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A natural hazard is a situation which has the potential to create an event that has an effect on people. They result from natural processes in the environment and some natural hazards are related - earthquakes can result in tsunamis, drought can lead directly to famine and disease, and so on.

Geological

Avalanche

An avalanche is a geophysical hazard involving a slide of a large snow (or rock) mass down a mountainside, caused when a buildup of snow is released down a slope, it is one of the major dangers faced in the mountains in winter. An avalanche is an example of a gravity current consisting of granular material. In an avalanche, lots of material or mixtures of different types of material fall or slide rapidly under the force of gravity. Avalanches are often classified by what they are made of. Notable avalanches include:

* The 1970 Ancash earthquake

* The 1954 Blons avalanches

* The 1999 Galtür Avalanche

* The 2002 Kolka-Karmadon rock ice slide

* The 1910 Wellington avalanche

Earthquake

An earthquake is a phenomenon that results from a sudden release of stored energy that radiates seismic waves. At the Earth's surface, earthquakes may manifest themselves by a shaking or displacement of the ground and sometimes tsunamis. 90% of all earthquakes - and 81% of the largest - occur around the 40,000km long Pacific Ring of Fire, which roughly bounds the Pacific Plate. Many earthquakes happen each day, few of which are large enough to cause significant damage. Some of the most significant earthquakes in recent times include:

* The 2004 Indian Ocean earthquake, the second largest earthquake in recorded history, registering a moment magnitude of 9.3. The huge tsunamis triggered by this earthquake cost the lives of at least 229,000 people.

* The 2005 Kashmir earthquake, which cost 79,000 lives in Pakistan.

* The 7.7 magnitude July 2006 Java earthquake, which also triggered tsunamis.

Lahar: 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. These flows can destroy entire towns in seconds and kill thousands of people. The Tangiwai disaster is an excellent example, as is the one which killed an estimated 23,000 people in Armero, Colombia, during the 1985 eruption of Nevado del Ruiz.

Landslides and Mudflows: A landslide is a disaster closely 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. Mudslides, or mud flows, are a special case of landslides, in which heavy rainfall causes loose soil on steep terrain to collapse and slide downwards (see also Lahar); these occur with some regularity in parts of California after periods of heavy rain.

Sinkholes: A localized depression in the surface topography, usually caused by the collapse of a subterranean structure, such as a cave. Although rare, large sinkholes that develop suddenly in populated areas can lead to the collapse of buildings and other structures.

Volcanic eruption

A volcanic eruption is the point in which a volcano is active and releases its power, and the eruptions come in many forms. They range from daily small eruptions which occur in places like Kilauea in Hawaii, or extremely infrequent supervolcano eruptions (where the volcano expels at least 1,000 cubic kilometers of material) in places like Lake Taupo, 26,500 years ago, or Yellowstone Caldera, which has the potenetial to become a supervolcano in the near geological future. Some eruptions form pyroclastic flows, which are high-temperature clouds of ash and steam that can trial down mountainsides at speed exceeding an airliner. According to the Toba catastrophe theory, 70 to 75 thousand years ago, a super volcanic event at Lake Toba reduced the human population to 10,000 or even 1,000 breeding pairs, creating a bottleneck in human evolution.

Hydrological

Flood

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.

* The Huang He (Yellow River) in China floods particularly often. The Great Flood of 1931 caused between 800,000 and 4,000,000 deaths.

* The Great Flood of 1993 was one of the most costly floods in US history.

* The 1998 Yangtze River Floods, also in China, left 14 million people homeless.

* The 2000 Mozambique flood covered much of the country for three weeks, resulting in thousands of deaths, and leaving the country devastated for years afterward.

Tropical cyclones can result in extensive flooding, as happened with:

* Typhoon Nina, striking China in 1975,

* Tropical Storm Allison, which struck Houston, Texas in 2001 and

* Hurricane Katrina, which left most of New Orleans under water in the year 2005.

Limnic eruption

Also referred to as a 'lake overturn', a limnic eruption is a rare type of natural disaster in which CO₂ suddenly erupts from deep lake water, posing the threat of suffocating wildlife, livestock and humans. Such an eruption may also cause tsunamis in the lake as the rising CO₂ displaces water. Scientists believe landslides, volcanic activity, or explosions can trigger such an eruption.

To date, only two limnic eruptions have been observed and recorded:

* In 1984, in Cameroon, a limnic eruption in Lake Monoun caused the deaths of 37 nearby residents

* At nearby Lake Nyos in 1986 a much larger eruption killed between 1,700 and 1,800 people by asphyxiation.

Maelstrom

A large tidal whirlpool. The largest known maelstrom is Moskstraumen off the Lofoten islands in Norway. Powerful whirlpools have killed unlucky seafarers, but their power tends to be exaggerated in fiction. Maelstroms can reach speeds of 20-40km/h.

Seiche

A seiche is a standing wave in an enclosed or partially enclosed body of water. Seiches and seiche-related phenomena have been observed on lakes, reservoirs, bays and seas. The key requirement for formation of a seiche is that the body of water be at least partially bounded, allowing natural phenomena to form a standing wave.

Tsunami

A tsunami is a wave of water caused by the displacement of a body of water. The word comes from Japanese words "津波" meaning harbor and 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. Meteotsunamis are caused by meteorological phenomena. A megatsunami is an informal term used to describe very large tsunamis. The largest waves are caused by very large landslides, such as a collapsing island, into a body of water. The highest Tsunami ever recorded was estimated to be of 524m (1742 ft.) vertical run-up on July 10, 1958,in Lituya Bay,Alaska.

Climatic / Atmospheric

Blizzard

A severe winter storm condition characterized by low temperatures, strong winds, and heavy blowing snow. Significant blizzards in the United States include:

* The Great Blizzard of 1888

* The Schoolhouse Blizzard earlier the same year

* The Armistice Day Blizzard in 1940

* The Storm of the Century in 1993

Drought

An abnormally dry period when there is not enough water to support agricultural, urban or environmental water needs. Extended droughts can result in deaths by starvation or disease, and can result in wildfires. Well-known historical droughts include:

* 1900 India, killing between 250,000 and 3.25 million.

* 1921-22, Soviet Union, in which over 5 million perished from starvation due to drought.^[1]

* 1928-30, northwest China, resulting in over 3 million deaths by famine.

* 1936 and 1941, Sichuan Province, China, resulting in 5 million and 2.5 million deaths respectively.

As of 2006, Western Australia, New South Wales, Victoria and Queensland (all states of Australia) have been under drought conditions for five to ten years. The drought is beginning to affect urban populations for the first time. Also in 2006, Sichuan Province, China experienced its worst drought in modern times, with nearly 8 million people and over 7 million cattle facing water shortages.

Scientists warn that global warming may result in more extensive drought in coming years.

Hailstorm

A hailstorm is a natural disaster where a thunderstorm produces numerous hailstones which damage the location in which they fall. Hailstorms can be especially devastating to farm fields, ruining crops and damaging equipment. A particularly damaging hailstorm hit Munich, Germany on August 31, 1986, felling thousands of trees and causing millions of dollars in insurance claims.

Heat wave

A heat wave is a disaster characterized by heat which is considered extreme and unusual in the area in which it occurs. Heat waves are rare and require specific combinations of weather events to take place, and may include temperature inversions, katabatic winds, or other phenomena. The worst heat wave in recent history was the European Heat Wave of 2003. There is also the potential for longer term events causing global warming, including stadial events (the opposite to glacial 'ice age' events), or through human induced climatic warming.

Hurricanes, Tropical cyclones, and Typhoons

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 causes the storms to spin, and a hurricane is declared when this spinning mass of storms attains a wind speed greater than 74 mph. Hurricane is used for these phenomena in the Atlantic and eastern Pacific Oceans, tropical cyclone in the Indian, typhoon in the western Pacific. The deadliest hurricane ever was the 1970 Bhola cyclone; the deadliest Atlantic hurricane was the Great Hurricane of 1780, which devastated Martinique, St. Eustatius and Barbados. Another notable hurricane is Hurricane Katrina, which devastated the Gulf Coast of the United States in 2005.

Ice age (Glacial Event): An ice age is a geologic period, but could also be viewed in the light of a catastrophic natural disaster, since in an ice age, the climate all over the world would change and places which were once considered habitable would then be too cold to permanently inhabit. A side effect of an ice age could possibly be a famine, caused by a worldwide drought.

Ice storm: An ice storm is a particular weather event in which precipitation falls as ice, due to atmosphere conditions

Tornado: 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, 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.

Fire

Wildfire

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.

Biosphere (Health and disease)

Epidemic

An outbreak of a contractible disease that spreads at a rapid rate through a human population. A pandemic is an epidemic whose spread is global. There have been many epidemics throughout history, such as Black Death. In the last hundred years, significant pandemics include:

* The 1918 Spanish flu pandemic, killing an estimated 50 million people worldwide

* The 1957-58 Asian flu pandemic, which killed an estimated 1 million people

* The 1968-69 Hong Kong flu pandemic

* The 2002-3 SARS pandemic

* The AIDS epidemic, beginning in 1959

Other diseases that spread more slowly, but are still considered to be global health emergencies by the WHO include:

* XDR TB, a strain of tuberculosis that is extensively resistant to drug treatments

* Malaria, which kills an estimated 1.5 million people each year

* Ebola hemorrhagic fever, which has claimed hundreds of victim in Africa in several outbreaks

Famine

A social and economic crisis that is commonly accompanied by widespread malnutrition, starvation, epidemic disease and increased mortality. Although some famines occur - or are aggravated - by natural factors, it can and often is a result of economic or military policy that deprives people of the food that they require to survive.

In modern times, famine has hit Sub-Saharan Africa the hardest, although the number of victims of modern famines is much smaller than the number of people killed by the Asian famines of the 20th century.

Extra-Terrestrial (Space)

Impact event: An impact event is a natural disaster in which an extraterrestrial piece of rock or other material collides with the Earth. The exact consequences of a direct Earth impact would vary greatly with size of the colliding object, although in cases of medium to large impacts short-term climate change and a general failure of agriculture. An example would be the Tunguska event.

Solar flare: A solar flare is a phenomenon where the sun suddenly releases a great amount of solar radiation, much more than normal. It is theorized that these releases of radiation could cause a widespread failure of communications technology across the globe. The exact implications of such a failure are unknown. Further studies are being carried out. Some known solar flares include:

* An X20 event on August 16 1989

* A similar flare on April 2 2001

* The most powerful flare ever recorded, on November 4 2003, estimated at between X40 and X45

* The most powerful flare in the past 500 years is believed to have occurred in September 1859

References