flash flood is a rapid flooding of low-lying areas : washes , rivers , dry lakes and depressions . 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 regular floods by having a timescale of fewer than six hours between rainfall and the onset of flooding . The water that is temporarily available is often used by plants with rapid germination and short growth cycles and by specially adapted animal life
Johnstown Flood
Johnstown Flood
Flash flood