IN SEARCH OF ICE-STREAM STICKY SPOTS

The basal shear stress of an ice stream may be supported disproportion ately on localized regions or ''sticky spots''. The drag induced by la rge bedrock bumps sticking into base of an ice stream is the most like ly cause of sticky spots. Discontinuity of lubricating till can cause sticky spots, but they will collect lubricating water and therefore ar e unlikely to support a shear stress of more than a few tenths of a ba r unless they contain abundant large bumps. Raised regions on the ice- air surface can also cause moderate increases in the shear stress supp orted on the bed beneath. Surveys of large-scale bed roughness would i dentify sticky spots caused by bedrock bumps, water-pressure measureme nts in regions of thin or zero till might reveal whether they were sti cky spots, and strain grids across the margins of ice-surface highs wo uld show whether the highs were causing sticky spots. Stick spots prob ably are not dominant in controlling Ice Stream B near the Upstream B camp, West Antarctica.