A Large Rock Avalanche onto Morsárjökull Glacier, South-east Iceland. Its Implications for Ice-surface Evolution and Glacier Dynamics

In spring 2007, a large rock avalanche descended onto the Morsárjökull valley glacier in southeast Iceland, leaving one fifth of the glacier buried. The insulating effect of the deposit on the ice was quickly observed as a difference in the ablation between the exposed ice and that under the deposit. After three melt seasons, the ice surface under the deposit was 29 m above the surrounding glacier surface. A reduced rate of ice melting beneath the area of the deposit would likely alter the longitudinal profile of the glacier. Introduction Mass movements from oversteepened mountain slopes adjacent to glaciers are a common source of debris on ice surface (Benn and Evans, 1998; Hambrey and Alean, 2004), resulting from paraglacial adjustment of rock slopes (Ballantyne, 2002). Spectacular examples of large-scale rock avalanches falling onto glaciers are documented in the literature, mainly from Alaska, United States, the Himalaya and New Zealand. A characteristic of such rock avalanches is the exceptionally long distances reached by the deposits on the ice surface. On March 2