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.