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Most Recent Natural Disasters Were Not the Century's Worst, USGS Says

Courtesy of the U.S. Geological Survey

Dateline: 12/30/99

Killer landslides in Venezuela and Mexico. Devastating earthquakes in Turkey and Taiwan. Massive floods along the East Coast of the United States. Nature has dealt staggering blows to the Earth and its people in 1999. But these were not the worst disasters of the century, either in the power of the events or in the loss of life and property that they caused.

"The costs of natural disasters -- lives lost, homes destroyed, economies disrupted -- have skyrocketed in this century, as the world's population has grown and has moved onto areas that are vulnerable to earthquakes, hurricanes, landslides, and other natural hazards," said USGS Director Chip Groat. "But there is reason for hope. By understanding how and where these natural events occur, so that we can build and live safely on the Earth, and by providing real-time information about floods, earthquakes, and other hazards, so that we can respond effectively when disaster strikes, the USGS is helping build stronger, safer communities that are resilient to natural disaster."

Landslides

Landslides, lethal mixtures of water, rocks, and mud, generally are triggered by earthquakes, volcanoes, or weather events. The two largest landslides in the world this century occurred at Mount St. Helens, Washington, in 1980 and at Usoy, Tajikistan, in 1911. At Mount St. Helens, a moderate earthquake caused roughly 1.7 cubic miles of rocks and mud to break free and slide down the side of the volcano, releasing pent-up pressure to produce the major eruption of May 18. Although this was the largest landslide recorded in historic time, fewer than 60 people were killed because most residents and visitors had been evacuated. The Usoy landslide, also triggered by an earthquake, moved 1.5 cubic miles of material and built a dam 1880 feet high (half again as high as the Empire State Building) on the Murgob River; the dam still impounds a lake nearly 40 miles long. This landslide took place in a sparsely populated area and thus caused few deaths.

An earthquake was responsible for the deadliest landslide this century, which caused 40,000-50,000 deaths in western Iran on June 20, 1990. A magnitude 7.8 earthquake at Mount Huascaran, Peru, on May 21, 1970, triggered a rock and snow avalanche that buried the towns of Yungay and Ranrahirca, killing perhaps as many as 20,000 people.

Weather-related landslides also proved deadly in recent years. The death toll is still unclear from the rain-caused landslides that hit Venezuela in mid-December of this year; official estimates are as high as 30,000 deaths. On October 30, 1998, the day of peak rainfall as Hurricane Mitch moved across Central America, the side of Casita Volcano collapsed, creating a landslide/mudflow that wiped out two towns in Nicaragua and killed more than 2,000 people.

The most costly landslide in U.S. history was a relatively slow-moving event in Thistle, Utah, in the spring of 1983. The landslide, caused by the wet El Nino winter of 1982-83, dammed the Spanish Fork River and buried U.S. Highway 6 and the main line of the Denver and Rio Grande Western Railroad. The town of Thistle was inundated under the floodwaters rising behind the landslide dam. Total losses were estimated at more than $400 million in 1983 dollars.

Earthquakes

The largest earthquake this century was a magnitude 9.5 event that struck Chile on May 22, 1960. More than 2,000 people were killed in Chile, Hawaii, Japan, and the Philippines from this earthquake and the deadly tsunami that the earthquake created. The most powerful earthquake in the United States, and the second largest in the world this century, was a magnitude 9.2 temblor in Alaska, the Good Friday earthquake of 1964. This great earthquake and ensuing tsunami took 125 lives and caused about $310 million in property loss.

The planet's deadliest earthquake of the century, by far, was a magnitude 8.0 that struck Tianjin , China, on July 27, 1976. The official casualty figure issued by the Chinese government was 255,000, but unofficial estimates of the death toll were as high as 655,000. The most destructive U.S. earthquake was the Great San Francisco earthquake of April 18, 1906. Though its magnitude was 7.7, and the energy less than 1/30th the energy released by the 1964 Alaska event, the San Francisco earthquake and resulting fires caused an estimated 3,000 deaths and $524 million in property loss.

Volcanoes

The largest eruption in the world this century occurred June 6-9, 1912, at Novarupta on the Alaska Peninsula. An estimated 9 cubic miles of magma was explosively erupted during 60 hours beginning on June 6 - more than twice the volume of the Pinatubo eruption in 1991, the second largest this century, and about 30 times the volume erupted by Mount St. Helens in 1980. More than a foot of volcanic ash from this enormous eruption collapsed roofs in the village of Kodiak, 100 miles away, and choked rivers and streams, devastating Alaska's fishing industry. Several villages along Alaska's southeast coast were abandoned forever. Because most of the native populations heeded the volcano's warning signals and evacuated before the climactic eruption, few or no people were killed, although animal and plant life suffered greatly--bears, other large mammals, and birds were blinded by ash and starved when the plants and small mammals they depended on were destroyed.

The eruption of Mount Pinatubo, Philippines, on June 15, 1991, blasted about 1 cubic mile of ash and rock into the atmosphere. Avalanches of hot ash, gas, and fragments of pumice roared down the mountainside, filling valleys with as much as 600 feet of volcanic debris. The deposits will retain much of their heat for decades; even 5 years later they were measured at 900 degrees F. Close cooperation between the USGS and the Philippine Institute of Volcanology and Seismology enabled the eruption to be forecast accurately, saving at least 5,000 lives.

The deadliest eruption of the century was at Mont Pelée in Martinique, Lesser Antilles, in 1902. The coastal town of St. Pierre, about 4 miles downslope to the south, was demolished, and nearly 30,000 inhabitants were killed by an incandescent, high-velocity ash flow and associated hot gases and volcanic dust. And a small eruption of the Nevado del Ruiz volcano in Colombia on November 13, 1985, melted about 10 percent of the volcano's ice cover, leading to a massive mudflow that inundated the city of Armero and killed more than 23,000 people.

Floods

On average, floods cause more deaths each year than any other natural disaster, and the Galveston hurricane-induced flood of September 1900 was by far the deadliest flood in the United States this century, taking at least 6,000 lives. In 1927, the lower Mississippi flooded, inundating around 27,000 square miles and killing hundreds of people - more than 1,000 by some estimates. The great Midwest flood of 1993 was the costliest flood in U.S. history, with estimated damages of $20 billion; however, only around 50 lives were lost.

U.S. losses of life are dwarfed by flood losses in other parts of the world. China and Bangladesh have been devastated repeatedly by floods - Bangladesh lost 300,000 people in November 1970 and more than 130,000 in April 1991, from cyclone-induced flooding, and the massive flooding of the Yangtze River in China in 1931 caused more than 3 million deaths from flooding and starvation.

"Earthquakes, landslides, floods - these hazards are part of the way the Earth operates," said USGS Director Chip Groat. "Although we can't prevent natural hazards from happening, we can learn from them, and use this knowledge to prevent natural hazards from turning into natural disasters." "The next century gives us a new chance to apply the lessons we have learned about natural hazards," said Groat. "As we look ahead to the next millennium, we must continue to improve both our understanding of how the earth works and our ability to provide timely, effective, warnings, so that we can live safely on our planet."

As the nation's largest water, earth and biological science and civilian mapping agency, the USGS works in cooperation with more than 2,000 organizations across the country to provide reliable, impartial scientific information to resource managers, planners and other customers. This information is gathered in every state by USGS scientists to minimize the loss of life and property from natural disasters, to contribute to the conservation and the sound economic and physical development of the nation's natural resources, and to enhance the quality of life by monitoring water, biological, energy, and mineral resources.

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