Quantifying glacial erosion on a limestone bed and the relevance for landscape development in the Alps

Abstract

Abstract Glacial erosion is the basic process that has shaped the landscapes of the Alps. Despite intense research over centuries, and the use of various techniques, determination of glacial erosion rates remains challenging. This is not only because the location where the process occurs is almost inaccessible, but also because it is dependent on many different factors, including ice thickness and velocity, glacier thermal regime and lithology. Reported glacial erosion rates range over several orders of magnitude (0.01 to >10 mm a −1 ). Most studies focus on crystalline bedrock, whereas few researchers have investigated glacial erosion on limestone. Here we analyse glacially polished bedrock surfaces at the recently deglaciated forefield of the Tsanfleuron glacier, Swiss Alps. The nearly horizontally bedded limestone hosts a well‐developed karst system. Meltwater from the glacier drains into the subsurface within a few metres of the ice margin. By combining geomorphological mapping, measurement of cosmogenic 36 Cl concentrations of glacially eroded bedrock surfaces and a numerical model (MECED), we quantify at each sample location the amount of rock removed during glacier occupation. The glacial erosion rates calculated from these values range from 0 to 0.08 mm a −1 . These are orders of magnitude lower than values measured at comparable sites on crystalline bedrock. The high 36 Cl concentrations we measured show that the Tsanfleuron glacier was unable to effectively erode the gently dipping, strongly karstified limestone. We suggest that this effect may play a key role in formation and preservation over many glacial cycles of high‐elevation, low‐relief limestone plateaus in the Alps. © 2020 John Wiley & Sons Ltd.

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