Relative age dating of Alpine rockglacier surfaces

摘要

The present work discusses the application of photogrammetry, and the measurements of Schmidt-hammer rebound values and weathering rind thicknesses, for the relative age dating of Alpine rockglaciers, based on data from six rockglaciers in the Swiss Alps. Rockglaciers are formed by the continuous deformation of ice-rich debris material, with the result that the age of the surface becomes greater along the flowlines from the root zone to the rockglacier front. This can be demonstrated by applying both the Schmidt-hammer rebound values (which diminish as weathering, or duration of surface exposure, increases) and the weathering rind thicknesses (which grow as weathering increases). The results of these two methods correlate well with chronologies estimated from photogrammetric streamline interpolations. They also indicate that the minimum surface age of the investigated rockglaciers is between 3 and 5 ka. This implies that most of these rockglaciers began to evolve during the early Holocene or, at the latest, after the end of the Holocene temperature optimum (approx. 5,000 y BP).