Natural disaster

2007 Schools Wikipedia Selection. Related subjects: Geology and geophysics

Mount Pinatubo eruption, 1991
Mount Pinatubo eruption, 1991

A natural disaster is the consequence of the combination of a natural hazard (a physical event e.g. volcanic eruption, earthquake, landslide) and human activities. Human vulnerability, caused by the lack of appropriate emergency management, leads to financial, structural, and human losses. The resulting loss depend on the capacity of the population to support or resist the disaster, their resilience . This understanding is concentrated in the formulation: "disasters occur when hazards meet vulnerability" . A natural hazard will hence never result in a natural disaster in areas without vulnerability, e.g. strong earthquakes in uninhabited areas. The term natural has consequently been disputed because the events simply are not hazards or disasters without human involvement . The degree of potential loss can also depend on the nature of the hazard itself, ranging from wildfires, which threaten individual buildings, to impact events, which have the potential to end civilization.

Natural hazards

A natural hazard is an event that has an effect on people resulting from the natural processes in the environment. Some natural hazards are related - earthquakes can result in tsunamis, drought can lead directly to famine and disease, and so on.


Avalanche on the backside (East) of Mt. Timpanogos, Utah at Aspen Grove trail
Avalanche on the backside (East) of Mt. Timpanogos, Utah at Aspen Grove trail
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
An earthquake is a phenomenon that results from and is powered by the 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, vary few of which are large enough to cause significant damage. Some of the most significant earthquakes in recent times include:
A Sumatran village, devastated by the tsunami that followed the 2004 Indian Ocean earthquake
A Sumatran village, devastated by the tsunami that followed the 2004 Indian Ocean earthquake
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.
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.
A supervolcano is an eruption which is thousands of times larger than a normal eruption. If a volcano expels at least 1,000 cubic kilometers of material, it is declared a supervolcano. The last eruption of this magnitude occurred over 75,000 years ago at Lake Toba. If such an eruption were to occur today, a wholesale general die-off of both animals and humans would occur, as well as a significant short-term climate change. The Yellowstone Caldera has the potential to become a supervolcano within the near geological future.


The Limpopo River, in southern Mozambique, during the 2000 Mozambique flood
The Limpopo River, in southern Mozambique, during the 2000 Mozambique 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 storms can result in extensive flooding, as happened with:
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.
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.
The tsunami caused by the December 26, 2004 earthquake strikes Ao Nang, Thailand.
The tsunami caused by the December 26, 2004 earthquake strikes Ao Nang, Thailand.
A tsunami is a giant wave of water which rolls into the shore of an area with a height of over 15 m (50 ft). It comes from Japanese words "津波" meaning harbour 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. The tsunami generated by the 2004 Indian Ocean Earthquake currently ranks as the deadliest tsunami in recorded history. The highest Tsunami ever recorded was estimated to be 85m (278 ft.) high. It appeared on April 24th, 1771, off Ishigaki Island, Japan.
Mega tsunami is an informal term used to describe very large tsunamis. They are a highly local effect, either occurring on shores extremely close to the origin of a tsunami, or in deep, narrow inlets. The largest waves are caused by a very large landslide, such as a collapsing island, into a body of water. They can potentially reach 20 km inland in low-lying regions.

Storms and weather

Young steer after a blizzard, March 1966
Young steer after a blizzard, March 1966
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
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 250,000 to 5 million perished from starvation due to drought.
  • 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 has 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.
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.
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 Ocean, tropical cyclone in the Indian, typhoon in the eastern 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 
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
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.


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.

Health and disease

The A H5N1 virus, which cases Avian flu
The A H5N1 virus, which cases Avian flu
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. 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 resistant to all known 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
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.


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

International campaigns

In 2000, the United Nations launched the International Early Warning Programme to address the underlying causes of vulnerability and to build disaster-resilient communities by promoting increased awareness of the importance of disaster reduction as an integral component of sustainable development, with the goal of reducing human, social, economic and environmental losses due to hazards of all kinds (UN/ISDR, 2000).

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