480 you had a big bucket of dry sand with your 0:11:04.480 --> 0:11:09.160 own hand. Sort of see this effect as you drop sand. Eventually, 0:11:09.160 --> 0:11:12.760 when it does collapse, it's gonna avalanche down the slip 0:11:12.800 --> 0:11:15.720 face and there is an angle it's called the angle 0:11:15.720 --> 0:11:21.240 of repose, where it's sort of where that beautiful, Um, 0:11:21.640 --> 0:11:25.680 what's the word I'm looking for. Not symbiosis, but when 0:11:25.720 --> 0:11:28.520 when something's pushing against something, the other things pushing right back, 0:11:29.040 --> 0:11:31.360 and it all agrees that just to stop there in 0:11:31.360 --> 0:11:33.520 the middle. I don't remember what it's called, but I 0:11:33.520 --> 0:11:36.240 know what you're talking about. It is beautiful, that's basically it. 0:11:36.240 --> 0:11:39.680 It's about thirty to forty thirty four degrees in general, 0:11:40.200 --> 0:11:42.640 and that's when it just reaches that perfect angle of 0:11:42.720 --> 0:11:46.839 steepness that it's all just stable and solid. Right, So 0:11:47.400 --> 0:11:50.439 now you have a dune. It's no longer being born. 0:11:50.559 --> 0:11:54.480 It's now living, and it's it's it still can keep growing, 0:11:54.880 --> 0:11:57.439 but it's going to keep growing along these lines where 0:11:57.800 --> 0:12:00.000 you know, if if enough gets built up, it's gonna 0:12:00.000 --> 0:12:03.120 fall down into the angle of repose. More likely, the 0:12:03.200 --> 0:12:06.480 sand will just continue going over the edge and then 0:12:06.480 --> 0:12:08.480 being built up on the back side too. It's a 0:12:08.559 --> 0:12:12.120 rump will grow basically. Yeah. And if you're like, winds 0:12:12.120 --> 0:12:14.880 are really strong, it's probably gonna be taller. If the 0:12:14.880 --> 0:12:17.000 winds are really gentle, it's probably going to be more 0:12:17.040 --> 0:12:20.400 spread out. And the direction of the wind, the angle 0:12:20.480 --> 0:12:23.720 of the wind um and like we mentioned earlier, whether 0:12:23.800 --> 0:12:27.160 or not its unidirectional, bi direction or multidirectional, that's all 0:12:27.240 --> 0:12:29.040 gonna play a part into what kind of dune you're 0:12:29.040 --> 0:12:31.559 gonna get. So let's take a break and then we'll 0:12:31.600 --> 0:12:34.280 come back and talk about the different kinds of dunes. Okay, 0:12:34.400 --> 0:12:59.920 all right, Chuck. Have you ever read the book Dune? Nope? 0:13:00.440 --> 0:13:02.520 I haven't either. Have you ever seen the movie? Nope? 0:13:02.960 --> 0:13:06.320 Me either. That's interesting. You know they're making they're making 0:13:06.360 --> 0:13:11.920 it again. Uh, that's great. That Dennis villaenieu guy. So 0:13:12.400 --> 0:13:16.160 oh he's good. Yeah, he's amazing. He did the arrival, right, 0:13:17.200 --> 0:13:20.200 I think so? Yeah? Or just a arrival. The arrival 0:13:20.240 --> 0:13:22.360 is like old Charlie Sheen movie. I think, I think 0:13:22.360 --> 0:13:26.880 it's just a arrival. Okay, yeah, so, um, neither one 0:13:26.920 --> 0:13:29.000 of us has seen or red dune. We're gonna get 0:13:29.040 --> 0:13:31.520 some email about this, I think. Yeah. And I'm not 0:13:31.640 --> 0:13:33.400 knocking David Lynch either, of course, I want to throw 0:13:33.440 --> 0:13:38.480 that in there, or Frank Herbert. Yeah, I'm just kidding. 0:13:38.480 --> 0:13:42.400 I don't know anything. So um. So, like you were saying, 0:13:43.080 --> 0:13:46.720 dunes are the result of the winds that are im 0:13:46.800 --> 0:13:50.840 prevalent in the area, and the most common dune on 0:13:50.960 --> 0:13:55.040 Earth and um, little known fact, well maybe not little known, 0:13:55.080 --> 0:13:58.720 but interesting fact. Um, the most common dunes on Mars 0:13:59.240 --> 0:14:02.200 or what it called a cynic or crescent shaped dunes 0:14:03.080 --> 0:14:05.840 and these are far and away the most common. Um, 0:14:05.880 --> 0:14:09.480 which means that more often than not, in any given area, 0:14:10.040 --> 0:14:13.600 the wind is going to be blowing in the same 0:14:13.640 --> 0:14:16.600 direction basically all the time. Yeah. And this got a 0:14:16.600 --> 0:14:19.040 little confusing for me because the more I researched the 0:14:19.080 --> 0:14:22.560 types of dunes, like I saw one place it said 0:14:22.560 --> 0:14:28.120 there are five main types of sand dunes Barkin, transverse, blowout, linear, 0:14:28.160 --> 0:14:34.480 and composite. Who said that a website that seemed very 0:14:34.600 --> 0:14:38.080 educational and reliable. Weird, But I believe they are just 0:14:38.160 --> 0:14:40.200 different words for some of these, and some of these 0:14:40.240 --> 0:14:45.240 are subtypes of the main five. Because I believe a 0:14:45.360 --> 0:14:49.920 crescentic is a bark in dune. Yes, if I'm not mistaken, 0:14:50.520 --> 0:14:55.920 you're not horseshoe shaped front facing the wind, I guess. So. Yeah, 0:14:55.960 --> 0:14:58.920 that's the big thing is where is the curve pointing 0:14:59.200 --> 0:15:03.240 is the big differentiator for chryscentic. Yeah, Like I look 0:15:03.320 --> 0:15:05.920 these up online, all these pictures, and like when I 0:15:05.920 --> 0:15:09.440 saw the chriscentic, uh, these look like sort of those 0:15:09.480 --> 0:15:13.040 big beautiful dunes from Star Wars or Lawrence of Arabia. Yeah, 0:15:13.040 --> 0:15:14.720 it's what most people think of when they think of 0:15:14.960 --> 0:15:18.720 a dune. It's like a desert dune, right, exactly, thank you. 0:15:19.160 --> 0:15:21.800 So chryscentic is if you imagine it is like a 0:15:21.920 --> 0:15:25.520 U shape or a V shape. The underside or the 0:15:25.560 --> 0:15:28.320 bottom of the U or the point the outside point 0:15:28.400 --> 0:15:32.360 of the V is going to be pointing in the 0:15:32.520 --> 0:15:36.760 direction opposite the wind, so it's pointing up wind. So 0:15:36.800 --> 0:15:39.480 the wind is blowing and hitting that outside point of 0:15:39.480 --> 0:15:42.000 the V or the bottom of the U, which doesn't 0:15:42.000 --> 0:15:46.520 really make sense um to me. The parabolic, which we'll 0:15:46.520 --> 0:15:49.880 talk about later, makes more sense. But anyway, the parabolic 0:15:49.960 --> 0:15:52.160 the same as a blowout, because a blowout dune is 0:15:52.200 --> 0:15:55.880 the opposite of a bar can, and that the curve, 0:15:56.040 --> 0:15:59.480 the horseshoe curve, faces away from the wind. Yes, okay, 0:15:59.800 --> 0:16:02.160 it's gonna take five minutes to undo the confusion we 0:16:02.280 --> 0:16:05.360 just created. Well, and there are some who studies this, 0:16:05.440 --> 0:16:09.440 what kind of geologists I believe, desert ecologists. Yeah, I'm 0:16:09.440 --> 0:16:11.480 sure they are having a ball with this one. Just 0:16:11.880 --> 0:16:14.880 up a drink, everybody, Yeah, all seventeen of them, buckle up. 0:16:15.640 --> 0:16:19.040 So crescent shaped ones again, say they're U shape or 0:16:19.120 --> 0:16:20.880 V shaped, and the bottom of the U or the 0:16:20.920 --> 0:16:24.040 point of the V is pointing facing the wind, so 0:16:24.360 --> 0:16:27.960 pointing up wind, the wind blows it. The wind the 0:16:28.080 --> 0:16:30.800 sand that it's blowing onto the backside, onto the rump 0:16:30.880 --> 0:16:37.040 of this dune blows up, it falls down avalanches, uh 0:16:37.200 --> 0:16:40.280 under the slip face which is the inside of the 0:16:40.400 --> 0:16:44.040 U or the V, and it's not as protected from 0:16:44.080 --> 0:16:47.480 the wind. And what's amazing about this is because the 0:16:47.560 --> 0:16:51.760 crescent shaped dune is the result of a wind regime 0:16:51.800 --> 0:16:54.360 where the wind is blowing in one direction basically all 0:16:54.400 --> 0:16:57.240 the time. These are the dunes that can actually move 0:16:57.880 --> 0:17:01.000 and they can move pretty fast. They're one of two kinds, 0:17:01.040 --> 0:17:05.679 but they can move pretty fast across the desert, so 0:17:05.760 --> 0:17:09.480 much so that sometimes these dunes, when there's many of them, 0:17:09.600 --> 0:17:11.720 will catch up to one another, and they'll do some 0:17:11.760 --> 0:17:15.160 pretty amazing things when they catch up to one another. Yeah, 0:17:15.200 --> 0:17:18.320 and so much so that they can threaten uh like villages, 0:17:19.119 --> 0:17:21.800 and people have to try and stop these dunes. Yes, 0:17:21.920 --> 0:17:24.240 some people have been known to pour motor oil on 0:17:24.359 --> 0:17:26.800 dunes to keep them from moving. Because it winds the 0:17:26.880 --> 0:17:30.600 sand without it drying out. It's not a good one. Um. 0:17:30.680 --> 0:17:33.000 You could plant vegetation, although if you're in the desert, 0:17:33.040 --> 0:17:35.520 that's not a great great thing because your plants are 0:17:35.560 --> 0:17:38.119 just gonna die. Um more often than not. If you 0:17:38.200 --> 0:17:41.679 just put up fencing, that that becomes an obstacle for 0:17:41.800 --> 0:17:43.760 the dune, and the dune will stop in its tracks 0:17:43.760 --> 0:17:45.919 and it will just keep building up on the back side. 0:17:46.320 --> 0:17:48.960 Eventually it might be big enough to overcome the dune, 0:17:49.000 --> 0:17:51.760 but it will certainly slow it down for a good 0:17:51.760 --> 0:17:55.880 many years for sure. But the thing about that crescent shape, 0:17:55.880 --> 0:17:57.920 when when a small one catches up to a bigger one, 0:17:58.240 --> 0:18:00.760 a lot of things can happen. One thing is that 0:18:00.960 --> 0:18:04.120 it can appear as if the small one passes straight 0:18:04.160 --> 0:18:08.919 through the big one. It is amazing. And then another 0:18:09.000 --> 0:18:12.119 thing that can happen is to to um dunes. I 0:18:12.160 --> 0:18:14.359 don't remember how if they're the same size or different 0:18:14.359 --> 0:18:18.600 size when they come together, so that the arms are 0:18:18.640 --> 0:18:21.880 the wings of the horns of that crescent shape, right, 0:18:22.080 --> 0:18:25.040 not the main part, but the points that come out. 0:18:25.560 --> 0:18:28.120 Those are called the horns of actually seen arms too. 0:18:28.119 --> 0:18:30.520 There's all sorts of different names. It's a giant mess. 0:18:30.560 --> 0:18:33.840 Nobody can agree on anything with dune ecology. But when 0:18:34.160 --> 0:18:37.080 a different dune catches up and merges with it, it 0:18:37.080 --> 0:18:41.399 can actually go from two dunes to three, which is 0:18:41.440 --> 0:18:44.920 called breeding and the two So there's the one dune 0:18:44.920 --> 0:18:47.960 that remains and then the other one basically splits into 0:18:48.040 --> 0:18:51.160 two dunes that come out. The arms are the points 0:18:51.200 --> 0:18:54.280 of the original dune. So when you had two, now 0:18:54.320 --> 0:18:57.239 there's three, which is pretty astounding if you ask me, 0:18:57.320 --> 0:19:02.440 because we're talking sand dunes here and breeding new dunes. Amazing. 0:19:02.840 --> 0:19:06.440 I think it's pretty amazing too. So among the five types, 0:19:06.440 --> 0:19:09.960 there's also enlisted as a transverse dune. I didn't understand 0:19:10.000 --> 0:19:12.680 them at all. Well, I think these are the ones 0:19:12.720 --> 0:19:16.119 that their long lines of rigid dunes and they're perpendicular 0:19:16.160 --> 0:19:19.359 to the wind. Uh. They have really steep slip faces 0:19:20.000 --> 0:19:24.000 at the backsides, and they're kind of wavy. So there's 0:19:24.040 --> 0:19:25.960 a lot of sand and not a lot of plants. 0:19:26.560 --> 0:19:30.280 And I think the dunes that like you see um, 0:19:30.320 --> 0:19:33.040 like behind the beach are a lot of times are 0:19:33.080 --> 0:19:38.080 transverse dunes. Okay, if I'm not mistaken, my understanding was 0:19:38.119 --> 0:19:43.199 that parabolic we're the most um coastal dunes, maybe not 0:19:43.560 --> 0:19:47.320 the most coastal, right, and I think there are different 0:19:47.359 --> 0:19:49.680 kinds of dunes even along the coast, right, Yeah, yeah, 0:19:49.760 --> 0:19:51.840 for sure. Again, it just depends on what the wind 0:19:51.960 --> 0:19:55.000 is like in an area. And because wind regime is 0:19:55.000 --> 0:19:57.160 going to be different for every kind of area, there's 0:19:57.200 --> 0:20:00.760 different kinds of dunes. And um, what we're talking about 0:20:01.880 --> 0:20:05.960 are the standard simple kinds of dunes. Dunes can like 0:20:06.000 --> 0:20:08.439 we like we were just saying, can merge with one another. 0:20:08.840 --> 0:20:12.000 Winds can change and different types of dunes will start 0:20:12.040 --> 0:20:15.560 to form. You've got um compound and complex dunes to 0:20:15.760 --> 0:20:21.360 which can be two different kinds of dunes merged together. Um. 0:20:21.560 --> 0:20:23.520 So there's a lot of weird things that can happen 0:20:23.520 --> 0:20:28.080 with dunes. They're they're very rarely just a simple, straight up, 0:20:28.640 --> 0:20:32.600 straightforward kind of dune. Yeah, there are linear dunes. Uh. 0:20:32.640 --> 0:20:35.240 These are mostly parallel to the wind, and these form 0:20:35.320 --> 0:20:39.240 these long straight ridges and they think geologists think that 0:20:39.280 --> 0:20:42.119 they are caused by wind that blows in one They 0:20:42.119 --> 0:20:44.640 are definitely bi directional as far as the wind goes, 0:20:45.240 --> 0:20:47.560 but they think they're cause when wind blows from one 0:20:47.600 --> 0:20:50.919 direction in one part of the year and then another 0:20:50.960 --> 0:20:53.640 direction and another part of the year, right, So they're 0:20:53.680 --> 0:20:57.520 they're like long lines basically. Yeah. But it's interesting that 0:20:57.560 --> 0:20:59.600 you know, the winds will shift over you know, like 0:21:00.320 --> 0:21:02.320 the course of a year, so it's not like every 0:21:02.359 --> 0:21:06.000 day they're shifting, no, but it's enough and they're powerful 0:21:06.160 --> 0:21:09.720 enough that they're blowing any any kind of um rump 0:21:09.840 --> 0:21:12.600 or base of these and it's just a big long 0:21:12.640 --> 0:21:15.800 line of saying sometimes very sharp depending on you know, 0:21:15.880 --> 0:21:18.639 just how sharp the bi directionality of the wind is. 0:21:20.119 --> 0:21:23.119 Um star ones. This is one of my favorites. These 0:21:23.119 --> 0:21:26.200 are pretty cool. So if you tell what you would think, Yeah, 0:21:26.400 --> 0:21:28.440 if it's like a sand dune that looks a bit 0:21:28.480 --> 0:21:31.880 like a star, they have a pyramidal mound that goes 0:21:32.040 --> 0:21:35.359 up in the middle um and then at least three 0:21:35.880 --> 0:21:40.399 arms with um slip faces, you know, the avalanche face 0:21:41.480 --> 0:21:44.360 radiating out from that middle And these are the results 0:21:44.400 --> 0:21:47.480 of a bunch of different wind directions throughout a year 0:21:48.000 --> 0:21:51.040 building up. So rather than moving along the face of 0:21:51.040 --> 0:21:54.240 the earth, these things is kind of build up in space. 0:21:54.680 --> 0:21:56.680 And they're actually some of the tallest ones. I think 0:21:56.680 --> 0:22:03.600 there's some that are like fivet tall in deserts in China, um, 0:22:03.640 --> 0:22:06.240 which is pretty pretty amazing. I mean that's tall, especially 0:22:06.280 --> 0:22:08.280 if you're a sand border. Yeah, I mean you can 0:22:08.320 --> 0:22:10.760 simulate all this stuff, like you can make your hand 0:22:10.880 --> 0:22:13.280 the wind if you're at the beach and you're playing 0:22:13.320 --> 0:22:15.520 with sand. I mean you just think about if you're 0:22:15.560 --> 0:22:18.239 pushing the sand in one direction only, it's gonna look 0:22:18.280 --> 0:22:21.480 a certain way. If you push then in another direction, 0:22:21.520 --> 0:22:23.800 that's gonna look a certain way. And then in the 0:22:23.800 --> 0:22:26.240 case of a star, if you're using your hand pushing 0:22:26.280 --> 0:22:29.480 sand in and all these different directions, it's gonna grow 0:22:29.560 --> 0:22:32.919 upward and it's not gonna grow laterally. Right right. We 0:22:32.960 --> 0:22:35.520 should have probably said at the outset that it helps 0:22:35.680 --> 0:22:38.280 a lot if you go look up images of the 0:22:38.280 --> 0:22:41.800 different types of dunes we're talking about. Help me and 0:22:41.840 --> 0:22:47.040 look up. Look up dune porn. Yeah, I'm sure it's 0:22:47.040 --> 0:22:53.840 out there. Um okay, Now there's parabolic or parabolic I say. 0:22:54.119 --> 0:22:59.080 You say parabolic, I say parabolic. So these are basically 0:22:59.119 --> 0:23:04.280 the opposite of crescent shaped, where this time, the inside 0:23:04.280 --> 0:23:06.320 of the U or the inside point of the V 0:23:07.119 --> 0:23:09.919 is what the wind is blowing into, and then the 0:23:09.960 --> 0:23:12.879 outside of the U or the outside of the V 0:23:13.320 --> 0:23:16.520 is what's facing in the direction that the wind is going. 0:23:16.560 --> 0:23:19.600 But it's down wind, right. It's what you would think of, 0:23:19.640 --> 0:23:22.240 like if you're just thinking about moving sand with wind 0:23:22.359 --> 0:23:25.679 via physics. This this one makes the most sense. But 0:23:25.800 --> 0:23:29.080 the thing about parabolic that really distinguishes it from crescent 0:23:29.560 --> 0:23:34.080 is that usually they're made of sand that is, has 0:23:34.119 --> 0:23:37.680 some sort of water attached to it or vegetation so 0:23:37.720 --> 0:23:41.159 that the arms are anchored, So the arms stay in 0:23:41.200 --> 0:23:44.080 the same place. They just get longer and longer as 0:23:44.119 --> 0:23:47.439