Jökulhlaups are outburst floods caused by the rapid release of water from a glacier dammed lake. Glacier dammed lakes are formed when a glacier blocks the flow of water out of a tributary valley. Throughout the seasons rainfall, rainfall runoff, snowfall, snow melt and glacier melt all accumulate in the lake. At a semi-regular interval, which differs for each lake, the lake begins a self-dumping process. This process begins when the lake floats the glacier or as a fracture in the blocking glacier begins to release water. As the water flows through the opening it is enlarged by melting due to the heat created by the potential energy of the flowing water. After the water has drained, the opening begins to close off and the lake begins to fill again
Numerous glacier dammed lakes exist in Alaska. Snow and Skilak Glacier lakes are familiar to those along the Snow and Kenai River due to the flooding or high water levels which can occur after the lake releases. Visit the link below for additional information regarding Alaskan glacial dammed lakes.