The Nature and Rates of Post-Depositional Changes in Recently Deposited Till from South-East Iceland

Abstract

Investigations of the pattern of variation in texture and structure of an extensive lodgement till currently being exposed by glacier retreat reveal the roles of three groups of processes. These are depositional processes which influence the sorting of the till, post-depositional processes of sub-glacial shearing and crushing which increase the silt concentration immediately below the glacier sole and reduce the density of the till by dilation due to shear, and soil-forming processes operating beyond the glacier margin.Once the till is exposed the structure of the dilatant layer is destroyed by compaction due to drainage, percolating water carries fines down through the profile and wind action produces stone pavements by deflation near to the glacier and loess accumulation further away. The surprising speed at which these processes operate and the extent to which the sedi-mentological character of the till is changed after glacier retreat have important implications for both pedologists and glacial geologists.