Tectonic hazards Flashcards
Three plate boundary types
Convergent
Divergent
Transform / conservative
Ridge push
At an ocean v ocean constructive plate boundary, when new plate is formed in the middle by the upwelling magma. This new plate is hot and therefore more dense than the old plate, pushing it sideways, on both sides of the ridge.
Slab pull
When Oceanic plate meets a continental plate, which is more dense, and therefore pulls the oceanic plate below. This is then enhanced by the slippage of the oceanic crust underneath the continental crust, which is caused by the weight of the crust pulling itself further into the mantle because of gravity and the convection currents underneath the lithosphere.
Vacuum pull
When the oceanic plate breaks apart during subduction, due to the pressure of the mantle, leaving a vacuum bubble behind, which further causes slippage of the plate below the continental plate.
Continental crust
Thickness: 50km thick
Temp: 200-400*c
Composition: Silicone, oxygen, aluminium
Properties: Rigid
Oceanic crust
Thickness: 25km thick
Temp: 200-400*c
Composition: Iron, Magnesium, Calcium
Properties: Rigid
Asthenosphere
Thickness: 100-300km thick
Temp: 1300*c
Composition: Peridotite, plastic
Properties: Solid / viscous
Mantle
Thickness: 350-2800km thick
Temp: 1000-3700*c
Composition: oxygen, silicone
Properties: Solid
Outer core
Thickness: 2200km thick
Temp: 4,500-5,500*c
Composition: Liquid iron + nickel
Properties: Liquid
Inner core
Thickness: 1200km thick
Temp: 5,200*c
Composition: Liquid iron + nickel
Properties: Solid
Paleomagnetism
When ocean spreading produces matching parallel bands, due to their matching polarity, which changes every 400,000 years approximately.
More evidence for plate tectonics (use in conjunction with paleomagnestism)
The age of the rocks on the ocean floor, and how they become older the more they spread apart from the area of sea floor spreading.
Acid lava volcano
Formed at destructive plate boundaries, Oceanic Crust vs Continental Crust, Oceanic crust and marine sediments melt when they are subducted, and therefore create an acidic magma, which is very viscous (doesn’t flow easily) rises to the surface, and explodes, which can create a caldera.
Basic lava volcano
Formed at constructive plate boundaries, magma upwelling from mantle, to form a shield volcano, grouping to form an island arc occasionally, perfect for farming
Montserrat - LIDC ERUPTION
Soufriere hills, acid stratovolcano, ovc, caribbean / NA
* First erupted in 1995
* Evacuated Plymouth (capital)
* Cordoned off for 2 years
* Some went back
* Then erupted in 1997
* pyroclastic flow killed 20
