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Natural disaster

Related subjects: Geology and geophysics

Background Information

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A natural disaster is a major adverse event resulting from natural processes of the Earth; examples include floods, volcanic eruptions, earthquakes, tsunamis, and other geologic processes. A natural disaster can cause loss of life or property damage, and typically leaves some economic damage in its wake, the severity of which depends on the affected population's resilience, or ability to recover.

An adverse event will not rise to the level of a disaster if it occurs in an area without vulnerable population. In a vulnerable area, however, such as San Francisco, an earthquake can have disastrous consequences and leave lasting damage, requiring years to repair.


A powder snow avalanche

During World War I, an estimated 40,000 to 80,000 soldiers died as a result of avalanches during the mountain campaign in the Alps at the Austrian-Italian front, many of which were caused by artillery fire.


The 1693 Sicily earthquake

An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. At the Earth's surface, earthquakes manifest themselves by vibration, shaking and sometimes displacement of the ground. The vibrations may vary in magnitude. Earthquakes are caused mostly by slippage within geological faults, but also by other events such as volcanic activity, landslides, mine blasts, and nuclear tests. The underground point of origin of the earthquake is called the focus. The point directly above the focus on the surface is called the epicenter. Earthquakes by themselves rarely kill people or wildlife. It is usually the secondary events that they trigger, such as building collapse, fires, tsunamis (seismic sea waves) and volcanoes, that are actually the human disaster. Many of these could possibly be avoided by better construction, safety systems, early warning and planning. Some of the most significant earthquakes in recent times include: The 2004 Indian Ocean earthquake, the third largest earthquake recorded in history,registering a moment magnitude of 9.1-9.3. The huge tsunamis triggered by this earthquake killed at least 229,000 people.

  • The 2011 Tōhoku earthquake and tsunami registered a moment magnitude of 9.0. The death toll from the earthquake and tsunami is over 13,000, and over 12,000 people are still missing.
  • The 8.8 magnitude February 27, 2010 Chile earthquake and tsunami cost 525 lives.
  • The 7.9 magnitude May 12, 2008 Sichuan earthquake in Sichuan Province, China. Death toll at over 61,150 as of May 27, 2008.
  • The 7.7 magnitude July 2006 Java earthquake, which also triggered tsunamis.
  • The 6.9 magnitude 2005 Azad Jammu & Kashmir and KPK province Earthquake, which killed or injured above 75,000 people in Pakistan.

Volcanic eruptions

Artist's impression of the volcanic eruptions that formed the Deccan Traps in India.

Volcanoes can cause widespread destruction and consequent disaster in several ways. The effects include the volcanic eruption itself that may cause harm following the explosion of the volcano or the fall of rock. Second, lava may be produced during the eruption of a volcano. As it leaves the volcano, the lava destroys many buildings and plants it encounters. Third, volcanic ash generally meaning the cooled ash - may form a cloud, and settle thickly in nearby locations. When mixed with water this forms a concrete-like material. In sufficient quantity ash may cause roofs to collapse under its weight but even small quantities will harm humans if inhaled. Since the ash has the consistency of ground glass it causes abrasion damage to moving parts such as engines. The main killer of humans in the immediate surroundings of a volcanic eruption is the pyroclastic flows, which consist of a cloud of hot volcanic ash which builds up in the air above the volcano and rushes down the slopes when the eruption no longer supports the lifting of the gases. It is believed that Pompeii was destroyed by a pyroclastic flow. A lahar is a volcanic mudflow or landslide. The 1953 Tangiwai disaster was caused by a lahar, as was the 1985 Armero tragedy in which the town of Armero was buried and an estimated 23,000 people were killed .

A specific type of volcano is the supervolcano. According to the Toba catastrophe theory 75,000 to 80,000 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. It also killed three quarters of all plant life in the northern hemisphere. The main danger from a supervolcano is the immense cloud of ash which has a disastrous global effect on climate and temperature for many years.

Hydrological disasters

It is a violent, sudden and destructive change either in quality of earth's water or in distribution or movement of water on land below the surface or in atmosphere.


A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Flooding may result from the volume of water within a body of water, such as a river or lake, which overflows or breaks levees, with the result that some of the water escapes its usual boundaries. While the size of a lake or other body of water will vary with seasonal changes in precipitation and snow melt, it is not a significant flood unless the water covers land used by man like a village, city or other inhabited area, roads, expanses of farmland, etc.

The Limpopo River, in southern Mozambique, during the 2000 Mozambique flood

Some of the most notable floods include:

  • The Johnstown Flood of 1889 where over 2200 people lost their lives when the South Fork Dam holding back Lake Conemaugh broke.
  • 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 United States history.
  • The North Sea flood of 1953 which killed 2251 people in Holland and eastern England
  • The 1998 Yangtze River Floods, 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.
  • The 2005 Mumbai floods which killed 1094 people.
  • The 2010 Pakistan floods, damaged crops and infrastructure, claiming many lives.

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

  • Bhola Cyclone, which struck East Pakistan (now Bangladesh) in 1970,
  • Typhoon Nina, which struck China in 1975,
  • Hurricane Katrina, which struck New Orleans, Louisiana in 2005, and
  • Cyclone Yasi, which struck Australia in 2011

Limnic eruptions

A cow suffocated by gases from Lake Nyos after a limnic eruption

A limnic eruption occurs when a gas, usually 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 gas 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.


Tsunamis can be caused by undersea earthquakes as the one caused by the 2004 Indian Ocean Earthquake, or by landslides such as the one which occurred at Lituya Bay, Alaska.

  • The 2004 Indian Ocean Earthquake created the Boxing Day Tsunami.
  • On March 11, 2011, a tsunami occurred near Fukushima, Japan and spread through the Pacific.

Meteorological disasters

Young steer after a blizzard, March 1966


Blizzards are severe winter storms characterized by heavy snow and strong winds. When high winds stir up snow that has already fallen, it is known as a ground blizzard. Blizzards can impact local economic activities, especially in regions where snowfall is rare.

Significant blizzards include:

  • The Great Blizzard of 1888 in the United States in which many tons of wheat crops are destroyed.
  • The 2008 Afghanistan blizzard
  • The North American blizzard of 1947
  • The 1972 Iran blizzard resulted in approximately 4,000 deaths and lasted for 5 to 7 days.

Cyclonic storms

Cyclone, tropical cyclone, hurricane, and typhoon are different names for the same phenomenon a cyclonic storm system that forms over the oceans. 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.


On the outskirts of Dadaab, Kenya, during the 2011 East Africa drought.

Drought is unusual dryness of soil, resulting in crop failure and shortage of water for other uses, caused by significantly lower rainfall than average over a prolonged period. Hot dry winds, high temperatures and consequent evaporation of moisture from the ground can contribute to conditions of drought.

Well-known historical droughts include:

  • 1900 India killing between 250,000 to 3.25 million.
  • 1921-22 Soviet Union in which over 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.
  • In 2006, states of Australia including South Australia, Western Australia, New South Wales, Northern Territory and Queensland had been under drought conditions for five to ten years. The drought is beginning to affect urban area populations for the first time. With the majority of the country under water restrictions.
  • 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.
  • 12-year drought that was devastating southwest Western Australia, southeast South Australia, Victoria and northern Tasmania was "very severe and without historical precedent".
  • In 2011, the State of Texas lived under a drought emergency declaration for the entire calendar year. The drought caused the Bastrop fires.


Hailstorms are falls of rain drops that arrive as ice, rather than melting before they hit the ground. A particularly damaging hailstorm hit Munich, Germany, on July 12, 1984, causing about 2 billion dollars in insurance claims.

Heat waves

A heat wave is a period of unusually and excessively hot weather. The worst heat wave in recent history was the European Heat Wave of 2003.

A summer heat wave in Victoria, Australia, created conditions which fuelled the massive bushfires in 2009. Melbourne experienced three days in a row of temperatures exceeding 40°C (104°F) with some regional areas sweltering through much higher temperatures. The bushfires, collectively known as "Black Saturday", were partly the act of arsonists.

The 2010 Northern Hemisphere summer resulted in severe heat waves, which killed over 2,000 people. It resulted in hundreds of wildfires which causing widespread air pollution, and burned thousands of square miles of forest.


A tornado is a violent, dangerous, rotating column of air that is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is also referred to as a twister or a cyclone, although the word cyclone is used in meteorology in a wider sense, to refer to any closed low pressure circulation. Tornadoes come in many shapes and sizes, but are typically in the form of a visible condensation funnel, whose narrow end touches the earth and is often encircled by a cloud of debris and dust. Most tornadoes have wind speeds less than 110 miles per hour (177 km/h), are approximately 250 feet (80 m) across, and travel a few miles (several kilometers) before dissipating. The most extreme tornadoes can attain wind speeds of more than 300 mph (480 km/h), stretch more than two miles (3 km) across, and stay on the ground for dozens of miles (perhaps more than 100 km).

Well-known historical tornadoes include:

  • The Tri-State Tornado of 1925, which killed over 600 people in the United States;
  • The Daulatpur-Saturia Tornado of 1989, which killed roughly 1,300 people in Bangladesh.


Wildfires are large fires which often start in wildland areas. Common causes include lightning and drought but wildfires may also be started by human negligence or arson. They can spread to populated areas and can thus be a threat to humans and property, as well as wildlife.

Notable cases of wildfires were the 1871 Peshtigo Fire in the United States, which killed at least 1700 people, and the 2009 Victorian bushfires in Australia.

Health disasters


The A H5N1 virus, which causes Avian influenza

An epidemic is an outbreak of a contractible disease that spreads through a human population. A pandemic is an epidemic whose spread is global. There have been many epidemics throughout history, such as the 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 water flu pandemic
  • The 2002-3 SARS pandemic
  • The AIDS pandemic, beginning in 1959
  • The H1N1 Influenza (Swine Flu) Pandemic 2009-2010

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 1.6 million people each year
  • Ebola hemorrhagic fever, which has claimed hundreds of victims in Africa in several outbreaks

Space disasters

Fallen trees caused by the Tunguska meteoroid of the Tunguska event in June 1908.

Impact events

One of the largest impact events in modern times was the Tunguska event in June 1908.

Solar flares

A solar flare is a phenomenon where the sun suddenly releases a great amount of solar radiation, much more than normal. 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

Gamma-ray burst

Gamma-ray bursts (GRBs) are flashes of gamma rays associated with extremely energetic explosions that have been observed in distant galaxies. They are the brightest electromagnetic events known to occur in the universe. Bursts can last from ten milliseconds to several minutes. The initial burst is usually followed by a longer-lived "afterglow" emitted at longer wavelengths ( X-ray, ultraviolet, optical, infrared, microwave and radio).

All the bursts astronomers have recorded so far have come from distant galaxies and have been harmless to Earth, but if one occurred within our galaxy and were aimed straight at us, the effects could be devastating. Currently orbiting satellites detect an average of about one gamma-ray burst per day. The closest known GRB so far was GRB 031203.

Protection by international law

International law, for example Geneva Conventions defines International Red Cross and Red Crescent Movement the Convention on the Rights of Persons with Disabilities, requires that "States shall take, in accordance with their obligations under international law, including international humanitarian law and international human rights law, all necessary measures to ensure the protection and safety of persons with disabilities in situations of risk, including the occurrence of natural disaster." And further United Nations Office for the Coordination of Humanitarian Affairs is formed by General Assembly Resolution 44/182. People displaced due to natural disasters are currently protected under international law (Guiding Principles of International Displacement, Campala Convention of 2009)

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