Physical Geography


What are the different types of rocks?

- there are three types of rock 

1. igneous - volcanic rock, made of solidified magma from the mantle

2. sedimentary - particles deposited by wind, water or ice

3. metamorphic - rocks are changed chemically or structurally due to intense heat or pressue

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Explain convection currents

1. radioactive decay in the mantle and core generates heat

2. lower parts of the asthenosphere heat up, become less dense and then rise

3. as it gets higher in the asthenosphere, magma cools, gets more dense and falls

4. this circular movement is referred to as convection currents

5. this causes tectonic plates to move

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What evidence is there for subduction?

1. gases and steam from the crater

- high levels of nitrogen in volcanoes at destructive plate margins are similar to the levels found in animals at the bottom of the sea

2. composition of water 

- the composition of water in the crater matches that of the Pacific Ocean

3. Benioff Zone

- location of earthquake foci at point of subduction

- as we know where the foci are, we can map out the subduction zone 

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What are the features of extrusive volcanic activi

1. hotsprings 

- groundwater emerges at the surface

- if the groundwater source has flowed close to an area of recent intrusive vocanic activity it will be heated e.g Rio Hondo in Argentina 

2. Fumeroles

-hot water fumeroles are clouds of steam and form as water is heated up by the mantle 

- solfatera are fumeroles where there is a large sulphur content, resulting in a sulphurous stream

3. geysers

- groundwater is heated up by magma deep in the crust, becoming pressurised 

- water expands when heated, forcing it up from a large cavern through a narrow gap creating an explosion of water

- mud pools are a type of hot spring, found when water mixes with fine grained soil e.g Yellowstone 

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What happens at constructive plate margins?

- contructive margins are when plates diverge (move apart)

1. convection currents diverge in the asthenosphere pulling the lithosphere apart

2. this relieves pressure on the mantle, making it molten and less dense

3. this allows magma to rise, filling the gaps and erupting at the surface as new crust (often a volcano) 

4. the earth is spherical so the crack between the plates is not uniform, causing parts of the plate to move faster than other parts and so pressure builds up

5. pressure causes cracks, faults and earthquakes

6.transform faults are created by adjacent segments of plates moving past eachother, creating continued pressure and earthquakes 

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What evidence is there for continental drift?

1. geology - some rocks in South America and Africa have the same age and composition

- the age and rock type of mountains are the same in Europe and North America match 

- these rocks must have been formed in the same place under the same conditions 

2. fossils - fossil distributions match

- migration that far is unlikely, as is evolution 

3. living species  - earthworms found in Africa, North America and New Zealand give reason to believe in continental drift 

4. climatology - glacial deposits in Africa, Australia, Antarctica and South America show they must once have been closer to the South Pole 

- coal deposits formed in tropical conditions are found in North America and Europe show these places must have been nearer to the equator

5. paleomagnetism - every 200,000 years the earth switches polarity, magma rises through a mid ocean trench and the iron particles align with magnetic north, the crust solidifies and is polar opposite to the previous crust creating a series of magnetic strips on the sea floor, it shows crust is older the further from the trench and so shows there must be continental drift

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What is the theory of continental drift?

- continental drift was a theory established by Alfred Wegner in 1912

- the theory suggested there was once a super continent called Pangea

- over time it split up and drifted across the oceans forming the continents we see today 

- the theory is mainly based upon fossil records

- however a major flaw of the theory is that it doesnt say how the continents drifted 

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What happens during sea floor spreading?

1. diverging convection currents at the base of the lithosphere cause the plates above it to diverge 

2. a gap is created between the plates

3. magma rises to fill the gap and cools at the surface 

4. over time the new crust is dragged apart creating even newer crust

5. when this process occurs under the sea, the sea floor widens creating sea floor spreading 

6. this process is what causes mid ocean ridges 

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What happens at destructive plate margins?

1. oceanic - continental 

- convection currents 'drag' the lithosphere over the asthenosphere causing the oceanic and continental plates to converge. the heavier, denser, oceanic plate is subducted. a deep sea trench is formed as well as fold mountains. impurities in the sea water reduce the melting point of the plate. magma becomes less dense and so rises through the continental crust. the magama becomes more acidic and tends to collect in chambers, erupting at the surface as a volcano. earthquakes also occur as the plate movement is not smooth 

2. oceanic - oceanic

- the denser, older plate is the one that will subduct. island arcs, volcanoes, earthquakes and deep sea trenches all form here

3. continental - continental

- neither plate is subducted at this type of boundary. no volcanoes are formed but earthquakes and fold mountains are likely e.g the Himalayas 

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What evidence is there for constructive plate marg

1. bathymetry 

- maps the depth of the sea floor

- the sea floor is shallower in the middle of the ocean e.g the mid atlantic ridge

2. crustal age

- we can now date the age of crusts

- the older crust is found furthest from the plate margin 

- therefore crust must be created at the margin

3. paleomagnetism 

- every 200,000 years the earth switches polarity 

- iron aligns with magnetic north and so shows stripes of opposing polarities on the sea floor 

- newer alignments are found near the plate boundary therefore crust must be created 

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What happens at conservative plate margins?

- only earthquakes occur here

- this is where two plates move alongside or past eachother 

- plates lock together in place and pressure builds up

- plates jerk past eachother creating fault lines and energy is released along these fault lines as earthquakes 

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How do super volcanoes form?

1. created at hotspots or destructive margins where magma cant burn through the continental crust so it accumulates beneath the crust and become more acidic over time 

2. magma builds up and the crust is forced upwards which makes it thinner and can cause some cracks, major clues of this are earthquakes and geysers

3. magma builds up and the pressure causes cracks in the overlying crust, small amounts of lava erupt 

4. the huge magma chamber empties and the cavern which is left cannot support the overlying crust so the roof collapses, leaving a caldera, releasing all of the magma and creating a supervolcanic eruption 

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What are hotspots?

- hotspots are random sections at the core - mantle boundary (gutenberg discontinuity) that are hotter than the surrounding area

- Helium-3 is found at the site of eruption, giving evidence that the magma is from near the core

- the hot section causes the mantle to melt in sections, causing a rising magma plume which is less dense than the surrounding magma

- the mantle plume pushes the crust upwards, making it thinner, oceanic crust is already thin and so magma can easily break through it 

- the plume is stationary but the crust moves over it creating a chain of volcanoes 

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What factors affect how destructive an earthquake

1. location 

2. magnitude

3. depth 

4 .distance from the epicentre 

5. local geographic conditions 

6. secondary effects 

7. architecture 

e.g in Loma Prieta, California (1989) 

the epicentre was in the south west, Santa Cruz with a magnitude of 8 on the Ricter scale whereas the magnitude reached 9 to the far north in San Francisco because of the soft, water saturated soil 

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What are the types of seismic waves?


1. P

- primary waves, can travel through solids and liquids, they push and pull in the same direction as the wave and are the fastest type of wave 

2. S

- secondary waves, can travel through solids but not liquids, they move earth at 90 degrees to the direction of the wave and cause damage because of their shearing effect

Surface Waves...

1. Lore 

- these waves only move through solids and move side to side, causing damage because of their shearing effect

2. Rayleigh 

- these waves travel through solids and liquids and cause the surface to move in a rolling motion

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How do we measure earthquakes?

- seismometers measure the magnitude of earthquakes as well as the duration and direction and over time they show the frequency 

1. ricter scale 

- the ricter scale measures the magnitude of earthquakes, it has no upper limit and is a logarithmic scale. 1-2 is barely felt but most major earthquakes are above 7 

2. mercalli scale

- the mercalli scale measures the impacts of earthquakes and uses observations. the scale is between I and XII where I is only detected by instruments and XII is total destruction 

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What landforms are found at constructive plate mar

1. midocean ridges

- two plates diverge underwater e.g mid atlantic ridge

- underwater volcanoes become volcanic islands e.g Hawaiian islands and Iceland

2. rift valleys

- convection in the mantle causes crust to fracture and buldge 

- gaps in the crust allow magma to rise and form volcanoes 

-the crust cracks creating faults and faults slip, causing the land to subside 

- lakes fill the gaps 

- plates continue to move and the rift valley widens, the sea rushes to fill it 

- new constructive margins are formed and sea floor spreading will follow 

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What are the basic keywords for earthquakes?

- earthquakes are found at all 3 types of plate boundary, pressure which is released causes seismic waves (vibrations) and the vibrations are the earthquake 

focus - is the place on the lithosphere where it starts, this is where the strongest waves are which cause the most damage 

epicentre - is the point on the surface where the earthquake is felt, this is straight above the focus

intraplate - where earthquakes are in the interior of the plate 

interplate - where earthquakes are found at plate margins 

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How do tsunamis form?

1. subduction zone - heat, pressure and time causes plates to bend

2. earthquake - pressure is released, underwater earthquake is released, the plate retracts and water is displaced 

3. drawdown - this proceeds the wave and makes the wave appear smaller than it is 

4. sea level - waves spread from the epicentre to balance the sea level 

5. waves break - the wave reaches the shore, growing in amplitude and breaking at the shore

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What are the different shapes of volcanoes?

1. fissure e.g ejaffjallajokull 

- linear cracks in the crust, usually at constructive plate margins, the magma is basaltic, fluid and can travel long distances

2. sheild e.g mauna loa, Hawaii

- gently sloping layers of less viscous magma found at constructive margins or hotspots 

3. composite e.g Mount Etna 

- acidic magma in layer of ash and lava at destructive plate margins 

4. ash/ cinder e.g stromboli

- basaltic magma which explodes in short frequent outbursts as mini lava bombs forming steep volcanoes

5. acid/dome e.g Puy de Domes, France 

- found at continental crust with steep sides and very viscous lava which cannot travel far so magma builds in the vent, solidifying to create a volcanic plug and is pushed up by magma and creating a dome 

6. caldera e.g yellowstone 

- found at destructive margins, gases build beneath the blocked vent, the eruption destroys the summit and leaves an enormous crater 

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What are the different types of magma?

1. basic/basaltic/mafic

- high temperature, low silica, darker coloured, constructive margins, travels less so less minerals removed

2. acidic 

- lower temperatures, high silica, lighter coloured, destructive margins, travels further, more assimilation, more minerals removed 

assimilation - the further magma travels, the more rock it comes into contact with causing partial melting, adding to acidity 

fractional crystallization - as magma cools, minerals are lost, making it more acidic therefore the longer it is in the earth, the more acidic it is 

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What are the different types of volcanic eruption?

1. Hawaiian e.g mauna loa

- non explosive, gentle eruptions with highly fluid, basaltic lava with a low gas content. thin lava builds to broad sheild volcanoes eruptions occur along long fissures radiating from the sumit

2. hydrovolcanic e.g surtseyan, iceland 

- magma comes into contact with groundwater or surface water (ice) 

3. Strombolian e.g stromboli, Italy 

- basaltic or intermediate magma with irregular, explosive lava bombs 

4. Vulcanian e.g Vulcano, Italy 

- explosive eruptions with high eruptive columns and pyroclastic flows, viscous magma making it difficult for magma to escape 

5. plinian e.g mount st helens, usa

- highly explosive, acidic lava creates sustained eruption columns 

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What are the features of intrusive volcanic activi

- this is magma beneath the earths surface

1. batholith 

- cooled magma chamber e.g dartmoor where 625km squared of granite is exposed 

2. dyke 

- magma cuts vertically through the crust (sedimentary rock) and cools e.g Kildonan (isle of Arran) where the dykes are up to 8m high 

3. sill 

- magma cuts horizontally through the crust e.g drumadoon (isle of arran) and whinsill (northumberland) 

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What is the structure of the earth?

1. inner core - solid iron and nickel, high pressure and density, 1100km deep

2. outer core - molten as less pressure, thicker fluid moves due to convection because of radioactive decay, 2400km deep 

3. mantle (upper and lower) - less dense, lighter elements e.g Mg

4. core-mantle = gutenberg discontinuity 

5. mantle-crust = mohovoric discontinuity 

6. asthenosphere + lithosphere = upper mantle 

asthenosphere - semi molten, less pressure

lithosphere - rigid upper mantle and crust, "floats" on assthenosphere 

7. oceanic crust - 10km thick, younger denser

8. continental crust - 80km thick, older, less dense, crust is less dense than mantle and core because its made of lighter elements e.g oxygen 

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