 Hello and welcome to another day of Geoscience Standard. This one is maybe a little bit like an old style fraternity initiation. We make you run through something really hard to get started. And so we're going to go cranking through a lot of material in a fairly big hurry here. You will find this material is supplied to you in the textbook in much slower and greater detail. You also will find there's a lot of v-trips, virtual field trip slideshows that are online, so you can see the pictures that I'll show you here in much greater detail and at your leisure. There's actually only a few big ideas that we're going to go through here, but they may be different for you. You may have seen them in some earlier class, but if you haven't, I hope you'll find this interesting. We have started into the big picture of how do you make mountains. After we make mountains, then later we will tear down mountains, and then we will see about how people live on earth, how animals live on earth, what the history of the planet is. So that's sort of the broad outline of the course, building mountains, tearing mountains down, living on the planet. And we're going to start with making mountains, we'll do some earthquakes, and we will look a little bit at what we call plate-tag conics, which is the vast underlying processes that make the mountains. We're going to do this by starting at one of the more interesting places that you could go for a national park, which is to go to Death Valley. So we'll look at Death Valley, we will look at how it is spreading apart, how that spreading is being driven by the heat within the planet, and then we will briefly pop by Yellowstone just long enough to see that it's shaking, and what we can learn about that, about the interior of the earth from earthquakes and so on. You will be given for each of the parks we visit one or more v-trips, virtual field trips, we would love to take you and zip out to the parks and have a good time. We haven't quite figured out how to do that, and so we've done the next best thing, we've gone ourselves, some of our friends have gone, we've collected pictures and put them together so that you can see virtual field trips, and so you will find these online. This is Death Valley, Death Valley is tremendous. You are looking at the lowest spot on the continent, right here, and in the background, you're looking at a spot that is more than two miles higher. It is just phenomenal. These pictures were actually taken by Peter Fawcett shown here. Peter worked with me a number of years ago and is now a professor in New Mexico, and he was out there in the dead of winter. You can see the snow way up high on the peaks above Peter's head. You can see a little bit of water behind Peter. It does snow, it does rain in Death Valley. The water does come down in the valley, and in the winter, it may puddle for a little while, and then it poof, it evaporates, and it's gone very, very quickly, and when it evaporates, it leaves salts behind, and so you can see the white salt behind Peter there at the picture. That was economically important to Death Valley. Some interesting things dissolve out of the rocks. They come down in the valley with the water. They're left when the water evaporates, and you could go and mine these, and so early people actually did mine in here. The 20 mule teams hoarded the hulled moron salts, morax, out, and this was used in soaps and paints and glass making and all sorts of other things, and it contributed to economic development in this area. It also, one of our former presidents, President Reagan, earlier in his career before he was president, sold soap, and he sold boratine, which had borax, which came with the 20 mule teams, and so he was something of a celebrity in part based on Death Valley soaps. So a point. In this course, you will get the joy and privilege of taking quizzes occasionally. In each time we visit a park, we're going to give you introductory material such as this, and we do this because we find it interesting. We think you will. We hope that someday you'll be off on a road trip and you'll get to go see these things, and this will help in your visit. We would never on a quiz ask you which president sold soap, nor would we ever ask you which soap did the president sell. This is strictly for your edification and enjoyment. Once we get to the point of saying, okay, geology is tearing Death Valley apart, that could show up on a quiz. But this early stuff, what's pretty, what's neat, what's exciting that you want to go see this park, this is for you. So please do not attempt to memorize the soap that President Reagan sold before he was president. That doesn't. That's just for you. Okay. But Death Valley is something. This picture, the scale here, if you have ever been to Penn State's University Park campus, and we're very impressed around here with our mountain, Mount Nittany. If you put Mount Nittany in this picture, it would tower over that little white line on the far side of the picture, almost a third of the way up that first slope. There's nothing in the appellations that you could put in this picture that would look even vaguely large. You drop the whole appellations in this picture and they would not go halfway up. This is immense. It's just truly an awesome place to get to. You find the right place in Death Valley, such as the one you see right here, and there's beaches. During the Ice Age, when it was colder, the rains that came in didn't evaporate as fast. There was a big lake in Death Valley, which has now evaporated. You go and look various places in Death Valley and you'll find that the floor of it is salt and it's gravels and things. The streams are tearing down the mountains. They're dumping stuff down in the valley to fill it up, and yet the valley is there. The valley is there, even though they're trying to fill it up. There's a little bit of sand. A little bit of sand dunes, not too much. Usually the desert is not sandy, but there are such beautiful things as this. There are really amazing things. You can look at this picture. You see those big rocks out on the salt flat, and those rocks have moved. People have come and surveyed them, and they do move. We're still not absolutely positive how. The best picture is when it rains. You get a little water here, and then a really cold day in the winter, it might freeze, and then these rocks are locked in the ice, and the wind blows, and it pushes along on the ice, and it actually sort of skates these things along. But no one's sure. Racetrack Playa, the rocks move somehow. Neat place. Neat place to visit. It's actually growing. It's widening, and it's deepening. And if you look at this picture, you can see the Great Mountain Range towering more than two miles above the valley. And you'll see right along the bottom, it's just a straight line. Well, that straight line is actually an earthquake fault, and here's another view of it. The near side has dropped. The far side has been raised. These things happen there ongoing. It is part of our world today. And that's really what's very interesting, and why we're visiting Death Valley at this point, is why are things moving? What's going on on the planet? Where this motion occurs, occasionally volcanoes come leaking up along the cracks, and so you can see volcanic craters if you go and visit Death Valley. You can see some places. This is an old, little volcanic feature which has been torn apart by motions. This is a slightly different motion. Most of Death Valley's motion is sort of an up-and-down thing. This one's a little bit of side-to-side as well, and the diagram will show you what's going on. Things are moving away there. So, there's some pictures of Death Valley. If you get the chance to go, if you want to impress your friends, go in mid-summer. If you want to have fun, don't. It's really stinking hot. But it's a wonderful park, big park sitting on the California Nevada border. Now, what's going on? Death Valley is getting bigger, and it's doing so from heat down within the planet. So, that's what we have to look at a little bit now, and then we'll go see what that does at Yellowstone. So, let's do the Death Valley. Eastern California Nevada border, the lowest, the hottest, the driest spot in the country. The water does come down. It does evaporate. It does leave salts behind. This drove various economic activity. It's largely turned off. Now, let's see what we do. This is a cross-section of Death Valley. If you could go in and you could take a giant saw and hack your way down, and then look at it sort of as a cliff, you have spaces up above in this picture, and the earth is down below, and it's shown to you as blue. And we're going to look at it. That little line across the top is just for your reference in there. And so, what's going on? Death Valley measured. If you go in and you put in GPS receivers across Death Valley and on across Nevada and over to Utah, and then you survey what's happening, what you will find is that very slowly, about as rapidly as your fingernails grow, the west is getting wider. One side and the other side of the valley are very slowly pulling apart. As they do so, the valley drops down, and it drops down on what we call pull apart fart, false, because you pull it apart, and then the fault allows the drop. The fault is a break where there's motion. So the block in between is going to drop down as we pull apart, and it is measured. This is not storytelling anymore. The early geologists look at this and they said this has to be happening. We understand that, but we can't measure it. It's pretty hard to measure a state spreading at the rate your fingernails grow. But we can do that now. This is directly measurable by GPS. It does work. And so this is the picture. You can actually put out your GPS and measure that the mountains on the east of the valley and the mountains on the west of the valley are moving apart. It's actively going on. This is real. It's happening today. And as they do, they allow earthquakes and the earthquakes drop the valley down. Erosion takes stuff off the top. It fills it in the bottom, but then the bottom drops and the sides are raised as the whole thing is pulled apart. And so the valley is getting bigger. The west is getting bigger. And a fault to break in the rock along which there's motion, there's one on each side of the valley. And basically every valley in Nevada and Utah has this same structure going on. If you were to find a rock layer, an old friend that you happen to know, the pretty purple rock, the pretty red rock, whatever it is, you can see the pretty red rock scribbled in on either side. If you wanted to find that in the valley and you drilled in your oil, well, you're not allowed to drill there now, but if you were, you'd drill down, you would find that same rock layer. It's down there. And you would find it down there. Now, this is one of the things that geologists were quite confident that this motion was going on before they had a GPS satellite to help them measure it because of things such as this. You say, okay, what happened to the layer in the middle? There it is. It's way down below the valley. The west is getting wider. The bottom is dropping down. Now, here's a map version if you want to get in your satellite and look from above down onto these things. Death Valley you'll see labeled way up at the top of the map there above Las Vegas. That's sort of along the California and Nevada border. And Death Valley and through Las Vegas and on down past Scottsdale and headed to the south, all of that region is getting wider. You'll also see, looking farther down past San Diego and Tijuana down there, that we get down to water. We get down to very pretty beaches, fun places that you could go diving. And what you find is that this pull apart action of Death Valley is running all the way down to the ocean, down to the Gulf of California, down past Baja there. This whole area is being pulled apart. Baja, that piece out on the left and Mexico as a whole are pulling apart. The same spreading that tends to open Death Valley is opening this whole area. And so we've drawn in here. You can see a circle up by Death Valley and then a green line that runs down to the Gulf of California. And the Gulf of California actually is getting wider, it's unzipping, it's open. Given enough time, it possibly will open all the way up to Death Valley. It is conceivable that you could over time actually have the ocean extend on up into the center part of the west there. We're not sure if it will get there or not, but that's what's going on, is that whole thing is measured to be unzipping. Okay, with Baja moving out towards the Pacific, Mexico moving over towards the Atlantic, the space in between the ocean base and getting larger. Now, this is part of a much bigger phenomenon as you might possibly imagine if it's going, we started in a cool place. But you start moving things around on the continent and if I move here, it's going to bump my neighbor and bump the other neighbor and you start to get the idea that this must extend much farther along. And so what you find is this sort of spreading behavior, this pulling apart behavior happens not only at Death Valley, not only where Baja is moving away from the mainland of Mexico across the Gulf of California, but it actually happens through the world's oceans. The places that they pull apart from, it turns out, tend to be raised a little bit. We know that there's these big mountains next to the valley at Death Valley and so there's high stuff associated with that. If you go down under the Gulf of California, the center where it's pulling apart is a little bit higher than the rest of the sea floor. It's sort of arched up a little bit. And so we talk about spreading from ridges and so that's spreading ridges and so we find a lot of places in the oceans have these places that it's been pulled apart from and they're a little bit high. If you played baseball or if you played tennis, it would work too, but you'll find that the ball has a seam on it and that seam sort of wraps around it and we often say that you can follow these spreading ridges of the earth and they wrap around the planet like the seam of a baseball and they're raised a little bit like the seam of a baseball. And so here is a map and the black lines, you'll see one black line disappearing up there pointing towards Death Valley and the black lines wrapped around the rest of the planet primarily running through the oceans. If you look very carefully way over on the far right of the picture you can see where one black line sort of points down into Africa towards the Great African Rifts and so there are other places that these black lines, these spreading ridges are trying to tear a continent apart the same as is happening up in Death Valley. But for the most part they're out in the oceans wrapping around and again sort of like the seam of the baseball if you're not a Metz fan well just imagine that that's whatever team you like to cheer for. You will see that these black lines look a little bit like the edges of jigsaw puzzle pieces and so you can sort of see between the black lines what you might think of as being jigsaw puzzle pieces. These are plates and you'll see they're labeled in there the Antarctic Plate, the Pacific Plate, the Cocoa's Plate and so on. These plates are going to be very important in our story of how the world works here as we try to put this together. You'll also see the Ring of Fire all the way around the Pacific at the edge of the plates there's volcanoes that's sort of fiery and so that gives us the Ring of Fire that is something we will revisit a little bit later. Where we started again was in Death Valley where you can see one of these spreading ridges disappearing and trying to unzip the continent and then you can follow that out and then on around. These are some of the plate boundaries. We will see in a little bit that while plates, these big chunks of the jigsaw puzzle pieces often have a spreading ridge at the edge sometimes they will have something else at the edge and so some of the plate boundaries are shown by the red lines in here but there are other sorts of plate boundaries that we will revisit. There's your baseball and again I can't say I grew up a Metz fan I'm from Ohio and since it had air Cleveland but that's life. Now if you go to Death Valley you find there's volcanoes. If you go to the center of the Gulf of California you'll find it's hot along that spreading ridge and in fact there's a volcano there there's melted rock leaks up along that crack and as Baja moves away from Mexico melted rock will sneak up along that crack and freeze and then they move away and more melted rock sneaks up and freezes and it moves away and more melted rock. And so that should tell you one thing it's hot down below because there's heat coming up from there to drive the volcanoes. Certainly if you see a volcano at Death Valley there has to be a heat source and so we're going to talk a little bit about heat because it turns out that all of this action on top is being driven by heat from below. So let's take a quick look at what is heat and how it moves around. I'm sure for some of you this is really old hat. Some of you may have not encountered this before and I hope you get something interesting out of it. The normal way we look at it if you were able to look inside of me very very careful you could see all the little pieces of which I made are vibrating. There is heat in me there's vibration going on and the atoms that make me up. Atoms as you know smallest units of matter that are sort of recognizable as something. If you started to please don't do this if you started to break me up into pieces using chemistry using fire using other tools that you have available to you you can make smaller and smaller smaller pieces down to some limit. Below that if you wanted to break it up more you're going to need an atom smasher or something like that and so the things that you can get to with a fire or your stomach or something like that are atoms and they have we talk about different types I made mostly of carbon and oxygen and hydrogen and a little nitrogen tiny bit of iron and other things and each one of those carbons you could pull it out and you could weigh it and say oh that's carbon and that's because of how many pieces are in it little protons and neutrons and so there's a little blurb in your textbook if chemistry is completely foreign to you it might be worthwhile to go back and read through in the textbook if this is old hat great don't worry about it. Now we will come back to some of that terminology it is true that a carbon inside of me one of them may be a little heavier than its neighbor and so if you've never run into an isotope in your life you might have a quick look at that this is going to show up for us in just a little bit but again if you've never had chemistry or you completely forgot your chemistry oh my goodness don't tell me about chemistry there's about a half a page or three quarters of a page in the textbook it will get you completely up to speed so you might have a look at that now suppose we started making it cold the vibration slows down it slows down and absolute zero the vibration stops very nearly this little quantum stuff but don't worry about that so as you warm from absolute zero the stuff in me vibrates and that's heat and that's there and it's very good if it wasn't going on I would freeze and that would be the end of us so now suppose we have some heat there's some place that doesn't have molecules in me are vibrating like crazy does the heat always stay in me or does it go somewhere else and the answer is it goes somewhere else there are other ways to get things going and so if something cold were next to me if you put an ice cube on my head it will melt, the atoms in it will start vibrating faster the atoms in me will vibrate slower and so I will transfer heat to it and so there are ways that heat is moved around in things how does it work? one way that heat gets moved around is by what we call radiation the lights are shining on me I am picking up just a little warmth from the lights that are shining on me it gets here by radiation through space radiation works great if you wanted to get a sun tan you go out and lie in the sun and you soak up the sun then you get skin cancer so that's maybe not a good idea but our cats are very clearly solar powered radiation brings energy all the way from the sun all the way down to the cat and the cat just sits there and soaks it up and then the cat goes and runs around like crazy at two in the morning so radiation moves heat around very well through space and as noted don't soak too much of it up or when you're old and feeble you won't be happy about that how else do you move heat around? conduction if you um turn on the stove burner and you let it get hot and then you hold your hand out to one side you feel a little bit of heat coming off the side that's radiation actually if you take your finger and you touch the burner you will notice very quickly you feel a whole lot of heat you're feeling that heat by conduction the atoms in the stove burner are vibrating really fast and when you put the atoms in your finger against the atoms in the stove burner the collisions between the two make the atoms in your finger vibrate really really really fast and then they jump out of the places where they're supposed to be and they sizzle and combine with oxygen and disappear in the atmosphere and your finger burns up so don't do that either that is really all it is though conduction moving heat around by collisions between a fast one running into a slow one and then they sort of share their speed that works really well over short distances you touch your finger to that stove burner and immediately you'll notice it it doesn't work very well over space if I vibrate really fast I can't make a molecule on the moon vibrate faster it doesn't even work really well over miles and miles if I vibrate really fast if I had a neighbor that I could shake and the neighbor would shake the neighbor by the time you try to go a few miles away it's really hard to get your neighbor to shake the neighbor to shake the neighbor to go a few miles away and so conduction works really well over short distances not over long distances convection is where we're headed this is sort of the third big way of moving heat around and essentially this is just taking something hot and moving it if you cook dinner and the dinner's on the stove and it's hot and you want hot food on the table you could go bring the hot food over you could wait for radiation to bring the heat you could wait for conduction to bring the heat but I think you're going to go get the food and bring it over convection is just sort of that it's the natural way for hot things to move to somewhere else and heat with them you've probably seen convection work if you've ever cooked spaghetti on the stove you make it hot at the bottom it expands it's lower in density then it rises it gets to the top and it cools and then it's going to sink again but it can't sink where it's rising so it gets out of the way and goes around in a loop wherever you have soft solids, really soft or liquids or gases and you heat them and they expand you end up with convection cells running after a bit and it works in spaghetti it works in spaghetti sauce even though that's a little thicker as you can imagine if we're talking about it here it's going to work in the planet as well convection, heat and material moves to a new place carrying the heat with it primarily because hot things are less dense the vibration as you heat it up it shakes around more it shoves its neighbors away now you've got the same amount of stuff taking up more space you get a little lower mass in a place it's less dense it tends to rise in case you forget what density was it's mass divided by volume so what happens if you have a low density thing down it tends to rise if you have a high density thing up it tends to sink and they get organized and that's not a terribly tough thing and you've probably seen it in the atmosphere what happens and what's very interesting is that over the times of geology slow times even rocks will do this if they're very warm it gets hotter and hotter it's mostly solid except in a couple of places but most of what's down there is solid but it's soft and you know if a blacksmith takes a horseshoe and heats it almost up to the melting point it can be deformed it can be worked well if you get a huge mass of stuff and you heat it up almost to melting it gets soft if you heat it at the bottom it can convect even though it's essentially solid and that's a cool thing but you know if I had a chocolate bar in my pocket I'd eat it right now and I'd be happier but if I had a chocolate bar in my pocket it would be fairly soft just to melting it gets soft and I could deform it I could make it do things and so the same is true in the earth it's warmed almost to the melting point it's soft and because it's soft it can do things so that's a convection cell here's a picture now we're going to very briefly sort of divide the world up for you what you see here is a diagram of the planet there's a much nicer diagram just that you might want to look at the planet is layered as described in the text the center is sort of an iron ball it's got an outer core which is liquid and an inner core that's solid it's basically iron around that there's this vast shell it's got some iron but it's got some silicon and oxygen and a few other things and that is soft it's not melted but it's almost melted there's sort of a layer that's too cold to flow very well it prefers to break rather than flowing we call that the lithosphere and it's got the very top of it especially the crust has a little bit more silicon oxygen in it and a little less iron than the rest and it's got a little water and a little us and some other things so it's fun but anyway here's the picture if you can see it and so you've got stirring below you'll see the surface of the earth labeled there you'll see that this is only part of the earth it has the whole planet it's spherical and you'll see the center marked down below there just so you know what we're looking at and what's going on the spreading ridge is right in the middle on top there where it says ridge you'll notice that the convection cell comes up and it spreads and as it does that a little bit of melt will leak up and get pulled away and leak up and freeze and so you'll get the volcanoes at the the volcanoes in Death Valley and you will get spreading and making of new sea floor at those places that allow the motion of Baja away from the mainland of Mexico and so on okay the process here we've got this old stuff on top the jigsaw puzzle pieces we call those plates the moving around of these on the convection cells we call plate tectonics it's a big fancy word, it's a fun word and it's written out there for you in case you can't spell for my speaking so again pull apart, we started in Death Valley it's pulling apart a little bit of melt leaks up you go south from Death Valley into the Gulf of California Baja is moving away from Mexico there's pull apart going on a little bit of melt leaks up we're doing so righting on the back of giant convection cells the stuff on top is just rafting around on what's underneath with the ridges at Death Valley being where we started okay, heated rock rises, less dense cools with the surface of the earth then you sink back and this gives you the completion of the loop and this gives us action this gives us motion this gives us drama you pull apart here into something somewhere else we're going to have risks and collisions and earthquakes and volcanoes and fun and so you get ultimately the heat of the earth making this go on raising rocks push aside the cool rocks surface, the cool rocks travel sideways and there will be interaction when cool rocks run into other cool rocks which we have to look at okay where's the heat come from a little bit of it may be left from when the planet formed there's some other things going on mostly it's radioactivity if you get a rock and you put it in a Geiger counter you'll get occasional action there's always a little bit of radioactive stuff now, not huge amounts you usually don't get wiped out by the radioactivity in the rocks next to you but it's a big planet there's a lot of radioactivity there's a lot of rock that makes heat and that heat is ultimately of what drives the planet okay there is a little left from the formation of the planet a little bit from separation of the planet and freezing of things but mostly it's radioactivity that does it wonderful story if you're into history don't get too bogged down on this but if you're into history the physicist Lord Galvin says okay I'm a physicist I'm smart I know all this stuff the earth started melting and it's cooling off and I measure how much heat is coming out of it that tells me how old the earth is 24 million years and the geologist said oh no no no no it's longer than that it's lots longer than that it's more than 100 you gotta go way back and he said no no no I'm a physicist I have it right well he didn't know about radioactivity he got it completely wrong because his assumptions were entirely wrong Darwin as well as the geologist we need a longer clock than this and it took actually it took the discovery of radioactivity Marie Curie who's shown here and others to find the energy source and say no there's heat down there this will work your physics was right your assumptions were wrong something worth it so geologists we like this those who studied the earth like this okay so brief summary heat inside the earth from radioactive decay it drives convection cells the cells move plates the jigsaw pieces on top where it's cold they go rafting around on the surface of the planet where they pull apart you get faults you get spreading you may get a little volcanoes leaking up death valley is one you get ocean spreading centers beyond that you're welcome to pause right now and take a deep breath okay if not we'll go screaming right along we're going to briefly visit another park and we will look at one of the implications of this you might say why should I care who cares who cares what's going on here one of the reasons this matters is occasionally things that are moving get stuck and then they move again and then when they move they go fast and if you're standing on top you get knocked out from under you and if you're building you fall down and that's not good so we're going to go to Yellowstone Yellowstone has everything it has geysers and it has bears and it has beautiful trees and lakes and it has earthquakes and volcanoes and river erosion, Yellowstone has everything the first national park the first serious European western exploration people are there and they had earthquakes the ground shook that's a skull this is sort of everything is here it must be going on Yellowstone itself there's a huge volcanic pan of volcanic caldera left from giant eruptions and there will be another one someday with fairly high confidence it's due plus or minus 100,000 years the next one is due you can count 1.8, 1.2, not 0.6 we're due not to worry those were big eruptions really seriously big eruptions but we're going to visit there and talk about earthquakes you go to Yellowstone and if you read into the history back here a little bit there was actually a beauty pageant going on at the old Faithfully and I don't think they do this anymore and in the middle of the pageant in the late 1950s there was an earthquake and there's this wonderful text you can read about in our textbook about all these people watching the queen walking down the aisle and the ground start shaking and they all screamed and ran out and what had happened is just west of the park there was a big earthquake and the picture you're looking at in front of you the side that I'm standing on taking the picture the side that the bottom of the tree is on dropped about 20 feet relative to the other side and in the middle of the night it went pfft and it just this huge motion now you can imagine what happens there's a hill there and this is a serious hill this is a couple thousand foot high hill and it stops well if I had something balanced precariously on me and I dropped it falls down what happened is the whole hillside fell down and it killed a bunch of people it was not very nice but there's these dramatic stories and the hillside fell down it slid across the river and it pushed the air out of the way in front of it and there's this story of this guy that had his clothes blown off of him in the middle of the night it was truly an amazing thing you can see the pictures here those are big pine trees along the edge of that failure so this entire hillside just fell off it dammed the river it bounced up the other side this rock is towering over me and this rock came down into the valley and several hundred feet up the other side in the landslide that was caused by this earthquake once it dams the river it makes a lake the army corps engineer said boy we got trouble because what happens the water is going to fill up it's going to go over the lake go over the dam the dam is loose rocks it will cut through the dam there will be a giant failure it will kill people that happened hundred years ago just outside the Grand Tetons and so fortunately the army corps engineer got in there real fast and they fixed this sucker and things worked you can still see the damage that was done by this earthquake there's great stories of this lady this house the land sort of tilted and the lake is filling up and there was another lake just above it that had already been there and her house is getting flooded and the waves are coming at her and it's middle of the night the earthquake shook up Yellowstone it changed the timing of the geysers it did all sorts of things and so there are earthquakes and we know they matter they matter in natural places they kill people they cause troubles this is a different earthquake 1964 Alaska had a big one and you can see one of the things that happened there we usually build buildings to stand up against gravity we make them so they don't fall down in an earthquake they shouldn't fall sideways and we usually don't build things to be strong against falling sideways well you notice what happened things moved and that bridge just fell sideways or it fell off it's an interesting mess here's another one this one is from the World Series earthquake in California 87 I believe it was and again we build things not fall down but it shook and it sort of slid off so this isn't good you really wouldn't want to drive your car in front of that bridge right now and when you shake the ground and things move you get cracks and that's not good and it's not good for houses the road is a little perched you put a real strong thing and it sits on a post and then you put a road on top of it and then it shakes the post just poked through the road I didn't design it that way did I so earthquakes are a very bad thing when they happen in the World Series earthquake you can see the road is not going to be useful for a little while there so what's going on with earthquakes the land moves we've seen that it pulls apart if it's pulling the part somewhere somewhere else it must be running together and occasionally there's sliding pasts that go on and so this is a diagram of the west this is a diagram of what you might see going on for the World Series earthquake for the San Francisco earthquake for the San Andreas Fault what you have out there in fact is that there's sort of the far western piece of California is headed for Alaska and so it's sort of sliding along and the join between that far western part and the rest of the country is the San Andreas Fault so let's see if we can walk through this we're going to see what happens when a fault gets stuck and it then it breaks and what happens is it gets stuck for a while and things sort of bend and then eventually they let go and when they let go things happen and so let's see what we can do here with this so we have plates they're moving the North American plate is probably what you're sitting on if you're in Pennsylvania for example you're on the North American plate but the very far western part of California is out on the Pacific plate there's a lot of motions everything is sort of going that way and then there's a little of this but if we just focus on how they're moving compared to each other the Pacific plate is headed for Alaska and the North American plate is that and so there's a little of this slide pass going on the break between them the San Andreas Fault and so you can just take that blue line as the San Andreas and the Pacific plate moving relative to the North American plate now let's start if you have a fence or a road or a building or something you build it across the San Andreas Fault and then things are moving so what's going to happen is the different sides are trying to move but the fault is not letting go you're trying to go maybe they're moving a little bit but they're not going real far and so you actually start things bending far away from the fault it's moved right at the fault rocks you know they sort of get locked around each other and they're getting bent and they're getting bent well eventually what's going to happen is that bend that we have circled there something's going to break you can't bend rocks forever and when it breaks there you go and so you go stop and that snap is the earthquake it's been caught on bumps or bumps or jumps in the rock so what happens then if something snaps these big chunks of rock everything from San Francisco to LA just move north by 25 feet now if that happens it's sort of elbows its neighbor a little bit and so other sorts of things are going to be going on with that snap and it could get very interesting and it will release energy and so when it goes 20 feet north it shoves what's just north of that and that shoves what's just north of that the big earthquake the whole planet will get shaken a little bit it's not just shaking yourself it's shaking lots of other places where are earthquakes well the red dots here are earthquakes this happens to be 1978 to 1987 fairly large quakes and what you will find is that these quakes actually outline the plates the big tectonic plates the jigsaw puzzle pieces moving around on the planet outlined by these red dots as you can see by comparing to this one and so if you sort of remember what this looks like and remember what this one looks like you will be able to see and you can compare them on your own time you'll be able to see that the plates are primarily outlined by the earthquakes the action is mostly at the edge there's a few places in the middles that get more interesting but not too many okay there's a couple things out there the pull apart of the valley the slide past if that is confusing you a little bit there's sort of a little of both going on there's a little of this sort of thing and so in fact we're not telling you anything that's wrong but we don't want to get this too complicated and so we'll try to keep it so now the rocks shake they shake their neighbors this sort of pushes things off and so you get deformations and the waves knock down buildings and do other sorts of things there's various kinds of waves if you're hearing me I'm speaking and the sound is going to a microphone and what I'm doing is essentially compressing and expanding the air it's called a push wave or a sound wave or a P wave it very clearly goes through gasses and liquids as well as through solids because you can hear me because it's going through the air and getting to the microphone there's another kind of waves if you were to grab a rope and shake it that um it's sort of this kind of thing that actually imagine for a moment going to the football game getting in the stadium and doing the wave okay now what's a wave do your part of the wave wave wave wave okay your part of the wave is up and down but the wave moves around the stadium so in that case what you're doing and what the waves are doing you're going in different directions that kind of wave is called a shear wave or an S wave and it turns out that unless your neighbor really wants to do what you want your neighbor to do they don't go through liquids or gases because if you move and your neighbor doesn't cooperate you can't really grab your neighbor and grab your neighbor up and so it turns out they do not go through liquids or gases oddly enough so two kinds of waves are generated the P wave compressional push they will go through liquids or gases sound waves they're squeezing and then expanding the shear waves don't go through water or air they're more like moving the wave in the stadium you go up and down but the wave goes around okay now you go look in the textbook you find out the earth is layered and you find out the outer core is liquid we say so it's right in there why in heaven's name would we say a silly thing like this one thing that can happen as you can see in the diagram down there you make an earthquake if you put out a listening device that listens for this kind of waves and this kind of waves if you put it near the earthquake you'll hear both kinds P waves and S waves come winging by if you put your listening device on the other side of the planet from the earthquake you won't hear any S waves you'll only hear P waves and no matter where the earthquake is as long as your listening device is on the other side of the planet there's a zone that doesn't give any S waves now S waves won't go through liquid and so you start looking down there and you can see the diagram and what will happen is that any S wave that hits that outer core disappears it gets soaked up it makes heat ultimately and so because every earthquake has a zone on the other side of the planet that there's no S waves there must be a ball of liquid in the middle of the planet that keeps the S waves from getting there so the seismic energy leaves the earthquake it goes zipping through the planet and if it's a big earthquake you will hear it on the other side of the planet and we say that the outer core is liquid because none of these S waves or shear waves get through it and we can look at the global map of earthquakes listen on no because now there's listening devices all around the planet and the other side of the planet never gets one so there must be a ball of liquid in the way don't go through the outer core which is liquid now the textbook will tell you why we think there's a solid inner core in there that's even a little more complicated but this much basically makes sense earthquakes we talk about earthquakes we say wow that was a 9 that was an 8 that was a 7 and we get really really excited if it's an 8 rather than a 7 why well we sort of cheat in the way we do this sometimes scientists get lazy and we really like talking about 9 and 8 rather than 100 million and 10,000 and so we sort of play an interesting game in how we scale these things when you move up one in how big an earthquake was that really means that the ground moves 10 times more we just do that because it's easy and it turns out that if you move the ground 10 times more it takes about 30 times more energy so if you have a 1 earthquake it's not very much a 2 earthquake actually is 10 times more ground motion and 30 times more energy a 3 is 30 times more energy than a toe a 4 is 30 times more energy than a 3 a 5 is 30 times more energy than a 4 and by the time you get up to these big ones they're bigger than all the nuclear arsenals of the world they're really really really bad things and they are out there occasionally what this turns out is that most of the action most of the damage is in those few really big ones there aren't many big ones but they are so huge that they really dominate what happens so there's thousands and thousands of earthquakes but you don't hear about them until that one rarity went the whole world shakes quick summary earthquakes mainly at plate boundaries not entirely faults get stuck then they suddenly slip when that happens the energy is spread away on waves it causes a lot of destruction you can measure them to get information about how the earth works when we say that it was a little bit bigger we mean it was a lot bigger and most of the action is from a few big events and so we're started on this very interesting I hope, interesting to us, I hope to you this very interesting journey to understand why there are mountains and what you can see is that the heat of the earth is stirring things it's moving things around it's causing things to come up and down to stick and slip there's action you can surely see and we will get to that more action next time