sheet or stream of soil and rock material saturated with water and flowing downslope under the pull of gravity; it represents the intermediate stage between creep and mudflow. Earthflows usually begin in a large basin on the upper part of a slope where debris and weathered material accumulate; the movement, usually set off by heavy rainfall, may be relatively slow or very fast, depending on the amount of water present, the angle of the slope, and other aspects of the terrain.