4.1 Natural Hazards

Question 1

What is the difference between a hazard and a risk?

Answer 1

A hazard = an event that could cause damage to or loss of life and damage to infrastructure eg buildings, roads etc.

A risk = the probability of loss of life or damage to infrastructure

Question 2

What are the four main natural (geo) hazards?

Answer 2

1. Tsunamis
2. Earthquakes
3. Landslides
4. Volcanic eruptions

Question 3

What do earthquakes cause?

Answer 3

Ground movement
Liquefaction
They can also cause tsunamis and landslides if the earthquake is strong enough

Question 4

What is ground movement and what happens?

Answer 4

When faults move and create earthquakes huge amounts of energy are transferred through the earth by seismic waves

When this happens:
Buildings collapse
Roads collapse
Pipe lines break which can cause flooding and fires

Question 5

What are the three different types of seismic waves?

Answer 5

Primary waves
Secondary waves
Surface waves

Question 6

Explain primary waves?

Answer 6

They are the fastest type of seismic wave and not very damaging

Question 7

Explain secondary waves?

Answer 7

They are the slowest type of wave and sheer the rock from side to side causing some damage

Question 8

Explain surface waves?

Answer 8

They are even more slower than the primary wave and secondary wave and cause the most movement within the ground and therefore the most damage

Question 9

What is the effect of:

1. Primary waves
2. Secondary waves
3. Surface waves

Answer 9

1. Primary waves:
   In solid rock = no damage
   In sediment = no damage
   In wet sediment = no damage
2. Secondary waves:
   In solid rock = no damage
   In sediment = knocked things of shelves
   In wet sediment = walls cracking and chimneys falling off
3. Surface waves:
   In solid rock = no damage
   In sediment = cracked walls and smashed glass eg windows
   In wet sediment = collapsing buildings and liquefaction

Question 10

What is liquefaction?

Answer 10

During ground shaking sedimentary rocks can repack their grains to fit together more effectively.
Any water in the pore spaces is forced upwards into the unconsolidated (not stuck together) sediment forcing them apart.
This causes the surface soils and sediment to behave like a liquid and buildings/cars/roads can sink into the ground.

Question 11

What are landslides?

Answer 11

When the ground shakes sedimentary grains can lose contact with one another causing them to lose their strength due to a loss of internal friction.

This has the potential to cause large landslides if other geological factors such as dip and rock type are as suitable.

Question 12

Why are LEDCs more vulnerable from natural hazards than MEDCs?

Answer 12

1 poorer countries have worse building standards eg huts not houses or not earthquake resistant
California earthquake 42 died - Haiti over 100,000 died, 1.5 million homeless.
California could afford earthquake resistant buildings
2. Poorer countries have worse roads and drainage so disease spreads quicker
3 poorer countries have less money for emergency services
4 MEDCs can do more to prevent damage