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Causing $1-2 billion in damages and more than 25 deaths per year, landslides are a major geologic hazard, caused by earthquakes and floods. Although, landslides are generally not as exciting or costly as earthquakes, major floods, tropical storms, and other natural disasters, they occur in more expanded places and may cause more property damage than any other geologic hazards.
A wide variety of ground movements, such as rock falls, slope failure, and shallow debris flows can classify landslides. When a portion of a hill slope cannot support its own weight a landslide will occur. When rainfall or some other water source increases the water content of the slope the weakness is irritated, reducing the strength of the materials. Although gravity acting upon an increased slope is the main reason for a landslide, there are other elements that contribute to its cause. Loud sounds that occur during an earthquake also cause landslides. Erosion caused by rivers, glaciers, or ocean waves create oversteepened slopes. Heavy rains and melting snow weaken rock and soil slopes. Furthermore, vibrations from machinery, traffic, and even thunder may trigger failure of weak slopes. Excess water can run through slope material and can cause a debris flow or mud flow. The rock and mud left over after a landslide may pick up anything in its path, such as trees, houses, and cars, causing bridges and tributaries to become blocked which causes flooding throughout its path.
Even though, the natural cause of most landslides is unable to be stopped, geologic investigations, good engineering practices and effective enforcement of land-use management regulations can cut back landslide danger. Landslides effect every state in the United States territory. The Appalachian Mountains, the Rocky Mountains and the Pacific Coastal Ranges and few parts of Alaska and Hawaii have intense landslide problems. USGS marine scientists have recently identified over fifteen giant landslides surrounding the Hawaiian Islands. These slides are some of the largest known on Earth, and most have taken place throughout the past four million years. The youngest landslide is estimated to have occurred only one hundred thousand years ago, and there is evidence today that large blocks of the island are starting to slide, causing enormous earthquakes. Each landslide that has happened over the bast four million years has ended with huge land loss and gigantic waves that move rocks and sediments up to 1000ft above sea level. The geologic hazards are important to learn about because, they don't occur as frequently as volcanoes or other disasters, they have potential to destroy lives, property, and natural resources (Giant Landslides).
It is possible that any area made up of brittle and cracked materials lying on a steep slope will be subject to landslides. Scientists continue to try their best to lower the risk of landslides everywhere by producing landslide susceptibility maps for areas in the United States. Areas that are generally accessible to landslide hazards include: old landslides, bases of slopes, at the base of minor drainage hollows, at the base or top of an old fill slope or steep cut slope, and developed hillsides where leach field septic systems are used. However, there are areas that are safe from landslide activity: on hard bedrock that has not moved in the past, on flat land away from rapid changes in slope angle, and at the top or along the nose of ridges, set back from the tops of slopes.
In order to be prepared for landslides, pay attention to things that might occur before the hazard. These characteristics include wetness of ground that has not been wet before, new cracks or bulges in the ground, sidewalk, or street, cracks in concrete floors and foundations, leaning telephone poles, uneven fence lines, rapid increase of water level in creaks, and movement of soil away from foundations. Incase a landslide does occur, contact local fire, police or public works department, tell affected neighbors, and be sure to evacuate the area.
Giant Landslides Around the Hawaiian Islands. http://walrus.wr.usgs.gov/docs/projects/haland.html
maintained by Molly Gowen Groome
last modified June 10, 1998, accessed 12/10/98.
This page updated: 16 November 1998
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Page URL: http://landslides.usgs.gov/html_files/nlicsun.html 11/30/1998
The URL of this page is http://landslides.usgs.gov/html_files/nlic/new1ft.shtml
Updated: Monday November 16 1998
Landslides. http://germantown.k12.il.us/html/landslides.html 11/30/98
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