Hazard Distribution Flashcards
What is the Earth’s crust made up of?
Huge plates called tectonic plates that sit on top of the mantle.
What are two types of crust plates are made of?
- The thicker (but less dense) crust is called continental crust- it’s mostly above sea level.
- The thinner (but more dense) crust is called oceanic crust- it’s mostly below sea level.
Why do plates move?
Because of convection currents in the mantle- the currents are caused by temperature differences within the mantle.
What are the three types of plate boundary?
Constructive, destructive and conservative.
What is a constructive boundary?
A constructive boundary occurs where two plates are moving apart.
The mantle is under pressure from the plates above. When they move apart, the pressure is released at the boundary.
The release of pressure is what causes the mantle to melt, producing magma.
The magma is less dense than the plate above so it rises and can erupt and form a volcano.
What is a fault line?
Where a plate has cracked under pressure.
What is a destructive boundary?
Where continental crust and oceanic crust are moving towards each other, the more dense oceanic crust is forced under the less dense continental crust.
The oceanic crust is heated by friction and contact with the upper mantle, which melts it into magma.
The magma is less dense than the plate above so it rises and can erupt and form a volcano.
What is a conservative boundary?
A conservative boundary occurs where two plates are moving past each other.
The two plates get locked together in places and pressure builds up. As with destructive boundaries, this causes the plates to jerk past each other releasing the energy as an earthquake.
What are tropical cyclones?
Tropical cyclones develop above sea water that’s 26.5 degrees or higher. As warm, moist air rises and condenses, it releases energy which increases wind speed.
When do cyclones lose strength?
When they move over land because the energy supply from the warm water is cut off.
Why do cyclones spin?
Because of the Coriolis effect (the force that deflects the path of winds due to the Earth’s rotation).
Cyclones don’t occur 0-5 degrees either side of the equator because…?
The Coriolis effect isn’t strong enough to make them spin.
The Coriolis effect is also why they move away from the equator.
Why do cyclones move westwards?
Due to the east west winds in the tropics.
When are cyclones known as hurricanes and typhoons?
When they occur in the Atlantic Ocean or Caribbean Sea and typhoons when they occur in the Pacific Ocean.
