Glaciologist measuring deformation in the basal layers of the Glacier de Tsanfleuron, Switerland use a sophisticated electronic instrument. In the foreground is wet, striated rock (limestone) over which the ice slides, whilst deformation in the overriding ice and movement towards the left is indicated by the fold structure. Subglacial cave like this, near the receding ice margin, rapidly disappear, but new ones continually form where there are steps in the bed. MH