Natural Hazards

- A natural hazard is an event that causes loss of human lives and properties. They are caused by extreme weather conditions and earth movements.

Natural hazard	Places
High risk of drought	Chad, Western USA, Australia, Ethiopia
High risk of flood	Northeastern China, Venice, Pakistan, The Netherlands, Thailand
Frequent earthquakes	Japan, Taiwan, Central China, Indonesia
Active volcanoes	Iceland, The Philippines, Indonesia, Hawaiian Islands, Peru, Chile, Italy

 

Structure of the Earth
Crust	- Made up of rocks and soil which is not uniform in thickness, some parts are thicker, forming the continents; others are thinner, forming the ocean-floors.
Mantle	- Made up of very hot molten rocks called magma. - The upper layer is upper mantle. - The lower layer is lower mantle. - Semi fluid
Core	- Made up of heavy metals under high temperature and high pressure.

                      

 

Unstable zones on the earth

- Circum-pacific belt

- Mid-Atlantic belt

- Mediterranean belt

 

How does the crust move?

- The crust is not a single piece, it is broken into pieces called plates. The narrow zone between two moving plates is called plate boundary. The narrow zone between two moving plates is called plate boundary.

- Plates move slowly because of convection currents of magma in the mantle. The plates sometimes move away, move towards and slide past each other along the plate boundaries.

- Earthquakes, volcanic eruptions and fold mountains are caused because of plate movements.

Plate movements and plate boundaries
Constructive plate boundary	Destructive plate boundary	Conservative plate boundary
The plates move away from each other.	The plates move towards each other.	The plates move past each other.

 

 

What are earthquakes? Why do earthquakes occur?

Earthquakes are the violent shaking of the earth’s crust. Earthquakes occur where plates move towards (destructive plate boundary) or move past (conservative plate boundary) each other. Such plate movement creates pressure and causes the rocks to break. At the crack or the focus, shock waves spread out. The earth’s surface above will shake and earthquake is resulted.

The magnitude of an earthquake is measured on the Richter scale. The higher the scale, the greater the damage, the lower the frequency of occurrence.

Why are there volcanic eruptions? How do volcanoes form?

When plates move, magma rises through cracks and stored in the magma chamber of the earth’s crust. When there is too much pressure in the magma chamber, the volcano erupt, lava, ash and gases come out. Magma rises and flows out as lava layer by layer. Lava cools to form volcanoes.

What are the hazardous effects of earthquakes and volcanic eruptions?

Earthquakes	Volcanic eruptions
1. People and livestock are killed and injured. 2. Infrastructure (e.g. buildings, bridges and roads) is damaged 3. Water, electricity and gas supplies are cut
4. Landslides may occur 5. broken gas pipes and electricity wired cause fires 6. Dams collapse and cause flooding 7. earthquake on ocean floors cause tsunami	4. lava and mud flows bury fields and settlements 5. lava flows cause fire that burn forests and thus destroy the ecosystem 6. dust and ash from volcanoes lower the air quality/visibility 7. plane engines are jammed by dust and ash, this causes planes to crash

 

Feasible measures to reduce risk of natural hazards.

1. Prediction

- Watch out for nature’s weird/abnormal behaviors

- Check the temperature and pressure of volcanoes

- Study the history of earthquakes/volcanic eruptions

 

2. Planning

- Set up evacuation route with adequate road signs

- Avoid dangerous land use in hazard prone areas

- Earthquake-proof buildings/infrastructure

- Set up monitoring and warning systems

- Prepare for relief work, shelters, and rescue team

- Earthquake drills

What are the factors affecting the degree of damage caused by earthquakes?

1. Nature of the hazard
- Magnitude	The higher the magnitude, the greater the damage.
- Time of occurrence	If earthquake occurs in midnight, higher death toll would be resulted.
2. Background of the affected area
- Population density	Higher	Lower
The higher the population density, the higher the casualty
- Type of country	Less developed country e.g. Haiti, Iran	More developed country e.g. New Zealand, Japan
- Level of economic development	Lower	Higher
- Level of technology	Lower	Higher
Higher level of economic development implies the country has more resources and more advanced technology to cope with earthquakes, hence less loss would be resulted.
- Level of awareness/preparedness of people	Lower	Higher
Higher level of awareness/preparedness refers people know how to prepare for and respond to earthquakes.

 

Why do people still live in hazard prone areas?

Benefits of a place for living

Other reasons

1. Volcanoes are tourist attraction. 2. Gentle slopes at the bottom of volcanoes are suitable for farming and building houses. 3. Volcanic ash make the soil fertile. 4. Useful minerals (e.g. diamonds, gold, iron) are found in volcanic areas. 5. Steam and heat in the volcanic areas provide geothermal power. 6. Many big cities which are affected by earthquakes have a lot of money and technology. People think that the benefits outweigh the disadvantages.

1. Optimistic views of people on hazards. 2. People believe that their governments have enough money and high technology to cope with the hazards. 3. People prefer to stay because of family and social ties. 4. People have no choice because there are strict migration policies in other countries.