Development of minor outwash fans at kötlujökull, Iceland

Abstract

Throughout the 1980s, the development of minor outwash fans was studied at and beyond a northeastern section of the steep, advancing ice front of Kötlujökull, the largest outlet-glacier on the east side of the ice-cap Myrdalsjökull in central south Iceland. In contrast to the extensive outwash fans of gravelly and stony material deposited by high energy streams from underneath the glacier, the minor fans consist of fine-grained material, mainly of sand size, deposited by low energy streams draining the debris-covered glacier surface. The vertical alteration in texture of the minor fan deposits results from changing influx of sediments, which in turn is coupled to varying activity in the processes working in the supraglacial sediment source area. These processes are ablation, sudden drainage of pockets of water, influx of rainwater, and resedimentation of debris by fall, slide, and flow. Along with the glacier advance during the 1980s, slabs of fan sediments were incorporated in the push-moraine ridge being formed. The subsequent glacier retreat during the 1990s has largely curtailed the production of minor outwash fans. It is concluded that this type of outwash fan is likely to be produced along advancing, or stationary, glaciers where the frontal slope is steep and covered by debris. Similar minor outwash fans, termed hochsander fans, have been identified beyond ice-marginal moraine ridges bounding dead-ice morainic terrain in Pleistocene landscapes.