A - Tectonic Hazards Flashcards

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1
Q

What is the Earth’s crust divided into?

A

The Earth’s crust is divided into tectonic plates that float on the mantle (a layer of semi-molten rock).

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2
Q

2 types of crust

A

Continental and oceanic

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3
Q

Describe continental crust

A

Crust is thicker (30-50km) and less dense

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4
Q

Describe oceanic crust

A

Crust in thinner (5-10km) and more dense

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5
Q

How do plates move?

A

Plates move due to convection currents in the mantle.

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6
Q

What are the places called where plates meet?

A

The places where plates meet are called plate margins or plate boundaries.

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7
Q

3 types of plate margins

A

Destructive margins, constructive margins, conservative margins

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8
Q

Define destructive margin

A

Where 2 plates are moving towards each other
○ Where an oceanic plate meets a continental plate - the denser oceanic plate is subducted and destroyed, creating gas-rich magma, volcanoes and ocean trenches occur
○ Where 2 continental plates meet, the ground is folded upwards, creating fold mountains

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9
Q

Define constructive margin

A

Where 2 plates are moving away from each other

○ Magma rises from the mantle to fill the gap and cools, creating new crust

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10
Q

Define conservative margin

A

Where 2 plates are moving sideways past each other / moving in the same direction at different speeds
○ Crust is not created or destroyed

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11
Q

Where are earthquakes globally distributed?

A

Earthquakes are found along all types of plate margins.
They mostly occur along boundaries between major tectonic plates.
A few occur in the middle of plates.

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12
Q

Where are volcanoes globally distributed?

A

Volcanoes only occur at constructive and destructive plate margins.
They also occur at hot spots (parts of the mantle that are really hot) such as Hawaii in the Pacific Ocean.
A lot of volcanic activity occurs in the ‘ring of fire’ - a group of volcanoes located along the plate margin of the Pacific plate.

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13
Q

How do volcanoes form at constructive plate margins?

A

The magma rises up into the gap created by the plates moving apart, forming a volcano.

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14
Q

How do earthquakes form at constructive plate margins?

A

Tension builds along the cracks in the plates as they move away from each other, forming an earthquake.

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15
Q

How do volcanoes form at destructive plate margins?

A

The denser oceanic plate moves down into the mantle, where it melts. A pool of magma forms, which then rises through cracks in the crust called vents. The lava erupts, forming a volcano.

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16
Q

How do earthquakes form at destructive plate margins?

A

Tensions builds when one plate gets stuck as it moves past the other.

17
Q

How do earthquakes form at conservative plate margins?

A

Tension builds up when plates that are grinding each other get stuck.

18
Q

What happens when a volcano erupts?

A

When a volcano erupts, it emits lava and gases. Some volcanoes emit a lot of ash, which can cover land, block out the sun and form pyroclastic flows (super-heated currents of gas, ash and rock).

19
Q

How do earthquakes occur?

A

Plates jolt past each other, sending out shock waves - these vibrations are the eathquakes.

20
Q

Where is the epicentre and focus?

A

The epicentre in the point on the Earth’s surface straight above the focus.

21
Q

How are earthquakes measured?

A

Earthquake’s are measured using the moment magnitude scale:
• Measures the amount of energy released by an earthquake
• Logarithmic scale
○ Earthquakes of magnitude 6 and below can only cause slight damage to buildings, although they can be worse in very built up areas
○ Earthquakes of magnitude 7 and above can cause major damage and deaths