Landforms and sediments developed during the recent recession of debris-covered Ponkar Glacier, Nepal

Abstract

Understanding the evolution of debris-covered glaciers in High Mountain Asia, the physical processes governing the effect of debris cover on mass balance, and the response of debris-covered glaciers to climatic change are key for assessing water resources, the contribution of glaciers to sea level rise and the potential for glacier related hazards such as glacier lake outburst floods (GLOFs) related to moraine-dammed lakes. Here we illustrate the effects of recent glacier recession on the development of landforms and sediments at Ponkar Glacier, a debris-covered glacier in the Manaslu area of the Nepal Himalaya using a combination of 2019 RapidEye satellite image (5 m spatial resolution), drone imagery (50 cm) and field observations. We describe the key features of the glacier and its ice-surface morphology, including size and extent of flow units and tributary glaciers, supraglacial features of the debris cover and vegetation. Geomorphological mapping is used to describe the moraines, proglacial geomorphology, outwash plains and proglacial streams, the development of new ice-marginal ponds and changes in vegetation. Moraines generally have steep and rapidly degrading inner faces and mature vegetation, including trees, on their outer flanks. They are typically composed of diamicton and silty or sandy boulder gravel. Large outer moraines are separated from the surrounding valley sides by 'ablation valleys'. We conclude by putting the landforms and sediments developed at Ponkar Glacier into a discussion of the likely future evolution of high-elevation debris-covered glaciers.