IN SEARCH OF ICE-STREAM STICKY SPOTS

The basal shear stress of an ice stream may be supported disproportionately on localized regions or ''sticky spots''. The drag induced by large bedrock bumps sticking into base of an ice stream is the most likely cause of sticky spots. Discontinuity of lubricating till can cause sticky spots, but they will collect lubricating water and therefore are unlikely to support a shear stress of more than a few tenths of a bar unless they contain abundant large bumps. Raised regions on the ice-air surface can also cause moderate increases in the shear stress supported on the bed beneath. Surveys of large-scale bed roughness would identify sticky spots caused by bedrock bumps, water-pressure measurements in regions of thin or zero till might reveal whether they were sticky spots, and strain grids across the margins of ice-surface highs would show whether the highs were causing sticky spots. Stick spots probably are not dominant in controlling Ice Stream B near the Upstream B camp, West Antarctica.