Chapter 08 Tectonics Earthquakes and Volcanoes

hello welcome back and welcome to chapter 8 on tectonics earthquakes and volcanism here's the stuff we're going to ignore here's the big questions we're going to answer in this chapter what our Earth's history interior structure and materials how does plate tectonics explain changes in Earth's surface how to plate motions affect Earth's surface so up until now just about everything that we've looked at temperature patterns average temperature temperature range rainfall patterns hours of sunlight seasonal changes all those things we've been able to explain just looking at latitude and now we're going to get into the other the other most important factor in physical geography and that is plate tectonics and plate tectonics is going to answer pretty much everything that latitude can't so why are there mountains in some places that's plate tectonics why are there depressions or valleys that's plate tectonics and let's get into it so the first and most important thing to talk about is endo genic versus exogenic processes so when we're talking about plate tectonics with earthquakes and volcanoes and whole continents moving around those are all powered those are all termed endo genic processes driven by Earth's internal heat are endo genic so the stuff that's powered from inside earth is endo genic earthquakes volcanoes those are all endo genic processes processes driven by external factors so outside the surface gravity wind rain those are exogenic so rivers glaciers action at the beach all of those are exogenic processes if it's powered from the inside that's an endo genic process and if it's powered from external forces that's exogenic the external forces are exogenic it's powered from inside its endo genic so let's talk about time earth is old earth is roughly 4.6 billion years old the moon is about 30 million years younger it was formed when something about Mars Mars shaped Mars size hit earth when Earth was very very young melted earth partially and droplet of molten earth bleep came off the other side and cooled and became the moon so I'm gonna rattle off whole bunch of numbers is the abbreviation we use for billions of years billion is thousand million so is billions of years and my is millions of years earth is about 4.6 billion years old our oldest rock or evidence of the oldest rock is about four point two five billion years old life shows up about 3.4 billion years ago Pangaea which is the name for the supercontinent when all the last time that all the continents were together that assemblage was called Pangaea Pangaea broke up about 200 and started breaking up about 225 million years ago the Cretaceous Paleogene boundary which marks the end of the dinosaurs that happened about 66 million years ago relatively recently the Cretaceous Paleogene which is abbreviated KPG the KPG boundary about 60 6.4 million years ago the Pleistocene as the last ice age the last ice age started up about 2.5 million years ago the Holocene is the term for the most recent period it's also been proposed that the Holocene be renamed Anthropocene in in recognition of the efforts humans have made the efforts in recognition of the changes that humans have made to the planet so we started doing agriculture about 10,000 years ago the climatologist Ruddiman thinks that anthropogenic or human caused climate change also then dates to about 10,000 years ago when we domesticated rice and created giant artificial swamps rice paddies which released methane into the atmosphere which is greenhouse gas so we've got all these numbers and one of the problems with geologic time is that it is deep earth is relatively old but humans don't do well with big numbers Carl Sagan one of my favorite scientists ever realized this and said you know if you told most people that something happened 66 million years ago and asked them is that long time ago or not long time ago just about everybody would say that's long time ago sixty six point four million years ago but in terms of the age of Earth it's really not it's pretty recent so Carl Sagan said if you took all of Earth's history we took all four point five six billion years four billion five hundred sixty five hundred sixty million years of Earth's history and you compress that into one earth year so you took 4.6 billion years divided by 365 so each day on the cosmic year then would have taken twelve point four nine million years on earth so using this idea of compressing 4.6 billion years into one calendar year so that we can see when things happened relative to other things we get very different look so earth formed January 1st at the beginning of the cosmic year right now it's December 31st eleven fifty nine point nine nine nine nine nine seconds so it is New Year's Eve it's December 31st right now in the cosmic year so let's think let's take look and see when things happened relative to other things the oldest rock shows up about six weeks into the year on Valon fines day life shows up three months into the year on March 1st Pangaea splits up December 12th so if told you Pangaea split up 225 million years ago which is number that you're gonna need to know that sounds like really long time ago if told you it's December 31st and Pangaea split up December 12th you'd probably say well that's just couple weeks ago that's relatively recent exactly Pangaea split up relatively recently that dinosaurs get whacked the evening of December 25th so six days ago just under week on the cosmic year is when the dinosaurs got whacked the Pleistocene began December 31st at 7:15 p.m. humans show up December 31st 11:59 and 55 second so five seconds before the end of the years when humans show up all of human history all of recorded history is more recent than even that whole of recorded history is in the last half second of the cosmic year the roughly four thousand years of recorded human history so the cosmic year is important because it puts things into their perspective relatively speaking so things that happened millions of years ago using the cosmic year that's just December 31st or December 25th that's just little time ago here is chunk of the rock that contains the zircon crystals that are 4.4 billion years maybe so these these think are those oricon crystals those would be the oldest rock remnants on the planet from Australia the geologic time scale so we've got all that geologic time and it's usually shown on the geologic time scale there's two important things that want you to know about the geologic time scale and they're both right here number one the major divisions the major divisions mark key events in the fossil record so the breaks in the geologic time scale and I'll show you the geologic time scale in just minute you'll see that the breaks are based on identifiable identifiable records in the fossil record so that's thing number that's important to know number two the farther back we go the less we know because rocks are constantly being created and altered and destroyed and created and altered and destroyed it's very hard to find really old rocks because they're constantly especially rocks at the surface rocks at the surface are getting broken down and made into soil getting washed into the ocean so it's hard to find old rocks that are undisturbed because they're rare our understanding of the early Earth is limited then by the evidence the evidence would be old rocks and rocks are constantly getting worn down and modified so it's very hard to find old rocks and therefore the farther back in time we go the less we know this is the diagram out of the book showing different different periods in Earth's history the five mass extinction events we are in the middle of sixth mass extinction event so this is the this is like the the super super super simple geologic timescale let's take look at another one so we have the Precambrian and then we have the Cambrian is right here but paleozoic mesozoic Cenozoic Cenozoic Mesozoic Paleozoic so most of Earth's most of Earth's history is here and we know very little you can see after the Cambrian so the Cambrian the big the big development was fish fish so if there's fish the oldest fish are in the Cambrian if we find older fish this date this 542 million years ate for the beginning of the Cambrian will be changed to reflect reality so as we discover as we make new discoveries these dates shift and that's the way science works when there's new ideas that are proven to be better than old ideas the new ideas are adopted so we have fish diversification of animal life vascular plants plants with veins instead of little single-celled plants amphibians like frogs reptiles later also trees then we get different reptiles dinosaurs and the mammals show up dinosaurs diversify dinosaurs get whacked right here the KT boundary or KPG boundary the mammals takeoff let's take look at another version of the cheetah logic timescale this is the big bad boy this is it this is the geologic society of America's geologic time scale and don't really like it it's way too detailed but wanted to show you that it exists there's way more way more information and this over on the side is magnetic anomalies we haven't really talked about that we'll talk about this in this chapter is the idea that Earth's magnetic field flip-flops and goes from normal to reverse to normal to reversed on this sort of random scale so here's another one this is another artists trending of the geologic time scale down here at the bottom we have the formation of earth and you can see so from from the beginning 22.5 that's that's 2 billion years of Earth's history right there we don't know whole lot about it one of the things that would hope that you notice is the dates get closer and closer together like the Pleistocene here it says 1.8 this is an example of what was talking about between the time that this diagram was created and the present they've changed the beginning date for the Pleistocene from 1.8 to 2.5 million years ago so still it's about two and half million years in here from 5.3 to 2.5 the Pliocene so 23 to 5,000,000 so you're looking at 17 million years here as you go back for example right here going from 542 million years to 2.5 million from 2.5 to 4.6 as as we go back farther in Earth's history we know less and less and less about it like this this geologic time scale it's more whimsical than the other ones right so this is an artist impression of an event that happened 60 6.4 million years ago when an asteroid about 6 miles across traveling about hundred thousand miles an hour smacked into the Yucatan Peninsula off of Mexico with enough energy to ignite global forest fires that wiped out the majority of species on the planet you can go all over the world and find evidence of this impact event this is the Katie Orr KPBS Orr's here we have older rock as you get up to the surface younger and younger rock and right here is the boundary layer with layer of clay here we have different picture of different place on earth where you can see the boundary layer with clay the impact layer with glass balls made of fused earth and then layer on top of the high concentration of iridium which is common in objects from outer space it's rare in objects found on earth though so that's one of the lines of evidence that helps us know that the object came from outer space here we've got sediment core so going back to the last chapter on climate change this is sediment core taken from the middle of the ocean someplace you can see before the impact we have older rocks the moment of impact we have glass balls condensed from the hot vapor cloud that was rock so hit hit with enough energy to actually melt and then vaporize rock there was actually vaporized rock that condensed out and made these little glass balls that rained down all over Earth there's fireball layer that has high concentration of dust and ash which is how we know there was fires and then different species so we had many many different species they were large they were very complex form and effort in the oceans and then after the impact we see change in the distribution of species they're smaller they're simpler there's fewer different types of form anaphora after the extinction event this is the tree of life going back to the last Universal common ancestor as evolution took place we got bacteria for starters archaea eukaryotes plants fungi protozoans and kind of der Mata the spiny skin things like starfish we have fish and sharks here we have fish sharks amphibians birds mammals here at the end and there's these concentric rings of different mass extinctions and you can see the evidence of the mass extinctions as these family trees get pruned like coming up here whatever the heck that was they don't exist anymore whatever was growing along there it doesn't exist anymore so you can see these white lines that represent let me zoom in bit you can see where the family tree gets pruned and then it branches back out and it gets pruned and it branches back out it's happened again and again and again in Earth's history if you look here here's the end of the dinosaurs you can see they go extinct which allows birds to flourish also allows mammals to really take off so the tree of life geologic time when we're looking at geologic time there's two ways of dating it there's absolute time which is dating things with numbers how long before the present and there's relative time and we're looking at this layer of rock is older than this other layer of rock radiometric dating like potassium argon or uranium to lead those are examples of radio radiometric dating techniques that will tell us how old rocks are relative dating is based on the relative to position of rock layers and the principle of superposition which is the idea that the oldest rocks are at the bottom and younger rocks get deposited on top youngest rocks are on top unless tectonic activity has turned them over so here we've got diagram of some of the rock layers in the Grand Canyon and I've included link to really interesting interesting interesting there's big gap there's like billion years that are missing you can see the rocks down here are tilted and older and then they got shaved off and then rocks new totally different rocks were deposited horizontally on top of those older rocks the uncocks in the in the Grand Canyon the Hermit shale the supergroup the red wall lamb stone in terms of absolute time so if we were going to look at these rocks in terms of absolute time here's the kind of thing that we would say we'd say the supergroup is 285 to 318 million years old we'd say the red wall limestone is 318 to 359 million years old so again absolute time just how many years old is it so if we look at these rocks in terms of relative time we'd say the Hermit shale is on top of the Supai group and therefore it's younger the Hermit shale is younger than the supergroup the supergroup is on top of the red wall limestone so then we could say the Supai group is younger than the red stone the red wall limestone and the red wall limestone is the oldest of the red walls Supai Hermit shale the oldest would be the Vishnu's schist which is down here at the very bottom and the youngest would be the Kaibab formation up here on top so relative time is how old is that relative to something else part of part of part of Earth science is the idea of uniformitarianism uniformitarianism is the idea the present is the key to the past it is the scientific idea that processes going on right now like gravity how faster rivers run how fast two things fall how much does the ocean wear away at rocks on the shore all of those processes have been happening at the same speed throughout Earth's history that we have very old very slow earth the same physical processes active in the environment today have been operating throughout geologic time at the same speed so earth is looks like big jaw breaker earth condensed from cloud of dust gas and see comments about 4.6 billion years ago Western Australia has the oldest rocks we saw picture of some of those from the New Jack formation Earth is powered by the breakdown the radioactive decay of elements in the core so one of the things that scientists realized in the 60s and 70s is that Earth is powered internally the continents are being driven by these convection currents in the mantle the convection currents in the mantle are powered by Earth's internal heat so earth in cross-section looks like very very complicated candy there's the core it's made of the inner core and the outer core the inner core is solid iron the outer core is molten iron the outer core is actually hotter than the inner core but because of the enormous pressure on the inner core the inner core is solid iron there's the mantle the mantle is made up of solid rock although it does move slowly over long periods of time and there's the crust the material at the very outside layer of Earth is crust crust is also solid rock and there's the lithosphere so we have these four layers we've got the core made up of the inner and outer core we've got the man tole the mantle is made up of four more layers we have the crust made up of oceanic crust and continental crust and then we have the lithosphere which is all the rocky material on top of the asthenosphere the lithosphere is also solid rock so we have the core the core is made up of the inner core and the outer core the inner core is solid iron the outer core is liquid liquid molten metallic iron on top of the core we have the mantle and the mantle is made up of four layers they're all solid rock there's the lower mantle the upper mantle the asthenosphere and the uppermost mantle those four layers together make up the mantle uppermost mantle the asthenosphere the upper mantle and the lower mantle the asthenosphere here it's labeled plastic think of the asthenosphere is the gooey caramel layer this is the layer that flows and moves and takes with it the lithosphere the lithosphere is all the rocky material made up of the uppermost mantle so part of the mantle and on the crust continental and oceanic those two or three layers together oceanic crust continental crust and the lithosphere again those are all solid rock and they are moved by the plastic asthenosphere plastic again think of it as the gooey caramel layer like if you imagine caramel that's pretty much the way this flows it's kind of solid if you look at it you like if you hit caramel it's not going to move whole lot but if you slowly push on it it'll move lot so those are the eight layers the inner core the outer core make up the core the mantle is made up of the lower upper asthenosphere and uppermost mantle so those four layers the crust is made up of continental continental crust and oceanic crust and then the lithosphere is grouping of all the rocky material the uppermost mantle and the crust on top of the asthenosphere so everything on top of the asthenosphere these three layers are the loo those fear here's another version like this one because it looks all bitchin isn't really glowing glowing like that on the inside we've got the inner core just solid iron the outer core liquid iron the mantle which makes up 80% of earth by volume the mantle and on the crust which is very very very thin the deepest part of the crust is about 70 kilometers below the surface Earth's magnetic field is created by the movement of the outer core here's lines of magnetic force this is why the Northern Lights as the energy comes from the Sun the energy gets concentrated at the North and South Poles making the aurora borealis and the aurora australis but that magnetic field changes over time this is showing density don't know why included that here's an important weird idea the densest part of Earth is the inner core when Earth was molten the dense material was pulled to the center Earth's crust is the fluffiest material on earth granite for example very very very heavy rock but it is some of the least dense rock on earth it is the the fluffy stuff that rose to the top Hall earth was still relatively molten those Meghna are preserved in igneous rock so rock that used to be molten is igneous rock rock associated with volcanic eruptions that's magma which cools to become igneous rock so as the rock is heated the magnetic field of the molecules lines up with Earth's magnetic field when the rock cools the magnetic field of the molecules gets locked in place so if we look at rocks if we look at old rocks for example rocks along the recce Annis ridge we see this pattern of normal the red would be normal the purple would be reversed polarity so if you had compass and you were alive on earth at this time the time that these purple rocks are being formed the North Pole and your compass would point to Antarctica and then we've got the blue that's gonna be normal polarity it's gonna point at the North Pole green if you're around during this time you'd be your compass would be pointing at the South Pole again this was incredibly important evidence for plate tectonics that scientists could date the rock so we know how old the rock is so we know how far the plate has moved so we know how fast the plates are spreading apart at the spreading Center we know how old they are and we also know the magnetic orientation of Earth's magnetic field looking at igneous rocks here is longer record of Earth's magnetic field the Bruna's Chron the blue or turquoise whatever color this is is normal reversed normal reversed normal reverse normal reverse you can see it's random it's not like every five hundred thousand years some reversals lasts little bit some lasts long time it's poorly understood which think is really really interesting but there's agreement all over earth so if you found rock that was 2 billion years old it would be it would have negative polarity 1 billion it would have normal in between 1 billion and 3/4 of billion it would be reversed normal reversed all over the world so the mantle is hot mostly solid material it does move with these convection cells the mantle represents 80 percent of Earth's total volume again driven by convection currents here we can see not the greatest diagram but you can see the convection currents in the mantle here we have the lithosphere the lithosphere would then be oceanic crust and uppermost mantle the gooey asthenosphere which is moving even faster than the mantle closer to the surface in the mantle the temperature and pressure are less and so the rocks are more rigid and when put under stress they tend to break as opposed to deeper rocks those are going to be hotter and under more pressure and they flow they will Bend in fact good way of thinking of it as like chocolate chip cookies if they're straight out of the oven and they're still warm you can bend them so that would be the deeper deeper rocks in the mantle but once those cookies cool when you try to bend them they just break that would be rock that's closer to the surface because it's not as hot and there's less pressure on it the asthenosphere is from 70 kilometers below the surface to about 250 kilometers it's plastic it flows like caramel the lithosphere is the uppermost mantle and then crust either oceanic or continental or both the lithosphere is mu by the asthenosphere it's broken into about 14 major plates we'll take look at that later the motor of each each discontinuity or Moho separates the crust from the mantle above the Moho is the crust the rocky shell of the continents and the ocean floor that would be the lithosphere the crust is going to be made up of oceanic crust oceanic crust is chemically very similar to salt the salt has lot of iron and magnesium it has density of 3 grams per cubic centimeter that's going to be very important and it helps us understand white plate tectonics works the way it does that she annek crust is more dense than continental crust that we'll see in minute so when two plates come together if one of them is oceanic crust and the other plate is continental crust the continental crust will make the oceanic subduct the oceanic crust is darker and it's more dense so it's going to slip under the continental crust oceanic crust again higher in iron and magnesium it's about 5 kilometers thick so if just started walking straight down after an hour you would have walked about three miles you could have walked through all of Earth's crust or at least oceanic crust oceanic crust about five kilometers thick continental crust is much thicker it's also less dense oceanic crust and this is important and I'll come to it come back to it again and again and again oceanic crust flows like motor oil when it melts continental crust chemically it's similar to granite it has more silica more aluminum it is less dense it has density of 2.7 grams per cubic centimeter so it floats if you will on top of oceanic crust if they come into contact if they collide the oceanic crust is gonna go down because it's more dense the continental crust is high in silicon and aluminium and when it melts out 20 to 60 kilometers thick its thicker the thickest crust we're gonna find with the highest mountains so Mount Everest would be some of the thickest crust on the planet when continental crust melts when it's molten like in volcano it flows like mashed potatoes it is very thick very very very thick volcanoes that are made of continental crust tend to just explode we'll talk about that when we get to volcanoes the rock cycle so let's talk about the rock cycle the rock cycle is how we get new rocks it's what happens to old rocks it's an example we can use the rock cycle to help us understand exogenic and Indo genic again internal processes are endo genic they tend to build up landforms external process exogenic processes like weathering and erosion tend to wear down those landforms so another way of thinking of these two competing forces is one of them tends to build up new landforms endo genic volcanoes and earthquakes tend to build up new landforms and weathering and erosion tends to just wear them down over time here we've got of the geologic cycle which includes the hydrologic cycle the water cycle washing stuff into the ocean to make new sedimentary rock sedimentary rock can gets abducted by the tectonic cycle that will then melt and make new igneous rocks so the geologic cycle includes the water cycle the rock cycle going back and forth between sedimentary igneous and metamorphic rocks and then the tectonic cycle moving the plates around so again the geologic cycle is just made up of the rock cycle the tectonic cycle and the hydrologic cycle there are some rocks if you like rocks sedimentary rock is made up of sediment igneous rock is rock that used to be molten and metamorphic rock is rock that has been changed by heat or pressure it could have been igneous could have been sedimentary could have even been metamorphic rock but if it's altered by heat by compression or it's yeah by heat or pressure then it becomes metamorphic rock metamorphic rock is usually harder and more resistant to weathering so metamorphic rock went tend to stick around would be worn away more slowly so here's really weird idea earth is in terms of the materials it's made of not very diverse only eight elements make up 99% of Earth's crust and of those eight oxygen makes up about half about half the weight of Earth's crust as oxygen this is really really interesting oxygen combines readily with other chemicals that's why when you leave tools out overnight they rust because oxygen is combining with the iron to make iron oxide this is what happened with rocks on earth in fact people who are looking for extraterrestrial life are often just looking for oxygen in the atmosphere if there's oxygen in the atmosphere something is making it because otherwise all the oxygen in the atmosphere would get bound up with rocks by oxidation so if there's oxygen in the atmosphere something's making it and at this point the only process is the only process that we're aware of that makes oxygen it would be photosynthesis which is life so oxygen makes up about half the weight of Earth's crust silicon makes up about quarter of the weight of Earth's crust so about three-quarters of Earth's crust is just oxygen and silicon which is incredibly interesting because sio2 is the chemical symbol for quartz which is found in beach sand so the chemical formula of beach sand two parts oxygen one part silicon is about the same as the makeup of most of Earth's crust rocks are made of minerals and mineral is an inorganic natural substance with chemical formula and crystalline crystalline structure so if it has chemical formula it's crystalline structure it is mineral rocks are made of minerals rocks are made of minerals yeah igneous rock is rock that used to be molten it can get ground up and weathered and transported and become sedimentary rock sedimentary rock can gets abducted and become metamorphic rock which can wear away and become sedimentary rock which can gets abducted and become igneous rock it just goes around and around igneous rock melts under high temperature igneous rocks are divided up into intrusive that cool inside the crust and extrusive that cool outside the crust they cool externally and you can tell the difference because as the rock cools if it cools slowly there'll be time for visible minerals mineral crystals to form if it cools quickly there isn't time for those crystals to form magma is under the ground if it's yeah you can't fall into molten hot magma you could fall into molten hot lava if it's at the surface it's lava if it's below the ground its magma here we have granite basalt rhyolite three-three igneous rocks the basalt would be an extrusive rockets sorry about that the basalt would be an extrusive rock it's going to cool very quickly the granite is an intrusive rock it cools internally very slowly and that's why you get that salt-and-pepper appearance of granite because the rock cooled slowly enough for the crystals have time the crystals had time to grow before they cooled so igneous make up about 90% of Earth's crust so the mantle makes up about 80% of Earth's volume but igneous rocks make up most of Earth's crust continental crust is light-colored it's low in density it's similar to granite when it melts it makes explosive volcanoes oceanic crust is more dense it's darker color it's chemically similar to basaltic rock when it melts it flows like motor oil sedimentary rock forms from sediments from older rocks you can divide sedimentary rocks into three different classes there's plastic made up of broken bits of other rocks organics sedimentary rocks made up of organic material so limestone from dead microorganisms in the ocean would be an organic sedimentary rock coal is another organic sedimentary rock and then you can get chemical sedimentary rocks formed when different chemicals precipitate out of water and then settle to the bottom and make rocks example of sedimentary metamorphic rocks by heat or pressure like said before it often makes them harder more resistant to weathering so it's harder for natural forces to break them down and get rid of them the two types of metamorphic processes are regional metamorphism so in plate tectonics when you have two plates that are colliding with each other that would be regional metamorphism and contact metamorphism when magma rising to the surface cooks rocks by contact so if you had two continents that were colliding that would be regional metamorphism if you have molten magma and it cooks the surrounding non molten rocks that would be contact metamorphism the Taj Mahal is made of marble which is metamorphic metamorphic rock made of limestone sedimentary rock so if you take limestone the sedimentary rock and you heat it you compress it you get marble which is harder and more resistant to being worn away plate tectonics so enough about the rock cycle let's talk about plate tectonics there's my man Alfred Lothar Wagner he proposed the continental drift in 1912 he was ridiculed he was mocked because of couple things number one he was meteorologist not geologist so the geologists were envious of somebody coming in and telling them what what their science was about and he also didn't have mechanism he he had outstanding evidence he had geologic evidence he had fossil evidence he looked at the fit of continental margins the evidence that that Vagner had for continental drift what he called continental drift mean I'll call plate tectonics his evidence was great but he had no mechanism so he couldn't explain how the continents were moving and so people rejected his ideas right up until the 1960s in the 1960s there was flood of data and the data all supported each other and led to the rapid rapid adoption of plate tectonics plate tectonics was as huge for geology as evolution was for biology it it explained so many things overnight overnight so many earthquakes volcanoes mountains valleys all of it made sense the distribution of earthquakes we'll look at that in just minute so here we have 220 million years ago this was Pangaea we've got North America South America Africa India Australia and Arctica Eurasia and then it breaks up here we have Earth today you so this is an animation done by Kristopher Scotties and christopher Scotties does animations of plate tectonics does some of the best here's weird idea Pangaea was just the most recent time that the continents had come together that every 300-400 million years the continents jammed together and make new supercontinent and they break apart and they come together and they break cart break apart come together break apart so that's been going on throughout Earth's history so Pangaea is just the most recent assemblage of all the continents when they were together and if we move this up little bit 300 million years ago and I've included link to this really suggest that you take look enjoy it back it up run it forward so here we've got Pangaea here's North America here's Africa South America Antarctica India Australia Eurasia and as we move forward you'll see couple cool things India is going to break off and rush up just blow past blow past Africa and RAM into China we're about to see the opening of the North Atlantic so we're here we are about million years ago the Atlantic is opening up and now we've got Africa and South America breaking off from Australia Australia Australia and India and Antarctica 120 million years ago 110 million years ago so here you can see India and he's gonna break off here's Australia but yeah compare the speed of India to the speed of Africa to the speed of Australia it's like India really really has issues with China so now we're coming up on 60 million years ago so this is the this is the way earth looked about the time the dinosaurs got whacked here is where the impact would have occurred off the Yucatan Peninsula if we keep going got India about 40 million years ago or so is about when contact was made between the Indian plate and the Asian subcontinent now we have the up of the Himalayas which is going to expose limestone sedimentary rock as limestone weathers it absorbs carbon dioxide from the atmosphere that cooled the planet we think the massive exposure of the Tibetan Plateau beginning about 40 million years ago by 30 million years things were looking more recognisable there's some weird sea level things for example here this is this is dry land now well no it's ocean now but 10 million years ago it was dry land and we're gonna come up on the last ice age so at the last ice age this was dry land you could walk all the way out of Asia down into Indonesia you could walk from Australia to Papua New Guinea that was dry land you couldn't there was deep water channel that separated the two there was no was no English Channel you could walk from France to England so that brings us up to today here is some of the evidence that regular looked at he looked at the distribution of fossils so we've got freshwater reptile found across South America in Africa land reptile found across South American Africa another land reptile found across Africa India and Antarctica and then this tree fern or Glossop tourist fern found across Australia Antarctica India Africa and South America and the distribution of these doesn't make sense if you look at where the continents are today like how do you get freshwater reptile found in Africa in South America because they can't swim in salt water or they die well if you put the continents together in the shape that they were at when that animal was alive it was contiguous distribution it was all dry land so the continental margin fit this is the sea level margin if we were looking at the actual fit of the continents they would have fit much much better than this this is just the sea level fit not the actual continental margin fit based on the type of crust so figure had fossil evidence he had great fossil evidence he had paleoclimatic evidence so the white areas there's evidence of big ice sheets across Australia in India across Madagascar plates that are now tropical we've got ice sheets and we have places that used to be tropical swamps that are no longer tropical swamps they're not in the tropics parts of Europe parts of parts of North America where tropical swamps but they're no longer in the tropics but if you put the continents back to where they were when those rocks are being formed then you have tropical swamps in the tropics you've got glacial areas at the poles another diagram showing the distribution of glaciated areas in the past and if you put the continents together and then where those where those same glaciated areas are today so we have plates lithospheric plates made of crust and uppermost mantle floating on the asthenosphere the good stuff mostly happens at the boundaries between the plates where they're either getting pulled apart making new boundary or at the edges of two plates where they come together that's where you're gonna get earthquakes that's where you're gonna get mountains and volcanoes there's 14 plates we have an upwelling of magma from some places the plates spread out and then they sink at other places forming earthquakes volcanoes folding faulting warping of rocks here map of the different plates some of the plates like the Pacific plate are just oceanic crust some of them like the North American South American African and Eurasian plates our combination of continental and oceanic crust but they move as one big plate they move as one big plate they move as one big plate the arrows indicate the direction of movement of the plates so for example Africa is going up into Eurasia India is still crashing into China the Atlantic is getting bigger the Pacific is getting smaller so all the places would that look like cold fronts those are convergent boundaries where two plates are coming together in this case the Nazca plate is getting stuffed under South America melting and then making volcanoes here we have another cross-section showing the mantle the asthenosphere and then the lithosphere so here's the South American plate made up of continental and oceanic crust there's spreading Center spreading center of the mid-oceanic ridge where new materials coming up so the Atlantic is getting bigger the Pacific is getting smaller here we have subduction going on this is the thing Valley the thing that our valley in Iceland where it's actually the continent is actually getting ripped apart Iceland sits on top of one of these spreading centers and so it's actually getting getting pulled apart my god this map this this is the Marie Tharp map made by Marie Tharp in the 1960s this was another important evidence for plate tectonics that before this map existed scientists thought that the floor of the ocean would be totally smooth they knew that earth was old they knew that material had been washing off the continents for billions of years and so scientists figured that the ocean would have been filled up with dirt but oceanic crust is some of the youngest crust on the planet the oldest oceanic crust that we can find is about 280 million years old right here along the mid-oceanic ridge it's brand-new so that would be some of the youngest crust would be along the mid-oceanic ridge oceanic crust is still among the younger material on the planet the oldest that we've got think it's found in the Mediterranean about 280 million years old as opposed to the age of rocks the Canadian Shield is over three billion years old those rocks in Australia are 4 billion years old so we're talking 4000 million years as opposed to it's being formed this morning you can also see the great trenches great trenches great trenches where two plates are coming together so the Pacific all around the Pacific Ring of Fire because new materials coming up here earth isn't getting any bigger so for every centimeter of new material someplace else centimeter of material is gonna have to subducting melt just absolutely gorgeous gorgeous math this she was mansplain she had to do the math and prove to male scientist again and again and again that her analysis was in fact correct and it was just absolutely gorgeous cartography and scientifically incredibly important so this is showing just the red line those are the boundaries between two different plates so this is the North American plate the South American plate the Nazca plate here's the outlines of the plates themselves now we've got we're differentiating plate boundaries the yellow are convergent boundaries where two plates are coming together the red are where they're coming apart and the blue they're just grinding past each other horizontally this is the distribution volcanoes they back that up there you go so this is one of the things that geologists were thrilled about the volcanoes there's relationship between volcanoes and the plate tectonic boundaries for example convergent convergent convergent convergent convergent convergent convergent convergent convergent these are earthquakes again same deal earthquakes and plate boundaries the vast majority of the earthquakes are happening where two boundaries are coming into contact with each other either crushing into each other grinding past each other or getting pulled apart this is showing the ages of crust in 20 million year chunks so 0 to 20 20 to 40 40 to 60 60 to 80 20 40 60 80 100 120 million years old so the width tells you how fast that plate is moving like because this is the red is 0 to 20 you can see that right here the plates have moved lot farther apart than they have right here so by looking at the age of different different areas of crusts it'll tell us how fast the crust has been moving this is phenom website this is seismic Explorer I'm gonna recommend included link let's just open it up and see what happens so we can watch earthquakes in real time as they bubble along from 1980 to the present and there's all kinds of amazing amazing amazing things that we can look at because I'm hoping it's just going to stop so the colors indicate the depth how deep the earthquakes are so those red earthquakes are with long divergent plate boundaries where the plate boundaries are moving apart over here we have convergent boundary so what's happening is this plate in fact let's draw cross-section from here across here there yeah that'll work so we can actually see what we're seeing as descending plate this would be the Nazca plate getting subducted this would be the South American plate we can see that the earthquakes are steadily getting deeper and deeper and deeper and then they stop as they melt at some point the plates actually are melted and so there's no more earthquake there's no there's nothing to fight there's no resistance so those were earthquakes we can also take look at volcanoes because wish they had reset button for this but so we've got volcanoes volcanoes volcanoes and again at those plate boundaries so we've got plate boundary here with two plates colliding we've got volcanoes volcanoes volcanoes volcanoes here we've got Mount lassen Mount Shasta the Cascades mount st. Helens Mount Rainier Mount Baker Mount Cook all the way up into Alaska then from Alaska the Aleutians into the Kamchatka Peninsula down into Japan into the Marianas Trench the deepest part of the ocean the Philippines so again you can see convergent boundary in Indonesia and also some places at divergent boundaries so here in Africa this is the Rift Valley it's actually getting pulled apart creating this whole chain of volcanoes in Africa as Africa gets pulled apart so that was the seismic Explorer really really hope that do you that was the seismic Explorer really hope that you take the time to play around with that bit and enjoy it so let's look at the three types of plate boundaries we've got divergent boundaries where they're coming apart this would be along the mid-oceanic ridge Iceland is plopped right on top of one of these areas with divergent boundary seafloor spreading would be divergent boundary convergent boundaries are where the two plates are coming together so this was the way California looked about 80 to 120 million years ago with the Pacific plate subducting under the North American plate this is the way South America looks right now in fact that's just what we were looking at was cross-section of this showing where the earthquakes were on top there's volcanoes because the rock the plate melts and then bubbles up the Pacific plate would have been melting its way up through the North American plate so divergent convergent seafloor spreading all of the red areas with the baby crust this is another map of age of oceanic crust age of oceanic crust you can see the Pacific opening up quickly compared to the Atlantic subduction is when one plate when two plates come together one of them usually will sink the oceanic crust is more dense so the oceanic crust will sink or subduct oceanic crust has density of 3 grams per cubic centimeter continental crust has density of 2.7 grams per cubic centimeter so here we've got in fact we were just looking at the Aleutian trench the Aleutian trench with the Pacific plate subducting under the North American plate creating line of volcanoes line of volcanoes the Aleutian the Aleutian Islands are string of volcanoes being formed by subduction so plate motion is complex there's ridge push and slab pull I've included this video I'm not going to show it now would take minute go find the slides watch the video on plate tectonics it does much better job of explaining it that can but it's both there's new material coming up at the ridge pushing the plates apart but then the old slab because this is brand new this is going to be hotter and as it moves away and gets older it gets cooler and cooler and cooler as it gets cooler it becomes more dense and so it sinks and pulls the slab with it so the the slabs the plates are getting pushed apart at the ridges that are getting pulled down at the edges think mentioned before the in actions at divergent boundaries where they're being pulled apart or convergent where they're colliding or transformed when they're grinding past each other those are the three places that you really get things like earthquakes volcanoes mountain building so I've included some animations for you would click through take look at those what's the first one transform plate boundary okay here we've got transform boundary so you can't have transform boundary without divergent boundary so this is supposed to be along the mid-oceanic ridge here's the mid-oceanic ridge when you look at picture of the mid-oceanic ridge you'll notice that there's all these offset sections there's these cracks so if this was the ridge there's these cracks that run 90 degrees relative to the to the ridge so they're perpendicular to the ridge with these offsets and because new material is coming up here we've got new coming up there you go new material coming up new material coming up in this section they're just grinding past each other horizontally so that is the transform fault right there and it's caused again by the offsets along the divergent plate boundary so you can't have transform faults without divergent boundary so would take look at the transform plate boundary animation some good stuff in there three types of plates again divergent convergent and transform plate boundaries of the edges and here's what was talking about so this in fact right here is the offset this is the Mendocino triple Junction where the North American plate and the Juan de Fuca and the Pacific plate all come together but these these East yeah right left east-west running lines those are all transformed faults along the spreading Center earthquakes and volcanoes happening at plate boundaries subduction subducting plates melt and then bubble their way up through the other crust creating the Pacific Ring of Fire here we've got another diagram from the book showing distribution of earthquakes the little dots and volcanoes shown as the little triangles not all volcanoes take place at plate boundaries though some of them occur in the middle of the plate and those are called hotspots the best example of hotspot where you have an upwelling of mantle to the surface would be the Hawaiian Islands so the Big Island of Hawaii is the youngest parts of it are being formed as we speak and as you move off the hotspot they get older Maui about million Molokai about to Oahu about 3 million kawaii about 5 million some of the of the big Hawaiian Islands kawaii is the oldest at just over 5 million years old here you can see the Hawaiian seamount chain and the Emperor seamount chain the oldest the oldest mountains in the Emperor seamount chain are about 80 million years old these are about 40 million years old these are being formed this morning so you can see that the plate is moving in this direction the hotspot we think as stayed in the same place over time but the plate is moving on top of the hotspot here's diagram showing what's happening so the hotspot is stays in plate and the Pacific plate the lithosphere all the crusty stuff on top of the asthenosphere is getting moved along to the northwest ok let's talk about more plate tectonics plate tectonics can change the shape of the surface of the earth that's why we have mountains that's why you have valleys so stress affects rock by deforming it there's three types of stress there's tension which stresses rock which stretches Rock tension is pulling compression pushing shortens Rock and shear like the two blades of scissors when they shook when they slide past each other that's an example of shearing so here's the three types of the three types of stress we've got tension compression and shear stress those three types of stress will create earthquake faults three types of faults and we'll talk about those in minute rocks either bend or break deep warm rocks we were talking about this earlier like chocolate chip cookies warm cookies Bend cold cookies break it works the same way with rock shallow colder rocks are brittle deep warm rocks Bend they're ductile folding when two continents are coming together you can get folding the crust gets shorter and folded here's an example of folding this is from Humboldt thought this was really impressive because these rocks were bent more than 90 degrees and then when walked down the coast found that these rocks had been bent almost hundred and eighty degrees that this layer had been laid down horizontally and then folded back on itself this is laid down horizontally and then folded back just like closing book here's some more amazing Chevron folds from compression this is in Namibia and another example of folding another example of folding this one much sharper another example of folding think this is in Crete another example of folding some really impressive amazing folds alright let's talk about faulting so faulting leads to earthquakes there's three types of faults there's normal faults which you caused by tension reverse thought reverse faults caused by compression and then strike-slip or transform faults caused by shear stress so let's take look at these one of the fun things about earthquakes or faults rather is you if you know the stress is if you know that for example if you know that the rocks are getting pulled apart then you would expect to find normal faults and if you find normal faults that tells you that the rock is being pulled apart by tension so the side that hangs over is called hanging wall the other wall is called the footwall with tension the two sides get pulled apart and the hanging wall is actually going to drop down so if the hanging wall drops down that's normal for the hanging thing to drop down the hanging thing drops down that's normal that's normal fault caused by tension opposite of tension would be compression compression would make reverse fault or the hanging wall goes up so these two as they're compressed together the hanging wall is going to go up that's reverse fault so here again we have normal fault with the hanging wall dropped down caused by tension here is reverse fault or they've been shoved together this layer of rock and this layer of rock would have been at the same level but you can see this rock as they've come together has been shoved up don't know it was out 20 40 feet and then strike-slip is when they're just grinding past each other horizontally such as the San Andreas Fault nobody's going up nobody's going down this is right lateral fault so if you were standing here you can see that those rocks used to be over here but they've moved to the right so if was here I'd look over here and say those have moved to my right that's right lateral fault it's exactly the sort of fault so if this was if we were in San Francisco looking over at Oakland Oakland is moving to our right the San Andreas Fault is right lateral strike-slip fault let's review I'm gonna show you some pictures and you can try to guess what type of fault this is so this would be the hanging wall that would be the football this is the hanging wall this is the football so this has dropped down the hanging wall has dropped down caused by tension so that would be normal fault you can see this layer of rock used to be at the same level as that but it's gone up which is the reverse of normal so that's reverse fault caused by compression this is in Death Valley these are micro faults they are normal faults the hanging wall has dropped down so hanging wall on this side foot' wall hanging wall foot wall foot wall hanging wall here's the fault itself this side has dropped down this is the hanging wall the hanging wall has dropped down so it's another normal fault this is another normal fault although you can see all kinds of other things sedimentary rocks are laid down horizontally so there's been all kinds of tectonic activity because you can see there's this layer that layer that layer that layer those are all different layers of that layer that layer those rocks would have all been horizontal when they were formed and now they've been tipped up and also broken little tiny thrust fault there's the the fault itself you can see this layer has gone up relative to that area clear clearly there was more rock here back in the day but it's gone now enough about faulting let's look at applied faulting and earthquakes so with earthquake faults the faults the plates don't slide they get stuck but the pressure builds and builds until something breaks and then they slip and grind and make an earthquake and get stuck and the pressure builds until it breaks the rock so that sharp release of energy results in seismic wave an earthquake the theory that explains how rocks move is called the elastic rebound theory we'll take look at that we'll take look at that right now I've included another handy dandy link to the elastic rebound theory so at the rebound theory it's pretty straightforward that the plates move and as the plates move they will gradually deform and Bend that the rocks will deform under stress as the stress sorry about that the rocks will deform under stress the stress will build and build and build until the rocks break there's movement and then the rocks snap back to their original shape that's the elastic part so elastic is physics term for substance that deforms under stress and returns to its original shape when the stress is relieved so when there's stress on the rock it bends when that stress is relieved it snaps back into its original shape so here's some some animations to watch about the the elastic rebound theory and how that works some key words the epicenter you've all heard that that's where the earthquake is at the surface or rather the epicenters the location at the surface directly above the focus which is the subsurface location that the earthquake actually happened at so the place where the earthquake happens is the focus at the surface is the epicenter you can remember that epidermis is your skin the epicenter is on Earth's epidermis on the surface so we've got fault we've got the focus is where it happens underground the epicenter is at the surface and then if there's visible expression of the fault that's called fault scarp focus aftershocks and foreshocks so if you when you have an earthquake it's going to remove stress from part of the system but then as the stress gets moved around it could accumulate someplace else that could create another earthquake and that would be an aftershock so graphs are used to record the vibrations so this is an actual seismogram of an earthquake there are three scales that we're going to use to measure earthquakes each is going to measure something entirely different so the modified Mercalli scale measures damage the Richter scale measures the size of the seismic waves the Richter scale was the first scientific scale that allowed scientists to compare different earthquakes and that was huge for the first time ever scientists could compare how much energy was involved with earthquakes that happened in different places at different times the most modern scale is the moment magnitude scale that actually measures the energy released in the earthquake the Richter scale measures the size of the wave so all you need is seismometer to record them and then you measure how high the waves are that tells you what it is on the Richter scale the moment magnitude scale you actually need to go out look at the ground and see how far things moved see how strong the rock was in order to figure out the moment magnitude scale was so the modified Mercalli just measures damage it uses Roman numerals going from 1 to 12 insurance companies use it measures from 1 to 12 insurance companies use it it's not scientific at all it's just how much damage was done the Richter scale was developed by Charles Richter of Caltech it was the first quantitative scale that allowed scientists to compare how big an earthquake was to another earthquake it is logarithmic so every whole number increase going from 1 to 2 means that the waves were ten times as big and it means that 32 times more energy was released by that earthquake going from magnitude 1 to magnitude 3 the waves would be hundred times higher and it would result in 32 times 32 times 32 thousand times more energy being released Barb's are 32 times 32 moment magnitude scale is more accurate at measuring large earthquakes it measures the energy released by the earthquake you have to go out and look at how far the fault slipped house how large the surface area was where the fault was slipping larger surface area would require more energy to move and how strong was the rock because what happens ultimately is the strength of the rock is overcome by the stress of the fault movement so the stronger the rock the more energy it would take to break it the advantage of this is that you can compare more accurately similar large earthquakes and you can also look at earthquakes that happened before there were seismometers so because you actually have to go out and look at the fault and do some surveying you can use it to figure out how big earthquakes were in the past when nobody was even around it's also logarithmic the numbers on the moment magnitude scale are very very close to the numbers on the Richter scale earthquakes are impossible to predict in the short-term and the long-term it's easy there's hundred percent chance there's going to be an earthquake on the San Andreas Fault the next hundred years when that's going to happen we can't really say nobody's been able to do it use paleo seismology is the term for looking at the history of plate boundaries in the history of earthquakes there are obvious seismic risk zones based on plate tectonics so convergent boundaries in fact it's going to be the convergent boundaries they're going to have the largest earthquakes so the earthquake in Nepal the earthquake in Chile earthquake in Alaska those are some of the largest earthquakes ever recorded those are all at convergent boundaries the num people killed in an earthquake depends on the size of the earthquake the time of day and what people's houses are made out of so in California we have Building Code the Building Code takes into account earthquakes so in California you have to build your house in order to withstand earthquakes in other countries especially countries developing countries where people have houses made of mud bricks they tend to be crushed when the earthquake hits the walls have no resistance to getting shoved over sideways so the entire building collapses some examples of big earthquakes the Haiti earthquake in 2010 killed 300,000 people the Tang Shen earthquake in in China killed around quarter of million people were not exactly sure how many were killed Sumatra the earthquake there or rather the tsunami was responsible for killing the vast majority of those people the black our magnitude 9 earthquake and they are all thrust quakes where one plate is sliding horizontally under another sliding horizontally sliding horizontally sliding horizontally sliding horizontally the largest earthquakes are at convergent boundaries where there's predominantly horizontal movement of the crust these are megathrust earthquakes so Japan Indonesia Chile Alaska and the Paul so the the difference between reverse thrust or reverse fault and thrust fault is the thrust fault the movement is monly is more horizontal but the reverse fault the movement is more vertical if the movement is more horizontal like the Indian plate getting shoved more horizontally that's thrust fault again another another diagram showing the thrust fault with the Indian continent getting shoved under the asian continent the plates get stuck the pressure builds eventually they rip loose and then you get an earthquake Japan fell 12 earthquake there was massive tsunami destroyed the Fukushima nuclear power plant the 1989 magnitude six point nine earthquake and Loma Prieta that stops the World Series was six point nine magnitude earthquake and did not whole lot of damage it destroyed clearly the nimitz bridge or the nimitz section of the freeway but compared to other places that have had similar earthquakes very few people were actually killed or injured because of our building codes enough about earthquakes let's talk about volcanoes so globally about 1,300 volcanoes 600 of those are active which means that they have erupted in the last 10,000 years most of the volcanoes are under the ocean so we don't notice them they are found at convergent boundaries at subduction zones because you have crust getting subducted melting then bubbling back up you can divide them into explosive and effusive so the location just like real estate the location is going to determine how that volcano behaves so convergent boundaries and subduction zones you get explosive volcanoes spreading centers and hot spots you get effusive flowing volcanoes hot spots you also get effusive flowing volcanoes this is why people go to Hawaii to look at erupting volcanoes those are the hot spot volcanoes or seafloor spreading effusive volcanoes they're relatively safe they do not explode typically as opposed to Cascadian volcanoes they just explode so Mount st. Helens example of Cascadian volcano when it erupts it just explodes without warning often we have general idea when it's gonna erupt but the exact timing is is always always exciting so let's look at different places that you could have volcanic activity subduction zone explosive subjection zone explosive rifting where the crust is getting pulled apart for example those pick of Africa the Rift Valley in Africa effusive getting pulled apart this was volcanic activity much of the Pacific Northwest the Columbia flood basalts we'll look at those in minute they'll say yeah the flood basalts the crust was getting pulled apart and you get basalt coming up crust getting pulled apart you get basalt effusive effusive effusive hotspot effusive convergence explosive convergence explosive so just like just like real estate the type of activity is going to depend on the location so low viscosity very fluid magma made of basalt as opposed to the high viscosity the slow moving the thick the explosive magma that's gonna be like granite so continental crust like granite it's going to explode low viscosity basalt that's just going to lose it's going to flow like motor oil effusive eruptions are relatively gentle low viscosity very fluid magma making very flat boring earthquakes I'm sorry very flat very boring volcanoes you get shield volcanoes like all of the Hawaiian Islands are shield volcanoes they're very very flat because the lava is so fluid you can also get cinder cones on the sides of shield volcanoes we'll look at some pictures of that so let's take look at an erupting Hawaiian volcano there you go so as the magma gets close to the surface here's really weird idea magma contains dissolved gases and as the magma approaches the surface those gases bubble out of the magma so if the magma is very fluid if the lava is fluid like here in Hawaii you get lava fountains as the gas bubbles up through it makes these amazing lava fountains but because the lava is so fluid the gas just bubbles away harmlessly the same gas if it was in Cascadian volcano the pressure would build and build and build and build until it just explodes without warning we'll have some more fluid yeah Hawaiian volcanoes are amazing there's lot of put some Hawaiian volcano videos in the playlist for the tectonic section so those are fluid let's look at explosive eruptions you get really steep in fact Mount Fuji Mount st. Helens not Baker Mount Cook Mount Rainier all the classic volcano mountains you look at it and go yeah that's volcano it's probably composite or stratovolcano less lava but pyroclastic that's vocabulary term pyro means fire clastic broken up so it's ash dust cinders scoria pumice aerial bombs the material that is ejected violently during one of these explosive eruptions pirate clastic flow I'm not going to play this video really recommend watching it this is Maurice and Katia craft they were French volcanologists it was their dream to canoe down an active lava flow in canoe they were killed by one of these pyroclastic flows up yeah pyro refers to fire clastic broken up so it's material that's broken up are hanging out right by an erupting volcano and ironically they were killed in the Philippines Mount Unzen yeah they were nuts here is if died tomorrow that would be sad but it's okay because I'm happy so pyroclastic flow also called stone wind that one of my favorite terms is new AR dome which is French for glowing cloud so if this was nighttime in that cloud it could be 300 400 500 degrees traveling 200 miles an hour so it just looks like cloud of dust but that's superheated gas and ash and at night it would glow so new AR daunt means glowing cloud and it refers to the idea that if you saw it at night the gas and the rock would be so hot that it would actually be glowing Maurice and Katja were killed in this pyroclastic flow and in the video they point out ironically they were in place 41 people were killed at the same time and they were all in an area that they all thought they were all volcano experts and they were in region that they thought would be safe so it's it's ironic that they were killed while they were trying to be safe this is Mount Saint Helens Mount st. Helens think is the best example of the difference between the Hawaiian and the Hawaiian effusive eruptions and the explosive eruptions associated with continental crust so that's Mount st. Helens today all of that is gone but in 1980 1980 scientists were studying the mountain that's after the eruption this guy went out to take some pictures of it just before it erupted volcanic eruptions are easier to predict because you have to move magma to the surface when you move magma to the surface the mountain swells up they were studying the deformation they knew something was happening so they had people in place watching it and the first thing that happens is there's going to be big landslide the whole side of the mountain is just going to slip away and when that slips away enough the pressure inside that has been building is gonna blast out sideways and massive pyroclastic flow so there's the whole the whole mountain collapsing and then you'll see as it as it collapses this guy's still talking it erupts out sideways and obliterates everything woosh pyroclastic flow the most dangerous part of volcanic eruption and this is volcanic glass it's it's incredibly sharp this is what damages lungs volcanic glass is not ash from fires ashram fires is relatively soft this is these are micro particles of glass and you can see they're very very sharp this is why it causes lung damage so just like with real estate mentioned the shape cross-section this is stratovolcano it's got that steeper side formed of multiple layers of lava and ash as opposed to shield volcano formed with an effusive eruption very flat very boring in fact this is cinder cone this is the slope of the shield volcano very common to get cinder cones on so there could be cinder cone there little cinder cone there cinder cones are relatively small volcanoes these strata volcanoes are huge shield volcanoes are even larger these are two different forms of basaltic lava this would be this is pahoehoe if it's flowing and it comes to rest and then it cools it often has this smooth ropey appearance if as the lava is cooling it's still moving so it gets broken up you get this sharp angular broken up material called more pahoehoe rhyolitic lava making bread crust structure bread crust texture as it contract as it cools the Rift Valley in Iceland where it's getting pulled apart there's river flowing down so there's rifting it's getting stretched apart to the to the right on that side to the left on this side these are the Columbia River basalts said before when we were looking at the figure showing the locations of volcanic activity yeah I'll say there was rifting like the Columbia River basalts this is all basaltic magma effusive flowing over the landscape like motor oil this is Mount Hood Mount Hood is stratovolcano caused by convergence it is an explosive eruption it will done blow up when it erupts this is basalt very fluid effusive caused by rifting so two volcanoes in the same place or relatively close together formed out of totally different magma under totally different tectonic circumstances creating totally different volcanic landforms so the flood basalts they're just flat and the composite volcano very steep composite volcano made of lava tephra is that broken up material they are the largest they are tall they are steep Pompeii Mount Fuji Mount Saint Helens Mount Shasta they make explosive eruptions here we have Mount Fuji made of multiple multiple eruptions of lava and ash and lava and ash hazards of the composite the pyroclastic flow we've already talked about that in the context of Mount st. Helens high density mixture of hot dry rock hot gases if it's night time it'll be glowing you can travel 100 miles an hour believe this is screen grab from Mount Evans and found that someplace else pyroclastic flow lahar is volcanic mudflow so there's couple of different ways you can get lahar you could have an eruption of the tropics with lots of ash followed by heavy rain event that would give you mud flow you could also have it in the Cascades Mount lassen when it erupted in 1917 the eruption melted the snow and the ice on the mountain so the lava mixed together with the snow and ice to become volcano mudflow lahar it's an Indonesian word for volcanic mudflow lahar we saw one of these on day one looking at geovisualization here we have how long you can live from laughter think this was Mount Ranier after Mount Ranier erupts you'll have 10 minutes 15 minutes 20 minutes before the mud flow or lahar hits shield volcanoes are very wide very boring they're flat flat flat made of basaltic lava usually don't explode shield volcanoes are incredibly flat they are by volume some of the largest but they're very flat shield volcanoes flat cinder cones are small Sunset Crater there's bunch of lassen they're made of basaltic lava they don't explode frothy basalt has ejected lands close to the vent this would be cinder cone it could be on the on the side of shield volcano plug dome small to medium sized Lassen Peak is one of the world's largest if not the largest plug dome volcano they are made of very very stiff felsic felsic iron and silica lots of silicon lots of said the higher the silicon the more explosive they are so in this case the lava oozed out like toothpaste incredibly thick so whatever gases were trapped they are not going anyplace because they're trapped by the lava being so thick so it yeah let's just look at it this is Mount lassen you can see that there's core of solid rock and then the sides are just broken up material so they're often made up of core of material with broken up broken up pyroclastic material on the sides this is Mount Mount lassen when it erupted in 1915 this was think taken in reading or red bluff you can see although you can see the mushroom cloud from the eruption from Sen from Sacramento back in 1915 when Mount lassen erupted Caldera it's just crater at the top of many volcanoes it can either be formed if the magma chamber drains out before it erupts you can end up with caldera or if the top is blown off then you can end up with caldera crater lake is caldera well la caldera is caldera and La Paz so here we've got side view of maan Aloha which is shield volcano very very large very very flat as opposed to Mount Ranier which is steeper more dramatic but you can see the volume of Mount Ranier way way less than maan Aloha and here again is side view of shield volcano and you can just see how incredibly flat they are as opposed to composite think this is about shishkin in the chunk at come chat kapin insula in russia made of multiple flows of ash and lava this is the cinder cone in lassen and this is the shield volcano this is called prospect peak right here so you can see the slope of the shield volcano and then on the side there's this little cinder cone there's the cinder cone there's the slope of the shield volcano this is Mount lassen taken from the summit of the shield I'm sorry from the cinder cone this is the cinder cone this is Mount lassen Lassen's plug dome and this is prospect peak which is big shield volcano and lassen is unique in that shield volcanoes are associated with effusive eruptions and divergent boundaries the crust is actually getting pulled apart in this region but over here there's in fact towards the coast there's subduction with the Juan de Fuca plate getting stuffed under the North American plate bubbling to the top and making volcanoes so here's Mount lassen the world's largest plug Don volcano very very steep sides here is shield volcano much more gradual gentle slope Mount lassen some sort of shield volcano this is why people go play with shield volcanoes that basaltic lava it doesn't explode you can go play with it this is Cody Gibson former student out on the Island of Hawaii playing with an active lava flow composite volcano volcanic hazards are not as bad as as earthquake hazards although if volcano erupts the effects could be much worse because we have warning in fact if just get to the picture yeah so in order for the volcano to erupt you need new moot you need to move magma to the surface and when that happens the shape of the mountain it's going to swell up so by studying the deformation of the ground we know what's going on also is that magma moves towards the surface you get earthquakes called harmonic tremors that they can pick up with seismometers as the magma approaches the surface gas bubbles out and we can measure that so there's many different ways of monitoring volcanoes to make sure that they don't surprise us with interruption so volcanoes are one type of mountain but let's look at episodes of mountain building episodes of mountain building are called Oro Genesis Oro mountain genesis birth and we're pretty much gonna focus on convergent tectonic boundaries so there's three types of convergent boundaries because there's two types of crust you've got oceanic crust and continental crust the three combinations of those two things are oceanic continental oceanic oceanic and then continental continental each of these three types of boundary is going to produce distinct landscape with cool name so the first one this is an oceanic continental boundary this is called an Andean boundary named after the Andes Mountains so you've got oceanic crust getting stuffed under continental crust making chain of volcanoes this is an Andean boundary oceanic crust subducting with continental the oceanic crust is going to get stuffed under Japanese boundary you typically end up with an island arc or chain of volcanoes one or both of the oceanic crust is going to subduct in this case just the oceanic crust this again is Japanese boundary this is the way the Japanese islands are being formed many of the islands that when we were looking at the seismic Explorer the Aleutians those are all formed by this type of convergence so oceanic oceanic Japanese boundary and you typically get big chain of volcanoes and then finally continental continental crust creates himalayan boundary so there's no subduction because both of the crusts are continental so nobody goes down the crust gets shorter and thicker making for example the Himalayas you can also make men's you can also make mountains by faulting so either by pushing plates together or by pulling plates apart so by pulling plates apart with tension you get normal faults and those create down dropped fault blocks that landscape is made up of horst's and robins I'll just look at the diagram so here we have whole series of normal faults this area is getting pulled apart the Drowned dropped fault block is whole is Grob would remember that technique or tip may be grabbin like grave is the down dropped part the high part is the Horst Horst Robin Horst Robin Horst is the high part Robin is the trench Horst is the high part this is Death Valley death valley is big down dropped Robin we're on horse on the other side is another Horst another diagram is showing the same thing with Ag Robin Horst Robin Horst Robin the Red Sea is down dropped fault block so this all of these Horst and Robin found across the American Southwest across California and Nevada those are examples of normal faults caused by tension here is showing how this occurs and an amazing photograph in Iran of landscape that looks exactly like the diagram you almost never see that so down drop fault block caused by tension the crust being pulled apart and then this is dropping down hanging wall football the hanging walls dropped down relative to the football this is my old Subaru this is taken at the base of Mount Whitney on the east side of the Sierras so in 1872 the ground here was up here there was magnitude 6 earthquake that resulted and the ground dropped down as the crust was pulled apart so this would be fault scarp the 1872 Lone Pine fault scarp this is this is saline Valley over here is telescope peak on the other side is Death Valley so now we're in Death Valley looking back at telescope peak down dropped fault block Robin and turned around to take picture of these wildflowers and didn't realize until looked at on computer that got this fault scarp so you can see the foreground has dropped down relative to the background making this cliff that's fault scarp this would be normal fault caused by tension that's it for this incredibly long chapter this will be the last chapter that's going to be on the 3rd midterm that's it for today's lesson if you have any questions please let me know see you next chapter