Where a glacier is slowing up, the flow is compressive; in zones of compression, the ice may erode the valley floor. Compressional flow on the stoss side of hills causes till sheets to shear, and debris bands to stack (Gore et al. (2003) Antarc. Sci. 15, 2). See also Swift et al. (2006) Q. Sci. Revs 25, 13–14.