hello there and welcome to this revision session which is on eq1 of the tectonic processes and Hazards topic so eq1 says why are some locations more at risk from tectonic hazards and that's the aim of the next 30 minutes or so of this session a reminder to use the booklet that you've been given along with this session to help you review eq1 and the reminder that this is not detailed enough to replace all of the lesson learning you've done this is just an overview of the eqs in this topic one thing to say before we move on is that you've also got to remember that tectonics and pro and Hazards as a topic overall is actually only worth 16 marks of your entire AEV course a very very large topic to learn but actually you're not as a lot on it it's one of the smallest sections so you need to just have a good overview of knowledge of this topic so that you can apply and choose some different case studies that you might use for the questions that you might be asked the first part of eq1 is looking at where the volcanoes earthquakes and tsunamis happen in the world and to start that we need to know what a tectonic Hazard is so a tectonic Hazard is anything that threats human life or infrastructure because of the processes of plate boundaries and the movement of them and so we've got a number of General Factor about the distribution and general key terms to understand so it's useful to remember that most earthquakes occur on our app plate boundaries and the most powerful ones are at conservative plate boundaries the ocean fracture zone or ofz for short is earthquake activity along mid ocean ridges so for example in the Mid-Atlantic Ridge we that is the ocean fraction Zone and we have smaller earthquake activity alone there and then we also have a continental fracture zone or a cfz and that's earthquake activity along mountain ranges the Pacific Ring of Fire which is famous for being a ring of fire a ring of volcanoes under Quakes around the Pacific Ocean is a very active area tectonically for those volcanoes and earthquakes but earthquakes can also occur int plate which is inside the plate boundaries so not on the margins themselves and volcanoes occur in constructive and destructive margins where there is an opportunity for magma to rise from mantle so just a bit more detail on some of those the in plate earthquakes that were mentioned earlier these are earthquakes as we said that occur inside plate margins and that's because of the stresses and pressures that the rock deep under earth goes through during the movement of the plate boundary so doesn't always have to be on the plate margins and these earthquakes are usually weaker earthquakes because there is no margin involved so these earthquakes can happen in places like the UK and the UK gets lots and lots of earthquakes each year that are so small we don't actually notice them at all we also have something else that's int plate and that is volcanic hotspots and these are essentially inside the plate boundary as well and they happen because of a fla fracture in the crust where there's a magma plume a chamber of magma underneath that's Rising through the crust and this is what's actually created Islands such as Hawaii and Iceland over time remember with this the magma plume itself the magma chamber underneath the cross doesn't move but the plates still move and that's why Hawaii for example is in an island AR so is the Philippines it's because the actual plates above it still move they move the land with it but magma plume itself stays stationary now we're going to go through the margins really briefly and just have a brief outline of what each margin looks like so we're going to start with constructive margins now constructive margins as you can see from the diagram here move apart allowing a volcano to come up through the center of that Movement Like a mid ocean ridge two types so you can have Oceanic and oceanic plates moving apart or you can have continental and continental plates so when ocean and oceanic move apart we get magma rising to the surface they're normally basaltic um which means they're from bassal um normally they're quite small they're quite gentle they don't cause um severe damage normally whereas continental and Continental um constructive plates again move apart and these cause again small earthquakes and also small volcanoes key thing to remember is that the mantle convection the convection currents in the mantle cause the plates to move apart a crack or a fracture Zone opens up that might be an ocean fracture zone or a continental fraction Zone and the eruptions are usually effusive which means that they're usually not damaging they usually quite gentle and small and there is a low gas content there's no real gas that comes out of these volcanoes but there is a high viscosity of the magma we've then got destructive margins now destructive margins can come in three forms it can be again Oceanic Oceanic or Continental Continental but it can also be Oceanic and continental and oceanic and Continental is the one you probably know most about and that's what's shown here in the diagram on the right so an ocean iic plate is subducted under the continental plate and the reason for that is because the oceanic plate is more dense it's heavier so it is subducted underneath the continental plate this forms mountain ranges it forms large earthquakes and violent eruptions of volcanoes so this is the most dangerous type of plate for all types of different hazards that are tectonic so again it's the mantle convection that holds the plates towards each creates the subduction zone the dener plate which is the oceanic plate subduct and that leads to friction and melting happening of that oceanic plate as you can see in the diagram here that's what creates our magma for our volcano as well but we also have as I mentioned earlier Oceanic to Oceanic margins and one of these will be subducted under the other depending on which is more dense that generates frequent earthquakes it can also create a chain of volcanic islands like in Alaska there but we also have as we mentioned Continental to Continental and when you have the two continental land masses colliding that create our fold mountain belts eruptions are possible here but as the magma cools and Sol beneath the surface they are rare So eruptions are possible and we get infrequent major earthquakes at these Continental to continental plate boundaries and then we have conservative margins these ones are the simplest of all of the margins this is when you have two plates moving side by side as you can see in this diagram now they can be moving in the same direction as they are in this diagram or they move in opposite directions and they move at different speeds a great example of this is the salandreas fault line which is a 1200 kilometer fault line along the coast of California these are only Oceanic and Continental okay so they don't have two oceanic or two continental so they are only Oceanic and Continental boundaries so the plates slide past each other there's frequent earthquakes some of them are very large and very destructive the focal depth where the focus is is usually quite shallow so not very deep and there is no volcanic activity created at a conservative Mar to understand convection currents and to understand why this all happens we need to talk about the Earth structure so you can see a diagram on the right hand side here of the earth structure that you would have used in lessons the the a structure is made up of a number of different layers so we've got starting from the crust the crust is around 0 to 100 kmers thick and that's our continental and oceanic layer that is the part of the world we live on we've then got the lithosphere just underneath that and that's in the upper crust and the upper part of the mantle we've then got the asthenosphere which as you can see in the diagram is actually in the mantle and this is where we have the convection currents so in the asthenosphere is where the convection currents happen and that pushes the plates apart towards each other and side by side we then have the mantle which is the molten rock layer with high temperatures and a slow flow so there is a slow moving process of convection cents taking place in the mantle we then have the outer core and that's liquid it's made up of irons and nickels and we've got the inner core as well which is solid and made up of irons and nickels and it's about 65,000 km to get to the very center of core now mantle convection or convection current are essentially what makes the plates of the world move these are what generates the Heat this is what actually puts pressure on the crust to make that all of the different parts of the crust like jigsaw move around the earth and this is what happens to create our very dangerous in some cases plate boundary tectonic events so we have the constructive destructive and conservative margins moving as a result of these convection points essentially it's the internal heat engine of the world now we must consider some of the key disc discoveries and Frameworks or knowledge theory in which we have prove and to back up the ideas of plate boundaries and how earthquakes volcanoes and tsunamis happen I've got a number of key discoveries first so the Alfred venner's theory of continental drift from 1912 is a theory that says all of the continents were actually one large supercontinent called Pangia but today they have moved apart because of these convection we've also got the idea of convection currents by Arthur Holmes in the 1930s said The Mantel convection was the driving force and that's what moved tectonic plates we've also got Harry Hess in the 1960s who created the theory of plate spreading D Flor spreading and mid ocean ridg is being created and we've also got the paleomagnetism theory the paleomagnetism theory is about the Earth's magnetic field of the North and South Pole and how that creates patterns on the world's sea floor when the sea Flo spread to show that magnetism exists and to show that the seaf Flor does spread over time and so we've also got then the three ideas of subduction gravitational sliding and slab pull so the idea of subduction has been mentioned already whereby one plate which is more dense and heavy subducts or sinks under the lighter continental plate usually these create earthquakes and usually the depths of those earthquakes are between 10 and 400 kilometers on the subduction and they occur at destructive margins mainly where the oceanic plate deds on we've then got the idea of gravitational sliding now gravitational sliding occurs at constructive margins that move apart and so Rising heat from the magma under those constructive margins creates a slight slope between those plates and that is where we have naturally the slide of the plates so there is a gap that opens up between those two plates and finally we've got slab pole this is where we have Co the cold dense oceanic plate which subducts underneath the continental plate and the density of the oceanic plate pulls itself into the mantle so this is about the continental plate being lighter so it stays above floating on the convection currents whereas the oceanic plate which is much heavier more dense colder and it's sub it subducts itself into the mantle it's pulled into the mantle and that is what's known as slab form Okay so a round up then of the plate boundaries the activities that occur there the types of Hazards and an example of each of them so let's take them all individually that a constructive plate margin these are the ones that move apart we generally get shallow volcanoes sorry earthquakes that are less than 60 kilometers deep we generally also get low magnitude ones so the under five magnitude in strength which means that actually they're not very damaging these types of the volcanoes that are constructive margin are generally also small low they have a very low gas content so they're not explosive and they have high viscosity and an example of a constructive Marin there is the Mid-Atlantic Bridge mid ocean ridge between the Eurasian and North American PL so the next one is a destructive Marin and this time it's Oceanic and Continental okay so ocean and continent now these plates move towards each other and these create very large earthquakes they can be up to nine magnitude on the rcope as we seen earlier we get a friction Zone and pressure building up along where the oceanic plate abduct under the continental plate in terms of volcanoes we get frequent and violent eruptions from these they're usually composite volcano so they're the tall mountainous volcanos and usually they're quite explosive because of the high gas and silica cont within the magma an example of this is the nasca and South American plate boundary and that created the Chile 2010 earthquake another destructive margin think about is an oceanic and oceanic one this is where two oceanic plates are moving towards each other and these create frequent earthquakes but they're not as large as the oceanic and Continental destructive plate margins they're not as large as those we also get violent eruptions of volcanoes from an oceanic and oceanic PL margin going towards each other and it also creates a curve of volcanic islands such as Hawaii and we can use for example a 2018 Hawaii earthquake and more or lower of 1984 eruption as examples of these Oceanic and oceanic margins we then have a collisional plate margin which is continent and continent remember collisional plate margins are destructive margins but we can give them the name Collision this is where two continents move towards each other this generally creates large fault lines which are quite shallow and we have high magnitude earthquakes from these these plate boundaries do not have volcanic eruptions so these two land masses do not create volcanics just earthquakes the Andes in South America is a great example of a continental continent Collision boundary and it has had a recent earthquake of 4.9 magnitude in 24 and finally we have our conservative margins now remember conservative margins slide slide by each other in the same direction or in opposite directions and these create the largest types of earthquakes so we get high magnitude earthquakes we have a very shallow focal depth so the focus is not very deep and they are very structive to very disruptive to the environment and buildings Etc we do not get any volcanic eruptions at a conservative plate margin and an example of these would be the Pacific and North American plates which create the San Andrea's fault and in 1989 we had a near seven magnitude earthquake there and there is another one due anytime soon so now we need to look at the hazards that earthquakes actually creates so the earthquake is the hazard itself but that creates secondary hazards as well okay so what really creates the hazards and what really makes earthquakes so dangerous are the seismic waves that they create so there are a number of types of waves first of all there are primary waves or paves now these are the fastest types of seismic waves they cause the least damage or the least destructive because they have less energy and they basically cause land to compress because of the vibrations they emit they usually come first because they're the fastest type then when we have an earthquake event we have secondary waves or S waves and these these arrive straight after the pwes and these shake the ground violently and these are the ones that cause damage on the landscape so they travel slightly slower than p waves and finally we have L waves or love waves now these arrive last they travel the slowest and they only travel horizontally on the surface of the Earth but they cause significant damage including what's called crustal fracturing which is the fracturing of the crust so these travel horizontally they cause significant damage as do s waves and they cause visible scouring to the crust on the landscape let's go through some of the hazards that earthquakes cause and we've just mentioned crustal fracturing and this is a primary hazard from the earthquake so this happens because of the earthquake itself immediately so what we see is a bookling or fracturing of the Earth's surface cracks developing in the Earth's surface and this is happens particularly at large earthquake zones such as in the Indian Ocean in 2004 which was one of your case studies and that created a 1,000 kilometer fault line underneath the Indian Ocean so a very large Crystal fracturing that took place there we can also have liquifaction which is a secondary Hazard to the earthquake so this happens after the P ands waves and L waves take place and it happens where there may be a water logged ground surface and what happens is the earthquake waves loosens the soil under the ground surface and it causes the water to rise on the surface and comes through the cracks that have been created by Crystal fracturing and this causes significant damage to foundations of buildings it causes buildings to sink or subside and tilt and they can often collapse too and finally another secondary Hazard that earthquakes can create are landslides remember earthquakes loosen soil okay because of those PSN a waves the soil loosen loosens and dislodges so the geology is affected of a particular area and on mountain and hillsides that causes the sediment to become loose and to fall downhill and a good example of this was your sran 2008 case study where 30% of all of the deaths in that earthquake event were actually caused by the secondary Landslide going to look at the same again now so the hazards caused by this time volcanoes and volcanic activity we've got a number of them here and I've separated them into P or s p for primary and S for secondary and I'm just going to go through a list of what each of them are first of all we have pyroplastic flow this is a primary Hazard and these are very large dense hot and Ash and gas clouds with temperatures of up to 600 Degrees that flow down the side of a mountain or Hillside very very fast they can be 350 or 400 miles per hour in speed these are very destructive they are caused by the buildup of the pressure of gas and Ash another primary Hazard created by volcanoes is ashall itself so this is where ash particles which are thrown into the air fall back down onto the landscape and they can kill vegetation they can collapse buildings over time if there's if there's enough Ash and there's enough weight for it they poison water sources and that's another way in which volcanoes create a primary Hazard another primary Hazard is the lava flow from an earthquake of volcano itself so what we can get is extensive areas covered by lava flow the lava can solidify as well and create Rock so these lava flows can extend for several kilometers it can flow up to 40 kilom an hour and of course it destroys it's very destructive so it destroys anything within its path and the final primary Hazard caused by an earth a volcano is gas eruptions so the gases that are released into the atmosphere which is carbon dioxide and sulfur dioxide Etc pois can poison people and get into their lungs and poison people also animals in extreme cases as well so this can be very dangerous for human life and of course remember there is also the case that over time this can lead to climate change and adds to the greenhouse gases in the atmosphere as well so we've got two secondary hazards caused by volcanoes the first one is Lars now lahars are very simply volcanic mud flows so a lot like landslides only that they're volcanic so rainfall can actually mobilize the volcanic ash that's fallen and settled if the volcanic ash becomes very wet it becomes like a mud-like consistency and that can flow down the side of a mountain side at high speed into river systems towards towns and cities and create major destruction just like flooding wood and then we have finally jalops now these are also secondary hazards caused by volcanoes and they are essentially flooding that's caused by a volcanic eruption beneath a glacier or an ice cap melting that Glacier creating huge volumes of melt water and a good example of this is in Iceland on the catla or AFU um volcanoes where there is ice formed on the tops of those volcanoes on the craters and that in 201 in Iceland for example caused major flooding problems to the rural communities of I so they are all of the hazards created by a volcanic eruption both primary and secondary hazards one of the final things to look at here then is tsunamis and what causes tsunamis and what are their characteristics so tsunamis can be generated by a number of things they can be generated by what are called submarine earthquakes at subduction zones so they are earthquakes under the ocean but they can also be caused by volcanic eruptions on volcanic islands and also landslides and the most common types of tsunamis are caused by submarine earthquakes okay so what happens is if you have a submarine earthquake or an earthquake under the sea that disrupts The seabed Rock so it jolts the movement of rock underneath sea it's a violent movement which then usually has a domino effect if you think about bath water or a lake if you throw a rock into it that removes all of the water violently to the surrounding areas okay so you see that ripple effect and that is exactly what a tsunami is this basically creates a distinctive kind of Bulge of water that starts moving towards coastlines they're actually quite hard to see out at Sea in the open ocean because what happens is they move towards the shore they slow dramatically the wave length drops but the actual height of the wave increases because it can't go downwards if you going towards the shore SE is getting shallower so it has to move upwards it has to go somewhere so it moves upwards and really what you generally see is wave heights typically less than one meters out at sea but it can rise then as it moves towards the coast but the speeds can between can be between kind 250 kilm an hour and 950 kilm an hour so they are very fast moving oan waves this all causes shorelines to be damaged flooded and it can lead to severe secondary consequences of an earthquake and then a tsunami as well so that was eq1 of the tectonic processes and Hazards topic hopefully you found that useful just as a round up and overview of what was in eq1 of the topic and why tectonic hazards are so dangerous and how they develop the next jog pod the next SE session of this will be on eq2 I hope you found this useful and make sure you watch eq2 as well