What are Flash floods and what triggers them?

This is a phenomenon for me please inform me. Thanks.What are Flash floods and what triggers them?
Flash Floods are when massive amounts of water quickly inundate a land area.





It is ';common'; in areas where water naturally collects, like flood plains and river basins. When large amounts of rain are delivered over a relatively short time the water tends to ';run off'; rather than absorb in the earth which causes the water to rapidly converge in low lying areas leading to rapid flooding. Alternately it can also be caused by extensive long term rains where the earth has become saturated causing the afore mentioned ';run off';.What are Flash floods and what triggers them?
Flash floods often occur in areas where a large amount of runoff, usually from rainfall, will flow into typically underfed (intermittent) stream channels, which may be called, gullies, gulches, arroyos, barrancas, wadis, etc, and they quickly overflow the banks causing a flood. Warnings are issued because many people are unaware of the potential for flooding, even in areas like the grand canyon!
Really heavy rain, a damn bursting, a glacial damn suddenly letting snow melt loose. Think of anything that can release a lot of water at once
a ';flash flood'; is a river formed by a down pour in the mountains or over a canyon that spills out onto the valley floor all at once creating a ';flash flood';. it may not even be raining were this flooding occures.
they are when a vast amount of water suddenly hits an area and floods it.





normally occur after a sudden heavy rain when multiple streams / rivers converge in a single point, or when a contained body of water on higher ground bursts its banks and dumps a mass of water onto the lower ground
Rainwater that does not filter into the ground runs off into streams or valleys. The area of land that directs water from rainfall to a stream is called a catchment area. If the catchment area is large the quantity of water directed to a stream can be an enormous. As it rains, the flow in a stream or valley rises quickly forming a Flash Flood, a devastating phenomenon, it has been described as a wall of water moving downstream at speed. There is little warning as the stream could be far away from the catchment area.