Flash flood

A flash flood is very quick flooding of low-lying land, usually without prior warning. It may be caused by heavy rain or water from melted ice or snow. Flash floods can also happen after the collapse of a dam. A tsunami causes similar problems but is not usually called a flash flood.
How does a flash flood happen:
Flash floods occur when heavy rainfall exceeds the ability of the ground to absorb it. They also occur when water fills normally dry creeks or streams or enough water accumulates for streams to overtop their banks, causing rapid rises of water in a short amount of time.
Why does a flash flood happen:
A 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, or tropical storm, or by melt-water from ice or snow flowing over ice sheets or snowfields.
What to Do in Case of Flash Flood: 7 Tips to Stay Safe: