Landslides: Understanding Mass Movements

Study Notes

Landslides, though often overshadowed by other disasters, are potent forces causing significant damage.
Globally, landslides are responsible for thousands of deaths (32,322 between 2004 and 2010).
Yearly landslide damage in the U.S. alone exceeds $3-$4 billion.
Landslides are a type of mass movement, a broad term for gravity-driven sediment movement down a slope.
These movements can take place slowly over years or quickly within minutes; the scale ranging from small debris slides to massive events like the 1980 Mount St. Helens landslide.
Mass movements vary concerning their material, movement patterns, and speed.
A defining feature is the separation of a soil layer from the underlying bedrock.
Soil is a loose mixture of rock, minerals, water, air, and organic matter. Bedrock is the more rigid underlying layer.

While the term "landslide" is often inaccurately used for various mass movements, a true landslide involves a specific process.
In a landslide, rocks and sediment break away from underlying bedrock along a distinct weak point.
Rapid movement of separated material down a slope defines a landslide.
The movement is akin to a poster detached from a wall due to weakening of the adhesive (tape). Similar factors like added weight or moisture weaken the connection. Example forces: increased moisture, added weight.