1. What are the different types of hazard?
A natural hazard is a threat of a naturally occurring event that will have a negative effect on people or the environment. Many natural hazards are interrelated, e.g. earthquakes can cause tsunamis and drought can lead directly to famine. If this threat becomes a serious reality then it becomes a disaster. An example of the division between a natural hazard and a natural disaster is that the 1906. San Francisco earthquake was a disaster, whereas earthquakes are a hazard. A natural hazard becomes a natural disaster when it affects people, officially causing more than 10 deaths, injuring more than 100 people, and/or causing US$16,000,000 of damage.

Although roughly divided into geological and atmospheric, several of them overlap. For example, a lahar accompanies or follows on sometime later from a volcanic eruption, making it primarily a geological hazards, it is usually accompanied by heavy rainfall, an atmospheric event.

Geological hazards P3.1A_Avalanche.png
Include hazards that are related to the structure of the earth.


An avalanche is a slide of a large snow (or rock) mass down a mountainside, caused when a build-up of snow is released down a slope. It is one of the major dangers faced in the mountains in winter.


An earthquake is caused by the ground shaking or moving sideways. Most of these occur along the edges of tectonic plates (much more about these later). Most of the world's earthquakes (90%, and 81% of the largest) take place in the 40,000-km-long, horseshoe-shaped zone known as the Pacific Ring of Fire, which for the most part bounds the Pacific Plate. Many earthquakes happen each day, few of which are large enough to cause significant damage.


Landslides and mudflows

A landslide is related to an avalanche, but instead of occurring with snow, it occurs involving actual elements of the ground, including rocks , trees, parts of houses, and anything else which may happen to be swept up. Landslides can be caused by earthquakes, volcanic eruptions, or general instability in the surrounding land. The picture on the right shows one in Brazil.
Mudslides, or mudflows, are a special case of landslides, in which heavy rainfall causes loose soil on steep terrain to collapse and slide downwards. Lahars are related to these see later.

Volcanic eruption

A volcanic eruption is the point in which a volcano is active and releases its power Volcanoes, like earthquakes, in the main occur, along tectonic plates. They range from daily small eruptions which occur in places like Kilauea in Hawaii, or extremely infrequent large eruptions such as Mount Pinatubo in the Philippines in 1991. Some eruptions form pyroclastic flows, which are high-temperature clouds of ash and steam that can trial down mountainsides at speed exceeding an airliner. There are also Lahars, a kind of land slide associated with the aftermath of a volcanic eruption, but which can continue, in rainy seasons, long after the volcano has finished erupting.


A lahar is a type of natural disaster closely related to a volcanic eruption, and involves a large amount of material, including mud, rock, and ash sliding down the side of the volcano at a rapid pace, and are usally associated with heavy rains. These flows can destroy entire towns in seconds and kill thousands of people.

Atmospheric hazards:

Include hazards that are caused by the air and weather


Floods are the result of prolonged rainfall from a storm, including thunderstorms, rapid melting of large amounts of snow, or rivers which swell from excess precipitation upstream and cause widespread damage to areas downstream, or less frequently the bursting of man-made dams or levees. Tropical cyclones can result in extensive flooding and storm surge.


A tsunami is a wave of water caused by the displacement of a body of water. The word comes from Japanese words "tsu" meaning harbor and "nami" meaning wave (tsu+nami=harbor wave). Tsunami can be caused by undersea earthquakes as in the 2004 Indian Ocean Earthquake, or by landslides such as the one which occurred at Lituya Bay, Alaska.


Drought is defined as an acute shortage of water and crop failure that results when the average rainfall is very much less than the normal.
Cyclonic storms

Hurricane, tropical cyclone, and typhoon are different names for the same phenomenon: a cyclonic storm system that forms over the oceans. It is caused by evaporated water that comes off of the ocean and becomes a storm. The Coriolis Effect (due to the earth turning on its axis) causes the storms to spin, and a hurricane is declared when this spinning mass of storms attains a wind speed greater than 74 mph (119 km/h). Hurricane is used for these phenomena in the Atlantic and eastern Pacific Oceans, tropical cyclone in the Indian, typhoon in the western Pacific.


A tornado is a natural disaster resulting from a thunderstorm. Tornadoes are violent, rotating columns of air which can blow at speeds between 50 and 300 mph (480 km/h), and possibly higher. Tornadoes can occur one at a time, or can occur in large tornado outbreaks along squall lines or in other large areas of thunderstorm development. Waterspouts are tornadoes occurring over tropical waters in light rain conditions (see picture)

Wildfire hazardP3.1H_Wildfire.png

A wildfire is an uncontrolled fire burning in wildland areas. Common causes include lightning and drought but wildfires may also be started by human negligence or arson. They can be a threat to those in rural areas and also wildlife. Wildfires can also produce ember attacks, where floating embers set fire to buildings at a distance from the fire itself.


The textbook has divided hazards up differently - and added a few more!
Geological :Earthquakes, volcanic, land slides
Climatic: storms, floods and drought
Biological: Fires, pestd, disease
Technological : Nuclear explosions, accidents, pollution - hence the mine in Chile and the BP spill in the gulf both count here