If a larger flood occurs, then that structure will be overtopped. If during the overtopping the dam or levee fails or is washed out, the water behind it is released to become a flash flood. Failed dams or levees can create floods that are catastrophic to life and property because of the tremendous energy of the released water. Warnings of the Teton Dam failure in Idaho in June 1976 reduced the loss of life to 11 people. Flooding occurs upstream as water becomes stored behind the temporary dam and then becomes a flash flood as the dam is breached and rapidly washes away.
Landslides can create large waves on lakes or embayments and can be deadly.
Mudflow floods can occur when volcanic activity rapidly melts mountain snow and glaciers, and the water mixed with mud and debris moves rapidly downslope. These mudflow events are also called lahars and, after the eruption of Mt. St. Helens in 1980, caused significant damage downstream along the Toutle and Cowlitz Rivers in southwest Washington. Click here for an example of the streamflow information on the Internet . Most flood-related deaths are due to flash floods. Fifty percent of all flash-flood fatalities are vehicle related.