A flash flood can be as devastating as it is unexpected. It tends to occur under certain circumstances.
Elements of a flash flood:
(1) a source of a significant amount of water
(2) often some form of channeling that concentrates the water
(3) a rapid appearance (“flash”) with fast running water
Sources of water:
(1) monsoon or torrential storm
(2) a weather front with rain that stalls over an area for several days
(3) destruction of a dam or glacial lake
Often the underlying ground cannot absorb the water because of:
(1) saturation
(2) solid rock
(3) mud baked by the sun
(4) lack of ground cover
In a classic flash flood a large amount of water runs down a channel or valley very quickly.
While sometimes a flash flood can be anticipated based on location or heavy rains, at other times it can arrive unexpectedly (dam break, storm far away).
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