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Landslides occur in all U.S. states and territories and can be caused by a variety of factors including earthquakes, storms, volcanic eruptions, fire and by human modification of land. Landslides can occur quickly, often with little notice and the best way to prepare is to stay informed about changes in and around your home that could signal that a landslide is likely to occur.
A landslide is a downward movement of rock and soil debris that has become detached from the underlying slope. The material can move by falling, toppling, sliding, spreading and flowing. There are many landslide vulnerable areas with high-risk terrain. These include seismic sensitive areas, mountainous areas with high relief, moderate relief areas with land degradation, areas of thick loess and areas of high rainfall.
There are many possible causes of landslides these can either be geological, morphological or human-induced. A few of these include saturation of slope material (rainfall), seismic activity (earthquakes and volcanoes), undercutting of cliffs and banks by waves and rivers, removal of vegetation, and modification of slopes.
Mountainous areas throughout arctic and temperate regions which have slope angles between 25degrees and 60degrees are at risk. However, other conditions may affect the likelihood of an avalanche being triggered as already mentioned. The avalanche problem is more severe in Europe than North America due to the higher population densities in mountain ranges. Vibration is a physical trigger cause by thunder, a gunshot, by explosions or other loud noises such as shouting. Earthquakes can start avalanches, as well as noise from heavy machinery.
An avalanche is a mass of snow, often mixed with ice and debris which travels down mountain sides, destroying all in its path. There are three main types of avalanche: Powder, Slab and Wet.
Often start from a single point and accumulates snow as it moves down the slope forming a snowball effect. This type is most common following heavy snowfall of one inch per hour or more and often on a smooth surface such as after rain or frost. Without the cohesion with the snow layer underneath the snow is too heavy to settle. This type of avalanche can travel between 62 and 186 miles per hour.
Most common type of winter avalanche due to the build up fresh snow. A slab is a compact snow surface layer that can detach from a weaker snow layer underneath. The slab slips forward as a whole block or breaks into pieces.
Often occurs after a warm spell or during the spring thaw. Snow becomes heavier as it begins to turn into water. Occurs frequently and are generally small and generally easier to predict than the other types.
The following are things you can do to protect yourself, your family and your property from the effects of a landslide or debris flow:
Find additional information on how to plan and prepare for a landslide or debris flow emergency and learn about available resources by visiting the following websites:
Learn about the emergency plans that have been established in your area by your state and local government . In any emergency, always listen to the instructions given by local emergency management officials.
If you have questions about mitigation, e-mail Alaska's Hazard Mitigation Officer, Brent Nichols.
Army Guard Road,
JBER, AK 99505