A mountain stream is a brook or stream, usually with a steep gradient, flowing down a mountainside, its swift flow rate transporting large quantities of rock, gravel, soil, wood or even entire logs with it. The main characteristic of mountain streams in the Alpine region is their steep gradient and sharply varying rates of flow within a short period of time, as a result of snowmelt and sudden storms. Streams of such nature are rarer in gently rolling countryside, although they may occur on scarp slopes where, although the height difference is not so great, they tend to have a larger catchment area than mountain streams.