1 00:00:04,240 --> 00:00:07,160 This is Geology Bites with Oliver Strimpel. 2 00:00:08,640 --> 00:00:11,840 About 80% of Greenland is covered by ice. 3 00:00:12,680 --> 00:00:16,280 While we've been able to map the geology of the 20% that is 4 00:00:16,280 --> 00:00:20,960 exposed, our existing geological maps of the glaciated interior 5 00:00:20,960 --> 00:00:25,000 have relied on extrapolation from the exposed regions and 6 00:00:25,000 --> 00:00:30,760 educated guesswork. But in April 2024, Joe McGregor, 7 00:00:30,760 --> 00:00:34,880 a research physical scientist at the NASA Goddard Space Flight 8 00:00:34,880 --> 00:00:38,240 Centre, and his colleagues published a new geological map 9 00:00:38,240 --> 00:00:41,720 of Greenland. The map incorporates new data 10 00:00:41,720 --> 00:00:45,200 about the geology of the rocks below the ice, derived from 11 00:00:45,200 --> 00:00:49,840 seismic, gravity, magnetic and topographic surveys. 12 00:00:50,800 --> 00:00:55,240 The map features 3 hitherto unknown provinces that lie 13 00:00:55,240 --> 00:01:00,040 beneath the central part of the ice cap north of about 70°, as 14 00:01:00,040 --> 00:01:04,000 well as an extensive network of long subglacial valleys. 15 00:01:05,239 --> 00:01:08,840 How does the new data enable us to learn about the rocks buried 16 00:01:08,840 --> 00:01:10,800 by up to three kilometers of ice? 17 00:01:11,520 --> 00:01:14,920 And what is the significance of the three new provinces and the 18 00:01:14,920 --> 00:01:19,440 network of valleys? Joe McGregor, welcome to Geology 19 00:01:19,440 --> 00:01:21,400 Bytes. Thank you for having me. 20 00:01:21,400 --> 00:01:24,080 Oliver. What was the best map we had of 21 00:01:24,080 --> 00:01:26,480 Greenland's geology before yours appeared? 22 00:01:26,480 --> 00:01:29,280 And how was that one compiled? The best one that. 23 00:01:29,280 --> 00:01:32,000 Existed before ours was. Compiled by Peter. 24 00:01:32,000 --> 00:01:34,240 Dawes, a British geologist. Working for the. 25 00:01:34,240 --> 00:01:36,960 Geological Survey. Of Denmark and Greenland, and he 26 00:01:36,960 --> 00:01:40,560 published it in 2009. It represented. 27 00:01:40,680 --> 00:01:43,160 The best? Understanding that we had at the 28 00:01:43,160 --> 00:01:47,640 time of how the various provinces that had been mapped 29 00:01:47,640 --> 00:01:50,960 around the periphery of Greenland might connect within 30 00:01:50,960 --> 00:01:52,880 the interior. He described. 31 00:01:52,880 --> 00:01:56,560 It as conjectural and he. Left it at that. 32 00:01:56,800 --> 00:02:01,560 And so we have attempted to revise that map across the 80% 33 00:02:01,560 --> 00:02:04,600 of the island of Greenland. That is covered by ice, for 34 00:02:04,600 --> 00:02:07,880 which we have. Almost no direct geological 35 00:02:07,880 --> 00:02:10,520 information. I said in the introduction that 36 00:02:10,520 --> 00:02:15,400 your map uses data from seismic, gravity, magnetic, and 37 00:02:15,400 --> 00:02:19,120 topographic surveys. Let's talk about how we captured 38 00:02:19,120 --> 00:02:23,160 this data and what kind of information each data type 39 00:02:23,160 --> 00:02:27,040 provides. Taking seismic data first, did 40 00:02:27,040 --> 00:02:31,200 you use natural sources, IE earthquakes or artificial 41 00:02:31,200 --> 00:02:35,120 sources of seismic waves? And where were the seismometers 42 00:02:35,120 --> 00:02:38,080 placed? We used natural sources of 43 00:02:38,080 --> 00:02:41,080 seismic signals, so those include earthquakes and other 44 00:02:41,080 --> 00:02:42,840 seismic. Sources for example. 45 00:02:42,840 --> 00:02:46,880 Calving of icebergs around the periphery of Greenland and those 46 00:02:46,880 --> 00:02:49,200 seismometers. Are mostly located. 47 00:02:49,480 --> 00:02:53,600 On land around the periphery of Greenland, there are a handful 48 00:02:53,600 --> 00:02:56,400 that have been placed on the. Ice typically located. 49 00:02:56,400 --> 00:02:59,440 Next to major stations, but we're dealing with a very small 50 00:02:59,440 --> 00:03:01,120 number of seismometers compared to. 51 00:03:01,200 --> 00:03:03,600 The set that is. Distributed across the United 52 00:03:03,600 --> 00:03:07,640 States and the observations that they make of these earthquakes 53 00:03:07,640 --> 00:03:09,720 and other seismic sources. Allow us. 54 00:03:09,720 --> 00:03:13,240 To generate tomography. Of the subsurface. 55 00:03:13,280 --> 00:03:16,720 In Greenland and around the Arctic, roughly how many 56 00:03:16,720 --> 00:03:19,240 seismometers are we talking about here to cover the whole of 57 00:03:19,240 --> 00:03:21,320 Greenland? So currently it's on the order. 58 00:03:21,320 --> 00:03:24,280 Of two dozen, it's relatively few and it gets sparse. 59 00:03:24,280 --> 00:03:27,160 As you go farther north in Greenland, understandable given 60 00:03:27,160 --> 00:03:29,680 the population centers and so that leads. 61 00:03:29,680 --> 00:03:32,480 To a degree of. Bias in how we're able to 62 00:03:32,480 --> 00:03:35,560 interpret what the seismic structure is, particularly in 63 00:03:35,560 --> 00:03:38,520 what we think is the more complicated northern region 64 00:03:38,680 --> 00:03:41,840 because you rely on the ray paths between. 65 00:03:42,080 --> 00:03:45,760 Wherever those sources were. And those stations to infer what 66 00:03:45,760 --> 00:03:47,600 the velocity might have been between them. 67 00:03:47,760 --> 00:03:50,400 So the more stations you have, the more ray paths you're going 68 00:03:50,400 --> 00:03:53,640 to have and the wider variety thereof to infer that seismic 69 00:03:53,640 --> 00:03:55,440 structure. So that really goes to the 70 00:03:55,440 --> 00:03:58,400 resolution of the tomographic images you can generate, I 71 00:03:58,400 --> 00:04:00,240 suppose. Yes, so the. 72 00:04:00,240 --> 00:04:03,240 Deeper you want to sense. Typically the courser the. 73 00:04:03,240 --> 00:04:07,080 Resolution will be we're. Interested in the near surface 74 00:04:07,080 --> 00:04:10,440 geology, so the. Tomographic velocity anomaly 75 00:04:10,440 --> 00:04:11,360 pattern in. The upper. 76 00:04:11,360 --> 00:04:14,440 Five to 10 kilometers. Of crust that's relatively hard 77 00:04:14,440 --> 00:04:16,880 to resolve. Given the nature of the sources. 78 00:04:16,880 --> 00:04:20,279 That exist in the rate paths that they travel, but yeah. 79 00:04:20,279 --> 00:04:21,839 That's the challenge we're faced with. 80 00:04:22,079 --> 00:04:24,600 So we're getting an. Estimate that's of the. 81 00:04:24,600 --> 00:04:28,000 Order. Of 50 kilometers square across 82 00:04:28,000 --> 00:04:31,680 an island, that's roughly in rectangular terms 2000 83 00:04:31,720 --> 00:04:35,080 kilometers NS and 1000 kilometers. 84 00:04:35,080 --> 00:04:38,360 East West to be absolutely clear, although. 85 00:04:38,360 --> 00:04:41,360 Some of my co-authors have generated these seismic 86 00:04:41,360 --> 00:04:44,120 tomography maps. We didn't generate a new one for 87 00:04:44,120 --> 00:04:45,040 this. Study we took what? 88 00:04:45,040 --> 00:04:47,160 We thought was one of the best existing ones. 89 00:04:47,520 --> 00:04:51,520 When you try and interpret one of these tomographic images, do 90 00:04:51,520 --> 00:04:55,880 you interpret the seismic velocity as reflective of 91 00:04:55,880 --> 00:05:00,440 variations in temperature of the crust or mantle, or is it a 92 00:05:00,600 --> 00:05:02,960 combination of temperature and composition? 93 00:05:03,280 --> 00:05:05,560 So it's really a combination of the two. 94 00:05:05,760 --> 00:05:09,760 The density, the temperature, and the lithology can all factor 95 00:05:09,760 --> 00:05:13,440 in to what generates an anomaly relative to some reference. 96 00:05:13,440 --> 00:05:15,800 Field that we. Attempt to interpret in this 97 00:05:15,800 --> 00:05:19,840 context and before we start talking about the other data 98 00:05:19,840 --> 00:05:25,600 types, were there any areas just looking at the seismic that 99 00:05:26,000 --> 00:05:30,240 appeared to be significantly different or hotter than other 100 00:05:30,240 --> 00:05:32,200 parts of Greenland? There are. 101 00:05:32,200 --> 00:05:35,120 Places in Greenland. Particularly as you head towards 102 00:05:35,120 --> 00:05:37,480 the East Coast, the Blossville Coast. 103 00:05:37,680 --> 00:05:41,440 Where there are known basalt outcrops where it does in fact. 104 00:05:41,440 --> 00:05:44,160 Appear. That the seismic velocities are 105 00:05:44,160 --> 00:05:48,840 lower and that would be consistent with warmer rock, 106 00:05:49,160 --> 00:05:51,560 potentially a shallower mantle depending on how you. 107 00:05:51,680 --> 00:05:55,040 View that structure. OK, let's talk about the gravity 108 00:05:55,040 --> 00:05:58,960 surveys. How were those captured and what 109 00:05:58,960 --> 00:06:02,600 does a map of the gravity variations or gravity anomalies 110 00:06:03,080 --> 00:06:06,480 tell us about the bedrock? So those were captured in two 111 00:06:06,480 --> 00:06:08,200 ways. The first is. 112 00:06:08,240 --> 00:06:12,080 From satellite derived gravity measurements and here we use the 113 00:06:12,400 --> 00:06:16,360 Gravity and Ocean Climate Experiment mission that was run 114 00:06:16,360 --> 00:06:17,080 by. ESA. 115 00:06:17,520 --> 00:06:20,880 And that allows us. To resolve large scale. 116 00:06:20,880 --> 00:06:23,920 Gravity anomalies. That's also been combined. 117 00:06:24,280 --> 00:06:27,080 With Aero. Gravity measurements and that is 118 00:06:27,080 --> 00:06:29,480 one of the things that I've. Specialized in which is. 119 00:06:29,640 --> 00:06:33,080 Having Gravimeter's onboard aircraft and we travel across 120 00:06:33,080 --> 00:06:35,800 Greenland mapping the gravity anomaly as we. 121 00:06:35,800 --> 00:06:38,160 Cross the ice. That's a challenging measurement 122 00:06:38,160 --> 00:06:41,320 to make, because gravity and its variations are fundamentally 123 00:06:41,320 --> 00:06:45,280 about measuring the vertical acceleration and the minute 124 00:06:45,280 --> 00:06:47,040 variations. Associated with. 125 00:06:47,360 --> 00:06:50,320 Changing rock composition beneath, and when you're doing 126 00:06:50,320 --> 00:06:52,480 that measurement from the air, you've got the added 127 00:06:52,480 --> 00:06:54,880 complication of the turbulence. That the aircraft is. 128 00:06:54,880 --> 00:06:57,840 Experiencing and so that can knock you all. 129 00:06:57,840 --> 00:07:00,120 Sorts of different ways. And you have to. 130 00:07:00,120 --> 00:07:02,400 Record how? The aircraft is moving. 131 00:07:02,680 --> 00:07:06,320 In space, Very. Precisely with GNSS antennas so 132 00:07:06,320 --> 00:07:08,720 that they can then remove that noise. 133 00:07:08,720 --> 00:07:10,880 To get at the. Gravity signal beneath. 134 00:07:11,600 --> 00:07:14,600 Where you see higher gravity, that's indicative. 135 00:07:14,720 --> 00:07:18,200 Of denser rock or depending on the scale that you're looking at 136 00:07:18,200 --> 00:07:20,080 potentially. A deeper. 137 00:07:20,080 --> 00:07:24,520 Crust, mantle boundary and. That allows you to resolve the 138 00:07:24,520 --> 00:07:26,800 large scale structure of the rocks. 139 00:07:26,800 --> 00:07:30,280 That you're flying over. But unlike the seismic 140 00:07:30,520 --> 00:07:33,160 tomographic images, presumably if you're actually flying pretty 141 00:07:33,160 --> 00:07:36,480 low in an aircraft, you can get better spatial resolution. 142 00:07:36,880 --> 00:07:38,360 Yes, that depends on a number of. 143 00:07:38,360 --> 00:07:42,680 Factors how fast your. Platform is traveling, how high 144 00:07:42,680 --> 00:07:45,960 it's traveling and then of. Course the quality of your 145 00:07:45,960 --> 00:07:47,960 gravimeter. And in the ideal scenario, if 146 00:07:47,960 --> 00:07:50,280 you want to cover a lot of ground, you've got a low and 147 00:07:50,280 --> 00:07:52,080 slow aircraft. And in some of these 148 00:07:52,080 --> 00:07:55,400 measurements we have. Had that, so the field that we 149 00:07:55,400 --> 00:07:57,560 worked with was. The combination of these 150 00:07:57,560 --> 00:08:01,120 satellite gravity measurements and some of the aero gravity 151 00:08:01,120 --> 00:08:04,160 measurements that have been made by not just NASA over. 152 00:08:04,280 --> 00:08:07,080 The past couple decades. In Greenland, but also various 153 00:08:07,080 --> 00:08:10,240 Danish institutions who of course interested in Greenland 154 00:08:10,600 --> 00:08:13,360 and in some cases German institutions as well. 155 00:08:14,040 --> 00:08:17,960 So just looking at the gravity data alone for a moment, where 156 00:08:17,960 --> 00:08:20,880 there any regions that stuck out in the sense of having 157 00:08:21,040 --> 00:08:23,800 anomalously high gravity or low gravity? 158 00:08:24,440 --> 00:08:26,360 Yes, in the vicinity. Of the. 159 00:08:26,360 --> 00:08:28,200 Caledonian origin. We do. 160 00:08:28,200 --> 00:08:29,040 See. Often. 161 00:08:29,320 --> 00:08:31,880 A lower gravity so. That's in northeast Greenland 162 00:08:32,280 --> 00:08:35,080 and that signal seems. To propagate a little. 163 00:08:35,080 --> 00:08:36,919 Inland toward the center. Of the island. 164 00:08:37,360 --> 00:08:41,240 Conversely, in the northwest of Greenland and in the far north 165 00:08:41,240 --> 00:08:43,520 of Greenland. We see positive gravity. 166 00:08:43,520 --> 00:08:46,280 Anomalies those. Appear to be associated. 167 00:08:46,280 --> 00:08:49,200 With different type of. Origin perhaps a different. 168 00:08:49,200 --> 00:08:52,280 Rock composition and in one case, apparently a basin. 169 00:08:52,360 --> 00:08:56,280 Or a past basin. And how are the magnetic surveys 170 00:08:56,280 --> 00:08:58,840 performed? The magnetic map. 171 00:08:58,920 --> 00:09:01,720 That we used. Was generated in a similar way 172 00:09:01,760 --> 00:09:04,880 to the gravity map, but of course with different sensors. 173 00:09:05,160 --> 00:09:08,280 There are magnetometers on board satellites that can give you 174 00:09:08,680 --> 00:09:12,760 large scale magnetic anomalies. We're talking order 100 175 00:09:12,760 --> 00:09:17,200 kilometers and then those have been combined with aeromagnetic 176 00:09:17,200 --> 00:09:20,200 measurements. Those were also made by NASA in 177 00:09:20,200 --> 00:09:21,360 the. Past 2 decades. 178 00:09:21,600 --> 00:09:24,520 And other institutions. In the case of magnetics, it's 179 00:09:24,520 --> 00:09:27,160 not so much a concern how fast you're flying, but it is. 180 00:09:27,160 --> 00:09:29,640 Helpful to get. Low if you're trying to sense 181 00:09:29,800 --> 00:09:31,680 signals. Closer to the ice. 182 00:09:31,680 --> 00:09:34,360 Rock interface. In this case, we used a data set 183 00:09:34,360 --> 00:09:37,680 that was generated by the US NOAA, the National Oceanic and 184 00:09:37,680 --> 00:09:40,000 Atmospheric Administration. In 2017. 185 00:09:40,440 --> 00:09:43,200 We also flew an aircraft with NASA. 186 00:09:43,560 --> 00:09:46,240 That was particularly well suited to. 187 00:09:46,280 --> 00:09:48,880 The challenge of making airborne magnetic measurements. 188 00:09:49,280 --> 00:09:52,120 As you might imagine, you would like your magnetometer, which is 189 00:09:52,120 --> 00:09:55,400 very sensitive to magnetic. Fields to be as. 190 00:09:55,400 --> 00:10:00,040 Far away from your metallic plane as possible, and to have 191 00:10:00,040 --> 00:10:01,760 that plane be well characterized. 192 00:10:02,760 --> 00:10:06,800 NASA used AP3. Orion that it had inherited. 193 00:10:06,800 --> 00:10:09,360 From the US Navy. And that aircraft was originally 194 00:10:09,360 --> 00:10:12,960 designed as a submarine hunter by flying very low and having a 195 00:10:12,960 --> 00:10:16,760 magnetometer boom that allowed them to detect any rapidly 196 00:10:16,760 --> 00:10:19,120 changing magnetic signals that might be indicative of 197 00:10:19,120 --> 00:10:21,400 submarine. Just to give roughly an idea of 198 00:10:21,400 --> 00:10:25,480 the extent of the survey and how big a project it was, roughly 199 00:10:25,480 --> 00:10:30,160 how many traverses were made across the Greenland continent? 200 00:10:30,240 --> 00:10:35,200 To compile the data across Greenland, NASA flew somewhere 201 00:10:35,200 --> 00:10:39,520 north of 800,000 kilometers since 1993. 202 00:10:39,880 --> 00:10:42,240 That's mostly in reference to ice thickness, so not all. 203 00:10:42,240 --> 00:10:44,680 Of those surveys had. Magnetometry. 204 00:10:44,880 --> 00:10:47,800 But there are other predecessor surveys collected. 205 00:10:47,800 --> 00:10:50,680 In the 80s and early 90s. That did. 206 00:10:50,680 --> 00:10:52,040 Collect that kind of information. 207 00:10:52,040 --> 00:10:54,360 So there's a long history here again, not just the. 208 00:10:54,600 --> 00:10:56,880 US. Of going out and collecting 209 00:10:56,880 --> 00:10:59,880 these sorts of airborne measurements to unravel the 210 00:10:59,880 --> 00:11:02,920 mysteries of Greenland. Can you give me an idea of the 211 00:11:02,920 --> 00:11:05,280 resolution of these magnetic surveys? 212 00:11:05,640 --> 00:11:07,520 Sure. So that's a function of the. 213 00:11:07,520 --> 00:11:10,640 Altitude that the aircraft. Flies from that ice rock 214 00:11:10,640 --> 00:11:13,960 boundary. Ice is very kindly non magnetic, 215 00:11:13,960 --> 00:11:16,160 which makes it easier to interpret the signals. 216 00:11:16,680 --> 00:11:20,760 And you can think of us in most cases as gaining exceptional 217 00:11:20,760 --> 00:11:24,360 information along the flight line, getting an independent 218 00:11:24,360 --> 00:11:26,960 data point on the order of 500 meters. 219 00:11:26,960 --> 00:11:29,800 And then we have to combine interpolate all of those 220 00:11:29,800 --> 00:11:32,480 crisscrossing flight lines. That held all sorts of. 221 00:11:32,480 --> 00:11:35,280 Competing scientific priorities into. 222 00:11:35,280 --> 00:11:37,600 A larger grid. That is typically interpreted. 223 00:11:37,600 --> 00:11:41,080 On the scale of. Order 10 kilometers and is it 224 00:11:41,080 --> 00:11:44,200 fairly even coverage or do you have spots that are very well 225 00:11:44,200 --> 00:11:46,680 covered and then big gaps in other places? 226 00:11:47,240 --> 00:11:49,520 There are still. Gaps in the Greenland ice sheet. 227 00:11:49,520 --> 00:11:52,280 Which is roughly. 2,000,000 square kilometers in size. 228 00:11:52,560 --> 00:11:55,760 There are gaps of the order of. 10,000 square kilometers in 229 00:11:55,760 --> 00:11:56,760 size. There are several. 230 00:11:56,760 --> 00:11:59,560 Of those but. It's increasingly good, 231 00:11:59,880 --> 00:12:02,880 especially as compared to Antarctica which is 7 or 8 232 00:12:02,880 --> 00:12:04,280 times. Larger the ice sheet. 233 00:12:04,640 --> 00:12:07,120 A more challenging beast. To survey. 234 00:12:07,920 --> 00:12:10,640 And finally, what about the topographic surface? 235 00:12:11,160 --> 00:12:15,040 How were these performed and did they capture the topography of 236 00:12:15,040 --> 00:12:19,120 the rock surface below the ice or the topography of the ice 237 00:12:19,120 --> 00:12:21,200 surface? Great question. 238 00:12:21,200 --> 00:12:24,960 So those are collected. Using radar Sounders Radar 239 00:12:24,960 --> 00:12:27,960 Sounders are essentially an evolution of what some of your 240 00:12:27,960 --> 00:12:30,920 listeners may be more familiar with, which are radar altimeters 241 00:12:31,240 --> 00:12:35,440 in the. 50s or 60s? Pilots were flying aircraft over 242 00:12:35,600 --> 00:12:38,720 parts of the Greenland ice sheet and discovered that sometimes 243 00:12:38,720 --> 00:12:40,160 their radar altimeters didn't work. 244 00:12:40,160 --> 00:12:43,360 Very well relative to what they. Could see and they seemed to be 245 00:12:43,360 --> 00:12:45,440 returning. Much larger values in. 246 00:12:45,440 --> 00:12:48,480 Terms of the distance to the surface than what was actually 247 00:12:48,760 --> 00:12:50,800 apparent and what someone eventually. 248 00:12:50,800 --> 00:12:54,400 Realized is that that is because ice is relatively. 249 00:12:54,400 --> 00:12:57,520 Transparent to radio waves. Polar ice is typically. 250 00:12:57,520 --> 00:13:02,200 Quite dry and quite cold. All conditions that favor low 251 00:13:02,200 --> 00:13:05,520 attenuation of those radio wave signals, so that's been 252 00:13:05,520 --> 00:13:08,520 subsequently exploited. Throughout the world over. 253 00:13:08,520 --> 00:13:11,920 Ice To measure ice thickness relatively easily, the. 254 00:13:11,920 --> 00:13:15,080 Velocity through the ice. At radio frequencies is pretty 255 00:13:15,080 --> 00:13:18,360 well constrained, and so that allows us to make widespread ice 256 00:13:18,360 --> 00:13:21,720 thickness measurements more or less whenever we're flying an. 257 00:13:21,720 --> 00:13:25,160 Aircraft over the ice. For a scientific survey, when 258 00:13:25,160 --> 00:13:28,320 you say you can use the radar to tell you what the thickness of 259 00:13:28,320 --> 00:13:32,120 the ice is, are you basically comparing the reflection from 260 00:13:32,120 --> 00:13:34,960 the top of the ice with the reflection from the bottom of 261 00:13:34,960 --> 00:13:36,440 the ice and then taking the difference? 262 00:13:37,120 --> 00:13:39,680 Exactly, yes. And you mentioned are we using 263 00:13:39,680 --> 00:13:41,280 radar to observe? The top of the ice. 264 00:13:41,600 --> 00:13:44,800 We are, but we have another tool to measure that surface. 265 00:13:44,800 --> 00:13:47,400 Elevation very precisely, which is a laser. 266 00:13:47,400 --> 00:13:49,800 Altimeter and NASA has developed a. 267 00:13:49,800 --> 00:13:51,400 Series of those. Over the years, and that 268 00:13:51,400 --> 00:13:54,760 motivated most of our scientific surveys of Greenland and 269 00:13:54,760 --> 00:13:57,440 Antarctica. Which is to collect. 270 00:13:57,920 --> 00:14:02,240 Observations of changing ice thickness or ice elevation to 271 00:14:02,240 --> 00:14:04,840 interpret in terms. Of the broader. 272 00:14:04,840 --> 00:14:07,040 Response of these ice. Sheets to. 273 00:14:07,040 --> 00:14:09,240 Ongoing anthropogenic climate change. 274 00:14:10,000 --> 00:14:13,360 This began in the early 90s and has continued more or less ever 275 00:14:13,360 --> 00:14:17,560 since and has resulted in now 2. Satellites that are laser. 276 00:14:17,560 --> 00:14:19,080 Altimeters. One was. 277 00:14:19,080 --> 00:14:25,280 Called isat that orbited. From 2003 to 2009 and collected 278 00:14:25,280 --> 00:14:28,080 laser altimetry data in a way that we've never had before. 279 00:14:28,680 --> 00:14:31,200 And the second is. Called isat 2 which? 280 00:14:31,200 --> 00:14:36,040 Launched in 2018 and is continuing to produce excellent 281 00:14:36,040 --> 00:14:39,880 quality laser altimetry data across both ice sheets and allow 282 00:14:39,880 --> 00:14:40,680 us to have. A very. 283 00:14:40,880 --> 00:14:44,520 Precise understanding of their total mass change. 284 00:14:45,320 --> 00:14:48,240 When we spoke earlier, you mentioned stereo photogrammetry. 285 00:14:48,240 --> 00:14:51,640 Is that relevant to the topographic survey? 286 00:14:52,600 --> 00:14:54,280 Absolutely. We mentioned that we. 287 00:14:54,280 --> 00:14:57,360 Collect all these Criss. Crossing flight lines, We get 288 00:14:57,360 --> 00:15:01,840 incredible data along the track of the flight line, but we 289 00:15:01,840 --> 00:15:05,360 remain relatively ignorant as to what is going on between the 290 00:15:05,360 --> 00:15:07,600 flight lines. So that's where stereo 291 00:15:07,600 --> 00:15:09,000 photogrammetry. Can come in. 292 00:15:09,280 --> 00:15:14,000 It's not as accurate. As laser altimetry but it. 293 00:15:14,080 --> 00:15:18,360 Fills in the gaps extremely well, and so when those two are 294 00:15:18,360 --> 00:15:22,000 combined, we get a. Happy medium of the accuracy of 295 00:15:22,000 --> 00:15:26,880 laser altimetry. And the wide coverage of stereo 296 00:15:26,880 --> 00:15:30,560 photogrammetry. When you measure the topography 297 00:15:30,560 --> 00:15:34,680 of the rocks below the ice and then the topography of the 298 00:15:34,760 --> 00:15:38,840 surface itself, does the topography of what's happening 299 00:15:38,840 --> 00:15:42,920 below project itself onto the surface of the ice, even if it's 300 00:15:43,120 --> 00:15:45,520 kilometers above it? It does indeed. 301 00:15:45,720 --> 00:15:50,280 It's been known for a long time that when ice flows over a bump 302 00:15:50,440 --> 00:15:54,040 or a valley, even if it's a kilometer thick, 2 kilometers 303 00:15:54,040 --> 00:15:57,520 thick. It will leave a surface. 304 00:15:57,520 --> 00:16:01,240 Impression of that bump. Or valley at the. 305 00:16:01,240 --> 00:16:04,520 Surface Now that valley might be 100. 306 00:16:04,520 --> 00:16:07,640 Meters deep. And the resulting bump might 307 00:16:07,640 --> 00:16:13,920 only be a meter in amplitude at the surface, but therein lies 308 00:16:13,920 --> 00:16:16,200 the benefits of. Stereo photogrammetry and its 309 00:16:16,200 --> 00:16:18,720 ability to resolve. Relative surface elevation 310 00:16:18,720 --> 00:16:21,240 change and. Also these ice sheets. 311 00:16:21,240 --> 00:16:25,440 Acting as superb low. Pass filters of these. 312 00:16:25,440 --> 00:16:28,160 Signals. As our ability. 313 00:16:28,280 --> 00:16:31,240 To resolve relative changes. In surface. 314 00:16:31,240 --> 00:16:33,520 Elevation has improved. We now. 315 00:16:33,720 --> 00:16:35,960 Through this study have the ability. 316 00:16:35,960 --> 00:16:39,800 To see how the ice sheet is responding to all the bumps 317 00:16:39,880 --> 00:16:43,200 across Greenland and directly compare it. 318 00:16:43,320 --> 00:16:46,800 To places where we. Have ice thickness data and to. 319 00:16:46,800 --> 00:16:50,360 See that those. Line up and that allows us to 320 00:16:50,360 --> 00:16:54,920 look at a map of the surface. Of the ice sheet which at its. 321 00:16:54,920 --> 00:17:00,160 Thick is just three kilometers thick and then be able to infer 322 00:17:00,160 --> 00:17:01,800 where. All the valleys are. 323 00:17:01,840 --> 00:17:03,800 Even if we haven't measured them all. 324 00:17:03,920 --> 00:17:06,800 Directly what we learned. From that for example. 325 00:17:07,240 --> 00:17:10,880 Is that these fjords that have beautiful glaciers? 326 00:17:10,880 --> 00:17:14,839 That calve off into the ocean. That we see at the edge of the 327 00:17:14,839 --> 00:17:16,520 ice sheet. In some cases. 328 00:17:16,760 --> 00:17:18,160 Those fjords. More or less. 329 00:17:18,160 --> 00:17:19,599 Propagate. Back into the ice. 330 00:17:19,599 --> 00:17:23,520 Sheet sub glacially. In a straight line for up to 300 331 00:17:23,520 --> 00:17:26,000 kilometers. So as I said in the 332 00:17:26,000 --> 00:17:30,320 introduction, your map shows 3 new geological provinces under 333 00:17:30,320 --> 00:17:33,520 the ice. How do you define a province? 334 00:17:33,960 --> 00:17:36,600 We describe them generically as regions. 335 00:17:37,080 --> 00:17:38,880 And that they may yet be associated. 336 00:17:38,880 --> 00:17:42,880 With some of the known provinces that have been mapped at the 337 00:17:42,880 --> 00:17:45,920 periphery of Greenland, how we define a province is not 338 00:17:45,920 --> 00:17:48,080 intended to be any different from how. 339 00:17:48,400 --> 00:17:50,160 Geologists describe it elsewhere. 340 00:17:50,160 --> 00:17:53,760 Which is a common. Set of geologic features that 341 00:17:53,800 --> 00:17:55,800 are. Contemporaneous with each other 342 00:17:56,080 --> 00:17:58,880 that are reconcilable at. Large scale so for. 343 00:17:58,880 --> 00:18:02,560 Example Large igneous provinces We mapped part of the North 344 00:18:02,560 --> 00:18:05,200 Atlantic igneous province in the east of Greenland. 345 00:18:05,440 --> 00:18:08,320 Large basins such as the the independence of Fjord basin. 346 00:18:08,320 --> 00:18:12,080 In the north origins such as Engelfeld origin. 347 00:18:12,080 --> 00:18:14,320 In the Northwest, the Rinkian origin. 348 00:18:14,400 --> 00:18:16,760 Farther South. And cratons and. 349 00:18:16,760 --> 00:18:20,040 Other large scale features. That have common types. 350 00:18:20,040 --> 00:18:22,160 Of rock. Whether it's igneous rock. 351 00:18:22,160 --> 00:18:23,920 Associated with igneous provinces. 352 00:18:24,280 --> 00:18:27,640 Or sedimentary successions. Associated with basins. 353 00:18:28,000 --> 00:18:32,720 But when you decide to put a boundary between one region and 354 00:18:32,720 --> 00:18:37,400 another, are you looking at specific features and saying, 355 00:18:38,000 --> 00:18:41,880 OK, I think here we have a combination of data sets that 356 00:18:41,880 --> 00:18:45,640 indicate we're dealing with an igneous rock, say, and in 357 00:18:45,640 --> 00:18:48,480 another one here we're dealing with sedimentary rock. 358 00:18:48,840 --> 00:18:53,840 Or is it more that you just put all your data together and just 359 00:18:53,840 --> 00:18:58,000 look for the greatest amount of contrast considering all the 360 00:18:58,000 --> 00:19:01,600 data as a whole, without taking a view as to what the data is 361 00:19:01,600 --> 00:19:03,560 actually telling you about what's underneath? 362 00:19:04,160 --> 00:19:06,600 So it's really a combination of the two. 363 00:19:06,880 --> 00:19:09,600 In the case of igneous provinces, those are typically 364 00:19:09,600 --> 00:19:12,320 going to be associated. With large positive. 365 00:19:12,320 --> 00:19:16,920 Magnetic anomalies and relatively slow seismic speeds, 366 00:19:17,160 --> 00:19:19,720 and a little more nebulous with the gravity anomaly and the. 367 00:19:19,720 --> 00:19:23,040 Topography could be rough. That's the simplest case. 368 00:19:23,560 --> 00:19:25,560 In most other cases. In Greenland. 369 00:19:25,560 --> 00:19:28,880 Typically with very old. Rock and provinces that were 370 00:19:28,880 --> 00:19:31,120 formed 1 billion. Years ago plus. 371 00:19:31,120 --> 00:19:34,760 Except in the case of the very youngest ones and. 372 00:19:34,960 --> 00:19:37,520 We took our geophysical. Fields and looked at those 373 00:19:37,520 --> 00:19:42,760 fields island wide, including. At the periphery where? 374 00:19:42,760 --> 00:19:44,960 We have a much better understanding, obviously. 375 00:19:45,240 --> 00:19:49,240 Of what the geology is. And we looked at the pattern 376 00:19:49,240 --> 00:19:50,520 that we saw. There the. 377 00:19:50,800 --> 00:19:52,840 Magnitude of anomalies if they had a. 378 00:19:52,840 --> 00:19:56,240 Particular texture. A common wavelength or azimuth, 379 00:19:56,640 --> 00:20:00,200 and then looked at how that propagated inland and searched 380 00:20:00,200 --> 00:20:04,200 for contrasts in those fields, and we did that independently. 381 00:20:04,200 --> 00:20:08,000 For each of those fields. So what we ended up with was a 382 00:20:08,080 --> 00:20:12,080 mishmash of lines in some places, and relatively coherent, 383 00:20:12,080 --> 00:20:16,680 consistent boundaries between most fields in other places. 384 00:20:17,240 --> 00:20:19,160 More often than not, the. Coherent. 385 00:20:19,160 --> 00:20:22,440 Boundaries were in southern Greenland, and they were much 386 00:20:22,440 --> 00:20:25,600 more complex in northern Greenland, which appears to be 387 00:20:25,600 --> 00:20:29,080 an amalgamation of several relatively ancient provinces. 388 00:20:29,520 --> 00:20:32,920 Can you describe a little bit more about what characterizes 389 00:20:33,120 --> 00:20:35,800 each of these regions? You mentioned the simplest case 390 00:20:36,160 --> 00:20:40,200 that would indicate an igneous rock in terms of what you 391 00:20:40,200 --> 00:20:44,080 actually found in that northern region that you chose to divide 392 00:20:44,080 --> 00:20:47,040 into three regions. Would you be able to give them a 393 00:20:47,040 --> 00:20:50,920 qualitative description and then maybe even go so far as to say 394 00:20:50,920 --> 00:20:54,280 something about how they were assembled and what their origin 395 00:20:54,280 --> 00:20:56,920 is? We purposefully stayed away. 396 00:20:56,920 --> 00:21:00,360 From that latter question as to how they were assembled and 397 00:21:00,360 --> 00:21:02,520 instead focus on what distinguished. 398 00:21:02,520 --> 00:21:05,920 Them geophysically so that we have a. 399 00:21:06,200 --> 00:21:10,280 Baseline for future interpretation, recall from. 400 00:21:10,280 --> 00:21:13,040 The DAWS, 2000. Nine map, our reference map. 401 00:21:13,400 --> 00:21:16,920 They essentially used. No geophysical data to. 402 00:21:16,920 --> 00:21:20,560 Constrain what was happening across. 80% of the island. 403 00:21:20,560 --> 00:21:23,360 So here we're trying to. Take that next step where we 404 00:21:23,360 --> 00:21:26,160 look at different. Regions say OK, it seems like in 405 00:21:26,160 --> 00:21:28,760 the West we often. Have a shallower Moho. 406 00:21:28,760 --> 00:21:31,480 Boundary we seem to have. Faster shear wave. 407 00:21:31,480 --> 00:21:35,920 Velocities in the southern 2/3 of Greenland and the gravity 408 00:21:35,920 --> 00:21:38,320 anomalies and the magnetic anomalies, which typically a 409 00:21:38,320 --> 00:21:41,440 finer resolution, that's where. You really start to see a lot. 410 00:21:41,440 --> 00:21:44,800 Of the strange contrasts across northern Greenland. 411 00:21:45,040 --> 00:21:46,480 That give you a clue that this is a. 412 00:21:46,600 --> 00:21:51,240 Complicated region subglacially in terms of the geology, not 413 00:21:51,240 --> 00:21:53,920 just, as is apparent from the. Periphery of the ice sheet. 414 00:21:54,480 --> 00:21:58,520 When you looked at it after you generated the map and you 415 00:21:58,520 --> 00:22:01,800 defined what you think were the boundaries of the regions that 416 00:22:01,800 --> 00:22:06,280 created the greatest contrast, was there any particular data 417 00:22:06,280 --> 00:22:11,320 type that in retrospect seemed to map most closely into each of 418 00:22:11,320 --> 00:22:14,320 the different regions that you could say characterize those 419 00:22:14,320 --> 00:22:16,320 regions best if you were just to pick one? 420 00:22:17,120 --> 00:22:22,680 If I had to pick two data types. And revealing my bias. 421 00:22:22,680 --> 00:22:24,720 As a geophysicist here, I would pick the. 422 00:22:24,720 --> 00:22:27,600 Gravity and magnetics. Those give us. 423 00:22:27,800 --> 00:22:32,600 The best combination of resolution of what is going on 424 00:22:32,680 --> 00:22:34,520 in the subsurface. Beneath the ice. 425 00:22:34,960 --> 00:22:38,000 And insight into really what the nature. 426 00:22:38,000 --> 00:22:41,680 Of those rocks are topography, the bedrock topography. 427 00:22:41,720 --> 00:22:45,440 Both observed and inferred. That's an indirect indicator at 428 00:22:45,440 --> 00:22:48,200 best. And the depth to Moho and the. 429 00:22:48,280 --> 00:22:51,600 Shallow shear wave velocities. Those are helpful context, but 430 00:22:51,600 --> 00:22:53,440 they're. Relatively coarse resolution. 431 00:22:54,240 --> 00:22:58,120 We believe that the hotspot that is currently contributing to all 432 00:22:58,120 --> 00:23:02,360 the volcanism taking place in Iceland previously traced the 433 00:23:02,360 --> 00:23:05,880 path below Greenland as it drifted to the West as part of 434 00:23:05,880 --> 00:23:09,800 the North American plate. Were you able to identify a 435 00:23:09,800 --> 00:23:13,680 channel of basaltic rock marking the hotspot in your data? 436 00:23:14,040 --> 00:23:17,120 Not. Directly, it's widely accepted 437 00:23:17,120 --> 00:23:20,600 that. 50 to 60 million years ago, the Icelandic hotspot 438 00:23:20,840 --> 00:23:24,280 passed through Greenland. But where exactly it? 439 00:23:24,280 --> 00:23:27,320 Passed through Greenland on this northwest to east traverse 440 00:23:27,520 --> 00:23:29,120 remains. An issue of debate. 441 00:23:29,480 --> 00:23:32,200 And still not. Clearly resolved there are. 442 00:23:32,200 --> 00:23:34,560 Hints. That perhaps the hotspot didn't 443 00:23:34,760 --> 00:23:37,000 breakthrough the crust, but it left a. 444 00:23:37,280 --> 00:23:40,960 Thermal signature Lateral. To the path of the hotspot. 445 00:23:41,320 --> 00:23:43,880 There are other studies that have suggested that perhaps 446 00:23:43,880 --> 00:23:46,320 there's. Elevated geothermal activity in 447 00:23:46,320 --> 00:23:51,760 particular regions. We did notice that there are Co. 448 00:23:51,760 --> 00:23:57,080 Located gravity and seismic and in particular magnetic anomalies 449 00:23:57,440 --> 00:24:02,280 in this region that we called Central Region B that is in East 450 00:24:02,280 --> 00:24:04,600 Central Greenland, it's subglacial. 451 00:24:04,920 --> 00:24:11,000 It does not appear to have any known outcrop and it is an area. 452 00:24:11,000 --> 00:24:13,320 That three decades ago. Someone. 453 00:24:13,560 --> 00:24:15,960 Described as. Based on some preliminary 454 00:24:15,960 --> 00:24:19,440 magnetic and gravity data, the Central Greenland Magmatic 455 00:24:19,440 --> 00:24:22,520 province and we went back and forth between our group as to 456 00:24:22,520 --> 00:24:24,000 whether or not. We would give these. 457 00:24:24,000 --> 00:24:28,000 Specific genetic indicators to these regions, but ultimately. 458 00:24:28,000 --> 00:24:31,520 We decided to leave. Them as generic so as to not 459 00:24:31,520 --> 00:24:33,880 lead the witness too much. But. 460 00:24:34,040 --> 00:24:36,280 This is an interesting region. Whether it has high. 461 00:24:36,280 --> 00:24:38,400 Geothermal activity remains to be seen. 462 00:24:38,640 --> 00:24:41,920 Because it just so. Happens to be next to a. 463 00:24:41,920 --> 00:24:46,280 Glaciological feature, that is. Unique in Greenland and indeed 464 00:24:46,320 --> 00:24:47,920 relative to Antarctica. As well. 465 00:24:48,600 --> 00:24:50,920 That feature is called the. Northeast Greenland ice stream 466 00:24:51,520 --> 00:24:56,640 and it starts almost at a point close to the middle. 467 00:24:56,640 --> 00:24:59,920 Of the ice sheet. And then expands. 468 00:25:00,000 --> 00:25:02,880 As it slowly heads. Downstream for several 100 469 00:25:02,880 --> 00:25:05,880 kilometers until. It reaches the ocean. 470 00:25:05,880 --> 00:25:08,280 And becomes this very. Crevassed and beautiful glacier. 471 00:25:08,480 --> 00:25:11,440 In the far northeast, Greenland called Zechariah Isstrom. 472 00:25:11,800 --> 00:25:14,120 A glacier that's actually. Changing very rapidly. 473 00:25:14,120 --> 00:25:16,000 Today that we're quite concerned. 474 00:25:16,000 --> 00:25:18,680 About in terms of future mass change of the ice sheet? 475 00:25:19,520 --> 00:25:22,080 So what starts? The Northeast Greenland Ice St. 476 00:25:22,080 --> 00:25:24,200 There's nothing like it anywhere else. 477 00:25:24,200 --> 00:25:26,760 There are hints that there may have been similar features 478 00:25:26,920 --> 00:25:29,920 elsewhere in northeast Greenland, but it's the only one 479 00:25:29,920 --> 00:25:30,880 we. See today. 480 00:25:31,520 --> 00:25:35,200 And it's a quite interesting coincidence that it happens to 481 00:25:35,200 --> 00:25:37,920 be located right next to this anomalous. 482 00:25:37,920 --> 00:25:41,880 Subglacial geologic area. One of the things that you and 483 00:25:41,880 --> 00:25:47,400 your team are interested in was to learn about the flow of ice 484 00:25:47,440 --> 00:25:50,480 on Greenland and particular to see if there's a relationship 485 00:25:50,920 --> 00:25:53,520 between the bedrock and the flow of overlying ice. 486 00:25:53,520 --> 00:25:57,120 And you've just mentioned a specific correlation that you 487 00:25:57,120 --> 00:26:00,120 think strongly suggests there might very well be. 488 00:26:00,520 --> 00:26:03,240 You developed a new visualization technique to 489 00:26:03,240 --> 00:26:08,640 facilitate this, which you called Flow Aware Hill Shade. 490 00:26:08,640 --> 00:26:10,920 Can you tell us about that? Sure. 491 00:26:10,960 --> 00:26:14,640 So this is a hill shade. Of a digital elevation model. 492 00:26:14,840 --> 00:26:17,360 Which is a stereo. Photogrammetric model. 493 00:26:17,360 --> 00:26:21,840 That we talked about earlier. Instead of lighting the DEM from 494 00:26:21,840 --> 00:26:26,560 a single azimuth, it takes into account the direction of the. 495 00:26:26,560 --> 00:26:30,440 Flow of ice so that instead of. Being limited to a single 496 00:26:30,440 --> 00:26:33,640 azimuth, it can vary. Relative to the direction. 497 00:26:33,640 --> 00:26:35,520 Of ice flow. In this case, we found that 498 00:26:35,640 --> 00:26:39,400 orthogonal to ice flow seemed to work best, and that. 499 00:26:39,400 --> 00:26:42,440 Allows you to visualize. These bumps as the ice is 500 00:26:42,440 --> 00:26:44,840 flowing over features relatively cleanly. 501 00:26:45,160 --> 00:26:49,160 And what did you find by means of this visualization technique? 502 00:26:49,760 --> 00:26:51,920 What we found was clear evidence. 503 00:26:52,000 --> 00:26:56,520 That there are large. Networks of very long, sometimes 504 00:26:56,520 --> 00:27:00,920 hundreds of kilometers. Subparallel valleys across the 505 00:27:00,920 --> 00:27:03,440 ice sheet. And they're often quite straight 506 00:27:03,600 --> 00:27:06,120 and they. Have a. 507 00:27:06,280 --> 00:27:10,840 Predominant southwest, northeast azimuth, although not exclusive. 508 00:27:11,480 --> 00:27:15,880 They often reveal features. That you can see at the margin 509 00:27:15,880 --> 00:27:19,400 of the ice sheet that come out as, say, a river or a fjord. 510 00:27:19,760 --> 00:27:22,200 So you can look at this flow over a hill shade. 511 00:27:22,600 --> 00:27:25,000 And then see. Where you get towards the very 512 00:27:25,000 --> 00:27:27,200 edge of the ice sheet if you're. Following a single trend line, 513 00:27:27,200 --> 00:27:28,560 then oh. There's a river. 514 00:27:29,200 --> 00:27:31,360 And So what that tells. Us is that. 515 00:27:31,600 --> 00:27:34,000 We're dealing with something that's glaciologically useful. 516 00:27:34,240 --> 00:27:37,160 But it's also. Revealing a long term erosion 517 00:27:37,160 --> 00:27:39,840 pattern that is. Present across the ice. 518 00:27:39,840 --> 00:27:44,160 Sheet in this systematic way, so you were able to see the very 519 00:27:44,160 --> 00:27:49,840 long valley best by examining the ice flow on the surface 520 00:27:49,840 --> 00:27:52,920 rather than looking at the radar signal for example. 521 00:27:53,400 --> 00:27:56,200 So what the radar does is it allows you to get the depth of 522 00:27:56,200 --> 00:28:00,960 that valley precisely, however. We don't have blanket coverage 523 00:28:00,960 --> 00:28:02,000 of the entire. Ice sheet. 524 00:28:02,280 --> 00:28:05,880 So what happens is the radar. Only occasionally Criss crosses. 525 00:28:05,880 --> 00:28:07,800 Many of these valleys. Particularly in the deep 526 00:28:07,800 --> 00:28:09,840 interior and in some. Cases. 527 00:28:10,120 --> 00:28:13,160 Some of these valleys, not really the longest ones, but 528 00:28:13,160 --> 00:28:16,720 some of the more prominent ones. Curiously, we've never flown 529 00:28:16,720 --> 00:28:18,360 over. But it's clear that they're 530 00:28:18,360 --> 00:28:20,920 there. And they have an effect on the 531 00:28:20,920 --> 00:28:24,320 flow of ice above them. Kilometers above, they leave an 532 00:28:24,320 --> 00:28:26,560 imprint. Of the flow of ice kilometers. 533 00:28:26,560 --> 00:28:28,520 Above. I wouldn't say that they have a. 534 00:28:28,720 --> 00:28:32,880 Strong influence on how the ice is flowing, but they could 535 00:28:32,880 --> 00:28:35,080 potentially in the future because what valleys? 536 00:28:35,080 --> 00:28:38,360 Are are places where any water. That is generated. 537 00:28:38,360 --> 00:28:41,880 Beneath the ice. Is going to tend to end up and 538 00:28:41,880 --> 00:28:43,720 then. Flow toward the periphery. 539 00:28:44,240 --> 00:28:47,400 And that could ultimately influence how fast that ice is 540 00:28:47,400 --> 00:28:50,280 flowing because. Water, we know, is very 541 00:28:50,280 --> 00:28:52,320 effective. At lubricating the base of the 542 00:28:52,320 --> 00:28:55,960 ice and ultimately leading to sliding, do we think that these 543 00:28:55,960 --> 00:28:59,520 long valleys predated the ice and really have nothing to do 544 00:28:59,520 --> 00:29:01,200 with the ice? That. 545 00:29:01,200 --> 00:29:04,720 Is our working hypothesis the. Fact that there are. 546 00:29:04,720 --> 00:29:05,800 Long. Networks. 547 00:29:06,200 --> 00:29:09,080 They are subparallel to each other and straight. 548 00:29:09,320 --> 00:29:12,960 And also the radar observations that tend to observe more V 549 00:29:12,960 --> 00:29:15,160 shaped. Valleys than U-shaped valleys. 550 00:29:15,760 --> 00:29:19,520 That suggests that these valleys probably predate the ice sheet. 551 00:29:20,000 --> 00:29:22,320 And they may be indicative. Of some sort of. 552 00:29:22,400 --> 00:29:26,640 Tectonic imprint on the rock in which the valleys formed that 553 00:29:26,640 --> 00:29:29,200 led to preferential paths of erosion. 554 00:29:29,560 --> 00:29:32,200 For these valleys. Yeah, I'm wondering, do these 555 00:29:32,200 --> 00:29:35,280 represent sutures between different terrains or major 556 00:29:35,480 --> 00:29:38,920 strike slip faults that were weaker and so somehow rather 557 00:29:39,120 --> 00:29:42,800 gouged out by the ice? We did consider a hypothesis. 558 00:29:42,800 --> 00:29:45,880 Like that initially, but our conversations with 559 00:29:45,880 --> 00:29:49,000 geodynamicists suggest that the. Stresses that would be. 560 00:29:49,000 --> 00:29:52,000 Required to generate. Patterns like that are likely 561 00:29:52,200 --> 00:29:54,320 far too. Large to explain them directly, 562 00:29:54,800 --> 00:29:58,160 but it is very remarkable that you have these parallel valleys, 563 00:29:58,160 --> 00:30:01,840 thousands of kilometers long and roughly parallel to each other 564 00:30:02,040 --> 00:30:05,120 is not really something we see anywhere else in the world, is 565 00:30:05,120 --> 00:30:07,160 it? Yeah, it's not very common, and 566 00:30:07,160 --> 00:30:09,440 that's why we felt that it was very much worth noting. 567 00:30:10,400 --> 00:30:13,000 Do you have a new mission to Greenland in the works? 568 00:30:13,520 --> 00:30:15,240 We do. Actually, I'm part of a new 569 00:30:15,240 --> 00:30:18,440 mission called Snow for Flow. We will be. 570 00:30:18,440 --> 00:30:21,560 Measuring snow thickness and ice thickness in key. 571 00:30:21,560 --> 00:30:24,760 Glaciers that are relatively. Understudied both in 572 00:30:24,760 --> 00:30:26,760 southeastern Greenland but also elsewhere. 573 00:30:26,760 --> 00:30:28,040 In the Arctic. So that we can. 574 00:30:28,240 --> 00:30:32,160 Better project how these? Regions are going to change in 575 00:30:32,160 --> 00:30:35,040 the context of ongoing anthropogenic climate change. 576 00:30:35,880 --> 00:30:37,800 Joe McGregor, thank you very much. 577 00:30:38,320 --> 00:30:40,480 Thank you, Oliver. It was really nice to join you 578 00:30:40,480 --> 00:30:41,560 and talk about this. Study. 579 00:30:42,720 --> 00:30:45,400 To see pictures and illustrations that support this 580 00:30:45,400 --> 00:30:50,960 podcast, go to geologybytes.com, where you'll also find 581 00:30:50,960 --> 00:30:54,440 transcripts and a subject matter index of all the episodes. 582 00:30:55,000 --> 00:30:58,360 There you can also give me feedback which I welcome, as 583 00:30:58,360 --> 00:31:01,360 well as sign up to get my emails about new episodes.