Photo courtesy of the USGS at
http://landslides.usgs.gov

Photograph courtesy of the USGS at
http://landslides.usgs.gov

Landslides can be many things, such as rock falls and debris flows. Landslides fall, slide, or flow down a slope. Gravity on a slope is the main reason for a landslide, but there are other things that cause them.

1. Erosion by rivers, glaciers, or ocean waves create over steep 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.
(http://landslides.usgs.gov/html_files/nlic/page5.html)

A landslide normally destroys everything in its path and may create a variety of linked activity. The aftermath of landslides cause explosive eruptions, burry river valleys with tons of rock debris, cause lahars, triggered waves and tsunamis, and create deep horseshoe-shaped craters.

Slope material that becomes drenched with water may build up a debris flow, other wise known as a mudflow. The resulting rock and mud can pick up trees, buildings, bridges cars, houses, streetlights, anything in its path.

Landslides happen everywhere in the United States. Mountain ranges, including the Appalachian Mountains, the Rocky Mountains, and the Pacific costal ranges and some parts of Alaska and Hawaii, are the where the worst landslides happen.

USGS scientists continue to produce landslide weakness maps for many areas in the United States. In every state, USGS scientists monitor stream flow, 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.
(http://landslides.usgs.gov/html_files/nlic/page5.html)