Floods kill an estimated 25,000 people a year worldwide. They are caused by a number of thing, most of them related to large amounts of rain and storms. A United Nations study released in June 2004, predicted that 2 billion people could be vulnerable t floods as a result of global warming, deforestation and population growth in flood prone areas, Currently about 1 billion people are vulnerable to flooding.

Flooding is an overflowing of water onto land that is normally dry. It can happen during heavy rains, when ocean waves come onshore, when snow melts too fast, or when dams or levees break. Flooding may happen with only a few inches of water, or it may cover a house to the rooftop. The most dangerous flood event, the flash flood, happens quickly with little or no warning; other flooding events occur over a long period and may last days, weeks, or longer.

Deforestation, Flooding and Run Off Water

The trees and plants in a rainforest hold water like a sponge and gently distribute it the springs and streams. Without trees the water flows off the land n a great rush, eroding soil and quickly filling streams, causing floods and flood and drought conditions.

Rainforests also hold water from the wet season and slowly release it in the dry season. One study found that rivers flowing through primary forests release double the amount of water halfway through the dry season, and between three to five times more at the end of the dry season that those flowing through areas were forest have been replaced by coffee plantations.

Deforestation reduces the quality of the water that runs of the land surface and increases the amount of soil washed away. Water is cleansed when it percolates through soil with tree roots and soil that is anchored in place. It becomes dirty when the there are no roots and the soil washes away easily. One sign of a good healthy rainforest is clear river water. The slightest disturbance can set off erosion, causing the water to become muddy and brown.

A study released in 2005 by the United Nations and the Indonesia-based Center for International Forestry Research concluded that major flood was the result of major climatic patterns rather than deforestation and human elated activities such as logging and slash and burn agriculture. The study found that flooding was not significantly different in areas covered in rich forest and those that had been deforested and the floods were caused by prolonged periods of rain.

The conventional wisdom had been that forests prevented floods by acting as giant sponges, and soaking up water from heavy rains. According to the report, flooding “is a natural process that would have happened no matter what, Whether you had deforested, farmed, or logged, the amounts of water involved and the severity of these floods is just overwhelming.” Other studies have found that flooding in valleys increases after deforestation.

Types of Floods

A river flood occurs when water levels rise in a river due to excessive rain from tropical systems making landfall, persistent thunderstorms over the same area for extended periods of time, combined rainfall and snowmelt, or an ice jam.

Coastal flooding occurs when a hurricane, tropical storm, or tropical depression produces a deadly storm surge that overwhelms coastal areas as it makes landfall. Storm surge is water pushed on shore by the force of the winds swirling around the storm. This advancing surge combines with the normal tides to create the hurricane storm tide, which can increase the average water level 15 feet or more. The greatest natural disaster in the United States, in terms of loss of life, was caused by a storm surge and associated coastal flooding from the great Galveston, Texas, hurricane of 1900. At least 8,000 people lost their lives.

When tropical cyclones move inland, they are typically accompanied by torrential rain. If the decaying storm moves slowly over land, it can produce rainfall amounts of 20 to 40 inches over several days. Widespread flash flooding and river flooding can result.

Flash Floods

A flash flood is a rapid rise of water along a stream or low-lying urban area. Flash flooding occurs within six hours of a significant rain event and is usually caused by intense storms that produce heavy rainfall in a short amount of time. Excessive rainfall that causes rivers and streams to swell rapidly and overflow their banks is frequently associated with hurricanes and tropical storms, large clusters of thunderstorms, supercells, or squall lines. Other types of flash floods can occur from dam or levee failures, or a sudden release of water held by an ice jam. Heavy rainfall in the mountains can cause downstream canyon flooding.

Flash floods can occur with little or no warning. Flash flood damage and most fatalities tend to occur in areas immediately adjacent to a stream or arroyo. Flash floods are very strong -- they can roll boulders, tear out trees, destroy buildings and bridges, and scour out new channels. Rapidly rising water can reach heights of 30 feet or more. Flash flood-producing rains falling on steep terrain can weaken soil and trigger catastrophic mud slides that damage homes, roads, and property.

Densely populated areas are at a high risk for flash floods. The construction of buildings, highways, driveways, and parking lots increases runoff by reducing the amount of rain absorbed by the ground. This runoff increases the flash flood potential. Sometimes, streams through cities and towns are routed underground into storm drains. During heavy rain, the storm drains can become overwhelmed and flood roads and buildings. Low spots, such as underpasses, underground parking garages, and basements can become death traps.

Areas near rivers are at risk from flash floods. Embankments, known as levees, are often built along rivers and are used to prevent high water from flooding bordering land. In 1993, many levees failed along the Mississippi River, resulting in devastating flash floods. The city of New Orleans experienced massive devastating flooding days after Hurricane Katrina came onshore in 2005 due to the failure of levees designed to protect the city.

Dam failures can send a sudden destructive wall of water downstream. Heavy rainfall saturates and weakens earth-filled dams, which make up about 80 percent of the approximately 76,000 dams in the U.S. In 1889 a dam break upstream from Johnstown, Pennsylvania, released a 30-40 foot wall of water that killed 2200 people within minutes.

Vacationing or recreating along streams or rivers can be a risk if there are thunderstorms in the area. A creek only 6 inches deep in mountainous areas can swell to a 10-foot deep raging river in less than an hour if a thunderstorm lingers over an area for an extended period of time. Mountains and steep hills produce rapid runoff and causes streams to rise quickly. Rocks and clay soils do not allow much water to infiltrate the ground. Saturated soil also can lead rapidly to flash flooding

Very intense rainfall can produce flooding even on dry soil. In the West, most canyons, small streams and dry arroyos are not easily recognizable as a source of danger. A wall of water 10-15 feet high can scour a canyon suddenly. Additional high-risk locations include low water crossings, recent burn areas in mountains, and urban areas from pavement and roofs which concentrate rainfall runoff.

Ice jams and snowmelt can help cause flash floods. A deep snowpack increases runoff produced by melting snow. Heavy spring rains falling on melting snowpack can produce disastrous flash flooding. Melting snowpack may also contribute to flash floods produced by ice jams on creeks and rivers. Thick layers of ice often form on streams and rivers during the winter. Melting snow and/or warm rain running into the streams may lift and break this ice, allowing large chunks of ice to jam against bridges or other structures. This causes the water to rapidly rise behind the ice jam. If the water is suddenly released, serious flash flooding could occur downstream. Huge chunks of ice can be pushed onto the shore and through houses and buildings.


Landslides kill between 800 and 1,000 people a year. Many of the deaths are in Asia, where large numbers of people live in landslide-prone areas. Landslides generally occur on steep , unstable slopes after intense and extreme rainfalls. There are concerns that global warming could increase the risks of landslides.

A landslide is defined as "the movement of a mass of rock, debris, or earth down a slope". Landslides are a type of "mass wasting," which denotes any down-slope movement of soil and rock under the direct influence of gravity. The term "landslide" encompasses five modes of slope movement: falls, topples, slides, spreads, and flows. These are further subdivided by the type of geologic material (bedrock, debris, or earth). Debris flows (commonly referred to as mudflows or mudslides) and rock falls are examples of common landslide types.

Landslides can move slowly, (millimeters per year) or can move quickly and disastrously, as is the case with debris flows. Debris flows can travel down a hillside at speeds up to 200 miles per hour (more commonly, 30 - 50 miles per hour), depending on the slope angle, water content, volume of debris, and type of earth and debris in the flow. These flows are initiated by heavy, usually sustained, periods of rainfall, but sometimes can happen as a result of short bursts of concentrated rainfall or other factors in susceptible areas. Burned areas charred by wildfires are particularly susceptible to debris flows, given certain soil characteristics and slope conditions.

Although the physical cause of many landslides cannot be removed, geologic investigations, good engineering practices, and effective enforcement of land-use management regulations can reduce landslide hazards. Scientists to produce landslide susceptibility maps and monitor streamflow, noting changes in sediment load carried by rivers and streams that may result from landslides. Hydrologists with expertise in debris and mud flows are studying these hazards in volcanic regions.

Causes of Landslides

Although gravity acting on an over-steepened slope is the primary reason for a landslide, there are other contributing factors: 1) erosion by rivers, glaciers, or ocean waves create oversteepened slopes; 2) rock and soil slopes are weakened through saturation by snowmelt or heavy rains; 3) earthquakes create stresses that make weak slopes fail; 4) earthquakes of magnitude 4.0 and greater have been known to trigger landslides; 5) volcanic eruptions produce loose ash deposits, heavy rain, and debris flows; 6) excess weight from accumulation of rain or snow, stockpiling of rock or ore, from waste piles, or from man-made structures may stress weak slopes to failure and other structures

Almost every landslide has multiple causes. Slope movement occurs when forces acting down-slope (mainly due to gravity) exceed the strength of the Earth materials that compose the slope. Causes include factors that increase the effects of down-slope forces and factors that contribute to low or reduced strength. Landslides can be initiated in slopes already on the verge of movement by rainfall, snowmelt, changes in water level, stream erosion, changes in ground water, earthquakes, volcanic activity, disturbance by human activities, or any combination of these factors. Earthquake shaking and other factors can also induce landslides underwater. These landslides are called submarine landslides. Submarine landslides sometimes cause tsunamis that damage coastal areas.

Slope material that become saturated with water may develop a debris flow or mud flow. The resulting slurry of rock and mud may pick up trees, houses, and cars, thus blocking bridges and tributaries causing flooding along its path.

Where do Landslides Occur? Any area composed of very weak or fractured materials resting on a steep slope can and will likely experience landslides. The world's biggest historic landslide occurred during the 1980 eruption of Mount St. Helens, a volcano in the Cascade Mountain Range in the State of Washington, USA. The volume of material was 2.8 cubic kilometers (km).

The world's biggest prehistoric landslide, discovered so far on land, is in southwestern Iran, and is named the Saidmarreh landslide. The landslide is located on the Kabir Kuh anticline in Southwest Iran at 33 degrees north latitude, 47.65 degrees east longitude. The landslide has a volume of about 20 cubic kilometers, a depth of 300 m, a travel distance of 14 km and a width of 5 km. This means that about 50 billion tons of rock moved in this single event!

Large Landslides in the Early 20th Century

This list provides an overview of large landslides that have occurred around the world in the 20th and 21st centuries, and which have had notable socio-economic impacts. Socio-economic impacts include deaths, injuries, monetary losses, and effects on the built and natural environments. The criteria used for inclusion in the list are (1) at least 100 deaths and/or (2) major monetary losses, and/or (3) notable effects on the natural environment. The information includes: Year , Location, Name & Type, Trigger, Size, Impact.

1911 Tajikistan, Usoy rock slide, Usoy earthquake (Magnitude 7.4), 2 billion m3 (volume). Usoy Village was destroyed, causing 54 deaths. The rockslide dammed the Murgab River, impounding 65-km- long Lake Sarez,which presently still exists. The area remains a hazard due to the possibility of another landslide sliding into the lake, causing a wave, and/or breaching of the dam, as thousands of people live downstream of the dam.

1914, Argentina , Rio Barrancas & Rio Colorado debris flow, Failure of ancient landslide dam , 2 million government (volume), Length of flow: 300 km , Two small towns were devastated, and numerous ranches and farms destroyed along a 60-km- long valley. The flows devastated valleys of the Rio Barrancas and Rio Colorado.

1919 , Indonesia (Java) , Kelut lahars , Eruption of Kelut Volcano , 185 km (length) , Lahars caused 5,110 deaths, and destroyed or damaged 104 villages.

1920 , China, Gansu, Haiyuan , Loess flows, landslides , Haiyuan Earthquake Magnitude 8.5, 10 min. duration of shaking , 50,000 km2(area) , There were 100,000+ deaths from landslides and the failures in loess caused extreme fissuring, landslide dams, and buried villages.

1920 , Mexico , Rio Huitzilapan debris flows , Earthquake, Magnitude 6.5-7.0, based on reported intensities , more than 40 km (length) , There were an estimated 600 - 870 deaths. The flow destroyed village of Barranca Grande, and there were enormous debris flows of 40 to 65 m deep.

1921 , Kazakh Republic , Alma-Ata debris flow , Snow melt, subsequent rainfall , A debris flow in the Valley of Alma-Atinka River destroyed the town of Alma-Ata. There were 500 deaths.

Large Landslides in the Mid 20th Century

1933, China (Sichuan) , Deixi landslides , Deixi Earthquake, Magnitude 7.5 , more than 150 million m3 (volume) , The largest landslide formed a 255-m high landslide dam on the Min River. This landslide killed all but one of the 577 people in the town of Deixi. The dam then overtopped, causing a flood and 2,500 deaths.

1938 , Japan (Hyogo) , Mount Rokko Landslides and mudflows , Rainfall , There were 505 deaths (or missing) and 130,000 homes were destroyed or badly damaged by landslides and floods.

1941 , Peru , Huaraz debris flow , Failure of moraine dam , 10 million government (volume), The debris flow destroyed one-fourth of the town of Huaraz, and 4,000-6,000 deaths were reported. The debris flow dammed the Rio Santa River and the later dam failure caused flooding which destroyed downstream settlements and farms.

1945 , Peru , Cerro Condor-Sencca Rockslide , Erosional under-cutting , 5.5 million m3 (volume) , The rockslide formed a 100-m-high dam at Rio Montara, which failed after 73 days, causing a flood. Many roads, 13 bridges and extensive farmland was destroyed, and effects from the rockslide completely changed the morphology of the Rio Montara river valley.

1949 , Tajikistan (Tien Shan Mtns.) , Khait landslides, rock avalanches, flowslides , Khait Earthquake, Magnitude 7.4 , 245 million government (volume), The Khait landslide itself: 75 million m3 (volume) , There were approximately 7,200 deaths and the settlements of Khait and Khisorak were inundated. Many of the landslides were coalescing slides, composed of loess.

1953 , Japan (Wakayama) , Arida River landslides, mud flows, and debris flows , Rainfall, Heavy rain fell, due to a major typhoon. There were 1,046 deaths and many landslide dams were formed and subsequently failed in the Arid-Kawa valley.

1953 , Japan (city of Kyoto) , Minamiyamashiro landslides, mud flows, and debris flows , Rainfall , There were 336 dead or missing. 5,122 homes were destroyed or badly damaged by landslides and floods.

1958, Japan (Shizuoka) , Kanogawa landslides, mud flows, and debris flows , Rainfall , , There were 1,094 deaths and missing. 19,754 homes were destroyed or badly damaged.

1960 , Chile , Rupanco region , Valdivia Earthquake, Magnitude 7.5 Preceded by heavy rain , 40 million government (volume) , 210 deaths occurred, from many large landslides; A landslide dam was formed, and buildings, port, facilities, roads & agricultural fields were destroyed.

1962 , Peru (Ancash), Nevados Huascaran debris avalanche , Not known , 13 million m3 (volume) , There were 4,000 - 5,000 deaths and much of the village of Ranrahirca was destroyed. (Mt. Huascaran is the highest peak in the Peruvian Andes).

1963 , Italy (Friuli-Venezia Griulia , Vaoint Reservoir rockslide , Not known , 250 million m3 (volume) , There were 2,000 deaths. The city of Longarone was badly damaged. This high-velocity rockslide slid into Vaiont Reservoir and caused 100-m waves to overtop Vaiont Dam. The losses were $200 million, in 1963 dollars.

1964 , United States (Alaska) , Alaska earthquake Landslides (a.k.a. Prince William Sound earthquake) , Alaska earthquake, Magnitude 9.0 , 211 million government (volume) submarine landslide at Seward; Turnagain Heights landslide, 9.6 million m3 (volume); Government Hill landslide, 700,000 government (volume) , Estimated losses were $280 million (1964 dollars). There was major landslide damage in the cities of Whittier, Anchorage, Valdez and Seward. Submarine landslides generated a tsunami at Seward, as a 1.2 km-long waterfront section slid into water. There were 106 deaths from the Seward tsunami and 16 deaths from a tsunami that occurred in California and Oregon.

1965 , China (Yunnan) , Rockslide , Not known , 450 million m3 (volume) , Four villages were destroyed, causing 444 deaths.

1966 , Brazil (city of Rio de Janeiro) , Landslides, avalanches, mud flows and debris flows , Rainfall , There were 1,000 deaths, mostly in the city of Rio de Janeiro. , 12, 53, 59

Large Landslides in the Late 20th Century

1970 , Peru (Ancash) , Nevados Huascaran debris avalanche , Earthquake, Magnitude 7.7 , 30 - 50 million m3 (volume) , There were 18,000 deaths. The town of Yungay was destroyed, and the town of Ranrahirca was partially destroyed

1974 , Peru , Mayunmarca rockslide/debris avalanche , Rainfall , 1.6 billion m3 (volume) , This debris avalanche averaged a velocity of 140 km/hr. It dammed the Mantaro River causing 450 deaths. Many houses, farms, and roads were destroyed.

1976 , Guatemala , Guatemala earthquake landslides , Guatemala Earthquake, Magnitude 7.5, 10,000 landslides over an area of 16,000 km2 , There were at least 200 deaths, and highways and railroads were disrupted. In addition, 500 dwellings were damaged. Most damage occurred in Guatemala City.

1980 , China (Yichang, Hubei) , Yanchihe Rock avalanche , Mining activity - occurred on man-made layered slopes , 150 million m3 (volume) , The rock avalanche extensively damaged this phosphorite mining area and caused 284 deaths.

1980 , United State (Washington) , Mount St. Helens rockslide/debris avalanche , Eruption of Mount St. Helens volcano , 3.7 billion m3 (volume) , This is the world's largest historical landslide. There were 57 deaths and 250 homes, 47 bridges, and 24km of rail were destroyed. There was 298km of highway destroyed. The rockslide transformed into a 23-km-long debris avalanche with average velocity of 25 km/hr.; surface remobilized into a 95-km-long debris flow. Deaths were low due to prior evacuation of the area.

1983 , United States (Utah) , Thistle Debris slide , Snow melt and subsequent rainfall , 21 million m3 (volume) , This landslide destroyed major railroads and highways, and dammed the Spanish Fork Rive flooding the town of Thistle. There were no deaths, but it is the most expensive landslide to fix in U.S. history. The rerouting of a major road and railroad amounted to $600 million in losses (1983 dollars).

1983 , China (Gansu) , Saleshan landslide , Rainfall , 35 million government (volume) , The landslide caused 237 deaths and buried 4 villages, and also filled two reservoirs. This event is also known as a loess landslide.

1983 , Ecuador , Chunchi , Rain and/or snow (wettest year of century) , 1 million m3 (volume) , There were 150 deaths and the debris blocked the Pan American Highway.

1985 , Colombia (Tolima) , Nevado del Ruiz debris flows , Eruption of Nevado del Ruiz volcano , Four towns and villages were destroyed. The debris flowed into the Lagunillas River Valley, and there were 23,000 deaths in the city of Armero, as hazard warnings were not passed on to the population.

1985 , Puerto Rico (city of Mameyes) , Landslide , Rainfall from tropical storm , , There were 129 deaths, making it the most deadly landslide to occur In North America. Tropical storm rainfall together with a possible leaky sewer pipe saturated the hillside and destroyed 120 houses.

1986 , Papua, New Guinea (East New Britain) , Bairaman rockslide/debris avalanche , Bairaman earthquake, Magnitude 7.1 , 200 million m3 (volume) , The debris avalanche formed a 21 m-high dam and impounded a 50-million m3 lake; the dam then failed causing a 100-m-deep debris flow and flood downstream. The village of Bairaman was destroyed by the debris flow from the breached dam. Casualties were prevented by evacuation.

1987 , Ecuador (Napo) , Reventador landslides , Reventador earthquakes, Magnitude 6.1 and 6.9 and rainfall , 75 - 110 million m3 (volume) , There were 1,000 deaths and many kilometers of the Trans-Ecuadorian oil pipeline and highway were destroyed. Thousands of thin slides remobilized into debris flows in a tributary and in main drainages. Losses were reported to be $1 billion (1987 dollars).

1987 , Venezuela , Rio Limon, debris flow , Rainfall , 2 million m3 (volume) , There were 210 deaths, 400 injured, 30,000 homeless. 1,500 homes, 500 vehicles, three bridges, and 25 km of roads were damaged or destroyed.

1987 , Colombia , Villa Tina, soil slide , Pond leakage , 20 million m3 (volume) , There were at least 217 deaths, and 80 houses were destroyed.

1988 , Brazil , Rio de Janeiro and Petropolis landslides, avalanches, and debris flows , Rainfall , , Approximately 300 deaths occurred, and many structures were destroyed. , 18, 53 1989 , China (Huaying, Sichuan) , Xikou landslide , Rainfall, 221 deaths were reported.

1991 , China (Zhaotong, Yunan) , Touzhai landslide , Rainfall , 18 million m3 (volume) , 216 deaths were reported.

1991 , Chile , Antofagasta debris flows , Rainfall , 500 - 700 million m3 (volume) , "Hundreds" of deaths were reported, and a large number of homes were damaged. The water-supply system was heavily damaged as were many roads and railway lines. , 18, 53

1993 , Ecuador , La Josefina rockslide , Mine excavation & heavy rainfall , 20-25 million m3 (volume) , The landslide formed a 100-m high dam on Rio Paute. The failure of the dam 33 days later caused a flow of 10,000 M3/s. Many roads, 13 bridges, and much farmland was destroyed, however, there were no casualties.

1994 , Colombia (Cauca) , Paez landslides , Paez earthquake, Magnitude 6.0 , 250 km2 (area) , There were 272 deaths, 1,700 missing, 158 injured, and 12,000 displaced. "Thousands of landslides" resulted from this earthquake.

1998 , Northern India (Malpa Himalaya Region , Large rockfall/debris avalanche , Rainfall , "large" , This event caused 221 deaths. A landslide dam failed, and caused a debris-flow. Losses were reported as 0.5 million rupees for direct losses, and 0.2 million rupees, for indirect losses.

1998 , Italy (Campania) , Landslides and debris flows , Rainfall , More than 100 individual slope failures , 55 mm of rainfall occurred in one day. There were 161 debris flows individual slope failures deaths in the areas of Sarno, Quindicci, Bracigliano, and Siano. A broken water pipeline is thought to have made some slope saturation worse, although most landslides were not affected by the pipe leak.

1998 , Honduras, Guatemala, Nicaragua, El Salvador , Landslides and debris flows , Rainfall , Hurricane Mitch caused torrential rainfall. Approximately 10,000 deaths from the flooding and landslides occurred. Casitas volcano in Nicaragua experienced large debris flows, as torrential rains occurred at the rate of 10 cm of rain per hour. Large landslides in Tegucigalpa, Honduras, and elsewhere, occurred.

1999 , Venezuela (Vargas, northern coastal area) , Landslides & debris flows , Rainfall , Exact size unknown , Nearly 1m of heavy rain fell in a 3-day period. There were as many as 30,000 deaths. Hundreds of buildings, roads, and houses were destroyed. The landslides caused changes in stream morphology. Losses amounted to $1.9 billion in 2001 dollars. Thousands of landslides reported and debris flows occurred along 24 streams and along 40 km of coastline.

1999 , Taiwan , Landslides , Chi-Chi Earthquake, Magnitude 7.3 , 11,000 km2 (area) , Over 10,000 landslides and large rockslides occurred. The Tsao-ling Rockslide caused 29 deaths and the Ju Feng-er-shan rockslide caused 90 deaths. Urban area landslides caused 39 deaths.

Large Landslides in the 21st Century

2000 , Tibet , Yigong Landslide , Meltwater from, snow and glacier , 100 million m3 (volume) , There were 109 deaths and a landslide dammed the Yigong River. Two months later, the dam breached causing destructive flooding and property loss. 500,000 people were made homeless in 5 districts of Arunanchal Pradesh, India.

2001 , El Salvador , Landslides, lateral spreading, liquefaction , 2 earthquakes, 1/13/2001 Magnitude 7.7 and 2/13/2001 Magnitude 6.6 , , There were thousands of landslides, large landslide in Las Colinas resulting in ~585 deaths. There were reports of liquefaction. The January earthquake caused landslides over a 25,000 km2 area, (including parts of Guatemala). The February earthquake caused landslides over a 2,500 km2 area.

2002 , Russia (North Ossetia) , Kolka Glacier debris flow , Detachment of large glacier, causing a debris flow , Travel distance: 19.5 km; 110 million m3 volume of glacial ice deposited 2 - 5 million m3 of ice (volume) debris at end of runout , A 2.7-km-long glacier mass detached from its bed, accelerated to 65 m/s in under 6 km, and then traveled further, 13 km downstream partway, as an extremely rapid glacier debris flow. It caused 125 deaths, and created a landslide dam.

2003 , Sri Lanka (Ratnapura & Hambantota) , Landslides & debris flows , Rainfall , , There were 260 deaths (some due to floods), at least 24,000 homes and schools destroyed, and 180,000 families were left homeless.

2003 , United States (San Bernardino County, California) , Debris flows , Rainfall , more than 1 million government (total volume) , These debris flows resulted from rainfall on wildfire-burned areas. The fires were the Old and Grand Prix fires, which burned adjacent river basins. 16 people were killed and estimates of losses were 26.5 million, according to the California Office of Emergency Services and U.S. Army Corp of Engineers.

2005 , Pakistan, India , Landslides, rockfalls rock avalanches , Kashmir earthquake, Magnitude 7.6 , Thousands of landslides , The total deaths from all landslides was 25,500. The largest event, the Hattian Bala rock avalanche dammed 2 tributaries of the Jhelum river, and buried a village, causing 1,000 deaths. The size of this rock avalanche is 80 million m3.

2006 , Philippines (Leyte) , Rockslide, debris avalanche , Rainfall , 15 million m3 (volume) , There was 685 mm of rain in the preceding weeks. There were 1,100 deaths and 375 homes and a school were destroyed.

2008 , China (Sichuan) , Landslides, rock avalanches, and debris flows , Wenchuan Earthquake, Magnitude 8.0 , Still being assessed , There were 15,000 landslides, and 20,000 deaths from landslides. There were 66 landslide dams formed, 24 requiring emergency mitigation.

2008 , Egypt (East Cairo) , Al-Duwayqa rockslide , Destabilization due to man-made construction , Affected area was 6,500 m3 in volume and rocks weighed about 18,000 tons , A rockslide buried part of a village, destroying at least 150 houses. There were 107 deaths, 57 injured and a reported 400 missing, and most of these were probably buried under large rocks that could not be excavated. Some experts believe sewage and decomposing garbage on top of the rock scarp caused clay layers to expand, adding to destabilization already present due to construction activities.

2010 , Uganda (Bududa) , Debris flows , Heavy rainfall , Still being assessed and published studies are pending , 400+ deaths, 200,000 displaced

2010 , Brazil (city of Rio De Janeiro) , Debris flows , Heavy rainfall , Still being assessed and published studies are pending , 350 deaths, 61 houses destroyed . [Sources of Information: 1) Harrison, J. V., and Falcon, N.L., 1938, An Ancient Landslip at Saidmarreh in Southwestern Iran, The Journal of Geology, Vol. 46, No. 3, Part I (Apr. - May, 1938), pp. 296-309, The University of Chicago Press; 2) Schuster, Robert L., and Lynn M. Highland, 2001, Socioeconomic Impacts of Landslides in the Western Hemisphere, U.S. Geological Survey Open-File Report 01-9276. http://pubs.usgs.gov/of/2001/ofr-01-0276/ ; 3) USGS Cascades Volcano Observatory Web site: http://vulcan.wr.usgs.gov/home.html

Landslide Preparation and Precautions

Before a Landslide: 1) Avoid building near steep slopes, close to mountain edges, near drainage ways, or natural erosion valleys. 2) Get a ground assessment of your property. 3) Contact local officials, state geological surveys or departments of natural resources, and university departments of geology. Landslides occur where they have before, and in identifiable hazard locations. Ask for information on landslides in your area, specific information on areas vulnerable to landslides, and request a professional referral for a very detailed site analysis of your property, and corrective measures you can take, if necessary. 4) Watch the patterns of storm-water drainage near your home, and note the places where runoff water converges, increasing flow in channels. These are areas to avoid during a storm. 5) Learn about the emergency-response and evacuation plans for your area. Develop your own emergency plan for your family or business. 6) Be aware that strong shaking from earthquakes can induce or intensify the effects of landslides.

Minimize home hazards: 1) Have flexible pipe fittings installed to avoid gas or water leaks, as flexible fittings are more resistant to breakage (only the gas company or professionals should install gas fittings). 2) Plant ground cover on slopes and build retaining walls. 3) In mudflow areas, build channels or deflection walls to direct the flow around buildings. Remember: If you build walls to divert debris flow and the flow lands on a neighbor's property, you may be liable for damages. 4) Design and construction of walls and channels strong enough to resist or divert landslides is highly specialized work, best done by qualified professionals.

During a Storm/Landslide: 1) Stay alert and awake. Many debris-flow fatalities occur when people are sleeping. Listen to a NOAA Weather Radio or portable, battery-powered radio or television for warnings of intense rainfall. Be aware that intense, short bursts of rain may be particularly dangerous, especially after longer periods of heavy rainfall and damp weather.

If you are in areas susceptible to landslides and debris flows, consider leaving if it is safe to do so. Remember that driving during an intense storm can be hazardous. If you remain at home, move to a second story if possible. Staying out of the path of a landslide or debris flow saves lives. If you don’t evacuate: 1) Listen for any unusual sounds that might indicate moving debris, such as trees cracking or boulders knocking together. A trickle of flowing or falling mud or debris may precede larger landslides. Moving debris can flow quickly and sometimes without warning. 2) If you are near a stream or channel, be alert for any sudden increase or decrease in water flow and for a change from clear to muddy water. Such changes may indicate landslide activity upstream, so be prepared to move quickly. Don't delay! Save yourself, not your belongings. 3) Be especially alert when driving. Bridges may be washed out, and culverts overtopped. Do not cross flooding streams!! Turn Around, Don't Drown! Embankments along roadsides are particularly susceptible to landslides. Watch the road for collapsed pavement, mud, fallen rocks, and other indications of possible debris flows.

What to Do if You Suspect Imminent Landslide Danger: 1) Contact your local fire, police, or public works department. Local officials are the best persons able to assess potential danger. Dialing 911 may be the quickest way to get help and/or advice. 2) Inform affected neighbors. Your neighbors may not be aware of potential hazards. Advising them of a potential threat may help save lives. Help neighbors who may need assistance to evacuate. 3) Evacuate. Getting out of the path of a landslide or debris flow is your best protection.

Image Sources: Wikimedia Commons

Text Sources: New York Times, Washington Post, Los Angeles Times, Times of London, Yomiuri Shimbun, The Guardian, National Geographic, The New Yorker, Time, Newsweek, Reuters, AP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.

Last updated January 2012

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