Spatial distribution of sediment storage types in two glacier landsystems (Pasterze & Obersulzbachkees, Hohe Tauern, Austria)

Abstract

For the first time, geomorphological maps of the Obersulzbachkees (ca. 28 km2) and the Pasterze (ca. 39.7 km2) glacier landsystem at the catchment scale (1:10,000 and 1:12,500) are presented and the distribution of sediment storage types and (sub)recent sediment transfer processes are quantified and discussed. Special attention is drawn to the activity and function of sediment storages within the sediment cascade and on process (de)coupling of the sediment transfer systems. Glaciers cover ca. 50% of the landsystems and have retreated more than 1 km within the last six decades. The spatial distribution of sediment storage types delivers a record of the historical activity of the glaciers and the degree of sediment storage activity gives insights into the state of paraglacial landform adjustment. A typical landform assemblage is found in both landsystems. Moraine deposits are the dominant sediment storage type (coverage of ca. 3 km2 in both landsystems) and a significant source of (sub)recent sediment transfer. Deposits of reworked till account for ca. 4% of the total sediment coverage and paraglacial reworking is the main evolutionary factor for drift-mantled slopes with high activity in ice marginal and proximal locations (gully densities up to 3.7 per 100 metres of slope). With increasing distances from the glacier, the importance of paraglacial reworking decreases (gully density of 0.5 to 0.6). However, the contribution of paraglacial reworking to the overall sediment output is insignificant due to decoupling effects and till and debris are currently stored in both landsystems. The glacifluvial transport system is supply limited at the Obersulzbachkees and transport limited at the Pasterze. We consider the proglacial zone as a key control on sediment delivery from the glacier to the downstream fluvial system and hypothesize that the majority of sediment output from both landsystems is suspended load.