geography (plate tech) Flashcards
Differences in layers of earth
Gateway 1
BOC Thickness
crust – 70km
mantle – 3000km
core – 3500km
BOC Temperature
crust – around room temp
mantle – 800 - 3000 deg C
core – 3000 - 5000 deg C
BOC Type of rock
crust – solid granite and basalt
mantle – solid rock flowing in high heat
core – solid and liquid iron + nickel
Oceanic v Continential plate
BOC location
oceanic – under deep oceans
continential – beneath continents and shallow seas
BOC thickness
oceanic – 5-8km
continential – 35-70 km
BOC type of rock
oceanic – basalt rock
continential – granite rock
BOC age of rock
oceanic – < 200mil
continential – > 4bil
How to plates move? (CC)
- Mantle material heated up by core
- Expands rises and spreads outwards beneath the plates
- This drags the plates along, and can cause plates to move away from each other
- Mantle material cools and sinks, bringing the plate along with it
- Mantle material is heated up by core and process repeats itself again
How do plates move? (SPF)
- Denser, sinking plate at subduction zone pulls rest of the plate along
- Further driven by downward moving portion of mantle in convectional current
O - O divergence
mid oceanic ridge, undersea volcanoes, volcanic islands
- fractures form along plate boundary
- magma rises from the fractures to fill the gaps to create new ocean floor known as mid oceanic ridge
- at various points, magma builds up and solidifies to form undersea volcanoes.
- after many eruptions the volcano is stacked up by cooled magma to reach the surface and form volcanic islands
eg for o o divergent plates – N american and eurasian
eg for ridges – mid atlantic ridge
eg for volcanic islands – azores, surtsey
C - C divergence
rift valley, volcanoes
- fractures form along the boundaries as the plates are stretched
- land in between the two plates sink, forming a linear depression known as rift valley
- magma can seep through the fractures to form active volcanoes
eg for c-c divergent plates – african and arabian
eg for rift valley – E african rift valley
O - O convergence
oceanic trench, submarine volcanoes, volcanic islands
- oceanic plates move towards each other, denser plate subducts beneath less denser plate
- zone of subduction forms oceanic trench, and may cause earthquakes
- subducted o plate melts and forms magma material
- rises through cracks in crust to form volcanoes
- after many eruptions magma cools, solidifies and stacks up to form volcanic islands
eg for o o convergent plate – phillipine and pacific plate
eg for trench – mariana trench
eg for volcanic islands – mariana islands
C - C convergence
fold mtns
- continential plates collide and push against each other
- cannot subduct as both are too thick and buoyant
- plates break and slide along fractures in crust
- crust is compressed and causes plates to fold upwards, causing fold mountains
C - O convergence
oceanic trench, fold mtns, volcanoes
- denser oceanic plate converges and subducts under rarer continential plate
- oceanic trench forms at zone of subduction
- fold mtns form on continential plates when plates buckle and fold
- at subduction zone, sinking plate melts to form magma
- melted mantle materials rise up through cracks in continential crust to form volcanoes
eg for c o convergence – Australian and Eurasian
eg for trench – sundra trench
eg for fold mtns – barisan mtns
Fold mtn formation
Gateway 2
- caused by convergence of c-c or c-o
- plates of equal density so cannot subduct and plates compress against each other.
- compressional forces cause great pressure on rocks, causing it to buckle and fold upwards to great heights.
eg – himalayas formed by indian and eurasian convergent plates
Rift valley and block mtn formation
- formed by divergent c-c plates
- plates are pulled apart, faults form
- tension caused by the divergence causes fractures along plate boundaries
- land in between sinks which is rift valley
- land that is left standing is block mtn
eg – north african rift valley formed by divergent arabian and somalian plates
volcano (strato)
- magma builds up in the chamber, causing pressure to build
- when the pressure is released, the volcano erupts and pyroclasts are released.
- for every eruption, the pyroclasts solidify and stack up to form tall mtns
- lava builds up around the vent and solidifies to form crater
- vent may get blocked during eruptions so lava finds alternative routes to escape mtn, forming secondary vents
- when eruption is too violent, the summit of the volcano is blown off and a caldera forms
lava has high viscosity, high silica content, more explosive eruption
Risks of living near volcanoes
-destruction by volcanic materials
-pollution
mt st helens 1980 killed 57 ppl and released 540 mil tonnes of ash
Benefits of living near volcano
-fertile soil
-tourism
-precious stones
farming at mt vesuvius lacryma christi wines, arenal volcano tourism
formation of earthquake
- refers to vibration in earths crust due to the sudden release in built up energy along fault lines
- when movement of plates occur, friction also occurs
- rocks have slow buildup of stress, as they buckle and fold due to their uneven edges
- when the pressure is released, the plate may slip several metres, causing an earthquake
san andreas fault between pacific plate and n american
