Rapid geomorphological and sedimentological changes at a modern Alpine ice margin:Lessons from the Gepatsch Glacier, Tirol, Austria

The Gepatsch Glacier in Tirol (Austria) is a rapidly retreating valley glacier whose host valley and forefield reveal subglacial, proglacial, and reworked sediment–landform assemblages. Structures include roches moutonées develop on gneiss, compound bedrock-sediment bedforms (crag and tail structures), flutes, and small diamicton ridges. The glacial sediments and landforms are undergoing incision and terrace development by meltwater streams. Glacial geomorphological and surface geological maps, in concert with elevation models of difference between July 2019 and July 2020 highlight considerable changes to the forefield over a 12-month time period. Till exposed within the last 20 years has undergone substantial mass wasting and re-deposition as subaerial mass flows, or reworked into stream deposits. The lee sides of many roches moutonées completely lack subglacial sediment, and instead contain a sand and gravel deposit interpreted to result from glaciofluvial deposition. Thus, insights into the rates of erosion and deposition in a complex, proglacial setting, allow some of these processes to be quantified for the first time. Repeated monitoring of glacier forefields is expected to yield a better understanding of the preservation potential of proglacial sedimentary facies, and hence their preservation potential in Earth’s sedimentary record.