1 00:00:03,880 --> 00:00:06,760 This is Geology Bites with Oliver Strimple. 2 00:00:08,240 --> 00:00:11,840 One of my first geological field trips was to Sicker Point on the 3 00:00:11,840 --> 00:00:15,680 southeast coast of Scotland, the site of James Hutton's famous On 4 00:00:15,680 --> 00:00:19,000 Conformity. The underlying rock there is a 5 00:00:19,000 --> 00:00:24,280 440 million year old marine turbidite and I soon discovered 6 00:00:24,280 --> 00:00:28,080 similar looking turbidites on other trips from Greenland to 7 00:00:28,080 --> 00:00:31,680 South Georgia. I was struck by their ubiquity 8 00:00:31,680 --> 00:00:35,080 in the geological record. So how do they? 9 00:00:35,080 --> 00:00:37,760 Form and why they're so widespread. 10 00:00:37,760 --> 00:00:41,840 In the record. The answer lies on the sea floor 11 00:00:42,120 --> 00:00:45,280 in one of the most powerful and least witnessed phenomena in 12 00:00:45,280 --> 00:00:48,720 geology. Turbidity currents, massive 13 00:00:48,720 --> 00:00:51,480 underwater avalanches of sediment that can travel 14 00:00:51,480 --> 00:00:56,080 hundreds of kilometres, snap cables and reshape the deep 15 00:00:56,080 --> 00:00:58,000 ocean floor in a matter of hours. 16 00:00:59,080 --> 00:01:03,800 In 2006, a single earthquake off Taiwan triggered a cascade of 17 00:01:03,800 --> 00:01:07,040 turbidity currents that sequentially severed more than 18 00:01:07,040 --> 00:01:10,880 20 undersea cables, cutting Internet and phone connections 19 00:01:10,880 --> 00:01:13,360 across Southeast Asia for nearly two months. 20 00:01:14,160 --> 00:01:17,760 And yet, because these events happen in the deep ocean, often 21 00:01:17,760 --> 00:01:21,200 without warning, we've rarely observed them directly. 22 00:01:22,640 --> 00:01:26,840 Today's guest is one of the few researchers who has, sometimes 23 00:01:26,840 --> 00:01:28,680 more directly than she'd have liked. 24 00:01:30,040 --> 00:01:33,000 Esther Sumner is an associate professor of geology and 25 00:01:33,000 --> 00:01:35,520 geophysics at the University of Southampton. 26 00:01:36,120 --> 00:01:40,000 She studies turbidity currents by combining direct sea floor 27 00:01:40,000 --> 00:01:43,560 monitoring with laboratory experiments and field studies of 28 00:01:43,560 --> 00:01:47,560 ancient turbidite outcrops. In our conversation, she 29 00:01:47,560 --> 00:01:50,720 describes what it's like to instrument an active submarine 30 00:01:50,720 --> 00:01:54,480 Canyon, what these flows have revealed about the way sediment 31 00:01:54,480 --> 00:01:58,520 moves across the sea floor, and the day her team accidentally 32 00:01:58,520 --> 00:02:02,000 flew an underwater robot into a live turbidity current. 33 00:02:03,280 --> 00:02:05,840 Esther Sumner, welcome to GEOLOGY BITES. 34 00:02:06,200 --> 00:02:07,720 Thank you very much for inviting me. 35 00:02:08,280 --> 00:02:12,680 So what exactly are turbidites? Turbidites are the deposits of a 36 00:02:12,680 --> 00:02:15,960 type of sea floor avalanche called a turbidity current, and 37 00:02:15,960 --> 00:02:19,000 so turbidity currents are the same family as flows, as things 38 00:02:19,000 --> 00:02:21,200 like snow avalanches and pyroclastic flows. 39 00:02:21,200 --> 00:02:23,160 So that gives you an idea of what they look like. 40 00:02:23,640 --> 00:02:26,440 But the types of materials that are there carrying anything from 41 00:02:26,440 --> 00:02:29,440 clay sized material to sand sized material and even up to 42 00:02:29,440 --> 00:02:32,120 boulders and bigger. And these are really big flows 43 00:02:32,120 --> 00:02:35,400 that carry lots of sediments. They can travel big distances, 44 00:02:35,400 --> 00:02:39,280 so hundreds, sometimes even in excess of 1000 kilometers and 45 00:02:39,280 --> 00:02:42,120 they can have a range of durations that but that can be 46 00:02:42,240 --> 00:02:44,760 hours or in some cases even days. 47 00:02:44,760 --> 00:02:49,400 So when we look at a rock in the field, how can we distinguish A 48 00:02:49,400 --> 00:02:52,520 turbidite from other kinds of marine sedimentary rocks? 49 00:02:52,960 --> 00:02:55,480 Generally, if you're looking at a sort of sequence of 50 00:02:55,480 --> 00:02:57,760 turbidites, so a turbidite succession, you're going to be 51 00:02:57,760 --> 00:03:00,840 looking at sequence of interbedded sandstones and mud 52 00:03:00,840 --> 00:03:03,720 stones. Now if we're thinking about an 53 00:03:03,720 --> 00:03:06,520 individual turbidity current events or an individual 54 00:03:06,520 --> 00:03:09,960 turbidite, then I guess classically we would identify 55 00:03:09,960 --> 00:03:13,000 this as a normally graded sand with a mud cap. 56 00:03:13,080 --> 00:03:16,000 So normal grading being big grains at the bottom, small 57 00:03:16,000 --> 00:03:18,720 grains at the top, and then a characteristic series of 58 00:03:18,720 --> 00:03:21,360 sedimentary structures with structureless sand at the bottom 59 00:03:21,400 --> 00:03:25,440 overlaying by plain laminator sand oberlain by ripple scale 60 00:03:25,440 --> 00:03:29,360 cross laminated sand. I think in reality actually it's 61 00:03:29,360 --> 00:03:32,320 quite rare to see exactly that and deposits are much more 62 00:03:32,320 --> 00:03:34,120 varied. And that really probably 63 00:03:34,120 --> 00:03:37,600 reflects that that deposit would form if we had a very simple 64 00:03:37,600 --> 00:03:41,240 dilute decelerating flow and that's just not always the case. 65 00:03:41,640 --> 00:03:46,120 What triggers A turbidity flow? So my simple answer would be 66 00:03:46,120 --> 00:03:48,320 that we know that things like earthquakes can trigger 67 00:03:48,320 --> 00:03:51,600 turbidity currents, big storms. So if you've got a big storm, 68 00:03:51,640 --> 00:03:54,200 you might have storm waves basically pounding the 69 00:03:54,560 --> 00:03:57,320 continental shelf, re suspending sediment that can form a 70 00:03:57,320 --> 00:04:00,240 turbidity current. River discharge can cause 71 00:04:00,240 --> 00:04:03,000 turbidity currents, especially at for example, deltas. 72 00:04:03,280 --> 00:04:05,920 So there it might be that the sort of sediment laden river 73 00:04:05,920 --> 00:04:08,560 water is actually sort of plunging down into the ocean 74 00:04:08,560 --> 00:04:11,160 forming A turbidity current, or it might be that the delta 75 00:04:11,160 --> 00:04:14,440 front, which is relatively steep area collapses to form a 76 00:04:14,440 --> 00:04:16,920 turbidity current. Pyroclastic flows entering the 77 00:04:16,920 --> 00:04:20,360 sea can generate turbidity currents and so and things like 78 00:04:20,360 --> 00:04:22,360 fishing. So if there's human impacts like 79 00:04:22,360 --> 00:04:25,440 trawling in an area, basically anything where you're 80 00:04:25,440 --> 00:04:29,320 destabilizing some sediment in water can form a turbidity 81 00:04:29,320 --> 00:04:32,040 current. I think I should probably make 82 00:04:32,040 --> 00:04:35,240 the point that just because you have one of these triggers 83 00:04:35,240 --> 00:04:37,160 doesn't mean you'll get a turbidity current. 84 00:04:37,600 --> 00:04:40,000 And actually many times when we're measuring turbidity 85 00:04:40,000 --> 00:04:42,240 currents, we don't really understand what triggered them. 86 00:04:42,840 --> 00:04:47,280 And so I think what we're starting to understand is what 87 00:04:47,280 --> 00:04:50,520 might be equally important or or maybe even more important than 88 00:04:50,520 --> 00:04:52,520 triggers are actually preconditioning. 89 00:04:52,800 --> 00:04:56,760 So preconditioning often just means basically what sediment is 90 00:04:56,760 --> 00:04:59,680 there available to fail in the event of one of these triggers 91 00:04:59,680 --> 00:05:02,840 happening. So you can imagine, let's say 92 00:05:02,840 --> 00:05:05,120 you have an earthquake, but there isn't a lot of sediment 93 00:05:05,160 --> 00:05:07,880 available to be destabilized, then you won't necessarily 94 00:05:07,880 --> 00:05:12,160 generate A turbidity current. So I guess in a simple way is 95 00:05:12,160 --> 00:05:14,920 this combination of preconditioning combined with 96 00:05:14,960 --> 00:05:18,000 some kind of trigger? Is there a typical? 97 00:05:18,120 --> 00:05:21,560 Setting where turbidity currents happen, like on continental 98 00:05:21,560 --> 00:05:23,720 shells. Or on the flanks. 99 00:05:23,720 --> 00:05:26,960 Of seamounts. So in terms of sort of settings, 100 00:05:26,960 --> 00:05:30,720 so anywhere really where you've got a sediment water mixture 101 00:05:30,720 --> 00:05:34,840 going into another body of water, so you can form turbidity 102 00:05:34,840 --> 00:05:38,040 currents in lakes, you can form them in fields, you can form 103 00:05:38,040 --> 00:05:40,920 them in the oceans. And I think most commonly we 104 00:05:40,920 --> 00:05:44,840 think about them occurring in the oceans and there really they 105 00:05:44,840 --> 00:05:47,520 can flow all the way from the coastlines to the continental 106 00:05:47,520 --> 00:05:49,560 shelves right out into the deep sea. 107 00:05:49,840 --> 00:05:53,480 I think one of the interesting things about this is that they 108 00:05:53,480 --> 00:05:56,920 can actually do this on remarkably low gradients. 109 00:05:57,160 --> 00:06:01,200 So when we talk about slopes in the ocean, these are normally 110 00:06:01,200 --> 00:06:03,000 actually really quite pathetic slopes. 111 00:06:03,000 --> 00:06:05,280 So let's say we're in a submarine Canyon. 112 00:06:05,560 --> 00:06:08,640 There's probably a slope of say 2°, maybe a little more, a 113 00:06:08,640 --> 00:06:11,760 little less. If we exit that Canyon in deeper 114 00:06:11,760 --> 00:06:14,560 waters, so we go out onto a basin plain, you're looking at a 115 00:06:14,560 --> 00:06:18,280 slope of 1° or even much less than a degree, maybe half a 116 00:06:18,280 --> 00:06:22,080 degree or less. So I often say to people, well, 117 00:06:22,600 --> 00:06:25,240 as far as I'm aware, something like a Premier League football 118 00:06:25,240 --> 00:06:28,360 pitch has that kind of slope and over say half a degree for 119 00:06:28,360 --> 00:06:30,240 drainage. And we would think of that as 120 00:06:30,240 --> 00:06:32,120 flat. But these are the kind of Flopes 121 00:06:32,120 --> 00:06:34,800 that turbidity currents can travel along, and they can 122 00:06:34,800 --> 00:06:37,800 travel great distances, maybe hundreds of kilometers on those 123 00:06:37,800 --> 00:06:39,680 slopes, going at meters per second. 124 00:06:39,960 --> 00:06:43,000 That's interesting. So I guess this is all because 125 00:06:43,000 --> 00:06:46,120 these flows are happening underwater where because of the 126 00:06:46,120 --> 00:06:49,280 buoyancy effect, you can think of the gravity as being much 127 00:06:49,280 --> 00:06:52,600 lower. And so that can enable them to 128 00:06:52,600 --> 00:06:56,840 move down very gentle gradients and also have these much longer 129 00:06:56,840 --> 00:06:58,880 durations that you mentioned. Yeah. 130 00:06:58,880 --> 00:07:01,440 So certainly that has to play a part. 131 00:07:01,520 --> 00:07:04,360 You've got your sediment particles and they're settling 132 00:07:04,360 --> 00:07:06,800 in water. If we put the same particles in 133 00:07:06,800 --> 00:07:10,440 air, they fall out more quickly. And so the thing that's driving 134 00:07:10,440 --> 00:07:13,280 these flows is the density difference between the flow and 135 00:07:13,280 --> 00:07:16,160 the surrounding ambient fluid, in our case seawater. 136 00:07:16,920 --> 00:07:19,440 And so that's one part of the story, but I think there's more 137 00:07:19,440 --> 00:07:20,960 to the story. So there's some really 138 00:07:20,960 --> 00:07:25,320 interesting recent work showing that some turbidity currents can 139 00:07:25,320 --> 00:07:28,720 reach a steady state, and so really steady state, meaning a 140 00:07:28,720 --> 00:07:31,960 more or less constant velocity. And so when they're doing that, 141 00:07:31,960 --> 00:07:35,640 they must be achieving a more or less constant density because 142 00:07:35,640 --> 00:07:39,280 that's what's driving them. And the way that we image them 143 00:07:39,280 --> 00:07:43,520 doing this is that the flows that do this, at the front of 144 00:07:43,520 --> 00:07:45,320 the flow, there's a dense near bed layer. 145 00:07:45,320 --> 00:07:48,440 And that dense layer seems to be able to erode sediment into 146 00:07:48,440 --> 00:07:50,880 itself. So it's effectively feeding the 147 00:07:50,880 --> 00:07:53,040 flow. And then two things can happen. 148 00:07:53,040 --> 00:07:55,360 If it keeps feeding itself, your flow is going to speed up and 149 00:07:55,360 --> 00:07:57,920 get faster. But what often seems to happen 150 00:07:58,160 --> 00:08:01,120 is it must then Chuck some of that sediment into the rear 151 00:08:01,120 --> 00:08:04,040 parts of the flow where it can get deposited out. 152 00:08:04,240 --> 00:08:06,720 And so the flow as a whole is maintaining this constant 153 00:08:06,720 --> 00:08:08,760 density and therefore constant velocity. 154 00:08:09,040 --> 00:08:12,360 And so the long durations somewhat an effect of that 155 00:08:12,360 --> 00:08:15,000 probably that you reach this constant velocity. 156 00:08:15,040 --> 00:08:18,320 And then the other thing that's happening is that flow head 157 00:08:18,320 --> 00:08:20,960 tends to accelerate away from the body of the flow. 158 00:08:21,440 --> 00:08:23,400 So your flow stretches out and gets longer. 159 00:08:23,400 --> 00:08:26,040 So through time, it's quite weird, but through time, the 160 00:08:26,040 --> 00:08:28,640 length of your turbidity current is getting longer and longer. 161 00:08:28,920 --> 00:08:30,560 I mean, this gets called auto suspension. 162 00:08:30,560 --> 00:08:33,440 It's actually something which was sort of theorised in the 163 00:08:33,440 --> 00:08:37,760 1960s, nineteen 80s, that actually very recently we have 164 00:08:37,760 --> 00:08:41,080 data from direct monitoring of tubidity currents that suggests 165 00:08:41,080 --> 00:08:44,440 it does indeed happen and might be quite an important reason for 166 00:08:44,880 --> 00:08:47,160 how they can travel such long distances. 167 00:08:47,560 --> 00:08:50,480 And when we're talking about distances and lateral spatial 168 00:08:50,480 --> 00:08:52,520 scales, what are we talking about? 169 00:08:53,520 --> 00:08:56,400 In terms of distances travelled, so I mean, it depends on your 170 00:08:56,400 --> 00:08:58,720 turbidity current, right? Not all of them go these great 171 00:08:58,720 --> 00:09:01,040 distances and that's quite interesting in itself. 172 00:09:01,480 --> 00:09:04,880 But the really long duration flows can be travelling hundreds 173 00:09:04,880 --> 00:09:08,600 or in excess of 1000 kilometers of distance. 174 00:09:08,840 --> 00:09:11,800 How far they spread laterally really depends on their setting. 175 00:09:12,000 --> 00:09:14,200 So if they're combined within a submarine Canyon, they can't 176 00:09:14,200 --> 00:09:16,560 spread laterally. Once you get out of the Canyon, 177 00:09:16,560 --> 00:09:18,760 out of the mouth of the Canyon onto a submarine fan where they 178 00:09:18,760 --> 00:09:22,040 can spread out, then it's somewhat going to depend 179 00:09:22,040 --> 00:09:24,080 actually on the sort of characteristics of that 180 00:09:24,080 --> 00:09:25,760 submarine fan. Because even in that setting you 181 00:09:25,760 --> 00:09:29,720 have some confinement from channels, but individual flows 182 00:09:29,720 --> 00:09:33,520 could be many kilometres wide. So these are big, big flows. 183 00:09:33,560 --> 00:09:37,120 And how long can they last? So in terms of durations, when 184 00:09:37,120 --> 00:09:40,520 we're monitoring them, I think we have to say that the typical 185 00:09:40,520 --> 00:09:43,120 duration for a turbidity current is on the scale of hours. 186 00:09:43,600 --> 00:09:47,200 But then in certain settings, so Congo Canyon off West Africa 187 00:09:47,200 --> 00:09:50,240 being one of them, turbidity grants have been monitored for 188 00:09:50,240 --> 00:09:53,680 much, much longer durations, so days or even in excess of weeks 189 00:09:53,680 --> 00:09:56,080 in duration. So really long duration flows 190 00:09:56,360 --> 00:09:58,880 and these are the flows that are going really long distances. 191 00:09:59,160 --> 00:10:03,040 You mentioned the flows off the mouth of the Congo River. 192 00:10:03,200 --> 00:10:07,120 In fact, there's a giant submarine fan in the Bay of 193 00:10:07,120 --> 00:10:09,920 Bengal at the mouth of the Ganges River, which I suppose is 194 00:10:10,000 --> 00:10:12,760 filling up with sediment eroded down from the Himalayas. 195 00:10:13,320 --> 00:10:18,360 Are those kind of huge submarine fans also built up by repeated 196 00:10:18,360 --> 00:10:21,160 turbidity currents? Yes, yes, absolutely. 197 00:10:21,160 --> 00:10:24,200 Basically you've got the aggregation from lots of 198 00:10:24,200 --> 00:10:26,440 turbidity currents over long time periods. 199 00:10:26,880 --> 00:10:29,920 So with something like that system, you've got the Ganges 200 00:10:29,920 --> 00:10:33,240 and other rivers, which are effectively feeding sediment 201 00:10:33,240 --> 00:10:36,960 into your coastline. And then that sediment ends up 202 00:10:36,960 --> 00:10:39,600 in submarine canyons. So submarine canyons are 203 00:10:39,600 --> 00:10:41,720 basically just giant canyons on the sea floor. 204 00:10:41,720 --> 00:10:44,240 So you imagine a Canyon on land, they look somewhat like that, 205 00:10:44,240 --> 00:10:45,960 often on a slightly larger scale. 206 00:10:46,560 --> 00:10:49,640 So your sediment ends up in your Canyon, gets destabilised, forms 207 00:10:49,640 --> 00:10:52,280 the turbidity current. When that turbidity current is 208 00:10:52,360 --> 00:10:55,280 in that Canyon, it's quite an efficient place for it to be. 209 00:10:55,280 --> 00:10:56,920 It's confined, so it keeps going. 210 00:10:57,320 --> 00:11:00,640 Once it reaches that Canyon mouth, suddenly it's unconfined 211 00:11:00,680 --> 00:11:04,680 and it can spread out and so it slows down, it loses energy and 212 00:11:04,680 --> 00:11:06,920 so starts depositing its sediment load. 213 00:11:07,240 --> 00:11:10,160 And so you end up with this basically cone shaped pile of 214 00:11:10,160 --> 00:11:12,760 sediment at your Canyon mouth called the submarine fan. 215 00:11:13,160 --> 00:11:15,960 And then this is forming over really long time scales. 216 00:11:15,960 --> 00:11:19,440 So you're looking at millions, if not 10s of millions of years. 217 00:11:19,440 --> 00:11:21,920 So lots and lots of turbidity currents stacked up. 218 00:11:22,360 --> 00:11:25,040 And these are huge volumes of sediment. 219 00:11:25,040 --> 00:11:27,920 They're some of the largest sediment accumulations on Earth. 220 00:11:27,920 --> 00:11:31,720 So the Bengal fan that you mentioned, I mean, this is in 221 00:11:31,720 --> 00:11:35,480 excess of 3000 kilometers long, 1000 kilometers wide and in 222 00:11:35,480 --> 00:11:37,640 places greater than 15 kilometers thick. 223 00:11:37,640 --> 00:11:39,240 So that's a massive amount of sediment. 224 00:11:39,960 --> 00:11:42,480 And then you're saying, you know, this sediment comes from 225 00:11:42,640 --> 00:11:45,920 weathering of the Himalayas. And that's quite interesting in 226 00:11:45,920 --> 00:11:49,120 itself, that this big pile of sediment on the sea floor is 227 00:11:49,120 --> 00:11:53,040 basically an archive of how the Himalayas have eroded in 228 00:11:53,040 --> 00:11:55,200 response to changing tectonics and climate. 229 00:11:55,800 --> 00:11:59,520 So yeah, they're just really interesting, basically archives 230 00:11:59,520 --> 00:12:02,720 of sort of tectonic climate histories in the past. 231 00:12:02,720 --> 00:12:06,280 But I think if we think about in the present day, one of the 232 00:12:06,280 --> 00:12:09,240 things that turbidity currents might be doing is feeding 233 00:12:09,240 --> 00:12:10,960 pollutants to that submarine fan. 234 00:12:10,960 --> 00:12:14,480 So if we've got pollutants mixed up with our sediments on the 235 00:12:14,480 --> 00:12:17,240 continental shelf, and those might be things like plastics or 236 00:12:17,760 --> 00:12:21,160 pesticides, they also have the possibility of making the way 237 00:12:21,160 --> 00:12:23,040 all the way out to the submarine fan. 238 00:12:23,360 --> 00:12:26,120 Let's talk about how you go about studying turbidity 239 00:12:26,120 --> 00:12:29,760 currents, both with your experimental modelling and with 240 00:12:29,760 --> 00:12:32,600 your work in the field. I guess I'll start with the 241 00:12:32,600 --> 00:12:34,720 field. I may be a little bit weird 242 00:12:34,720 --> 00:12:37,040 because when I talk about the field, sometimes I'm talking 243 00:12:37,040 --> 00:12:40,160 about on land and sometimes I'm talking about field work at sea. 244 00:12:40,720 --> 00:12:43,520 So on land we're talking about sort of hiking up mountains and 245 00:12:43,520 --> 00:12:45,720 looking at outcrops on the sea floor. 246 00:12:45,720 --> 00:12:48,440 We can do something really similar by taking sediment. 247 00:12:48,440 --> 00:12:51,800 Cause so basically we throw a big metal tube with a weight on 248 00:12:51,800 --> 00:12:54,920 it at the sea floor. It sinks into those sort of 249 00:12:54,920 --> 00:12:56,480 layers of sediment beneath the sea floor. 250 00:12:56,480 --> 00:12:59,400 And hopefully we pull out a tube of sediment, split it open and 251 00:12:59,400 --> 00:13:01,520 actually we can look at the layers within. 252 00:13:02,280 --> 00:13:04,840 My reason for starting with field deposits is I think it's 253 00:13:04,840 --> 00:13:07,560 really important point to make that this is the biggest data 254 00:13:07,560 --> 00:13:11,360 set we have about turbidites, which tells us about their 255 00:13:11,520 --> 00:13:13,280 characteristics and their dynamics. 256 00:13:13,280 --> 00:13:16,120 And it's also a data set that spans geological time. 257 00:13:17,120 --> 00:13:20,440 In terms of how we actually look at turbidites in the geological 258 00:13:20,440 --> 00:13:22,720 record. It's actually really simple. 259 00:13:22,720 --> 00:13:25,200 We look at things like grading patterns, we look at things like 260 00:13:25,200 --> 00:13:29,160 sedimentary strictures, and then we try to interpret what does 261 00:13:29,160 --> 00:13:32,480 that mean about how that flow was behaving however many 262 00:13:32,800 --> 00:13:36,160 million years ago. Now, there's a slight issue in 263 00:13:36,160 --> 00:13:40,240 doing this, and this was once illustrated to me quite 264 00:13:40,240 --> 00:13:42,840 amusingly on a sort of conference field trip. 265 00:13:42,840 --> 00:13:45,640 So we were up in the Italian Apennines where there's some 266 00:13:45,640 --> 00:13:48,360 really exquisite sequences of turbidites. 267 00:13:48,880 --> 00:13:51,280 And so all the people stood around this outcrop, their job 268 00:13:51,280 --> 00:13:54,880 is to research turbidites. We're looking at this outcrop, 269 00:13:55,040 --> 00:13:58,080 we're making really similar observations to one another, but 270 00:13:58,080 --> 00:14:00,000 actually some of our interpretations are wildly 271 00:14:00,000 --> 00:14:03,160 different. And so this I think illustrates 272 00:14:03,160 --> 00:14:07,560 the problem of trying to interpret flow dynamics from 273 00:14:07,560 --> 00:14:11,120 deposits is that you're trying to interpret the dynamics of 274 00:14:11,120 --> 00:14:15,440 something that actually we have very few actual observations of 275 00:14:15,440 --> 00:14:17,000 the thing we're trying to interpret. 276 00:14:17,480 --> 00:14:21,680 And so for me, this is where experiments can be really, 277 00:14:21,680 --> 00:14:24,720 really useful. So there's different ways we can 278 00:14:24,720 --> 00:14:26,840 do experiments about turbidity currents. 279 00:14:26,840 --> 00:14:29,360 So one way is to generate sort of small scale turbidity 280 00:14:29,360 --> 00:14:33,160 currents in the laboratory, so actually generating a little 281 00:14:33,160 --> 00:14:36,080 density current. And the other thing we can do, 282 00:14:36,080 --> 00:14:38,720 which is I've what I've focused on more is actually trying to 283 00:14:38,720 --> 00:14:40,520 look at aspects of their behaviour. 284 00:14:40,840 --> 00:14:43,400 So for example, in my own experiments, what I've tended to 285 00:14:43,400 --> 00:14:48,120 do is sort of generate fast moving slurries of sand and clay 286 00:14:48,760 --> 00:14:51,080 and then change how the flow is behaving. 287 00:14:51,080 --> 00:14:53,200 So artificially change the velocity of the flow, 288 00:14:53,480 --> 00:14:56,560 artificially decelerate the flow in different ways, and then 289 00:14:56,560 --> 00:14:59,360 actually look how does that information about the flow get 290 00:14:59,360 --> 00:15:02,200 recorded in the deposit? Because then you can then 291 00:15:02,200 --> 00:15:05,120 hopefully take that information into the field to try and help 292 00:15:05,120 --> 00:15:09,480 you make better interpretations. What I would say is someone 293 00:15:09,480 --> 00:15:12,480 who's done quite a few experiments, they also make me 294 00:15:12,480 --> 00:15:15,040 slightly nervous because you always have this slight worry of 295 00:15:15,040 --> 00:15:18,920 how well does what I'm doing in the lab actually scale with 296 00:15:18,920 --> 00:15:22,040 these full scale flows in the real world. 297 00:15:22,680 --> 00:15:27,080 So I guess where we're at now is in the last couple of decades 298 00:15:27,080 --> 00:15:30,200 we've started being able to actually directly monitor 299 00:15:30,200 --> 00:15:33,000 turbidity currents in the oceans in some situations. 300 00:15:33,000 --> 00:15:35,920 So I I can talk a little bit more about that if you like. 301 00:15:35,960 --> 00:15:36,960 Yeah. That would be great. 302 00:15:36,960 --> 00:15:38,200 I'd love to hear. About how you. 303 00:15:38,560 --> 00:15:41,080 Monitor turbidity currents in real time in the ocean. 304 00:15:41,680 --> 00:15:45,680 The main way we do this is using moorings, so a mooring is 305 00:15:45,680 --> 00:15:46,800 something we put on the sea floor. 306 00:15:46,800 --> 00:15:49,160 It's got a big weight at the bottom, some floatation at the 307 00:15:49,160 --> 00:15:51,600 top, and a basically a vertical wire in between. 308 00:15:52,440 --> 00:15:54,800 And then we can attach instruments to that wire. 309 00:15:54,800 --> 00:15:58,480 So the overall mooring's a couple of 100 meters high and it 310 00:15:58,480 --> 00:16:01,320 sat on the sea floor. Now, one of the main instruments 311 00:16:01,320 --> 00:16:04,080 that we used to do this is a thing called an acoustic Doppler 312 00:16:04,080 --> 00:16:07,960 Current Profiler or ADCP. And so these are basically the 313 00:16:07,960 --> 00:16:11,040 speed traps of the ocean. So they work in quite a similar 314 00:16:11,040 --> 00:16:15,240 way to say, a police speed trap. But whereas the police officer 315 00:16:15,240 --> 00:16:19,240 is using radar, is firing out radio waves that are bouncing 316 00:16:19,240 --> 00:16:22,560 off moving vehicles, we're using sound pulses. 317 00:16:22,560 --> 00:16:24,640 So this instrument's basically looking down towards the sea 318 00:16:24,640 --> 00:16:27,200 floor, sending sound pulses down into the water column. 319 00:16:27,400 --> 00:16:30,920 They're then bouncing off moving particles and we can build up a 320 00:16:30,920 --> 00:16:33,480 really nice picture of the velocity structure of flow. 321 00:16:34,400 --> 00:16:36,760 We do have a major issue with these instruments is that they 322 00:16:36,760 --> 00:16:39,920 actually don't penetrate very well into concentrated layers 323 00:16:39,920 --> 00:16:43,160 within flows, which we keep finding in the oceans. 324 00:16:43,600 --> 00:16:45,360 The other issue we have sometimes have with them is they 325 00:16:45,360 --> 00:16:47,600 actually get transported by the flow because obviously these are 326 00:16:47,600 --> 00:16:50,080 destructive flows that we're trying to measure. 327 00:16:50,560 --> 00:16:54,080 So we have some other quite neat bits of kit to deal with this. 328 00:16:54,480 --> 00:16:56,560 So we basically have smart boulders. 329 00:16:57,000 --> 00:16:59,360 So a smart boulder, if you imagine it's about the size of a 330 00:16:59,360 --> 00:17:02,600 basketball and it's got its own pressure sensors, you know, 331 00:17:02,600 --> 00:17:05,760 water depth it's at, it's got an accelerometer in it. 332 00:17:06,200 --> 00:17:09,160 And that accelerometer is basically just telling us how is 333 00:17:09,160 --> 00:17:11,800 that boulder moving? Is it, say, sliding in the flow? 334 00:17:11,800 --> 00:17:15,280 Is it rolling in the flow? So what's the nature of the flow 335 00:17:15,280 --> 00:17:17,880 that it's moving within? And then other people use all 336 00:17:17,880 --> 00:17:20,440 sorts of instruments, so hydrophones to listen for 337 00:17:20,440 --> 00:17:23,160 turbidity currents, seismometers to sort of feel turbidity 338 00:17:23,160 --> 00:17:25,760 currents. One thing in all of these cases, 339 00:17:25,760 --> 00:17:29,280 though, is we have to go somewhere we know has frequent 340 00:17:29,280 --> 00:17:32,560 flows because we have to leave those instruments on the sea 341 00:17:32,560 --> 00:17:36,680 floor for quite long periods of time and then either go back and 342 00:17:36,680 --> 00:17:39,600 collect our instruments. Or in the case of a mooring, if 343 00:17:39,600 --> 00:17:42,600 we've been unlucky, it's it's been damaged and cut loose and 344 00:17:42,600 --> 00:17:44,840 floated to the surface. Or in the case of some 345 00:17:44,840 --> 00:17:46,640 instruments like those smart boulders, they're actually 346 00:17:46,640 --> 00:17:50,040 designed that with time they'll pop some weights out, float to 347 00:17:50,040 --> 00:17:52,240 the surface. If we're working in a coastal 348 00:17:52,240 --> 00:17:54,800 area, float to the shoreline. They've got GPS on them. 349 00:17:55,240 --> 00:17:58,320 We can go and collect them. In reality, beachcombers usually 350 00:17:58,320 --> 00:18:01,640 collect them for us. So those are kind of approaches 351 00:18:01,640 --> 00:18:04,840 to understanding flow dynamics. So I think it's really this 352 00:18:04,840 --> 00:18:08,680 combination of field work, experiments and then more 353 00:18:08,680 --> 00:18:11,120 recently we've been able to actually start directly 354 00:18:11,120 --> 00:18:14,200 monitoring flows. So as I mentioned in the 355 00:18:14,200 --> 00:18:18,640 introduction, you actually use remotely operated vehicles, sort 356 00:18:18,640 --> 00:18:25,400 of underwater robots to study turbidity currents and even flew 357 00:18:25,400 --> 00:18:28,720 into one once. Can you tell us about that? 358 00:18:29,320 --> 00:18:33,960 So we do use remotely operated vehicles to, for example, take 359 00:18:33,960 --> 00:18:35,360 sediment cores from the sea floors. 360 00:18:35,560 --> 00:18:38,040 There are methods by which we can attach coring devices to 361 00:18:38,040 --> 00:18:40,480 Rovs, collect turbidites from the sea floor. 362 00:18:40,720 --> 00:18:43,360 We did have quite an exciting day in the office, so to speak, 363 00:18:43,360 --> 00:18:47,240 back in 2013 where we did indeed get a remotely operated vehicle 364 00:18:47,360 --> 00:18:48,960 and trained in a turbidity current. 365 00:18:49,400 --> 00:18:53,000 So at the time I was working for an institute in California 366 00:18:53,000 --> 00:18:56,400 called Monterey Bay Chrome Research Institute, and we were 367 00:18:56,400 --> 00:18:58,680 doing some work in Northern California. 368 00:18:58,680 --> 00:19:00,760 We were actually meant to be collecting samples of gas 369 00:19:00,760 --> 00:19:02,880 hydrates, but it was really bad weather. 370 00:19:02,880 --> 00:19:05,720 It's a really awful set of days to be honest it. 371 00:19:06,400 --> 00:19:10,120 And what we realised is there was basically one place we could 372 00:19:10,120 --> 00:19:13,080 go and do some work on this particular day, and that was we 373 00:19:13,080 --> 00:19:15,880 could collect some cores using this remotely operated vehicle 374 00:19:15,880 --> 00:19:20,120 from Mendocino Canyon. And so I should explain probably 375 00:19:20,120 --> 00:19:21,520 what a remotely operated vehicle is. 376 00:19:21,520 --> 00:19:24,240 So this is basically an underwater robot. 377 00:19:24,320 --> 00:19:27,320 You can think of it as being about very roughly the size of a 378 00:19:27,320 --> 00:19:29,720 car. It's an unmanned vehicle, so 379 00:19:29,720 --> 00:19:32,120 there's nobody inside it, which is good news on this day. 380 00:19:32,480 --> 00:19:35,280 It's attached to the ship by a wire and it's controlled from a 381 00:19:35,280 --> 00:19:37,480 control room on board the ship. So you imagine on board the 382 00:19:37,480 --> 00:19:40,320 ship, you've got a room with sort of pilots looking like 383 00:19:40,320 --> 00:19:42,800 they're playing video games, flying the ROV round on the sea 384 00:19:42,800 --> 00:19:45,280 floor and scientists telling them what they'd like them to 385 00:19:45,280 --> 00:19:48,000 do. So we've basically flown this 386 00:19:48,040 --> 00:19:50,800 remotely operated vehicle down into this Canyon. 387 00:19:51,280 --> 00:19:55,240 We're sitting on the sea floor. Now, obviously it's very dark on 388 00:19:55,240 --> 00:19:57,680 the sea floor, but these vehicles have incredible light. 389 00:19:57,680 --> 00:20:00,440 So normally we can see many meters ahead of us. 390 00:20:01,120 --> 00:20:02,920 And that was our situation when we landed. 391 00:20:03,160 --> 00:20:06,240 But then suddenly it all goes dark and we're basically 392 00:20:06,240 --> 00:20:08,640 surrounded by sediment and there's a strong current coming 393 00:20:08,640 --> 00:20:10,920 down the Canyon. And the pilots are complaining 394 00:20:10,920 --> 00:20:13,760 that it's it's really quite difficult to keep the vehicles, 395 00:20:13,760 --> 00:20:16,720 the ROV in position. And so in order to try and 396 00:20:16,720 --> 00:20:19,800 stabilise the vehicle, they lift it off the sea floor. 397 00:20:20,120 --> 00:20:22,800 At the moment they lift it off the sea floor, the vehicle 398 00:20:22,800 --> 00:20:25,320 starts travelling down the Canyon at nearly a metre per 399 00:20:25,320 --> 00:20:28,040 second, despite the fact that they're trying to fly it up the 400 00:20:28,040 --> 00:20:30,360 Canyon at about a metre per second. 401 00:20:30,680 --> 00:20:33,600 So we got some very interesting observations basically from the 402 00:20:33,600 --> 00:20:36,760 perspective of being a particle within the turbidity currents. 403 00:20:36,760 --> 00:20:40,320 They did get the vehicle out of the turbidity currents and I 404 00:20:40,320 --> 00:20:42,680 think they described the situation quite well because 405 00:20:42,680 --> 00:20:45,720 they described it as like flying an ROV in a tornado. 406 00:20:45,920 --> 00:20:48,240 So that's what it feels like to be a particle in a turbidity 407 00:20:48,240 --> 00:20:50,200 current. There were some instruments on 408 00:20:50,200 --> 00:20:52,040 this vehicle. So actually we were able to get 409 00:20:52,040 --> 00:20:55,520 some quite nice data about the stratification in this flow. 410 00:20:56,040 --> 00:20:58,960 There's basically 2 layers to the flow, a layer at the bottom 411 00:20:58,960 --> 00:21:02,640 flow, which was relatively dense and then a really dilute cloud 412 00:21:02,640 --> 00:21:04,360 on top of that. So that near bed layer was a 413 00:21:04,600 --> 00:21:08,280 couple of meters thick, whereas the cloud on top of it was maybe 414 00:21:08,280 --> 00:21:11,960 in excess of 100 meters thick. And that actually ties in kind 415 00:21:11,960 --> 00:21:16,080 of more generally with other studies that we've done with 416 00:21:16,080 --> 00:21:19,920 more conventional methods and other canyons that we do see 417 00:21:19,920 --> 00:21:22,480 these dense layers at the base of flow, usually much denser 418 00:21:22,480 --> 00:21:24,600 than the one we measured with the ROV. 419 00:21:24,840 --> 00:21:26,840 And that as I said earlier, they're potentially really, 420 00:21:26,840 --> 00:21:29,640 really important part of actually how these flows are 421 00:21:29,640 --> 00:21:31,960 driven. When you were flying this ROV, 422 00:21:31,960 --> 00:21:34,360 what was the goal of the project? 423 00:21:34,360 --> 00:21:36,040 What were you trying to discover? 424 00:21:36,920 --> 00:21:38,880 We were meant to be doing something entirely different. 425 00:21:38,880 --> 00:21:41,920 We were meant to be collecting gas hydrates from a different 426 00:21:41,920 --> 00:21:43,960 part of the coastline, but that just was not possible. 427 00:21:44,440 --> 00:21:47,640 And what we'd been doing at that time as part of a larger study, 428 00:21:47,640 --> 00:21:51,520 was actually collecting sediment cores from lots of canyons along 429 00:21:51,520 --> 00:21:56,080 the California coastline in order to look at the nature of 430 00:21:56,080 --> 00:21:58,720 turbidites and therefore turbidity currents within those 431 00:21:58,720 --> 00:22:00,960 different canyons. So we've got some canyons where 432 00:22:00,960 --> 00:22:03,280 the heads are very close to the shoreline, some canyons where 433 00:22:03,280 --> 00:22:05,280 the heads are away from the shoreline and looking at 434 00:22:05,280 --> 00:22:08,000 basically what are the different processes acting in those 435 00:22:08,040 --> 00:22:10,880 canyons. So really what we realised was, 436 00:22:11,120 --> 00:22:14,280 well we don't want to do nothing on this day on this ship, you 437 00:22:14,280 --> 00:22:16,120 know, it's really expensive running ships. 438 00:22:16,280 --> 00:22:18,600 So what we could do, rather than doing nothing, is we could go 439 00:22:18,600 --> 00:22:21,920 and collect some cause from this Canyon. 440 00:22:21,920 --> 00:22:25,760 And it just so happened that we encountered A turbidity current. 441 00:22:25,760 --> 00:22:28,120 So I mean, I think it was quite fortuitous. 442 00:22:28,120 --> 00:22:31,400 You know, the vehicle survived and so did everybody, so. 443 00:22:32,200 --> 00:22:35,280 At those speeds, A metre per second, is the water flowing in 444 00:22:35,280 --> 00:22:37,280 a turbulent way or is it laminar flow? 445 00:22:37,760 --> 00:22:40,680 So the flow is probably going about two metres per second 446 00:22:40,680 --> 00:22:43,360 because we were actually trying to fly up the Canyon at about a 447 00:22:43,360 --> 00:22:45,640 metre per second and we're heading down at a metre per 448 00:22:45,640 --> 00:22:48,400 second. It's quite hard to say what the 449 00:22:48,400 --> 00:22:51,640 nature of that dense layer near the sea floor was doing exactly 450 00:22:51,640 --> 00:22:55,280 because a lot of the time the vehicle was really is actually 451 00:22:55,280 --> 00:22:59,120 thicker than that layer. But certainly on the interface 452 00:22:59,120 --> 00:23:02,840 between that dense near bed layer and the more dilute cloud 453 00:23:02,840 --> 00:23:05,280 on top, there was actually quite a stable waveform. 454 00:23:05,720 --> 00:23:08,120 So between the layers of fluid of different densities. 455 00:23:08,440 --> 00:23:12,600 And then that upper layer was very turbulent, which relates to 456 00:23:12,600 --> 00:23:14,880 that comment about like flying in a tornado. 457 00:23:14,880 --> 00:23:17,160 They were just sort of getting thrown all over the place while 458 00:23:17,160 --> 00:23:19,640 they're trying to keep this this vehicle stable. 459 00:23:19,960 --> 00:23:23,200 And where you experiments in the lab roughly consistent with what 460 00:23:23,480 --> 00:23:25,080 you were finding in the field there? 461 00:23:25,560 --> 00:23:29,880 So I guess the interesting thing there is it seems like if you 462 00:23:29,880 --> 00:23:33,400 compare it to lab experiments, the flow we measured in the 463 00:23:33,400 --> 00:23:37,640 field looks quite like what you get if you in the lab generate A 464 00:23:37,640 --> 00:23:40,160 turbidity current and then intrude another turbidity 465 00:23:40,160 --> 00:23:42,040 current into it. So you've basically got pulses 466 00:23:42,040 --> 00:23:46,320 of turbidity current, which is probably not uncommon within 467 00:23:46,320 --> 00:23:48,760 submarine canyons. So there was a storm going on at 468 00:23:48,760 --> 00:23:50,760 this point. So you may well have been sort 469 00:23:50,760 --> 00:23:52,920 of destabilizing the sediments at the head of the Canyon. 470 00:23:52,920 --> 00:23:54,600 You won't necessarily do that all in one go. 471 00:23:54,800 --> 00:23:57,160 So you may actually generate multiple stability currents that 472 00:23:57,160 --> 00:24:00,800 intrude into one another. And the structure of the flow we 473 00:24:00,800 --> 00:24:04,520 measured in that Canyon looked quite like the structure of flow 474 00:24:04,760 --> 00:24:07,440 seen in labs, although all the lab experiments that show that 475 00:24:07,440 --> 00:24:10,040 that I'm aware of are actually just done with dense fluids, not 476 00:24:10,040 --> 00:24:13,680 with sediment loading water. And I should say that the sort 477 00:24:13,680 --> 00:24:16,640 of near bed dense layer we saw in Mendocino Canyon, I think is 478 00:24:16,640 --> 00:24:19,200 quite different to the near bed dense layers we've seen in 479 00:24:19,200 --> 00:24:23,040 places like Monterey Canyon and Congo Canyon, which are much, 480 00:24:23,040 --> 00:24:26,640 much higher concentrations than what we saw with the ROV 481 00:24:26,640 --> 00:24:28,800 thankfully. Because I think we wouldn't have 482 00:24:28,800 --> 00:24:31,280 had an ROV at the end of it if it they'd been those kind of 483 00:24:31,280 --> 00:24:34,440 concentrations. There's a great deal of human 484 00:24:34,440 --> 00:24:38,680 infrastructure on the sea floor, such as fibre optic cables and 485 00:24:38,880 --> 00:24:42,160 oil and gas installations. Are they affected? 486 00:24:42,200 --> 00:24:44,840 By turbidity currents. Yeah, yeah, absolutely. 487 00:24:44,920 --> 00:24:47,080 This is really important reason actually for understanding the 488 00:24:47,080 --> 00:24:50,840 dynamics of these flows. So anything from say, fiber 489 00:24:50,840 --> 00:24:54,280 optic cables, high voltage cables, oil and gas pipelines, 490 00:24:54,280 --> 00:24:56,000 there's a lot of infrastructure on the sea floor. 491 00:24:56,800 --> 00:24:59,760 If we think about say, fiber optic cables, I mean, they are 492 00:24:59,760 --> 00:25:03,560 basically the network that we use that underpins the Internet. 493 00:25:03,880 --> 00:25:07,160 And certainly those fiber optic cables aren't actually typically 494 00:25:07,160 --> 00:25:08,880 protected on the sea floor in deep water. 495 00:25:08,880 --> 00:25:11,760 They're just lying on the sea floor and they're vulnerable to 496 00:25:11,760 --> 00:25:13,440 lots of things. So they're vulnerable to things 497 00:25:13,440 --> 00:25:17,400 like ships, anchors or trawling from fishing boats, basically 498 00:25:17,600 --> 00:25:20,960 dragging them and breaking them. They're also vulnerable to 499 00:25:21,000 --> 00:25:22,960 turbidity currents. And the issue we have with 500 00:25:22,960 --> 00:25:26,320 turbidity currents is whereas if say an anchor drags and it 501 00:25:26,600 --> 00:25:30,200 breaks a cable, you break 1 cable with a turbidity current, 502 00:25:30,240 --> 00:25:33,320 you can break lots and lots of cables at the same time. 503 00:25:33,600 --> 00:25:36,520 And that causes further problems because what you normally do 504 00:25:36,520 --> 00:25:38,800 when you break a cable is reroute the data traffic 505 00:25:38,800 --> 00:25:40,280 somewhere else around the network. 506 00:25:40,600 --> 00:25:43,520 If you've just broken a lot of the network, you can't do that. 507 00:25:43,960 --> 00:25:48,880 So I guess sort of a classic example of this, it's in Taiwan 508 00:25:48,880 --> 00:25:53,120 in 2006. So Taiwan experiences a lot of 509 00:25:53,120 --> 00:25:56,680 natural hazards from sort of earthquakes to typhoons. 510 00:25:56,960 --> 00:26:00,120 And both of these things can be responsible for generating 511 00:26:00,120 --> 00:26:02,360 turbidity currents or certainly be associated with turbidity 512 00:26:02,360 --> 00:26:04,600 currents. So in 2006, there was an 513 00:26:04,600 --> 00:26:09,000 earthquake, and in association with this earthquake, over 20 514 00:26:09,000 --> 00:26:11,600 cables on the sea floor were sequentially broken. 515 00:26:11,600 --> 00:26:13,880 So you've just broken a massive bit of the network. 516 00:26:14,240 --> 00:26:18,280 So temporarily, communications from Southeast Asia were 517 00:26:18,280 --> 00:26:21,320 basically severed. And then on a longer time scale, 518 00:26:21,320 --> 00:26:24,040 as they're trying to mend these cables, the Internet was slowed 519 00:26:24,040 --> 00:26:25,840 down. And I think that was for nearly 520 00:26:25,840 --> 00:26:28,480 two months. And you see the impacts of that 521 00:26:28,480 --> 00:26:30,160 on things like financial markets. 522 00:26:30,800 --> 00:26:33,560 So, yeah, these cables are definitely vulnerable to 523 00:26:33,560 --> 00:26:36,600 turbidity currents, similar issues with oil and gas 524 00:26:36,600 --> 00:26:38,360 pipelines. So this is one of the really 525 00:26:38,360 --> 00:26:42,040 important reasons we study them. I should say, and I I should say 526 00:26:42,040 --> 00:26:44,760 it quietly probably because there is a positive to these 527 00:26:44,760 --> 00:26:46,720 cables getting broken. It's not positive for many 528 00:26:46,720 --> 00:26:49,680 people, but it is positive if you study turbidity currents 529 00:26:49,840 --> 00:26:53,120 because they do give you quite a nice data set about the speed of 530 00:26:53,120 --> 00:26:56,240 some of these flows in the deeper ocean, say on submarine 531 00:26:56,240 --> 00:26:59,120 fans, which otherwise we aren't really monitoring. 532 00:26:59,120 --> 00:27:02,400 So if you imagine you've got a series of cables, you know when 533 00:27:02,400 --> 00:27:04,960 they got broken, you know the distance between the cables, 534 00:27:05,200 --> 00:27:07,840 then you're getting an idea of the velocity of the flows that 535 00:27:07,840 --> 00:27:10,200 are breaking them. So there are some positives. 536 00:27:11,320 --> 00:27:16,080 Does your work also help these companies figure out where not 537 00:27:16,200 --> 00:27:20,200 to put infrastructure? Yeah, that's a really important 538 00:27:20,200 --> 00:27:22,400 part. So they've always got to decide 539 00:27:22,400 --> 00:27:26,280 where am I going to route this pipeline or route this cable. 540 00:27:26,280 --> 00:27:30,920 And I think it's a really difficult job to do because 541 00:27:30,920 --> 00:27:33,600 you've got this trade off between hazards to your cable 542 00:27:33,920 --> 00:27:38,680 and the length of your cable. So often what happens if if it's 543 00:27:38,680 --> 00:27:41,600 known this, you've got to say an active Canyon fan system with 544 00:27:41,600 --> 00:27:44,240 turbidity currents, then that cable needs to be rooted into 545 00:27:44,240 --> 00:27:46,160 deeper water. That's going to cost a lot more 546 00:27:46,160 --> 00:27:49,120 money. Or for example with some oil and 547 00:27:49,120 --> 00:27:52,240 gas pipelines are sometimes actually directionally drilled 548 00:27:52,240 --> 00:27:54,800 into bedrock beneath sea floor canyons, which is phenomenally 549 00:27:54,800 --> 00:27:58,440 expensive thing to do. What are you working on at the 550 00:27:58,440 --> 00:28:00,160 moment? I guess a couple of different 551 00:28:00,160 --> 00:28:02,760 areas. So I think one of the really 552 00:28:02,760 --> 00:28:06,240 interesting things at the moment as we get more data sets from 553 00:28:06,240 --> 00:28:09,320 direct monitoring from different places is understanding actually 554 00:28:09,320 --> 00:28:11,560 the diversity of turbidity currents that exist. 555 00:28:12,160 --> 00:28:15,560 So if you think about something like a river, we all know what a 556 00:28:15,560 --> 00:28:18,600 river looks like, but you also know that, well, if I look at a 557 00:28:18,600 --> 00:28:22,240 bedrock river in the mountains versus say, a river on a plain 558 00:28:22,240 --> 00:28:25,480 like the Mississippi River, those two rivers look quite 559 00:28:25,480 --> 00:28:28,320 different from one another. And I think this is what we're 560 00:28:28,320 --> 00:28:31,320 starting to see with turbidity currents, that there's some 561 00:28:31,320 --> 00:28:33,480 similarities when we look at them in different places, but 562 00:28:33,480 --> 00:28:38,560 there's also some differences. And so and it would be great if 563 00:28:38,560 --> 00:28:41,360 we could predict their character with less need for monitoring. 564 00:28:41,360 --> 00:28:43,600 And that would really, really help with what you're talking 565 00:28:43,600 --> 00:28:46,680 about a moment ago, which is how we design things like cable 566 00:28:46,680 --> 00:28:48,920 routes. So that's sort of 1 area of 567 00:28:48,920 --> 00:28:50,720 interest. So another is actually 568 00:28:50,720 --> 00:28:52,800 understanding land detached canyons. 569 00:28:52,800 --> 00:28:55,680 So I don't think I've mentioned these yet, but we often divide 570 00:28:55,680 --> 00:28:59,480 sea floor canyons into either being land attached or land 571 00:28:59,480 --> 00:29:01,960 detached. So a land attached Canyon would 572 00:29:01,960 --> 00:29:04,880 be something like Monterey Canyon, where the Canyon head's 573 00:29:04,880 --> 00:29:06,320 really, really close to the shoreline. 574 00:29:06,320 --> 00:29:09,960 It's in really shallow water, it's almost up at the beach, and 575 00:29:09,960 --> 00:29:12,440 there's a really obvious sediment source for the 576 00:29:12,440 --> 00:29:14,520 turbidity currents. So you have longshore drift 577 00:29:14,520 --> 00:29:16,400 that's moving sediment along the coastline. 578 00:29:16,600 --> 00:29:19,800 That sediment effectively falls in the hole in the ground that 579 00:29:19,800 --> 00:29:22,560 is the canyons. Then actually most canyons 580 00:29:22,560 --> 00:29:25,040 around the world are actually land detached canyons. 581 00:29:25,280 --> 00:29:27,800 So their Canyon head is actually detached from the shoreline. 582 00:29:28,680 --> 00:29:33,640 Now for a long time we assumed that these types of canyons were 583 00:29:33,640 --> 00:29:35,920 inactive in sort of present day sea level. 584 00:29:35,920 --> 00:29:38,200 So if they had turbidity currents in them, they'd be 585 00:29:38,200 --> 00:29:40,280 quite small turbidity currents. We didn't need to worry about 586 00:29:40,280 --> 00:29:42,440 them. But more recently we've realised 587 00:29:42,440 --> 00:29:43,600 that this actually isn't the case. 588 00:29:43,600 --> 00:29:45,960 They can actually have quite fast and destructive turbidity 589 00:29:45,960 --> 00:29:50,000 currents in them. So for example, this summer part 590 00:29:50,000 --> 00:29:52,240 of an expedition which is going out into the Atlantic to a 591 00:29:52,240 --> 00:29:55,840 Canyon called Whittard Canyon. So Whittard Canyon is a Canyon 592 00:29:55,880 --> 00:29:58,360 over 300 kilometres southwest of the UK. 593 00:29:58,560 --> 00:30:00,120 So it's very, very land attached. 594 00:30:00,120 --> 00:30:02,200 There's a big distance between it and the shoreline. 595 00:30:02,840 --> 00:30:05,640 So this is an expedition led by my colleague Mike Claire, who 596 00:30:05,640 --> 00:30:07,920 works at National Oceanography Centre in Southampton. 597 00:30:08,280 --> 00:30:10,920 And so as part of his project, we're going to put an array of 598 00:30:10,920 --> 00:30:14,200 moorings into this Canyon. So we already know from previous 599 00:30:14,200 --> 00:30:16,520 work we've got fast and destructive turbidity currents 600 00:30:16,520 --> 00:30:20,720 in there, but it's really work in progress to understand why. 601 00:30:20,720 --> 00:30:23,880 So what's actually triggering them and then kind of how far 602 00:30:23,880 --> 00:30:26,600 down the Kenya system they go, how they actually behave as they 603 00:30:26,600 --> 00:30:29,760 do so? As to Sumner, thank you very 604 00:30:29,760 --> 00:30:31,360 much. Thank you very much for having 605 00:30:31,360 --> 00:30:35,280 me, that was a lot of fun. To see pictures and 606 00:30:35,280 --> 00:30:40,680 illustrations that support this podcast, go to geologybytes.com, 607 00:30:40,800 --> 00:30:43,560 where you'll also find a subject matter index of all the 608 00:30:43,560 --> 00:30:45,960 episodes. There you can also give me 609 00:30:45,960 --> 00:30:49,920 feedback which I welcome, as well as sign up to get my emails 610 00:30:49,920 --> 00:30:51,120 about new episodes.