1.1.1 Distribution & boundries

Question 1

Why are some locations are some locations more at risk from tectonic hazards?

Answer 1

• Lower quality of infrastructure.
• Geographical location.
• Poor management.
• Uneven hazard distribtion.

Question 2

Why do tectonic plates move?

Answer 2

• Mantle convection (now less accepted by scientists).
• Slab pull > sinking, denser oceanic crust at mid ocean ridges.
• Subduction zone movement > destroyed crust.
• Sea floor spreading > mid ocean ridges.

Question 3

Explain the structure of the earth

Answer 3

1. Crust (lithosphere) - 400 C - solid.
2. Mantle - 700-2890 km deep - 870 c - less dense to medium density.
3. Outer core - 2890-5150 km deep - 4400-6100 c - dense - liquid iron and nickel.
4. Inner core - centre - 7000 c , radioactive decay - very dense - 20% nickel, 80% iron, solid.

Question 4

What are the 7 major plates?

Answer 4

• Pacific.
• North American.
• Eurasian.
• African.
• Antarctic.
• Indo-Australian,.
• South American.

Question 5

Explain features and processes at divergent plate boundaries.

Answer 5

• Commonly found at mid-ocean ridges.
• Sea flooring spreading, the plates move apart.
• Generally a large amount of submarine, low hazard earthquakes.
• new, thinner oceanic plate is formed (denser than continental crust).
• Shield/rift volcanoes are found (less explosive).
• Rift valleys appear on the continent e.g. Iceland.

Question 6

Explain features and processes at convergent plate boundaries.

Answer 6

• Plates move together and the oceanic plate subducts under the continental plate.
• Subduction zone occurs generating huge friction.
• Deep ocean trenches appear.
• Energy release produces infrequent huge earthquakes that can sometimes cause tsunamis.
• Produces volcanoes when oceanic crust is destroyed (less frequent but more explosive).

Question 7

Explain features and processes at oceanic-oceanic plate boundaries.

Answer 7

• Two oceanic plates converge (denser one subducts) creating a trench.
• Oceanic plate descends and melts causing magma to rise and form volcanic island chains known as island arcs e.g. north-west Pacific Ring of Fire (the Aleutian islands).

Question 8

Explain features and processes at collision plate boundaries.

Answer 8

• Two continental plates meet and there is typically no subduction.
• Fold mountains form e.g. the Alps and Himalayas.
• High energy earthquakes can occur.

Question 9

Explain features and processes at conservative plate boundaries.

Answer 9

• Consists of transform faults (weaknesses) in the crust and the faults join-up in a zig-zag pattern creating a locked fault.
• Friction is created due to them sliding past each other at different speeds so earthquakes occur.
• No volcanic activity.
• E.g. The San Andreas Fault in California where the North American plate and Pacific plate move at different speeds.
• Site of shallow focus earthquakes (occasionally high magnitude).

Question 10

How thick is the oceanic and continental crust?

Answer 10

• Oceanic crust is 5 -10 km thick.
• Continental crust is about 25 - 70 km thick.
• Oceanic crust is thinner but denser.