Oceanic Crust: 5-10 km thick, dense, sinks into the mantle when oceanic and continental crust meets, forms constantly at constructive plate margins, destroyed at destructive plate margins.
Plate Boundaries: the border between two plates is called a boundary. All the tectonic plates are constantly moving in different directions.
Constructive Boundary: Two plates move apart from each other.
A gap appears and molten magma rises to fill the gap.
This solidifies to create new rocks on the sea bed.
Over time the layers of rock build up.
Destructive Boundary: Plates are pushed together and the oceanic crust gets subducted beneath the continental crust. Oceanic plate sticks and locks as it is trying to move from under the Cont plate. Heat from friction and the mantle start to melt the subducted plate.
Landforms at Plate Margins
Composite Volcanoes- found at destructive plate margins. Have steep sides. Made up of alternate layers of ash and lava. Eruptions can be violent- expelling steam, ash, lava and rock- but they don't happen often.
Why?- millions of years the atlantic plate had been pushed under the Caribbean plate. Magma formed and pushed it's way through the ocean floor, creating underwater volcanoes which turned into islands (Lesser Antilles arc). Plates moving-subduction happening.
Effects- More than half became uninhabitable. Infrastructure was destroyed. 19 died, many fled. Farms, homes and the capital were destroyed/abandoned. Tourism stopped. Economy was destroyed. Long-term health effects because the ash contained quartz which caused Silicosis.
Long-term responses- some returned, 2010 pop risen to 5000. Pop structure changed, many young people left and didn't return. British government spent £200million helping to restore electricity and water, build a new harbour , new airport and roads.
Montserrat's future- In 2005 tourists started to visit again. Little Bay is being developed as the new capital. It is hoped that Little Bay will stimulate economic growth
Supervolcanoes- Yellowstone National Park (USA)
Geology - The park is home to one of the world's largest calderas with over 10,000 thermal features and more than 300 geysers.
Earthquakes tend to occur in long belts. The biggest one goes around the whole Pacific Ocean. Another one runs down the middle of the Atlantic Ocean. These belts follow the plate margins.
If pressure is released suddenly, it can send out huge pulses of energy- causing the Earth's surface to move violently.
Earthquakes occur at all four types of plate margins.
Features of earthquakes- when an earthquakes strikes, the ground shakes violently.
2004 Boxing Day Tsunami
It hit several countries surrounding the Indian Ocean, with Indonesia being the worst affected.
Mangrove Swamps act as a natural barrier, so these are being restored, having been cleared in many areas to make way for building of hotels.