 Welcome to G-Side 10, Geology of the National Parks. My name is Shridharanandakrishnan. I'll be your guide through volcanoes this time. This is the second part of building mountains using subduction zone processes. Last time we talked about what a subduction zone is, what happens when you have oceanic crust running into continental crust. You produce these volcanoes and trenches and earthquakes. This time we're going to go into a little bit more detail about those volcanoes. In addition, we're going to talk about a special thing called hot spots. Hawaii's a hot spot. We'll find out what a hot spot is and what's special about them. So let's begin with a little bit of a tour of the Pacific Northwest. We saw some beautiful photographs last time of Crater Lake National Park and some of the extraordinary pictures of the destruction that went along with Mount St. Helens. Last time we'll go to a little bit more of a bucolic scene seashore of Olympic National Park. Not quite so violent, but still telling us a lot about the processes that are going on. What you're seeing on the screen here is a map of the West Coast of the US. That's the state of Washington there in the middle. On the left side is Vancouver Island. Vancouver is in British Columbia, which is in Canada. If we zoom in a little bit into the state of Washington, we come close to Seattle, where Boeing and Microsoft very famously are headquartered. Starbucks is headquartered. I'm sure you all had your triple latte frappuccino this morning. Well, it all started in Seattle. To the west of Seattle, you have the Olympic Peninsula. That's this big rectangular-shaped mass of rock and mountains and glaciers that is heavily forested, very wet, and just a beautiful place to go hiking or just simply driving around. It's also very, very heavily logged. That's the other thing that the Pacific Northwest is famous for is their logging industry, timber, paper, all those sorts of things are enormously lucrative for the Pacific Northwest. And so some of these places that look very beautiful from the road, you go walking back a little ways, and then some timber companies clear cut the place. So it's a trade-off. The Olympic Peninsula is an accretionary terrain. The seafloor has scraped off onto the North American coast. As it was scraped off and plastered against the North American coast, it created these mountains. And we're going to take a look at some of those rocks over here. This is Mount Olympus right in the middle. Those white lines are the mountains and the snow on top of those mountains, and then you have these deep valleys, river valleys that cut through them, and you get enormous amounts of rainfall and snowfall there. And surprisingly, it's somewhat temperate. You get almost semi-subtropical types of plants there just because of the amount of water. You get a rainforest type of environment going on over there. It's an extraordinary place. We're going to switch now over to look at some photographs from the Olympic Peninsula. Here are some gulls and starfish on a big, big old beach rock. You can see the rock is dark-colored. The beach itself, the sand there, is very dark in color. All of this is because the oceanic rocks that make up the Olympic Peninsula are basalts, if you remember that from last time. Basalts are dark in color and slightly higher in density, but the coloration comes from the fact that the Olympic Peninsula is made up of oceanic crust. Here you can see the Pacific Ocean off in the distance and all of these big jagged rocks sticking up underneath them. There's some huge cracks that are left behind, and the tide smashing up against it and the big waves. You can see a big wave breaking up against that rock. It's just a great spot to wander the beach and do some sea kayaking or simply lie there on the beach. If you walk a little bit inland, you'll go into the whole rainforest where you get these enormous slugs, six, eight inches long, banana slugs. They're a vast, really quite interesting looking thing. Some people are repelled by them. Some people are fascinated by them. You've got to go see them for yourself. It's very wet. It just rains and rains and rains constantly. You get these ferns, and you get these big waterfalls going through there. It's a lovely spot. Here's another photograph of all the mosses and lichen hanging off of the trees. And because of all that rainfall, you have all these streams which come cascading off of the big black rocks that make up the Olympic Peninsula. And you have to make sure you take your raincoat and your rain gear and everything else with you, because you're guaranteed to get rained upon on the Olympic Peninsula. Here's another beautiful shot of a nice waterfall and some lichen and moss on it. This is a photograph pulled back, and now we're looking at the higher peaks in the interior. This is a shot looking up towards Mount Olympus, right in the middle. You can see some snow patches. And if you go right up to the top, Blue Glacier is a well-studied glacier. University of Washington folks have had a long-term project. They've got a hut up there, and you can hike up to the hut, and you can do all sorts of studies on the glaciology of that glacier. And here you have a deer sleeping in the underbrush, looking a little suspiciously at the photographer. Here are some kids playing on the beach. You can see again the very black color of the sand, an indication of the basaltic nature of the peninsula. Here you have these lighter-colored material, which these are sedimentary rocks. These are materials that came off of land or deposited in the ocean. And then because of these huge forces involved, the collision of the Pacific Plate and the Continental Plate, these forces have turned these rocks up on their side and deformed them and tortured them like this, broken them up into, and you can see a big crack running through them. And it's all very indicative of all the very large forces involved in producing the peninsula. This is a close-up of some of those rocks. These are a very special type of rock called turbidites, where you have a material that goes swooshing down and jumbles up all the sands and gravels and so on. And you're left with a very layered rock. It comes out like that. And just a beautiful Pacific sunset with a gull flying off in the distance. Well worth a visit. If you're in Seattle anyway to go to the space needle or have a cappuccino at Starbucks, take a drive out to the Olympic Peninsula. This slide by now should start to make sense to you. This is the first time we've seen it. We hopefully have put everything together by now. This is a cross-section, a very idealized cross-section through the ocean on the left and a continent on the right. You can think of this as the coast of Washington state or the coast of Oregon state. But it really represents a more generalized situation. This could be the Philippines. This could be Japan. It could be Alaska. It could be one of very many places. In the middle, you have an oceanic spreading ridge where hot rock comes up, meets the surface, cools off, is shoved off to the right and to the left. That material, that oceanic crustal material, this basaltic material cools off. It gets much, much more dense. As it gets shoved off to the right, it collides with the continental crust, which is much less dense. And during the collision, you get subduction of the oceanic crust underneath the continental crust. In the process of the subduction, some of the seawater and sediments get carried down across the subducting plate. And as they get carried down, they melt and they come up as a volcano. That's all going on to the right of the screen over there. And we're going to go look into this in a little bit more detail. When basalt water and sediments heat up, they melt. The basalts by themselves don't really want to melt. But you mix in this water, you mix in the sediments, and at relatively low temperatures, that mixture starts to melt. If you didn't have the seawater, if you didn't have the sediments mixed in with it, that subducting plate would have to go much, much, much deeper before it started to melt. But because the subduction process has taken the seawater and taken the sediment and grabbed it and pulled it down along with it, this mixture melts more readily. And you've seen this yourself. When you take snow out on the streets of State College or whatever town that you're in, you mix salt with it, you mix these impurities in with it, it'll melt at a much lower temperature and you can drive your car over it. So most materials, if you make them less pure, if you mix in all these other chemicals with it, like the sediments and like the water, they'll tend to melt more readily, and that's what happens with this. That mixture, once it's melt molten, now has become much less dense and it will rise up to form a volcano. That's what's going on in the left of this image over here. This subducting plate has carried seawater and sediments down with it and at a relatively shallow depth because of that mixture, because of those impurities that are mixed into the basalt, you get melting and that starts to rise up to form a volcano. That's the material, that's the picture along the right-hand side of the image. So as this mixed basalt seawater sediment mass has melted and it rises up, it forms endocytic volcanoes. It's named after the Andes Mountains. It's just a type of rock that you find in the Andes. It turns out it's the same type of rock that you have in the Cascades, that you have in Mount Ruhopehu in New Zealand, that you have in Alaska in the volcanic belt. It's very typical of these subductions on volcanoes so we all call them endocytic volcanoes. As this magma rises up, it wants to polymerize. Polymerize is a word you need to know. All it means is turning into these long chains or bonds of material. It wants to clump together to turn into the solid material. That's all that rock does as it goes from being molten to being solid is it's polymerizing. It's turning into a solid by making these long chains, these long compounds of the chemicals. It makes these long stringy units sort of like lumpy oatmeal. As this magma comes up, it comes up the top, it freezes into these long ropey stringy lumps. And more material comes up. It comes out the top of the volcano. It immediately freezes onto the side and you get these very steep-sided volcanoes. So I'm gonna draw you a picture now. I'm gonna switch over and take a look at this process. This is our subducting slab. On the left, we have the ocean, as I keep saying. And on the right, we have continental crust. And the subducting slab is taking along with it some sediments and water. Water. At a relatively shallow depth, this mixture of basaltic rock, which is the slab of sediments and of water will start to melt. It will melt, become less dense, molten, and it will rise up. All right, so this molten rock is rising up to the surface. When it gets to the surface, it will polymerize, which is simply a fancy word for freeze. Turn into a rock, turn solid, turn into a polymer, all right? As more material comes out, it will come out the top of the volcano. It will come out the top of the volcano and spill down the sides. I'm gonna zoom in on this and draw it on the next page. This is the surface of the earth. You have this molten rock coming up. It polymerizes at the surface. It just freezes on. More stuff pushes through that, comes to the surface, spills down, and freezes on. And more stuff pushes through that, spills down the sides, and freezes on. And more stuff, eventually, you build a tall, steep volcano known as a stratovolcano. V-O-L-C-A-N-O, stratovolcano, means tall, steep volcano, all right? So this is the process by which all of the subduction zone volcanoes are made. You have molten rock, which is formed deep inside the earth where that subducting slab, off the bottom of the screen there, that subducting slab has melted because of the addition of the rock and of the sediment and the seawater. You have this molten material. It rises up, weird breakthrough, the crust. It freezes on in the air, and when it freezes on, more stuff breaks through that and spills down the side and over and over and over again. And you end up with these tall, steep stratovolcanoes, all right? And this process goes on and on and on. However, occasionally, what happens is you get this stratovolcano. For example, Mount St. Helens. And you have some hot molten material rising up through it. So this is molten rock. Let's see if we can't spell rock properly. Molten and acidic rock, it's rising up through there. It gets to the top and there's been a cap on top of this volcano that prevents the molten rock from getting out, all right? So this rock is rising up. And for one reason or another, you have a hard, impervious cap on top of the volcano. And this molten rock is trapped underneath this cap. And in the case of Mount St. Helens, more and more material was rising up underneath there and this cap was bulging and getting pressurized, all right? So let's switch back briefly to the PowerPoint presentation and we'll discuss how this then leads to those catastrophic Mount St. Helens explosive volcanic eruptions. The water, the magma of this molten rock, as it's rising, doesn't freeze within the earth. It stays liquid inside the earth. It's only when it gets to the surface that the CO2 and water that's inside escapes up out of the magma and that's when it freezes on. And that's why you get these steep volcanoes. The stuff is molten all the way up. As it gets near the surface, the water and CO2 are released from it into the atmosphere and then what's left behind is plain old basalt and it freezes on and you have a nice, wonderful steep volcano. Sometimes a rock forms a cap and when that happens, the pressure starts to build. You've got this magma coming up inside, you've got a cap over the thing, the steam, the CO2 can't escape, you're starting to build to a disaster. That's what happens with these straddle volcanoes. It's like releasing a cork on a champagne bottle or on a Coke bottle if you're under 21. The pressure, the CO2, is dissolved into the Coke and when you pop the top on that, it fizzes out. It's all liquid in there as long as it's under pressure. You've got a cap on that Coke bottle. As soon as you pop that Coke bottle, it fizzes out all over your hand if you've shaken it up a little bit and that's a very small example but that's exactly what goes on to the volcano. You've got a cap on it, the magma's coming up from underneath, the CO2 and the water can't escape, the pressure builds, the pressure builds, the pressure builds. Something happens to crack the cap. In the case of your Coke or Pepsi bottle, you simply pop the pop top and that's it. In the case of Mount St. Helens, a small earthquake cracked the cap and the CO2 and the water came shooting out, the pressure dropped and everything exploded. Mount St. Helens, 20th of May, 1980. Coke bottle writ large. Champagne bottle, disastrous champagne bottle, all right? This is another picture of Mount St. Helens again. Just a massive destructive force. The magma contains water and CO2. If there's a cap over it, can't get out, pressure builds, something comes along, a small earthquake that cracks that cap and now suddenly all of that pressure that's been built up starts to get released and then it just goes on and on, releases more, which opens the crack some more, you release some more, open the crack some more and the whole thing takes off and you get this huge explosion, all right? That's all it is, it's relatively simple. You can't predict perfectly when it's gonna happen but it happens over and over and over again. Mount St. Helens has exploded a number of times the last thousand years, all of the Cascades volcanoes have and so you have this cycle of pressure building up and then explosion. In the case of Crater Lake, that explosion was so enormous it just blew the whole top of that mountain off and all that's left is that big round lake. There's a different kind of volcano, one that isn't quite so destructive. These are the hotspot volcanoes. These are the volcanoes of Hawaii. Hawaii's the best example of them. There's a few of them around the world but Hawaii is the best example of them. It's the one that's easiest to get to, it's the one that has a national park associated with it. Sometimes a plume of magma will come up from deep inside the asthenosphere. Now this is not the same as a subduction zone. If you remember, subduction zone volcanoes, astral volcanoes was when you had oceanic crust going down and at a relatively shallow depth because of the mixture of water and sediments that basalt would melt and it would come up. The hotspot volcano is very different. In a hotspot volcano, that material is coming from deep inside, hundreds, maybe even 1,000 kilometers inside the asthenosphere. Maybe even as deep as a core mound boundary. We really don't understand hotspot volcanoes very well. They're one of the really most enigmatic features of the natural system today for volcanologists and for earth scientists. So they're really a fascinating thing. Why are they produced so deep inside in those places and not in other places? We don't really know. But for some reason, deep down inside the asthenosphere, this plume of magma comes up and this magma, because it comes from so deep inside the earth, picks up a lot of iron and that iron also prevents polymerization. It keeps the magma molten. Unlike stratovolcanoes, iron can't escape. With the stratovolcanoes, CO2 and water could escape and the magma would freeze instantly. With these hotspot volcanoes, they come up, the iron can't go anywhere. The iron's not gonna just evaporate and disappear into the atmosphere. And so even after the magma comes up to the surface, you still have it spreading out. It doesn't freeze instantly. You've probably seen pictures of Hawaiian big lava flows that spread for miles and miles. Big rivers of lava that just spread for miles and miles. They haven't frozen on. And the reason they haven't frozen is because you have so much iron mixed in with them that they stay molten even at really, really high temperatures. Even at really low temperatures. Sorry. So these lava flows stay molten. Long, long, even though they're up in the cold air, they still stay molten because of all this iron that's mixed in with them. And in the end, you end up with these broad, gentle, sloping mountains known as shield volcanoes. Stratovolcanoes are these big, steep ones. Why? Because the magma comes up, water and CO2 escapes, and the magma instantly polymerizes, and you just get these steep volcanoes because the magma can't run very far away from the mouth of the volcano. In Hawaii, on the other hand, the magma comes up. It's got lots of iron in it because it comes from deep inside the earth, comes up to the surface, comes into the cold air, and it still runs way off to the side before it finally freezes, and then more comes up and it spreads way off to the side, and you get these gentle, broad, large volcanoes. It's like a gladiator's shield. That's why they're called shield volcanoes. If you were to look at them in cross-section, they'd be broad and rounded. These hotspots are fixed in location inside the earth, but as we talked about before, the surface of the earth is moving around all the time. These plates on the surface are sliding to east and to west all the time, but the hotspot itself is fixed, and so as the overriding plate goes by, the position of the volcano changes because the hotspot is fixed in location, but the overriding plate is moving, and so you get these series of volcanoes one after the other, and I'll show a picture of that here. What we're looking at in the left picture is a fixed hotspot. The material's just always coming up in the same spot over and over again, but the plate above it is moving, and as that plate moves, a new volcano comes up in a different spot, and then the plate moves again and a new volcano comes up, and the plate moves again and a new volcano comes up. Those older volcanoes slowly get eroded and disappear as they go off to the side, all right? And that's why Hawaii is this long chain of islands. You have the big island where there's current eruption going on, and then you have this whole chain of islands off to the northwest, where older volcanoes have been carried off to the northwest and eroded one after the other. Hawaii is the best known hotspot, but there's a whole bunch of them around the world. Iceland is another one, and the Galapagos Islands and so on, so as I said, they're very poorly understood, but they're very intriguing nonetheless. This photograph here is showing that chain of islands. Hawaii is in the bottom left, and then you have this long line of volcanoes stretching off to the northwest, known as the Hawaiian Ridge, Midway Island, and the Emperor's Sea Mountain Chain continue on off to the north over there, and this is simply showing the Pacific Plate as it moved off to the northwest, carried volcano after volcano after volcano off into the distance. So, hazards. Volcanoes are hazardous, we know that. You can see that. All the pictures that I've showed you of this, the ash and the heat and the blast, that's the biggest hazard. Don't be on a volcano. If there's a danger that it's gonna explode, go somewhere else. All right, that's the first thing you can do. The second is you can't just go 100 feet away, or 1,000 feet away, or even 10 miles away, because this blast from the volcano can kill you even if you're 10 miles away. The gases are hot, 300 degrees plus, and that blast is fast, hundreds of miles per hour, it's on shooting down the side of the mountain, so it'll knock you over. The gases are heavy, and so they flow along the ground. They don't go straight up. They flow along the ground, it's known as a Nui Ardent, a glowing cloud in French. There's a famous tragic example on the island of Montserrat where one of these clouds came blasting through and killed everybody in the town, except for one guy who was locked up in the basement of the prison, and the heavy thick walls of it saved him, because it didn't get as hot in there, but everybody else in the town was killed. The second kind of hazard are the ashes and cinder. Those can spread much further away. Those can spread tens of miles, as much as 50 or 70 miles away from the Sanford Parse. These are the pyroclastic flows, all of the smaller pieces that spread out that can clog engines that can bury houses and roads. Finally, landslide and avalanche. All of the heat generated from this will melt glaciers, and then you'll get floods that go along with them. So these are some of the hazards associated with volcanoes. Another hazard that's a little bit less well known, but is still quite dramatic is the CO2. The carbon dioxide that comes up from one of these volcanoes can kill you in high enough concentrations. Lake Nios in Cameroon in Africa is on a hot spot, and the lake itself was filled up with CO2 until a small earthquake triggered a turnover of the lake. All the CO2 escaped out all at once, and there was a couple of villages near the lake where everybody died because they were suffocated. There was too much carbon dioxide and not enough oxygen in the air, and they just died of suffocation. So CO2 seeped into the lake. Something disturbed the lake and the CO2 escaped, and it suffocated hundreds of people that were living downhill from the lake. It was quite a tragic event back in the 80s. Nowadays, they just pump the CO2 out to keep it from building up, but this could happen in other places as well. The second type of, or the third type of hazard, so you have all the hazards associated with living right near a volcano, noir or dent, pyroplastic flows, those kinds of things. You have the second type of hazard, the CO2, the gases build up. The final type of hazard is a tsunami. A tsunami is a huge ocean wave that occurs when an earthquake occurs underwater, and then that earthquake can generate a big ocean wave. A large volcano can also generate one of these huge ocean waves. When there was an island in Indonesia, Krakatau, that blew up, and when Krakatau exploded, it created this enormous cloud of dust and debris that traveled around the world. But another thing that happened was when that island exploded, because it was an island, there was a huge wave that was generated that spread out from Krakatau that killed thousands and thousands of people. The tsunami that was generated in 2004 was an earthquake-generated tsunami, and earthquake in a subduction zone let loose and generated a tsunami that spread across. We're gonna show you a movie now, an animation of what happens when that tsunami occurs. This is an animation of the surface of the water in the Indian Ocean in the minutes and hours after that earthquake. As you can see, the effects of it spread outwards from the earthquake location, they do it relatively slowly. It took a couple of hours for it to spread right across the Indian Ocean, but for the island of Sumatra, which was right there, we're gonna run this animation again for you, for the island of Sumatra that's right there, the waves were enormous. Let's take another look at this. This is right after the earthquake, and as that wave spreads out, it piles up against the island of Sumatra, and you get these huge waves that spread way inland, and this wave also spreads to the west, across the Indian Ocean, and there's India and Ceylon off to the left of the screen, and if this animation were to run for long enough, you would see that that wave would eventually hit the island of Sri Lanka and the coast of India. We're gonna run it one more time, and you can see the wave as it spreads out. Oh, there it goes. It hits the island of Sumatra, and the waves build up on the coast, and that's where 250,000 people died. So tragically, the day after Christmas, Boxing Day, December 26, 2004. It was a truly monumental disaster. Okay, so we need to make sure that we prevent these kinds of hazards, these kinds of disasters from happening. What happens is as the wave gets closer and closer to shore, the sea bottom is getting closer and closer to the surface, there's less room left over for that water, so as this wave comes along, it builds up and builds up, and it strikes with great force flooding out villages, people, roads and infrastructure are gone, and once roads and infrastructure are gone, all the people that survived the direct effect of the wave now have to deal with disease and hunger. The wells are, quite often, the water wells are polluted and so they don't have clean drinking water, and it's just a disaster situation. All right, so next time, we're gonna talk about collision of continents. This time we were talking about collision of oceans with continental crust. Next time, we're gonna talk about collision of two continents and what happens when two continents collide. Stay tuned.