1_Restless Earth

1_Restless Earth

1. The Structure of the Earth

   • Crust: is the outer layer of the Earth. It can be up to 75km thick. It is made up of tectonic plates
     • Made of plates which are huge scabs of the Earths crust.
       • plate boundary: the place where 2 plates meet.
         • Constuctive Plate boundary.
           • At a constructive plate boundary the plates are moving apart. This type of movement mostly happens under the oceans. the gap left is filled with magma rising up from the mantle below the volcanoes: some of the volcanoes have been large enough to form island such as iceland and hawaii.
         • Destrucive plate Boundary.
           • at a destructive plate boundary the plates are moving together. The denser oceanic crust is subducted under the continental crust where it melts in the subduction zone.
             • Fold mountains at destrucive boundaries
               • The Friction from the oceanic plate causes the continental plate to crumple. creating fold mountains.
                 • Fold mountains can be hostile and problematic however certain features we can use in our favour.
                   • Pros: coniferous trees can be farmed and flat legdes can be used for grazing animals.
                     • Valley floors can be used for growing crops.
                     • valleys can be used to build damns and produce hydroelectric power.
                   • Cons: Mountain soils are thin and infertile.
                     • the valley floors can flood easily, when snow melts.
                     • Its difficult for roads and railways to be built. And they may be damaged by rock falls and avalanches in winter
             • Ocean trenches
               • An ocean trench is found at a destructive plate margin.
               • Where the oceanic plate is subducted under the continental plate a dip/v shape is created- this is called an ocean trench.
               • E.g. marianas trench, 11 000m (japan)
         • Conservative Plate boundary.
           • The plates are moving past each other either in the same direction or opposite directions. The two plates meet at the fault where the pressure builds up until the two plates jerk past each other. This can cause an earthquake or for the land at the fault to become crumpled and rigid. A good example of this is the San Andreas fault in California.
         • Collision Plate Boundary
           • where 2 plates collide head on
             • Fold mountains at a collison boundary
               • Rivers carried sediments to ancient seas. Sediments were deposited at the bottom of the seas.over millions of years the sediments were compressed to form sedimentary rock. As the two plates move towards each other they push layers of accumulated sediment in the sea between them up into folds. The fold mountains continue to grows as the plates constantly move toward each other.
                 • Types of folds:
                   • syncline: the low bit of the fold
                   • Anticline: the high bit of the fold.
                   • Also there can be an over fold where the fold falls onto its side to create an 's' shape.
                 • Case study: the Andes
                   • Location: south america
                     • The Andes mountains run the length of the west coast of south america, rising in the North of Colombia and finishing in Chile and Argentina in the south. They are the worlds longest mountains range running for over 7 000km and covering 6 countries including: Colombia, Ecuador, Argentina, Chile, Paraguay and Bolivia. 
                   • Formation: convergence of the Nazca plate and the south american plate. it is a destructive margin.
                     • The mountains have been formed as a result of the convergence of the nazca plate and the south American plate. The heavier oceanic crust of the nazca plate is pushed towards the South American plateand because it is denser subducted underneath. The South American plate is less dense so it sits on top of the subduction zone, but the rocks of the south american plate have been folded upwards and crumpled into mountains. there are also volcanoes and earthquakes along this destructive boundary. 
                   • The land is used for farming, hydroelectric power, tourism and mining.
                     • Farming: The use of terraces in boliva creates flat land where subsistance farmers are able to grow their food. These flat areas retain their water  and stops the soil being washed down the slope.  Hydroelectric power: The steep slopes and narrow valleys that can't be used for farming are perfect for hydro electric power. The melting snow in spring increases the flow. Tourism:   
                     • Farming: The use of terraces in boliva creates flat land where subsistance farmers are able to grow their food. These flat areas retain their water and stops the soil being washed down the slope.
                     • Hydroelectric power: The steep slopes and narrow valleys that can't be used for farming are perfect for hydro electric power. The melting snow in spring increases the flow.
                     • Tourism: There are many natural atrrctions in the andes including mountain peaks, volcanoes, glaciers and lakes.
                     • Mining: The Andes hold a range of important mineral including tin, nickel, silver and gold.
       • Ocenanic Crust
         • Rock type: Basalt
         • age: 200 million
         • density: very dense
         • it can be destroyed and renewed
         • depth- 6-10km
         • e.g. pacific plate
         • over the sea
       • Continental Crust
         • rock type: granite
         • 3.8 billion years old
         • less dense than oceanic
         • can't be destroyed and can't be renewed
         • depth- 20km
         • e.g. Eurasian plate
         • over the land
       • 7 major plates and many smaller ones.
         • Pacific
         • Eurasian
         • African
         • North American
         • South American
         • Indo-Austrailen
         • Antarctic
         • Smaller Ones: Coros; Carribean; Nazca; philippine; Arabian
       • Continental Drift Theory
         • Introduced at the beginning of the 21st century by Alfred Wegener
         • idea that the earths continents were once joinded but over millions of years drifted apart.
         • Evidence
           • the same fossiles were found in South Amercia and Africa.
           • the shape of South Africa fits with the west coast of Africs, ike a Puzzle.
   • Mantle: middle layer it can be upto 2800km thick. The upper parts form the lithospere and its rigid while the lower (semi-molten) parts form the Asthenophere, the rock is moved about by convection currents.
   • Inner core: composed of radio active Iron and Nickel. sold due to great pressure (5000degrees centigrade)
   • Outer Core: Liquid iron and Nickel (3000 degrees centigrade)

2. Earthquakes

   • Focus: the focus is the point the waves started.
   • Epicentre: directly above the focus
   • Cause
     • can occur at collision, construcive and destructive.
     • when the plates are moving past each other pressure builds up which is suddenly released an the stored energy is released in seismic waves. These travel trough the earth in all directions shaking everything.
       • as the rock settles into its new position there will be aftershocks.
   • different waves
     • longditudal waves
       • up and down movement
     • Transverse waves
       • side to side movement (cause the most damage)
     • primary and secondary waves
       • primary: back and forth very fast
       • secondary waves are slowersand cause side to side movements.
     • measuring earthquakes
       • Richter scale
         • measures the energy (magnitude) of an earthquake
         • measured with a seismometer
         • no top to scale as we don't know how big an earthquake can be.
         • logarithmic scale, each step is a 10x increase from last one E.g. 1x10=10 10x10=100 100x10=10 000 etc.
       • mercalli scale
         • how it feels, subjective (down to opinion)
         • measured with a key and your eyes.
   • Case Studies
     • Nepal
       • 25th april 2015
       • magnitude 7.9
       • collision boundary- indoaustralien and eurasian
       • depth of focus 15km
       • between kathmandu and pokhara
       • effects
         • primary
           • 8 000 dead
           • 14 000 injured
           • 2.8mil homeless
           • 18climbers were killed by an avalanche on everest.
         • secondary
           • economic downfall due to lack of tourism
           • historics sites lost
           • avalanches and rock falls
       • response
         • UK raised £41MILLION
         • Tarpulines and tents were provided aswell as noodles for food
         • Germany and the US provided specialist response teams
     • Christchurch
       • 22nd feb 2011
       • magnitude 6.3
       • australien and pacific destructive plate boundary
       • depth of 5km
       • effects
         • primary
           • 181 deaths
           • 2 000 injured
           • damage to roads and buildings
         • secondary
           • landslides in some suburbs
           • liquefation
       • responses
         • search and rescue
         • chemical toilets
   • prediction, protection and preparation
     • reduce impact of an earthquake
     • prediction: attempts to forecast an event based on current knowledge.
     • protection: constructing building so that they are safe to live in and will not collapse
     • preparation: organising activities and drills so that people know what todo in the event of an earthquake

3. tsunami's

   • tsunamis are formed by earthquakes displacing the water above
   • boxing day tsunami, 2004
     • effects
       • 275 000 deaths
       • 2 million homeless people
       • 650 000 injured
       • Affected: Indonesia, sri lanka, india, malaysia, thailand, somalia
     • 25m waves
     • travelled over 800m inland
     • response
       • £9 billion in aid
       • local rescued the stranded
       • large scale rebuilding took place
       • warning systems and education about tsunami's
   • the height of the wave is gained when the wave reaches the shore and friction builds causing the base of the tsunami to slow, the water from behind continues on causing a crest

4. volcanoes

   • distrubution: linear around the plate margins.found at constructive and destrucive plate boundaries
   • types of volcanoes
     • composite
       • destructive plate boundary
       • viscous lava (flows slowly and hardens quickly)
       • steep cone shaped
       • explosive eruption
       • periodic eruptions (but quite rare
       • e.g. mnt versuvious
     • sheild
       • constructive plate boundary
       • runny basaltic lava
       • e.g. hawaii
       • low flat with a wide base
       • not very explosive but lava flows along way
     • dome
       • destructive plate boundary
       • viscous lava with an acidic content cools very quickly
       • steep sided
       • regular eruptions
       • mnt st helens
   • monitering
     • geological observations: the volcano get bigger before it erupts
     • seismic activity: movements in the plate
     • gas emissions: when magma nears the surface its pressure decreases and gases escape through the fumerole. the gas emissions drop before the eruption as the the hardened magma blocks the path, increasing the pressure.
   • how it works
     • The plates move past each other and hot rocks escape as well as small earthquakes.
       • leakages cool to form the volcano
         • • plate movements and movements in the mantle can cause an eruption
             • gas builds up
               • when the pressure is too great it erupts
   • monserrat
     • 1997
     • 19 deaths
     • lahars destroyed large areas of monserrat
     • £57 million in aid
   • super volcanoes
     • yellowstone
       • predicted by sattelites, seismic measurments and radar measurements.
     • formation
       • rising magma pools under the surface unable to escape.
         • a growing magma chamber forces the ground upwards forming a bulge
           • eventually the crust cracks causing an eruptions
             • the empty magma camber is filled with crust and forms a caldera, the cycle begins again.