Climatic Sensitivity of high-alpine Cirques: The Sattelkar Cirque and its Neighbours
Glacial cirques, located immediately below the highest peaks and headwalls, represent the uppermost location for substantial sediment storage in high-alpine environments. Pronounced recent climatic warming causes considerable, potentially dramatic, changes in these areas. Rising air temperatures and increased liquid precipitation induce substantial, and possibly rapid, subsurface warming. For frozen debris deposits, this can result in significant permafrost degradation, leading to the reduction of cohesion and stability, and ultimately to the provision of sediment to potentially hazardous mass wasting processes such as landslides and debris flows. Due to intense recent and past (peri-)glacial erosion and their concave, deposition-friendly morphometry, cirques frequently possess considerable debris volumes. Changes in the sediment mobilisation regime are therefore especially impactful in these environments.
The remote Sattelkar cirque and its neighbouring cirques are located in the Obersulzbachtal, Hohe Tauern Range, in an elevation range between approximately 2.100-2.800 m above sea level (asl). Strong surface displacements have been observed in the Sattelkar since 2005. The initial displacements triggered massive degradation of the vegetation cover and the exposure and enhanced mobilisation of the debris cover. Terrain analysis revealed that a deep-seated, retrogressive movement in the debris cover of the cirque had been initiated. Heavy precipitation is assumed to cause spreading and sliding of the glacial and periglacial debris cover on the underlying, smooth bedrock cirque floor. Detailed aerial photo analyses, witness reports and damage documentations demonstrated that local mass movement and debris flow activity has steadily increased over the last decade. During this period, debris flows from the Sattelkar blocked the Obersulzbach river, and, in combination with the general flooding situation in the catchment, caused substantial destruction in the middle and lower reaches of the Obersulzbach river.
The Sattelkar has three neighbouring cirques with nearly identical properties that follow at upper locations of the valley: the Ofenkar, Mitterkar and Steinkar. Despite similar topographical, climatological and hydrological conditions, no significant debris flow activity has been observed here. So far, it is not clear, why the Sattelkar is active and its neighbours are not.
Based on a long-term monitoring approach, we systematically and continuously observe the atmospheric, surface and subsurface conditions to quantitatively assess ground thermal conditions and mass wasting activity. Based on these measurements, we hope to improve our understanding how high-alpine cirques react to climate change and which natural hazard potential can be expected in the foreseeable future.
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