geography ✿ global hazards (tectonic)

continental crust

crust found underneath large land masses

oceanic crust

crust found underneath the oceans. (ocean floor)

epicentre

the Earth's surface directly above the focus

focus

where the earthquake starts below the Earth's surface

how deep under the crust are shallow-focus EQs?

0-70km

how deep under the crust are intermediate EQs?

70-300km

how deep under the crust are deep-focus EQs?

greater than 300km

Describe what a hot spot is. [2]

an area of the earth’s crust where unusually high heat flow is linked to volcanic activity

constructive plates

• tectonic plates moving apart

• both volcanic eruptions and earthquakes can occur here (Mid-Atlantic Ridge)

destructive plates

• tectonic plates move towards one another.

• The oceanic crust is forced to sink, the continental crust rises above

Conservative plates

• tectonic plates move past each other

• only earthquakes occur here

Collison plates

• two plates move towards each other

• the crust is forced upwards forming fold mountains such as the Himalayas

Convection currents

Hot currents that make plates move

what are earthquakes caused by?

• EQs occur at all plate boundaries

• EQs happen when tectonic plates move, causing pressure and a sudden violent shake occurs

• they can also occur when humans drill or mine into the crust

Seismic waves

Shock waves from earthquakes

what does a Richter scale measure?

the magnitude of earthquakes

what are seismometers used to detect?

seismic waves from earthquakes

what does the Mercalli scale measure?

the damage caused by earthquakes (1-10)

Explain how the movement of tectonic plates at a destructive plate boundary causes volcanoes to form. [4]

• The tectonic plates move towards each other and one plate is forced to subduct

• this causes crust to melt due to friction

• pressure in magma chamber builds up

• molten material rises as it is dense

• magma moves through cracks of the crust

Volcanoes are formed on the margins ___________ and __________

Constructive and destructice

State 3 features about composite volcanoes

• found at destructive margins

• most violent eruptions

• lava is thick and heavy

state 3 features about shield volcanoes

• found at constructive margins

• Not as violent eruptions

• Lava is thin and runny

Name the process that causes the Earth’s tectonic plates to move. [1]

convection currents