Edexcel IGCSE Geography 复习笔记 3.1.1 Types of Hazards

Natural Hazards

• A hazard is an event which has the potential to cause harm to the environment, people or the economy
• A natural hazard is an event caused by environmental processes
• A disaster occurs when harm actually occurs to the environment, people or the economy
• Natural hazards can be categorised by their causes

• Natural events only become hazards and disasters due to their impact on people, the environment or the economy
• Natural hazards can also be categorised in a range of other ways:
  • Magnitude - the strength/power of the event
  • Frequency - how often the event occurs
  • Size - the area covered by the hazard
  • Duration - the time a hazard event lasts
  • Location - where a hazard event occurs

Tropical Cyclones

• Tropical cyclones are rotating, low pressure systems (below 950mb)
• They are known as hurricanes, cyclones and typhoons in different areas of the world
• Characteristics include:
  • Heavy rainfall
  • High wind speeds (over 119 kmph)
  • High waves and storm surges
• Measuring between 100-2000km across the rotating clouds surround a central, calm eye
• The magnitude of tropical cyclones is measured on the Saffir-Simpson Scale from 1 to 5
• They develop in tropical regions between 5^o and 30^o north and south of the equator

Distribution of Tropical Cyclones

Earthquakes

• A sudden, violent shaking of the ground
• Earthquakes occur at all types of plate boundaries
• Earthquakes are the result of pressure building when tectonic plates move
• The epicentre is the point on the Earth's surface directly above the focus
• The focus is the point at which the earthquake starts below the Earth's surface
• The magnitude of earthquakes is measure on either the Richter Scale or the Moment Magnitude Scale
• The damage caused by earthquakes is measured on the Mercalli Scale

Earthquake Distribution

Volcanoes

• When magma erupts onto the Earth's surface as lava
• Most volcanoes occur at constructive (divergent) and destructive (convergent) plate boundaries
• The majority of active volcanoes are located around the rim of the Pacific Ocean called the 'Ring of Fire'
• Hotspots occur away from plate boundaries and are plumes/columns of magma which escape through the Earth's crust
• The magnitude of a volcanic eruption is measured on the Volcanic Explosivity Index (VEI)

Active Volcano Distribution