Micro-weathering of limestone surfaces in a foreland of Hallstätter Glacier (Dachstein, Austria)

Abstract

ABSTRACT Since the end of LIA climatic amelioration results in retreat of glaciers worldwide and the development of glacial forelands with freshly abraded rock surfaces undergoing weathering. When the timing of glacier retreat is known, glacier forelands are highly valuable study sites to investigate initial and short-term weathering processes. The aim of this study is to quantify limestone surface decay in the foreland of Hallstätter Glacier in Dachtein massif, Austria, based on the measurement of surface micro-roughness and weathering rind characteristics. By establishing a post-LIA chronosequence we seek to gain insight into initial stages of weathering in a cold alpine environment. Micro-roughness was measured with a use of Handysurf E-35B electronic profilometer, and weathering rind characteristics were determined based on SEM equipped with a microprobe. The micro-roughness increases from locations close to the glacier front towards the LIA moraine. The greatest measured increase occurs within the first 50 years since deglaciation. Weathering rinds are manifested as zones of micro-cracks and micro-pits, and accumulation of mineral grains at the rock surface and along the micro-voids. Increasing rounding of the grains and their development along micro-fissures is attributed to limestone dissolution, which is probably responsible for the development of micro-pits, best observed after c. 100 years since deglaciation. No protecting shield in a form of a weathering coating was observed. Instead, the weathering rind thinning is attributed to the weathering rind erosion. Results obtained provide further insight into initial stages of limestone weathering in a cold alpine environment.