Tectonic processes and Hazards

Question 1

What is Mantle convection?

Answer 1

Heat produced by the decay of radioactive elements in the earths core heats the lower mantle - creating convection currents. The magma currents move in circles causing the plates to move

Question 2

What is Slab pull?

Answer 2

Newly formed oceanic crust at mid-ocean ridges becomes denser and thicker as it cools, causing it to sink into the mantle under its own weight – pulling the rest of the plate down with it

Question 3

What is Subduction?

Answer 3

Two oceanic plates (or oceanic + continental) move towards each other, one slides under the other into the mantle where it melts in the subduction zones

Question 4

What is Seafloor spreading?

Answer 4

Mid-ocean ridges form when magma is forced up from the asthenosphere and hardens forming new oceanic rock. This new crust pushes the tectonic plates apart.

Question 5

What is the Benioff zone?

Answer 5

Intermediate and deep earthquakes occur here due to the friction created between colliding plates

Question 6

What happens at a convergent boundary where Oceanic meets continental?

Answer 6

Oceanic is denser so slides beneath the continental into the mantle and melts, marked by deep ocean trenches. Earthquakes in the Benioff zone and volcanic activity happen lots.

Question 7

What happens at a convergent boundary where oceanic meets oceanic?

Answer 7

The denser/faster plate subducts beneath the other, deep ocean trenches form where this occurs, and the plate melts to magma. It rises from Benioff zone to form underwater volcanoes that rise above sea levels to form island arcs.

Question 8

What happens at a convergent boundary when continental meets continental?

Answer 8

A COLLISION MARGIN occurs. Both plates equal density so neither subducts and they crumple and are forced upwards, creating fold mountains. Some subduction inevitable, so some seismic activity happens - shallow focus so higher severity e.g. Nepal

Question 9

What happens at a divergent plate boundary?

Answer 9

Two plates are moving apart - which leads to the formation of new crust. Forming mid-ocean ridges and rift valleys.

Question 10

What are the 3 types of seismic waves?

Answer 10

Primary, secondary, and Love

Question 11

Why are primary and secondary waves known as body waves, and Love waves known as surface waves?

Answer 11

because they travel through the earth’s body, and ‘surface waves’ because they travel along the earths surface

Question 12

What is the MMS, and what factors does it use?

Answer 12

Moment Magnitude scale

• Size of seismic waves
• Amount of rock movement
• Area of fault surface broken by the earthquake
• Resistance of the affected rocks

Question 13

What does the Mercalli scale measure as opposed to the Richter or MMS?

Answer 13

Earthquake INTENSITY via observations of destruction

Question 14

Name 2 primary effects of earthquakes

Answer 14

• Ground shaking

- Crustal fracturing

Question 15

Name 3 secondary effects of earthquakes

Answer 15

• Liquefaction
• Landslides/avalanches
• Tsunamis

Question 16

What can the 1989 Loma Prieta earthquake be used as a case study for?

• What magnitude was the quake?
• Why were some parts of San Fran so badly damaged?
• What major incident occurred because of it?

Answer 16

How the geology of an area can have enormous impact on the effect of an earthquake
- 6.9

• Marina area built on man made landfill (soft, sandy soil)
  - amplified shaking
  - liquified causing building collapse
• Part of the Cypress freeway collapsed killing 42

Question 17

Why do ‘aftershocks’ occur?

Answer 17

They’re a result of the earth ‘settling down’/readjusting along the part of the fault that slipped at the time of the main quake

Question 18

Give a case study concerning aftershocks

• Why was this particular one so damaging?

Answer 18

The 2011 Christchurch, magnitude 6.3 aftershock after the 2010 quake.
- occurred closer to city centre and had shallower focus causing more shaking, than the 2010 original quake

Question 19

What are intra plate earthquakes? Give a case study example

- Why are they problematic?

Answer 19

They happen in the middle of plates, far from the margins, occurring when stresses build up in ancient faults causing them to become active again.

• Don’t happen often - 1812 Missouri 7.5 mag
• Problematic as they don’t occur in well defined patterns so they’re hard to predict

Question 20

Give 4 primary hazards of volcanoes

Answer 20

1. Lava flows
2. Pyroclastic flows
3. Tephra and ash falls
4. Gas eruptions

Question 21

Name 2 secondary hazards from volcanoes

Answer 21

1. Lahars

2. Jokulhlaup

Question 22

What can the Monserrat eruption case study be used to show?

Answer 22

How eruptions and their secondary hazards can have enormous effects on population, even changing them permanently perhaps

Question 23

Recall as much about the 1997 Montserrat eruption as you can

Answer 23

Started 1995 and for 5 years it erupted

• Dozens died
• 7,000 of 11,000 residents moved
• Capital, Plymouth was destroyed
• 2/3 houses, 3/4 infrastructure destroyed
• Unemployment rose as the islands tourist industry collapsed
• 2/3 island still uninhabitable

Question 24

Give an index that could be used to measure volcanic eruptions

Answer 24

VEI, Volcanic Explosivity Index

Question 25

What 3 factors does the VEI use?

Answer 25

• Amount and height of the volcanic material ejected
• How long the eruption lasts
• Qualitative description terms e.g. ‘gentle’, ‘explosive’

Question 26

What are three signs that a volcano might erupt?

Answer 26

1. Small quakes
2. Changes to surface of volcano
3. Changes to ‘tilt’ of volcano

Question 27

What is the hazard-risk formula

Answer 27

(R)isk = (H)azard x (V)ulnerability / (C)apacity to cope

Question 28

What is Vulnerability?

Answer 28

The ability to anticipate, cope with, resist and recover from a natural hazard

Question 29

What is Resilience?

Answer 29

The ability to protect lives, livelihoods and infastructure from destruction, and to restore