Geophysical Hazards - Part 2: Risks

Question 1

Outline the spacial distribution of earthquakes

Answer 1

Linear patterns that follow plate boundaries.
Broad belts - subduction/collision zones e.g. Himalayas
Narrow belts - constructive plates e.g. San Andreas

Isolated: Hotspots/plumes e.g. Hawaiian.

Question 2

Outline the spacial distribution of volcanoes

Answer 2

DIVERGING/CONSTRUCTIVE and CONVERGING/DESTRUCTIVE.

NW Pacific Ocean - Hawaiian Hotspots.
Jet of heat from fluid mantle.

Hotspots beneath continents e.g. East-African Rift Valley

3/4 of 550 active volcanoes = Pacific Ring of Fire e.g. Mt. Pinatubo

Molten rock forms due to subduction creating chains of volcanic islands.

Fold Mountains = The Andes, nazca subducts SA plate.

Question 3

Outline the distribution of landslides

Answer 3

Areas with active tectonic processes leading to high rates of uplift + seismic events
Areas w/ high precipitation
High pop. desnity
LIC’s with no mitigation schemes E.G. India, Indonesia, Mexico

Question 4

Mass Movement - Mudflow

liquidity, speed of onset, duration and extent.

Answer 4

Highest liquidity
Fast speed of onset + quick progression.
Speed and duration depends on rainfall and mud liquidity.
Heavy rain = quick flow = greater damage = can’t get away.

Question 5

Mass Movement - Slumping

liquidity, speed of onset, duration and extent

Answer 5

Slumping requires more water than soil creep.
Speed + duration = heavy rainfall + short lag time = quicker saturation + short duration.
Extent: a lot of damage quickly.

Question 6

Mass Movement - Soil creep

liquidity, speed of onset, duration and extent

Answer 6

Dryer than slumping, takes long time.
Speed and duration: takes years from beginning to end.
Not high risk for damage or death. Land less useful for residents or agriculture.
Occurring very slowly over time

Question 7

Mass Movement: Rockfall

liquidity, speed of onset, duration and extent

Answer 7

Very fast (less than 1 minute)
Small area
Huge damage due to boulders falling at high speeds = deaths + damaged property where humans are near.
Occurs most often

Question 8

Convergent/Collision/Destructive plate boundary.

Continental-Continental and Oceanic-Continental

Answer 8

Continental-Continental:

1. Two continental plates move towards each-other.
2. Little subduction due to low density rock.
3. Rock gets folded, faulted, thickened.
4. Magma cannot penetrate thick crust –> forms granite.

Example: The Himalayas and the Tibetan Plateau = 50 mill. yrs of collision between Indian-Eurasian plates.

Oceanic-Continental:

1. Oceanic plate subducts continental
2. Volcanic arcs arise
3. Oceanic = densert = high subduction potential
4. Volcanoes eurpt

Example: Cascade mountains of Western North America // The Andes of Western South Africa

Question 9

Divergent/constructive plate boundaries:

Oceanic and Continental

Answer 9

Oceanic:

1. Tectonic plates are pulled apart
2. Slab pull is created when plates SINK into the MANTLE at SUBDUCTION zones.
3. Convection currents lift crust

Example: Mid-Atlantic Ridge:

• Fissure eruptions
• Shallow earthquake activity
• New sea floor + widen ocean basin

Continental:

1. Pull is not strong enough.
2. Currents cause plates to arch upwards
3. Plates are pulled thin and fractured into rift-shape
4. Faults develop + central rock slides.
5. Earthquakes can occur

Example: East Africa Rift Valley or the Dead Sea

Question 10

Conservative/Passive/Transform

Oceanic and continental

Answer 10

1. Horizontal movement only.
2. Plates move past each other, rubbing along the edges.

Oceanic:

1. Short faults on the sea floor near mid-ocean ridges.
2. Plates split at different speeds.
3. Space is created between margins
4. Once the oceanic plate spreads beyond overlap, a fracture zone extends across seafloor.

Continental:

1. Extra forces (compression + extension) create mountainous welts and down-dropped valleys.
2. Thick crust = wide deformation zones.

Example: San Andreas, California = 100km of faults.

Question 11

Factors affecting Geophysical Hazard Risk

Answer 11

Economic factors (levels of development and technology, infrastructure, insurance)
E.G. 1976, 20k people killed in Guatemala due to low-quality housing. 

Social factors (education, awareness and gender, culture)

Demographic factors (population density and structure, migrants, disability)

Political factors (governance, allowing aid, effective communication, emergency protocols)

Question 12

What are the two schools of thought?

Answer 12

Behavioural:
People put themselves at risk by living in areas of high risk. E.G. on steep sides of mountains/on a plate boundary

Structuralist:
Economic/social/political circumstances limit choices on where to live. E.G. Farmers are closer to the hazard than richer people living farther away in the city.

Question 13

Factors that affect Hazard Impacts

Answer 13

1. Pop density
2. Econ development.
3. Magnitude and frequency.
4. Distance from event
5. Type of buildings
6. Type of rocks + sediments