Glacial outburst floods
change and rearrange the surrounding landscape.
Glacial outburst floods are hydrological events that rapidly release large volumes of water into the surrounding environment, often with cataclysmic results. Physical geographers use the Icelandic word "jokulhlaups" to describe the sometimes devastating floods. The floods occur with regularity in Iceland, often triggered by volcanic activity or earthquake tremors. Some glaciers in Alaska experience annual glacial outburst floods.
Jokulhlaups
Melting glaciers often form lakes contained by ice dams or terminal moraines. Water trickling under the ice dams can melt and float the buoyant ice, until the water is released in a catastrophic flood. The dams may be destabilized by increased water pressure, rockfalls, avalanches or landslides until they burst. In modern times, the geological event occurs in mountainous, glaciated regions such as the Himalayas, Andes and Alps. The floods are called jokulhlaups by geologists, from the Icelandic term for "glacier leap."
Ice Age Floods
Late Ice Age glacial outburst floods of 12,000 to 13,000 years ago were geological events on a grand scale, dwarfing historical glacier-induced floods. Ice dams trapped huge reservoirs of melt-water underneath the mile-thick sheets of ice as they liquified in response to a warming climate. When the dams burst, the resulting floods launched icebergs that dropped rocks across the North Atlantic Ocean in a geological phenomena known as a Heinrich event. Glacial period outburst floods formed much of the Northern Hemisphere's topography.
Geological Impacts
Glacial outburst floods can flood nearby rivers, causing them to overflow their banks, inundating areas far from the glacial lake. Large amounts of rock debris and sediment are deposited downstream by the rushing waters. Ravines and canyons can be cut into the earth. Glacial floods in coastal regions often degrade ocean waters with a sediment plume. Tertiary river and stream channels are undercut and eroded. Old landslide and debris flow deposits may be reactivated by the destabilizing effects of the flooding.
Human Impacts
An immediate impact of glacial outburst floods is the loss of human life in towns and villages directly below the glacial lakes. Large quantities of rocky debris dumped on the flood plains disrupts agricultural activity. Infrastructure such as electrical lines, roads and buildings may be wiped out. The jokulhlaup from Iceland's Skeiararjokull Glacier in 1996 destroyed two large bridges with transported ice floes and icebergs. The flood left a 3.7-mile long, 328-foot deep ice canyon on the glacier.
Tags: outburst floods, glacial outburst, Glacial outburst floods, glacial outburst floods, Impacts Glacial
