The term "mass wasting" in geology is used to describe any process that moves mass under the influence of gravity. It includes the common term "erosion", but excludes the term "weathering" which is used to describe process that take place on site with no net mass transfer. Mass wasting can take many forms, from a deadly mudflow rushing down a mountain slope, to destructive landslides which in a few seconds deliver tons of debris, to more subtle forms in which the downslope movement is almost imperceptible.
Slopes are the most common of landforms, so mass wasting operates over virtually the entire surface of the Earth.
Think of mass wasting as a continuous chain of processes that move Earth materials from the tops of the highest mountains down to the deep ocean floor.
The two driving forces behind mass wasting are tectonic activity, the uplift and mountain building that continuously maintains the slopes, and gravity, which tends to pull the slopes down even out the landscape.
Mass wasting is a natural process that continuously shapes the landscape, and it occurs without human involvement. However, it's important for us to recognize that our decisions, such as where we build our roads and structures, and the ways in which we alter natural landscapes can affect this process and sometimes trigger mass wasting events.
Water can play a significant role in mass wasting, sometimes acting as the key component to a mass-wasting event, or serving as a lubricant within a mass of sediment and rock, enabling it to travel faster and further than it would otherwise.ÊÊ Ê
Credit for most of this text is given to the USGS at the location http://walrus.wr.usgs.gov/infobank/programs/html/school/moviepage/15.01.02.html . Also helpful was the website of Bruce Perry of the Department of Geological Sciences, California State University Long Beach http://seis.natsci.csulb.edu/bperry/Mass%20Wasting/Introduction_to_Mass_Wasting.htm. That site has lots of examples and photographs.