A
flash flood is a rapid
flooding of
geomorphic low-lying areas: washes,
rivers,
dry lakes and
basins. It may be caused by heavy
rain associated with a
severe thunderstorm,
hurricane,
tropical storm, or
meltwater from ice or snow flowing over ice sheets or snowfields. Flash floods may occur after the collapse of a natural
ice or
debris dam, or a human structure such as a man-made
dam, as occurred before the
Johnstown Flood of 1889. Flash floods are distinguished from a regular flood by a timescale of less than six hours. The temporary availability of water is often utilized by foliage with rapid germination and short growth cycle, and by specially adapted animal life.