Global Hazards Flashcards
What is the Earth’s structure?
Inner core, outer core, mantle and crust
What are the two types of crust?
Oceanic crust and Continental crust
Describe the types of crust.
Oceanic- Younger. Under 200 million years old. Thinner and more dense.
Continental- Older. Up to 3.8 billion years old. Thicker but less dense.
What are the four kinds of plate boundary?
Destructive, Constructive, Conservative and Collision
Describe what happens at a destructive plate boundary.
An Oceanic plate and Continental plate are driven towards each other by convection currents in mantle. They meet, lock and pressure and energy builds. Eventually Oceanic plate jolts forward and is forced under the Continental plate. This movement causes earthquakes. The subducted crust melts and that magma rises up through the cracks to form volcanoes.
Describe what happens at a constructive plate boundary.
Two plates are pushed away from each other by convection currents ans as they move minor earthquakes occur. A gap is formed in the crust and magma rises up through the gap and erupts. The magma hardens on gaps edges forming oceanic ridges and on land rift valleys form.
Describe what happens at a constructive plate boundary.
Two plates move alongside each other (same or opposite direction). They meet, lock and pressure and energy builds. One plate jolts forward and causes an earthquake where the energy is released in seismic waves. These earthquakes can be very powerful.
Describe what happens at a collision plate boundary.
Two continental plates move towards each other. They meet, lock and energy an pressure build. One plate jolts forward causing an earthquake, releasing the energy in seismic waves. These earthquakes can be very powerful. The crust here is crumpled and folded due to pressure.
Explain why there is a convection current in the mantle.
The core heats the magma in the lower mantle which rises because hot materials are less dense. It nears the crust, cools down and sinks. When it sinks it drags or pulls the tectonic plates with it.
What are hotspots and how to they form?
They form away from plate boundaries, when a plate moves past a particularly hot part of the mantle. A super-heated plume of hot magma rises up and “punches” through weakness in the crust causing volcano eruption and islands to form. As the crust moves past the hotspot, new islands are formed in an island chain (archipelago).
What are the four types of volcano?
Composite, Shield, Caldera and Fissure
Describe a Composite Volcano.
Found at destructive boundaries. Magma is sticky and more viscous, so moves slowly. Explosive eruptions. aa lava is erupted. Steep sided, built with layers of ash and lava. Cone shaped.
Describe a Shield Volcano.
Found at constructive boundaries. Magma is runny and less viscous, so can travel far. Quiet eruptions. Pahoehoe lava is erupted. Gentle eruptions.
Describe a Caldera Volcano.
Formed when a volcano erupts so violently that the magma chamber empties and the crater collapses into itself. A new cone will eventually form as magma rises again.
Describe a Fissure Volcano.
Forms at constructive boundaries when plates separate to leave a rift. There is no cone to erupt from, but lava erupts along a linear crack in the crust.
