Quick Snowmelt

The storage of water in the form of snow temporarily removes that water from the hydrologic cycle. In many cases this sequestration of water is short term. Snow accumulates during winter especially at higher elevations and latitudes. With the onset of warmer spring and summer conditions, snowmelt supplies water to streams. A typical early warming may mean that snowmelt may be accelerated with large amounts of runoff entering stream channels. Mountain ranges in mid-latitude coastal regions such as the Coast Ranges and Sierra Nevada of California receive a signifi-

Figure 4 Arizona flash flood Wenden, Arizona, This community was flooded twice in late October 2000 when waters from Centennial Wash swept into the town. (Photo courtesy of U.S. Small Business Administration.) See ftp site for color image.

cant portion of their annual precipitation in the form of snow. It is possible for warm early spring rains to fall oil the snowpack, causing much faster runoff than normal (Bolt ct al., 1975; Church, 1988), Another source of snowmelt is the subsurface introduction of heat from volcanic activity. Large volcanoes can be high enough to support permanent snow and ice cover. High temperatures associated with volcanic activity lead to the instantaneous melting of snow and ice. The melt water is commonly mixed with pyroclastic debris to form lahars (Smith, 1996).

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