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close this bookNatural Disasters - Be Prepared! (UNESCO, 1997, 50 p.)
View the document(introduction...)
View the documentMonth by month
View the documentSafety first
View the documentA decade for international action
View the documentNature on the rampage
View the documentMaking cities safer
View the documentThe do’s and don’ts of risk reduction
View the documentSounding the alarm
View the documentWomen in the front line
View the documentInsurance: halting an ominous trend
View the documentFact file
View the documentCommentary Federico Mayor
View the documentGREENWATCH New Caledonia: threats to biodiversity
View the documentHeritage. Taxila - The cradle of Gandhara art
View the documentREFLECTIONS. Spreading the world
View the documentInterview. Manuel Elkin Patarroyo
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Nature on the rampage

Natural hazards originate from the air (storms, wildfires, droughts), the earth (earthquakes, landslides, volcanic eruptions) or water (flooding).

When communities cannot cope with them they turn into disasters.

Gyumri, formerly Leninakan (Armenia), stricken by an earthquake In December 1988. [© T. Orban/Sygma, Paris]


Small quakes happen every day all over the world. Large ones, which are rarer, can cause more damage than floods and severe storms. Earthquakes are dangerous because they strike without warning, trigger disaster in less than a minute and forecasts of their effects are difficult. Undersea earthquakes can generate tsunami flood waves which can have effects at great distances. Buildings and communities near active earth-fault zones, or on soft or unstable soil or slopes, or at the water’s edge are especially vulnerable to ground shaking, earthquake-triggered fires and tsunamis. Some recent earthquake disasters:

- Kobe (Japan), 17 January 1995. This 6.9 magnitude¹ tremor was the world’s most costly earthquake disaster, with losses of about $140 billion. Centred 20 km from Kobe, it struck just before dawn and destroyed 200,000 homes, set off 600 fires, put the city’s port out of operation, severely damaged the Hanshin elevated expressway, and left 6,000 dead and 34,000 injured.

1The Richter scale is widely used to express the magnitude of an earthquake by the quantity of energy released. The highest value yet registered is 9.5. Editor

- Northridge, California (U.S.A.), 17 January 1994. Also striking before dawn, this 6.8 magnitude quake affected 3.5 million people and led to the highest earthquake insurance payout in history - more than $13 billion in claims. Its centre was 20 km from downtown Los Angeles and damage was estimated at $40 billion. It damaged parts of the elevated freeway system, left 50,000 people homeless and 15,000 injured. Sixty-one people were killed. Spitak (Armenia), 7 December 1988. A 6.9 magnitude earthquake in mid-morning, it demonstrated the well-known weakness of unreinforced old buildings. But many new reinforced concrete buildings collapsed too, among them schools and hospitals. Some 25,000 people were killed and reconstruction cost $16 billion.

- Mexico, 19 September 1985. Its epicentre was 400 km (240 miles) from Mexico City, but its magnitude (8.1) brought down 400 government buildings, hospitals, schools, businesses and high-rise apartment blocks in the old lake bed area of the city. Between 5,000 and 10,000 people were killed and losses were estimated at $5 billion.

- Tangshan (China), 28 July 1976. A 7.8 magnitude quake which struck in the middle of the night while most of the million people living and working in this industrial and coal-mining centre in northern China were asleep. The city - mostly unreinforced buildings - was devastated. At least 240,000 people died and 800,000 were injured. Reconstruction took more than a decade.


Droughts may be annual or may occur once every few years. They can last for many years, devastating agriculture and creating deserts. Two major droughts:

- The Sahel (Africa), 1969-73. From 1968, a lengthy drought in West Africa extended across the Sahara Desert southwards in the Sahel countries of Mauritania, Senegal, Mali, Burkina Faso and Chad. It was no worse than many previous ones, but 250,000 people died and millions of refugees poured into cities. Millions of head of livestock died. Farm production dropped sharply.

- The “Dust Bowl,” Mid-Western U.S., 1930s. This 10-year drought spread across the entire Great Plains from North Dakota to Texas. One dust storm in May 1934 carried hundreds of millions of tons of earth for thousands of kilometres. In one day, Chicago was covered with 12 million tons of dust and distant New York City had many gloomy, dusty days. Wheat and corn production fell by up to 75%. Hundreds of thousands of people fled the area for places further west.

In Somalia, a development worker and a local official discuss a sand dune stabilization programme designed to combat desertification. [© Jeremy Hartley/Panos Pictures, London]

St. Charles (U.S.A.), one of many towns in the states of Illinois and Missouri that were flooded in July 1993 when the Mississippi River overflowed its banks. [Ira Schwartz/Reuters/MAXPPP, Paris]


The most common natural hazard, mainly caused by flash floods after very heavy rain or from melting ice and snow. Towns and villages on the coast or in river plains are most at risk. Floods cause property damage, social disruption and health care problems and damage the environment (mainly soil erosion and pollution). Some major recent floods:

- The U.S. Midwest in April 1997 and the eastern U.S. in January 1996. Heavy snowfall and then a rapid thaw along with heavy rain flooded North Dakota in 1997 and river valleys from New York to Philadelphia to Virginia in 1996. More than 100,000 people, including entire communities, were evacuated. Losses exceeded $2 billion - mainly damage to buildings, infrastructure, dams and bridges.

- Italy, 4-5 November 1966. After many hours of rain, the River Arno burst its banks. Florence was soon under five metres of water. Moving at more than 130 km/hour, the flood made 12,000 people homeless, inundated more than 5,000 homes, destroyed some 10,000 cars and the contents of half the city’s shops, knocked out the electricity, water and sewage systems and destroyed bridges. Worst of all, oil from broken oil tanks mixed with nearly a million tons of mud and ruined more than a million art treasures.


Chart showing the travel-time of a tsunami caused by an undersea earthquake in the middle of the Pacific. [© International Tsunami information Center, Honolulu]

These are usually set off by undersea earthquakes and can travel across oceans at the speed of a jet airliner, smashing into coastal towns and villages with waves 30 metres high.

On 22 May 1960, a 9.5 magnitude undersea earthquake set off a tsunami which destroyed 400,000 houses along 1,000 km of coastline, leaving 5,000 people dead. The ground shook for three and a half minutes and subsided as much as two metres. Tsunamis with waves as high as 10 metres affected every Pacific rim country, damaging ships, flooding coastal areas and destroying buildings and factories.


These occur daily all over the world and are caused either by heavy rains or earthquakes. A big quake can can set off tens of thousands of landslides of all sizes.

One such disaster occurred in Peru, on 31 May 1970, when a 7.6 magnitude earthquake centred 25 km off Chimbote, on the north coast of Peru, caused Latin America’s biggest recorded landslide. A mass of ice 5,500 metres up Mt Huascaran was dislodged and in three minutes had slid down a glacier and travelled another 10 km to bury the towns of Yungay and Ran-rahirca, killing all but 400 of their 20,000 inhabitants. In Chimbote, 96% of the town’s adobe houses were destroyed by ground tremors and more than a thousand people killed.

Hurricanes, cyclones, typhoons and tornadoes

In the wake of Hurricane Gilbert, Jamaica (September 1988). [© Richards/Liaison/Gamma, Paris]

These tend to be seasonal and confined to certain parts of the world. Coastal settlements are most at risk. Physical damage and social disruption are caused by high winds, storm surge floods, very heavy rain, beach and coastal erosion, lightning and hail.

Notable storm disasters in recent years:

- East Pakistan and Bay of Bengal, 12-13 November 1970. Winds of up to 240 km/hr and a storm surge flood killed about 596,150 people in Bangladesh. More than four million people were affected, 335,000 houses damaged and 264,000 head of cattle killed.

- Bangladesh, 30 April 1991. A typhoon whipped up an eight-metre storm surge which hit the city of Chittagong after midnight, leaving 10 million people homeless, some 200,000 dead and 139,000 injured. More than 1.5 million buildings were damaged. An early warning system, evacuation and the use of cyclone shelters meant that casualties were fewer than in the 1970 disaster.

- The Caribbean, 10 September 1988. Hurricane Gilbert, dubbed “the storm of the century”, hit the eastern Caribbean and caused unprecedented devastation as it swept across Guadeloupe, Martinique, St Lucia, Puerto Rico, the Dominican Republic, Haiti, Jamaica and Mexico. A fifth of all the houses in Jamaica were destroyed or badly damaged by high winds and half a million Jamaicans were left homeless. Banana plantations, coffee trees and food crops were ruined by flooding, winds and landslides. Surprisingly few lives were lost but economic losses were more than a billion dollars.

A village devastated by a mud flow during the eruption of Mt. Pinatubo (Philippines) in June 1991. [Aventurier/Loviny/Gamma, Paris]

Volcanic eruptions

The world’s 500 active volcanoes erupt infrequently, but when they do, the effects can be devastating. Nearby towns can be affected by clouds of volcanic ash (which can also seriously threaten aircraft in the area), lateral blasts, pyroclastic flows of red-hot rocks and gases, lava flows and lahars (debris flows). A major explosive eruption can affect the world’s climate.

Notable volcano disasters include:

- Mt. Pinatubo, in the Philippines, 15-16 June 1991. This was the biggest volcanic eruption of the century. It lasted 15 hours and sent ash 30 km into the sky and set off pyroclastic flows and lahars. More than 200,000 people, including those at the U.S. dark Air Force Base, were evacuated - the largest-ever evacuation before a volcanic eruption. Typhoon Yunya passing 50 km to the north added to the disaster. Because of the evacuation, the death toll was limited to 320, but the region was economically devastated. Strategic military alliances were altered by the eruption as the Clark base was abandoned.

- Nevado del Ruiz (Colombia), 13 November 1985. After being dormant for 140 years, the volcano erupted and hot pyroclastic material melted the mountain’s ice cap and set off lahars. These travelled at 30 km/hr along four river beds to the towns of Armero and Chinchina. The debris buried the towns late at night, killing 24,740 people, injuring 5,485 and destroying 5,680 homes.

- Agung (Ball), 1963. Two violent eruptions in March and May generated a huge hot ash cloud and set off lahars, which killed 1,148 people and injured 296. Seventy-three villages were destroyed, leaving 70,000 people homeless and 400,000 destitute. They also destroyed 54,289 hectares of farmland and 11,745 hectares of forest and swept away bridges and roads.


A forest fire near Marseilles (France) on 26 July 1997. More than 3,000 hectares of pine forest and scrub were destroyed. [Philippe Laurenson/Reuters/MAXPPP, Paris]

Thousands of wildfires flare up every year around the world, threatening towns and villages. Many are caused by hot, dry summers and set off by lightning. Others are started by lava flows or triggered by earthquakes. A few are the result of arson.

One recent major wildfire disaster occurred in Great Khingan Range (China), on 6 May 1987. Fanned by high winds for 20 days, the fires burned down 750,000 cubic metres of forest over a million hectares - 13% of the total forested area or a fifth of the annual timber production of the region. The fire killed 191 people.