1 00:00:05,000 --> 00:00:08,000 This is geology B with all of us trampled. 2 00:00:09,200 --> 00:00:11,400 Much of the Earth's land surface is flat. 3 00:00:12,000 --> 00:00:15,400 There are huge steps in Eurasia tundra, in the Arctic, 4 00:00:15,700 --> 00:00:18,000 grasslands, and farmland in North America. 5 00:00:19,000 --> 00:00:22,400 We can easily imagine a simple flat planet with nothing but 6 00:00:22,400 --> 00:00:27,100 planes, but in fact, dramatic mountain ranges rise up on every 7 00:00:27,100 --> 00:00:30,600 continent. The distinguished geologist Mike 8 00:00:30,600 --> 00:00:35,100 cell has been studying mountain ranges for 40 years Mike cell. 9 00:00:35,300 --> 00:00:39,700 Welcome to geology B mountain ranges such as the Himalaya the 10 00:00:39,700 --> 00:00:43,000 Andes or the Rockies are some of the most prominent features on 11 00:00:43,000 --> 00:00:46,500 the surface of our planet. Anyone trying to understand how 12 00:00:46,508 --> 00:00:50,000 the others evolved over geological time has to explain 13 00:00:50,000 --> 00:00:52,600 how he get these huge, topographic landmarks. 14 00:00:53,400 --> 00:00:56,700 So I'm going to jump right in and ask you how do mountains 15 00:00:56,700 --> 00:01:00,900 form Well, most mountain ranges are formed along plate 16 00:01:00,900 --> 00:01:03,600 boundaries. So everyone's heard of plate 17 00:01:03,600 --> 00:01:06,300 tectonics. This is the theory that divides, 18 00:01:06,300 --> 00:01:10,200 the Earth's crust up insist seven or eight fairly large 19 00:01:10,200 --> 00:01:15,400 plate and the plates move around driven by convection in the 20 00:01:15,400 --> 00:01:21,000 mantle and those convection currents come up and generate 21 00:01:21,000 --> 00:01:23,300 new crust along mid-ocean ridges. 22 00:01:24,200 --> 00:01:28,500 And they consume ocean crust as the crust plunges. 23 00:01:28,500 --> 00:01:33,500 Down subduction zones, when we see convection say in the 24 00:01:33,500 --> 00:01:38,100 atmosphere, when air rises and makes clouds, it tends to be a 25 00:01:38,100 --> 00:01:41,900 fairly chaotic Affair. So I suppose, the convection in 26 00:01:41,900 --> 00:01:45,200 the Earth's, mantle that drives these tectonic plates is also 27 00:01:45,200 --> 00:01:48,200 periodic orbit at much larger scales. 28 00:01:49,000 --> 00:01:51,400 This means that the plates must all be moving in different 29 00:01:51,400 --> 00:01:53,500 directions with plates, moving away. 30 00:01:53,600 --> 00:01:56,400 A from each other along some of their margins such as at the 31 00:01:56,400 --> 00:02:00,100 mid-ocean ridges you mentioned but also bumping into each other 32 00:02:00,100 --> 00:02:03,500 on the other side. Well that's the interesting part 33 00:02:03,500 --> 00:02:08,100 when mountains get made. So the Alpine Himalayan, Shane 34 00:02:08,100 --> 00:02:13,600 runs pretty much all around the world and it's a result of the 35 00:02:13,600 --> 00:02:17,900 Collision of a series of southern continents that were 36 00:02:17,900 --> 00:02:21,200 all part of this great. Super continent called gondwana 37 00:02:21,800 --> 00:02:24,900 colliding. With the Some consonants which 38 00:02:24,900 --> 00:02:29,500 are part of Asia that collision between the two continental 39 00:02:29,500 --> 00:02:35,000 plates varies along the strike, but it has very similarity in 40 00:02:35,000 --> 00:02:38,800 processes that are happening at the same time, all the way for 41 00:02:38,800 --> 00:02:43,200 example, from the Alps to the Himalayas, and even down towards 42 00:02:43,200 --> 00:02:46,000 Indonesia. Well, that makes sense 43 00:02:46,000 --> 00:02:49,400 intuitively that mountain should form where plates are colliding 44 00:02:49,400 --> 00:02:52,700 with each other but that is a truly gigantic scale. 45 00:02:52,700 --> 00:02:55,200 You're talking about From the Himalaya to the Alps. 46 00:02:55,400 --> 00:02:57,200 There must be a lot of diversity in. 47 00:02:57,200 --> 00:02:59,700 What's happened along this Collision belt, though, because 48 00:02:59,700 --> 00:03:02,000 the Himalaya quite different from the apps. 49 00:03:02,400 --> 00:03:05,400 Yes, that's true. The Alps in the Himalayas were 50 00:03:05,400 --> 00:03:09,200 both formed by two, continental Collision but they are very 51 00:03:09,200 --> 00:03:12,500 different indeed. As you say, the Himalayas is 52 00:03:12,500 --> 00:03:16,300 probably one of the simplest of the Collision belts that we see, 53 00:03:16,300 --> 00:03:19,700 which is why it's such a beautiful place for a geologist 54 00:03:19,700 --> 00:03:23,500 to work because we have along the Himalayas a mountain chain. 55 00:03:23,600 --> 00:03:26,000 In about two and a half thousand kilometers long. 56 00:03:27,000 --> 00:03:30,100 Probably 100 to 200 kilometers wide. 57 00:03:30,700 --> 00:03:35,200 And the processes of collision are very, very similar all the 58 00:03:35,200 --> 00:03:39,800 way along that mountain chain from Pakistan to India, to Nepal 59 00:03:39,800 --> 00:03:44,000 to Southern Tibet. And we can determine them using 60 00:03:44,200 --> 00:03:49,700 the geology and stratigraphy and geochronology how you date rocks 61 00:03:49,700 --> 00:03:53,100 using fossils or using radioactive minerals like 62 00:03:53,100 --> 00:03:56,200 Zircon, we can determine the processes. 63 00:03:56,300 --> 00:03:58,900 That formed that major Collision belt. 64 00:03:59,500 --> 00:04:02,000 So, for example, in the Himalayas we know that the 65 00:04:02,000 --> 00:04:06,600 Indian plate and Asian plate. Collided about 50 million years 66 00:04:06,600 --> 00:04:12,400 ago, roughly down at equatorial latitudes since when India has 67 00:04:12,400 --> 00:04:16,100 ploughed on North Woods, indenting into Asia as it goes, 68 00:04:16,600 --> 00:04:20,200 and creating the Himalayas in the last 50 million years. 69 00:04:21,100 --> 00:04:24,600 Okay, let's talk then about what's gone on and still going 70 00:04:24,600 --> 00:04:27,800 on during this drawn out, 50 million year collision. 71 00:04:28,700 --> 00:04:32,400 And I want to throw in an amazing fact, namely that we 72 00:04:32,400 --> 00:04:36,400 find fossils of marine creatures, right at the very top 73 00:04:36,400 --> 00:04:39,100 of Everest. So, how did rocks from the 74 00:04:39,100 --> 00:04:42,200 bottom of an ocean manage to find their way to the summit of 75 00:04:42,207 --> 00:04:43,900 the highest mountain in the world? 76 00:04:44,700 --> 00:04:47,700 That's absolutely correct. The summit rocks of Mount 77 00:04:47,700 --> 00:04:52,500 Everest, the highest rocks on the planet. 650 meters above 78 00:04:52,500 --> 00:04:54,700 sea. Level are actually Marine 79 00:04:54,700 --> 00:04:57,600 limestone's. They were formed during the 80 00:04:57,600 --> 00:05:03,500 ordovician about 450 million years ago and they still contain 81 00:05:03,500 --> 00:05:07,400 relics fossils in them. They had little tiny crinoids 82 00:05:07,500 --> 00:05:10,600 ossicles. Ossicles of the stems of 83 00:05:10,600 --> 00:05:14,700 crinoids which has see fans or sea lilies, but are still in the 84 00:05:14,700 --> 00:05:18,100 oceans today and they are perfectly preserved. 85 00:05:18,100 --> 00:05:21,800 In these limestone's taken from the summit of Mount Everest. 86 00:05:22,300 --> 00:05:26,900 Well, how did sedimentary rocks formed at sea level end up at 87 00:05:26,900 --> 00:05:29,000 nearly nine kilometers above sea level. 88 00:05:29,700 --> 00:05:34,700 And that is because as India is colliding with Asia, the Indian 89 00:05:34,700 --> 00:05:39,400 place is diving down beneath the Asian plate, and as it Dives 90 00:05:39,400 --> 00:05:44,500 down, it is stacking units up. So all the rocks that form the 91 00:05:44,500 --> 00:05:48,000 northern boundary of India, the sedimentary rocks that form the 92 00:05:48,000 --> 00:05:50,800 northern boundary of India are all folded. 93 00:05:51,300 --> 00:05:57,000 And thrust and that folding and thrusting shortens the rocks and 94 00:05:57,000 --> 00:06:01,300 as India is diving down, it is completely jacking up the crust 95 00:06:01,300 --> 00:06:04,300 of Tibet. As it goes, it's a bit like 96 00:06:04,300 --> 00:06:08,900 putting a jack underneath the car to fix your puncture and as 97 00:06:08,900 --> 00:06:12,400 the jack is continually wound up, the car goes up and up and 98 00:06:12,400 --> 00:06:14,900 up. So was that devastating 99 00:06:14,900 --> 00:06:19,300 earthquake in Nepal in 2015 part of that jacking up process and 100 00:06:19,300 --> 00:06:22,200 where the mountains suddenly a bit higher after that 101 00:06:22,200 --> 00:06:24,400 earthquake. Yes, exactly. 102 00:06:24,800 --> 00:06:30,000 The Gawker earthquake of 2015 was just one of a whole series 103 00:06:30,000 --> 00:06:33,300 of hundreds and thousands of earthquakes that have similarly 104 00:06:33,700 --> 00:06:37,600 affected the Himalayas through time and that's how you build up 105 00:06:37,600 --> 00:06:39,900 mountain ranges. Like the Himalayas, each one of 106 00:06:39,900 --> 00:06:43,200 those earthquakes results in the Rocks. 107 00:06:43,500 --> 00:06:47,500 Moving up to 10 metres, in some cases in some of the largest 108 00:06:47,500 --> 00:06:50,200 earthquakes. With regard to The Gawker 109 00:06:50,200 --> 00:06:53,700 earthquake in Nepal. That was a thrust fault so it 110 00:06:53,700 --> 00:06:58,400 records shortening on the basil thrust as India is diving down 111 00:06:58,400 --> 00:07:03,900 beneath the Himalayas and the Rocks beneath Katmandu shortened 112 00:07:03,900 --> 00:07:08,300 by anything up to a meter and a half instantly and the mountains 113 00:07:08,300 --> 00:07:12,300 immediately to the north of the Kathmandu Valley, Rose by just 114 00:07:12,300 --> 00:07:16,300 over one meter. In a few seconds, it may seem 115 00:07:16,300 --> 00:07:21,100 ironic global positioning We have scattered around the pool 116 00:07:21,100 --> 00:07:24,100 showed that the highest peaks around Mount Everest actually 117 00:07:24,100 --> 00:07:27,300 sank a little bit. But in fact, they sank because 118 00:07:27,300 --> 00:07:31,700 the whole of Nepal was tilted down to the north and up to the 119 00:07:31,700 --> 00:07:35,000 South. So the most devastating parts of 120 00:07:35,000 --> 00:07:38,700 that earthquake were all around the parts along the northern 121 00:07:38,700 --> 00:07:42,000 side of the Kathmandu Valley. For example, where the Rocks 122 00:07:42,000 --> 00:07:46,800 raised by over a metre and horizontally shortened okay, I 123 00:07:46,800 --> 00:07:50,000 can see how a plate can jack up. Another plate when it's squeezed 124 00:07:50,000 --> 00:07:53,600 underneath it, but that still doesn't really explain how we 125 00:07:53,600 --> 00:07:57,900 get these spectacular Peaks and valleys as opposed to say a flat 126 00:07:57,900 --> 00:08:01,000 Plateau. Well, it does make a flat 127 00:08:01,000 --> 00:08:04,100 plateau in Tibet to the north of the Himalayas. 128 00:08:04,800 --> 00:08:09,800 So Tibet is by far the largest area of highest elevation and 129 00:08:09,800 --> 00:08:12,500 thick crust anywhere on the planet. 130 00:08:13,400 --> 00:08:16,600 The average elevation of the Tibetan Plateau is 5 kilometers 131 00:08:16,600 --> 00:08:19,700 above sea level. And the crust is double the 132 00:08:19,700 --> 00:08:23,100 thickness of anywhere else around it in India, or on the 133 00:08:23,108 --> 00:08:26,700 continent, it's up to 70 or 80 km today. 134 00:08:27,400 --> 00:08:30,200 So, the Himalayas of the collisional mountain range that 135 00:08:30,200 --> 00:08:33,400 borders, the southern edge of this plateau. 136 00:08:34,299 --> 00:08:39,000 And the only reason we know what the structure of the crust is 137 00:08:39,000 --> 00:08:42,900 like, underneath Tibet is from geophysics, you can't see it in 138 00:08:42,900 --> 00:08:46,300 the The layers, you can see it. You can walk up any of the 139 00:08:46,300 --> 00:08:50,200 valleys which drain north-south on the most incredible thing 140 00:08:50,200 --> 00:08:54,200 about the Himalayas is the early geologists discovered a hundred 141 00:08:54,200 --> 00:08:58,100 years ago was the further north, you tracked, along those valleys 142 00:08:58,100 --> 00:09:03,500 towards Tibet, the deeper the Rocks exposed, so you're putting 143 00:09:03,800 --> 00:09:08,100 deeper hired pressure higher temperature, rocks on top of 144 00:09:08,100 --> 00:09:12,300 shallower sedimentary rocks, and that is pretty unusual. 145 00:09:13,100 --> 00:09:15,700 Emily on the planet, the deeper you go. 146 00:09:15,700 --> 00:09:18,800 You increase pressure and you increase temperature. 147 00:09:19,400 --> 00:09:22,000 So you would convert a sedimentary rock like a 148 00:09:22,000 --> 00:09:27,100 limestone or a Shale to a metamorphic, rock like a marble 149 00:09:27,500 --> 00:09:32,400 or AP like sappy light is just a metamorphose Shale and it has 150 00:09:32,400 --> 00:09:36,700 these distinctive minerals in metamorphic minerals that we can 151 00:09:36,700 --> 00:09:41,700 derive, an idea of the depth of burial of those rocks and as you 152 00:09:41,700 --> 00:09:45,700 walk, Woods across the Himalayas, you're going 153 00:09:45,700 --> 00:09:49,200 progressively deeper, as you go to the north, and this is what 154 00:09:49,200 --> 00:09:52,000 we call an inverted metamorphism. 155 00:09:52,500 --> 00:09:55,200 So the whole of the sudden, slopes of the Himalayas, all the 156 00:09:55,200 --> 00:09:58,300 way along the mountain range are actually upside down. 157 00:09:59,100 --> 00:10:02,100 I don't to keep harping on this question, but it's still not 158 00:10:02,100 --> 00:10:04,600 clear to me. Just how any of these geological 159 00:10:04,600 --> 00:10:07,900 processes actually makes the mountains into the shapes that 160 00:10:07,900 --> 00:10:12,400 we see well that is largely to do with the geomorphology. 161 00:10:12,600 --> 00:10:16,000 What we See today, along the Himalayas is the results of 162 00:10:16,000 --> 00:10:21,600 dominantly glacial erosion mountains are above 5 km high 163 00:10:21,600 --> 00:10:24,600 are going to be glaciated. So when you track up to Everest, 164 00:10:24,600 --> 00:10:27,900 for example, the Western Combe which is the classic climbing 165 00:10:27,900 --> 00:10:31,100 route up from the Nepal side up through, Everest is a classic 166 00:10:31,100 --> 00:10:34,300 U-shaped valley. And those glaciers that khumbu 167 00:10:34,300 --> 00:10:39,300 Glacier has eroded maybe three or four kilometers deep into the 168 00:10:39,300 --> 00:10:43,400 crust of Everest. so what we're seeing today on the surface, all 169 00:10:43,400 --> 00:10:48,100 those beautiful geomorphological mountains are actually a result 170 00:10:48,100 --> 00:10:53,000 of dominantly glacial erosion but also flew the alliteration 171 00:10:53,300 --> 00:10:57,300 further to the South, the rivers cut these v-shaped valleys in 172 00:10:58,000 --> 00:11:01,700 and as you go further north towards the highest peaks those 173 00:11:01,700 --> 00:11:06,000 v-shaped valleys become glacial u-shaped valleys with the 174 00:11:06,000 --> 00:11:12,200 classic geomorphology of glacial erosion, really the Glacial 175 00:11:12,600 --> 00:11:16,200 erosion is only the upper few kilometers of the crust, and 176 00:11:16,200 --> 00:11:18,900 that's what makes the mountains that we see today. 177 00:11:20,200 --> 00:11:23,200 Okay, so we've talked about making mountain ranges like the 178 00:11:23,200 --> 00:11:26,600 Alps and Himalaya. When two, continental plates, 179 00:11:26,600 --> 00:11:30,100 collide, what happens when we get an ocean plate colliding? 180 00:11:30,100 --> 00:11:33,700 With a continental plate? Well, the classic example of 181 00:11:33,700 --> 00:11:38,200 that is the Andes in South America, which is a long linear 182 00:11:38,200 --> 00:11:43,100 mountain range, thousands of kilometers long and formed in a 183 00:11:43,108 --> 00:11:45,700 completely different process. It's the Collision of two 184 00:11:45,700 --> 00:11:49,100 plates, but as you say, the Pacific Ocean plate is 185 00:11:49,100 --> 00:11:53,300 subducting eastwards, beneath the South American crust. 186 00:11:54,000 --> 00:12:00,500 And as that plate subducts, it is releasing fluids, which melt 187 00:12:00,500 --> 00:12:03,800 the base of the crust to form. Very distinctive rocks that we 188 00:12:03,800 --> 00:12:07,100 call Granite. Granite is a quartz and 189 00:12:07,100 --> 00:12:11,900 feldspar, Rich rock which intrudes up forming these. 190 00:12:11,900 --> 00:12:15,500 Great Granite batholiths. That we see a batholith is 191 00:12:15,500 --> 00:12:21,000 simply a long linear, granitic structure that it actually forms 192 00:12:21,000 --> 00:12:24,400 the substrate of some of the most explosive volcanoes on the 193 00:12:24,400 --> 00:12:27,400 planet. Things like Mount Saint Helens. 194 00:12:27,400 --> 00:12:31,600 The great eruptions that we see in South America and Central 195 00:12:31,600 --> 00:12:35,300 America. Roll the most siliceous volcanic 196 00:12:35,300 --> 00:12:39,600 rocks, that are the Upper Crust, all parts of the deeper Granite 197 00:12:39,600 --> 00:12:42,400 backless. And the granite batholiths are 198 00:12:42,400 --> 00:12:46,400 exposed in some of the most classic climbing, areas of the 199 00:12:46,400 --> 00:12:49,500 world Yosemite Valley. For example, the El Capitan 200 00:12:49,500 --> 00:12:53,900 Granite is an example of one of these or the Patagonian Granite 201 00:12:53,900 --> 00:12:58,500 spires down in the southern parts of South America and the 202 00:12:58,500 --> 00:13:00,600 Upper Crust above. Those granite's. 203 00:13:00,600 --> 00:13:04,400 Are these explosive Volcanoes, which are made dominantly of 204 00:13:04,400 --> 00:13:08,500 rocks we call and decides named after the Andes and they are 205 00:13:08,500 --> 00:13:13,900 much richer in silica than the rocks formed in the oceans and 206 00:13:13,900 --> 00:13:16,200 hence, they're much more explosive and much more 207 00:13:16,200 --> 00:13:19,600 dangerous. So there's one more type of 208 00:13:19,600 --> 00:13:23,400 collision between two plates. And that's when no continental 209 00:13:23,400 --> 00:13:26,800 plate is involved. And we have one oceanic plate 210 00:13:26,800 --> 00:13:30,900 colliding, with another. If those also produce mountains, 211 00:13:30,900 --> 00:13:33,700 they certainly can't be built. On top of a continent. 212 00:13:34,200 --> 00:13:34,800 Yes. No. 213 00:13:34,800 --> 00:13:39,600 Those are examples of island arcs and Island arcs are very 214 00:13:39,600 --> 00:13:43,000 important mountain ranges because they actually form some 215 00:13:43,000 --> 00:13:46,100 of the highest topography that we see on the planet, the 216 00:13:46,100 --> 00:13:49,300 classic examples of island arcs are in the Western Pacific. 217 00:13:50,000 --> 00:13:53,400 And most notably the Mariana Islands Arc which is an island 218 00:13:53,400 --> 00:13:55,600 arc that stretches from south of Japan. 219 00:13:56,100 --> 00:13:58,800 All the way down through the Philippines to Indonesia. 220 00:13:59,800 --> 00:14:04,300 And the trench where the Pacific Ocean is subducting to the West 221 00:14:04,900 --> 00:14:08,900 is actually the deepest part of the Earth today, 12 km below. 222 00:14:08,900 --> 00:14:13,100 Sea level, remember Mount Everest is just under 9 223 00:14:13,100 --> 00:14:16,800 kilometers above sea level, but the deepest parts of the oceans 224 00:14:16,800 --> 00:14:19,800 are even more. So, you could actually say that 225 00:14:19,800 --> 00:14:23,600 the highest mountains on Earth, are the volcanoes that make up 226 00:14:23,600 --> 00:14:26,100 parts of the Mariana Islands, dark. 227 00:14:26,200 --> 00:14:28,400 If you go from the bottom of the trench, to the top of the 228 00:14:28,400 --> 00:14:35,100 volcano, It's 12 km the Rocks produced at Island arcs, and 229 00:14:35,100 --> 00:14:39,600 much more basaltic that there are sort of intermediary between 230 00:14:39,600 --> 00:14:43,300 the explosive andesitic. Volcanoes, we see in the Andes 231 00:14:43,300 --> 00:14:47,800 for example, so there's other incredibly explosive volcanoes 232 00:14:47,800 --> 00:14:50,900 along Island Arts that we see in Kamchatka. 233 00:14:51,200 --> 00:14:55,300 Mount Fuji in Japan, Mount Pinatubo in the Philippines. 234 00:14:55,300 --> 00:14:59,400 All of these examples forming Island aren't Mountain chains in 235 00:14:59,400 --> 00:15:02,900 the All of the oceans. Okay, so you've told us about 236 00:15:02,900 --> 00:15:05,700 three very different kinds of mountain ranges that form near 237 00:15:05,700 --> 00:15:08,400 the edges of tectonic plates when they Collide. 238 00:15:08,900 --> 00:15:14,500 So do we only see mountains on plate margins dominantly yes. 239 00:15:14,600 --> 00:15:18,100 The longest mountain range is probably in the oceans along the 240 00:15:18,100 --> 00:15:23,000 Mid-Atlantic Ridge which runs all the way across the globe and 241 00:15:23,600 --> 00:15:26,800 fortunately in the north the middle and sick Ridge is 242 00:15:26,800 --> 00:15:29,100 actually Exposed on the island of Iceland. 243 00:15:29,700 --> 00:15:34,200 Where we can see volcanoes forming along a rifting margin 244 00:15:34,200 --> 00:15:38,300 underneath the ocean that is a very very prominent mountain 245 00:15:38,300 --> 00:15:42,700 range that stretches right the way down the Atlantic and the 246 00:15:42,700 --> 00:15:46,200 Atlantic is a growing ocean so it's expanding with time. 247 00:15:46,900 --> 00:15:50,600 So mid-ocean ridges are important mountain ranges. 248 00:15:50,700 --> 00:15:54,300 There are not that high compared to the Andes, but they're very 249 00:15:54,300 --> 00:15:57,600 very prominent, you drain all the water out of the Atlantic 250 00:15:57,600 --> 00:16:00,100 Ocean. This would be a very Melons 251 00:16:00,500 --> 00:16:04,000 range of mountains stretching the entire globe and they're all 252 00:16:04,000 --> 00:16:07,700 made of battled. So they're much much simpler and 253 00:16:07,700 --> 00:16:11,000 anything on the continent and wondering whether these kinds of 254 00:16:11,000 --> 00:16:14,300 mountains, perhaps with the exception of Iceland happen only 255 00:16:14,300 --> 00:16:17,700 under the ocean. No, they also occur under the 256 00:16:17,700 --> 00:16:20,700 continents and the classic example of this is the East 257 00:16:20,700 --> 00:16:24,100 African Rift. Where the very old continent of 258 00:16:24,100 --> 00:16:28,500 Africa is splitting apart all the way down, its eastern 259 00:16:28,500 --> 00:16:32,100 margins. And in the far north of this 260 00:16:32,200 --> 00:16:37,000 East African Rift in Ethiopia is a place where you can see this 261 00:16:37,000 --> 00:16:41,300 ocean, propagating from the Red Sea down into the continent. 262 00:16:41,800 --> 00:16:46,100 So the afar triangle region, the danakil depression in Ethiopia 263 00:16:46,500 --> 00:16:48,400 is an absolutely incredible place. 264 00:16:48,400 --> 00:16:51,900 It's below. Sea level is highly volcanic. 265 00:16:52,500 --> 00:16:55,900 And you can see faults and basaltic. 266 00:16:56,000 --> 00:16:59,300 Eruptions forming new ocean crust. 267 00:16:59,800 --> 00:17:01,500 And that ocean crust in the North. 268 00:17:01,500 --> 00:17:04,800 And the Red Sea has been there for about 10 million years. 269 00:17:05,599 --> 00:17:10,200 And as it's propagating down towards the African continent is 270 00:17:10,200 --> 00:17:13,700 forming, this Great Rift Valley where the two sides of Africa 271 00:17:13,700 --> 00:17:17,700 are being pulled apart dominantly by mantle convection 272 00:17:17,800 --> 00:17:22,700 in the Deep crust and the mantle below southern Africa, and they 273 00:17:22,700 --> 00:17:27,400 are typified by huge volcanoes. Like Mount Kilimanjaro. 274 00:17:28,300 --> 00:17:32,100 And these are Again, very distinct volcanic rocks. 275 00:17:32,100 --> 00:17:34,500 They are not the same as the Rocks, we see along the 276 00:17:34,500 --> 00:17:37,200 mid-ocean ridges. And there's certainly not the 277 00:17:37,200 --> 00:17:40,500 same as the Rocks. We see in the Andes or an island 278 00:17:40,500 --> 00:17:44,100 arcs. There are much more Alkali Rich 279 00:17:44,600 --> 00:17:48,200 battled because they are more rich in elements like sodium and 280 00:17:48,200 --> 00:17:51,100 potassium. But the whole of the African 281 00:17:51,100 --> 00:17:57,000 place is actually rifting apart East West and the island of 282 00:17:57,000 --> 00:18:01,600 Madagascar is an older part So, back Rica that Rift it off 20 or 283 00:18:01,600 --> 00:18:05,400 30 million years ago. And there's now oceanic crust in 284 00:18:05,400 --> 00:18:11,500 between the two and predicting ahead, maybe 20 or 30 million 285 00:18:11,500 --> 00:18:15,900 years time, the Red Sea will be expanding pushing Arabia and 286 00:18:15,900 --> 00:18:18,800 Africa apart. And the African continent will 287 00:18:18,800 --> 00:18:24,800 be split into East Africa to Western and central Africa. 288 00:18:26,000 --> 00:18:29,300 So we've seen that mountain, ranges form, not only at exist. 289 00:18:29,400 --> 00:18:32,600 Ting plate, boundaries where a collision is going on, but also 290 00:18:32,600 --> 00:18:35,800 within the plate where a plate is splitting apart and you 291 00:18:35,800 --> 00:18:40,000 plate, boundaries are forming. Do these multiple types of 292 00:18:40,000 --> 00:18:43,500 mountain building on the edges of plates account for all of the 293 00:18:43,508 --> 00:18:46,600 mountains on the planet? But not all of them. 294 00:18:47,000 --> 00:18:49,700 There are other distinct mountains in the middle of the 295 00:18:49,700 --> 00:18:54,300 ocean islands, like Hawaii, or the Galapagos Islands are very 296 00:18:54,300 --> 00:18:59,900 unique because they are huge. Volcanic edifices sitting Top of 297 00:18:59,900 --> 00:19:04,200 what we call hot spots. These are anomalous thermal hot 298 00:19:04,200 --> 00:19:07,500 spots that go deep into the mantle and they've been 299 00:19:07,500 --> 00:19:10,600 generating basaltic magma for a long, long time. 300 00:19:11,400 --> 00:19:16,300 So Hawaii is the classic example of a hotspot Island and we can 301 00:19:16,300 --> 00:19:20,000 see if we look at a map of the Pacific, but there is a train of 302 00:19:20,000 --> 00:19:23,500 islands, going off to the Northwest and eventually all the 303 00:19:23,500 --> 00:19:26,500 way across the Pacific to the Kamchatka trench. 304 00:19:27,000 --> 00:19:29,300 This is the Hawaii. Emperor seamount chain. 305 00:19:29,400 --> 00:19:33,100 Say, and those islands are getting progressively older. 306 00:19:33,400 --> 00:19:36,800 As you go Northwest words away from the big island of Hawaii, 307 00:19:37,400 --> 00:19:40,500 which is the site of the presently, active top spot, 308 00:19:41,100 --> 00:19:43,200 you've talked about several different kinds of mountain 309 00:19:43,200 --> 00:19:45,800 ranges that we can't really see because they're largely 310 00:19:45,800 --> 00:19:51,000 submerged the island arcs, the mid-ocean ridges and the hotspot 311 00:19:51,000 --> 00:19:55,300 chains, if we emptied out the oceans, would they look 312 00:19:55,300 --> 00:19:59,000 different from each other? They would if you drain the 313 00:19:59,000 --> 00:20:03,100 oceans, you would be surprised because you would end up looking 314 00:20:03,100 --> 00:20:09,200 at thousands and thousands of isolated volcanic seamounts. 315 00:20:09,800 --> 00:20:13,000 The Pacific has literally thousands of these islands and 316 00:20:13,000 --> 00:20:17,900 90% of them are under sea level. We don't see them, The big ones 317 00:20:17,900 --> 00:20:23,400 that we do see like Hawaii and Galapagos are major hot spots 318 00:20:23,400 --> 00:20:28,300 that have been around for 40 50, 60, million years, or more other 319 00:20:28,300 --> 00:20:30,000 ones that you see in the Indian Ocean. 320 00:20:30,000 --> 00:20:33,600 For example, the island of reunion is a very interesting 321 00:20:33,600 --> 00:20:37,400 volcano because that is another one of these Hawaiian type 322 00:20:37,700 --> 00:20:41,700 Alkali, Basalt ocean Islands, a fixed hotspot. 323 00:20:42,300 --> 00:20:45,800 And there is a chain of islands. Going to the north of rainy on 324 00:20:45,800 --> 00:20:49,900 which goes along the Ow, gasps Mall died lacquered, I've chain, 325 00:20:50,300 --> 00:20:54,800 and it eventually ends up at the Deccan battles in Western India. 326 00:20:56,000 --> 00:20:59,900 Mount Everest has nearly nine kilometers high, and you've said 327 00:20:59,900 --> 00:21:04,200 that the Mariana Trench has nearly 12 kilometers deep. 328 00:21:05,000 --> 00:21:07,000 What determines this? What determines? 329 00:21:07,000 --> 00:21:11,600 How high mountains can grow various points. 330 00:21:11,600 --> 00:21:16,500 Mostly the tectonics defines, whether you have a steady 331 00:21:16,900 --> 00:21:20,700 eruption of larvas like Hawaii, which is gradually built up over 332 00:21:20,700 --> 00:21:24,700 a long period of time. Whether you have sudden, huge 333 00:21:24,700 --> 00:21:29,000 eruptions, like the, some of the island arc volcanoes along the 334 00:21:29,000 --> 00:21:32,100 Mariana Trench. But with the case of Mount 335 00:21:32,100 --> 00:21:36,400 Everest, the reason the Himalayas are so high and 336 00:21:36,700 --> 00:21:39,800 Everest in particular, being the highest point of the planet, 337 00:21:40,600 --> 00:21:45,500 it's a trade-off between tectonics that creates mountains 338 00:21:45,700 --> 00:21:50,300 uplifts them and erosion forces that break them down by the 339 00:21:50,300 --> 00:21:54,600 weathering or chemical erosion. And that forces mountains to 340 00:21:54,600 --> 00:21:58,200 come back down to sea level, erosion, always wants to 341 00:21:58,700 --> 00:22:03,500 maintain the status quo. So the quicker, the place is 342 00:22:03,500 --> 00:22:05,900 moving the higher. The mountains of the Himalayas 343 00:22:05,900 --> 00:22:10,300 of forming and erosion cannot keep Pace with tectonics along 344 00:22:10,300 --> 00:22:14,600 the Himalayas as soon as the Indian plate starts to slow down 345 00:22:15,000 --> 00:22:19,800 and tectonics will give way through erosion, erosion, will 346 00:22:19,800 --> 00:22:23,400 eventually Wipe Out the Himalayas and It's a sea level. 347 00:22:24,200 --> 00:22:27,700 This is what's happened in the past a lot of Precambrian 348 00:22:27,700 --> 00:22:30,300 mountain ranges. We see, for example, in Northern 349 00:22:30,300 --> 00:22:35,000 Canada were probably Himalayan type Mountain belts in their day 350 00:22:35,700 --> 00:22:40,700 and then 500 600 million years ago, they were eroded back down, 351 00:22:40,700 --> 00:22:44,900 towards sea level, and planed off, and to an extent. 352 00:22:44,900 --> 00:22:48,100 That's what you see today in the Great Northern Prairie lands of 353 00:22:48,100 --> 00:22:53,500 America and in the Tundra's of the Arctic Canada, Those were 354 00:22:54,000 --> 00:22:57,500 big mountain. Ranges 500, 600 million years 355 00:22:57,500 --> 00:23:00,500 ago and they've been flattened by erosion. 356 00:23:01,100 --> 00:23:04,100 So, does that mean that when we see flat planes on Earth that 357 00:23:04,100 --> 00:23:08,800 they've all been mountainous and then flattened by erosion or 358 00:23:08,800 --> 00:23:11,500 have some of them actually, escaped mountain building events 359 00:23:11,500 --> 00:23:15,700 for all of geological time. No, no, a lot of the great flat 360 00:23:15,700 --> 00:23:18,700 places of the Earth today have escaped mountain ranges. 361 00:23:18,700 --> 00:23:21,500 They would they never were. So if you look at the Great 362 00:23:21,500 --> 00:23:25,100 Plains of central Asia, for example, the oldest mountain 363 00:23:25,100 --> 00:23:30,400 ranges in Europe, go up towards Northern to that and along the 364 00:23:30,400 --> 00:23:32,600 Carpe. The ins that sort of area, 365 00:23:33,100 --> 00:23:36,000 everything to the north of that has never really been in a 366 00:23:36,008 --> 00:23:38,700 mountain building. Phase ever. 367 00:23:39,600 --> 00:23:43,900 Other places, for example, in North America, most of Northern 368 00:23:43,900 --> 00:23:47,200 Canada has been involved in big mountain range mountain, 369 00:23:47,200 --> 00:23:52,200 building processes right up until 500 600 million years ago. 370 00:23:52,800 --> 00:23:55,600 And before that, they were very active mountain ranges. 371 00:23:56,000 --> 00:23:58,900 Some of them like we see, for example, in the Himalayas today, 372 00:23:59,600 --> 00:24:03,400 but they've been eroded down and being pretty close to sea level 373 00:24:03,400 --> 00:24:06,300 for the last four or five hundred million years. 374 00:24:07,000 --> 00:24:10,400 So, no, not all Flatlands of the Earth, been through mountain 375 00:24:10,400 --> 00:24:14,200 building processes. As plates continue to drift 376 00:24:14,200 --> 00:24:18,300 around the surface of the Earth and mountain building on their 377 00:24:18,300 --> 00:24:21,000 margins. And within them above hotspots, 378 00:24:21,000 --> 00:24:24,800 continues is the earth going to get more and more mountainous 379 00:24:24,800 --> 00:24:28,800 over time. Probably not the Earth during 380 00:24:28,800 --> 00:24:32,500 Earth history has gone through cycles of big mountain building 381 00:24:32,500 --> 00:24:36,500 processes. So the Alpine Himalayan cycle 382 00:24:36,500 --> 00:24:40,200 that we see at the moment for the last 50 or 60 million years 383 00:24:40,800 --> 00:24:45,300 has created many of the mountain belts that we see stretching all 384 00:24:45,300 --> 00:24:48,300 the way from the Pyrenees and the Alps down through Central 385 00:24:48,300 --> 00:24:51,800 Ron through Oman cross the Himalayas down towards 386 00:24:51,800 --> 00:24:54,300 Indonesia. That's the very young. 387 00:24:54,300 --> 00:24:56,200 Very active collisional processes. 388 00:24:56,300 --> 00:24:58,000 Process. That's forming mountains. 389 00:24:58,700 --> 00:25:03,300 In the geological past, we've seen other very large mountain, 390 00:25:03,300 --> 00:25:05,800 ranges across huge tracts of the Earth. 391 00:25:06,800 --> 00:25:12,100 There was one in the Caledonian and the Appalachian timing which 392 00:25:12,100 --> 00:25:15,500 was back in the ordovician 450 million years ago. 393 00:25:15,500 --> 00:25:19,000 But that was another huge collisional mountain range that 394 00:25:19,000 --> 00:25:21,800 stretched all along the Eastern Seaboard of south of North 395 00:25:21,800 --> 00:25:25,100 America, right? The way from the Amazon all the 396 00:25:25,100 --> 00:25:29,900 way across up to Scandinavia. There was another one across 397 00:25:29,900 --> 00:25:36,100 Central Europe in the pacinian about 250 to 300 million years 398 00:25:36,100 --> 00:25:38,500 ago. That formed the mountain range 399 00:25:38,500 --> 00:25:41,700 that we see across most of central and Northern Europe 400 00:25:42,100 --> 00:25:45,200 today. So these things do go in Cycles. 401 00:25:45,900 --> 00:25:52,200 But the average over the huge amounts of geological time that 402 00:25:52,200 --> 00:25:55,700 we're looking at 500 million years in the case of the 403 00:25:55,700 --> 00:25:59,900 phanerozoic, four and a half billion years in terms of total 404 00:25:59,900 --> 00:26:05,600 Earth, history probably maintains a continuance Now for 405 00:26:05,600 --> 00:26:11,800 my last question, I'm going to ask you to speculate if we could 406 00:26:11,800 --> 00:26:16,200 be Time Travelers and we sped about 100 million years into the 407 00:26:16,200 --> 00:26:18,600 future. What would we see? 408 00:26:19,600 --> 00:26:21,100 Well, you're asking me to play God. 409 00:26:21,100 --> 00:26:28,800 Now mean what we would see in my purely speculative mode is a 410 00:26:28,800 --> 00:26:31,300 very different planet from what we're looking at today. 411 00:26:32,400 --> 00:26:35,600 I would expect that the Pacific and the Indian Ocean Ian's would 412 00:26:35,600 --> 00:26:40,100 be getting smaller and closing as those subduction zones are 413 00:26:40,100 --> 00:26:44,300 consuming crust, I would expect the Atlantic Ocean to be 414 00:26:44,300 --> 00:26:49,200 expanding so that could become the Great Pacific of its time in 415 00:26:49,200 --> 00:26:53,000 a hundred million years time. Everything depends on the 416 00:26:53,700 --> 00:26:56,100 mountain ranges. For example for Himalayas are 417 00:26:56,100 --> 00:27:00,500 all formed because India has been pushed northwards by the 418 00:27:00,500 --> 00:27:04,000 spreading Oceanic spreading centers in the central, and 419 00:27:04,000 --> 00:27:06,900 southern Indian Ocean. And it says stop. 420 00:27:06,900 --> 00:27:11,900 Then the Indian plate would no longer indents and collide with 421 00:27:11,900 --> 00:27:15,600 Asia and erosion would take over in the Himalayas would be 422 00:27:16,100 --> 00:27:18,900 flattened down to sea level. God, forbid. 423 00:27:19,200 --> 00:27:22,700 Now, the most beautiful mountains on the planet, and we 424 00:27:22,700 --> 00:27:26,200 rely on the Indian plate. Still to actively collide with 425 00:27:26,200 --> 00:27:28,900 Asia to make these beautiful high mountains. 426 00:27:28,900 --> 00:27:34,100 We see today Mike cell. Thank you very much, my 427 00:27:34,100 --> 00:27:34,500 pleasure.