Rainfall Floods

• Rainfall floods are the most commonly thought of type of flash flood. When large amounts of rain fall in a short period of time, rivers, lakes and other bodies of water can swell; sewage systems can overflow; and low-lying streets can become overwhelmed with water. Rainfall flash floods occur most commonly after intense rain from slow-moving thunderstorms, or during hurricanes and tropical storms. Flash flood warnings are typically issued by the National Weather Service if a rainfall flood is possible, allowing those in danger to quickly get to higher ground.
  
  

Glacial Lake Outburst Floods

• A glacial lake outburst flood (GLOF) occurs when the ice walls of a glacial lake begin to crack and release waters into the rivers and streams surrounding the area. Erosion is a common cause of this type of flood, but major movements in the earth such as volcanic eruption, earthquake and avalanche can be at fault as well. This can result in a quick release of water that overwhelms the surrounding area, or the slow overflow of rivers and lakes that eventually results in flooding. The waters released in glacial lake outburst floods is ice cold, and can be rapid enough to wipe out housing.
  
  

Landside Dam Outburst Flood

• Landslide dam outburst floods can be the most destructive if the dams are not monitored and properly cared for. They occur when the structural integrity of a landslide dam rapidly deteriorates, and the water pressure becomes too much for the dam to handle, causing the water to burst forth with no warning. People who are most at risk for experiencing a landslide dam outburst flood are those who live in areas where landslides are common, and the need to dam the area exists in the first place.
  
  

Rapid Melting Flood

• As the end of winter approaches, the threat of rapid melting floods becomes real. This type of flooding happens with a quick change in weather, bringing temperatures from below freezing to warm enough to quickly melt snow. If large amounts of snow have been piled up over a long, snowy winter season, and a heat wave hits, causing the snow to melt, flooding can occur. This type of flash flooding is easier to predict than the others, because weather can be an indication that snow melt will occur.