surge

Glacial surges are short-lived events where a glacier can advance substantially, moving at velocities up to 100 times faster than normal. Surging glaciers cluster around a few areas. High concentrations of surging glaciers occur in the Karakoram, Pamir Mountains, Svalbard, the Canadian Arctic islands, Alaska and Iceland, although overall it is estimated that only one percent of all the world's glaciers ever surge. In some glaciers, surges can occur in fairly regular cycles, with 15 to 100 or more surge events per year. In other glaciers, surging remains unpredictable. In some glaciers, however, the period of stagnation and build-up between two surges typically lasts 10 to 200 years and is called the quiescent phase. During this period the velocities of the glacier are significantly lower, and the glaciers can retreat substantially. Types Glacier surges have been divided into two categories depending on the character of the surge event. Glaciers in Alaska exhibit surges with a sudden onset, an extremely high maximum flow rate (tens of meters/day) and a sudden termination, often with a discharge of stored water. These are called Alaskan-type surges and it is suspected that these surges are hydrologically controlled. Surges in Svalbard typically exhibit different behavior. Svalbard surges are typically associated with slower onset with an acceleration phase, rising to a maximum velocity which is typically slower (up to four or five meters per day) than Alaskan surges, and a return to quiescence often taking years. Features observed during the active or surge phase include potholes, known as lacunas and medial moraines. Examples of events In the Norwegian Arctic, Svalbard is an archipelago containing hundreds of glaciers. Svalbard is more than 60% covered by glaciers and of these glaciers, hundreds have been observed to surge.