Continuity comes first: recent progress in understanding subglacial deformation

Subglacial till deformation is glaciologically and geologically important, but is difficult to model owing to numerous uncertainties related to till generation and the flow law for till deformation. I review recent results with the hope of at least focusing the uncertainties. Fine-grained subglacial tills often are sufficiently soft that continuity issues are more important than the 'flow law' of the till in affecting glacier behavior. Non-steady forcing, coarse clasts and an irregular ice-till contact favour till deformation to significant depths and thus rapid subglacial transport of till. Over long times, site history is important in till continuity and thus in glacier behaviour.