Kamb Ice Stream flow history and surge potential

A basal zone, tens of meters thick, of debris-laden ice was observed in Kamb Ice Stream, West Antarctica, using a video camera lowered into boreholes made by hot-water drilling. The debris content varies, sometimes abruptly, forming a sequence of layers that reflect the complex history of fast ice flow and bed interaction. In most parts, the concentration of debris is low, a few percent by weight, with particles, often mud clots, dispersed in a matrix of clear ice. The nature of the debris distribution can be interpreted in terms of specific time intervals in the history of fast motion of Kamb Ice Stream including processes leading up to the termination of its streaming behavior and possible reactivation. INTRODUCTION AND BACKGROUND Ice streams are an expression of the inherent instability of the West Antarctic ice sheet, and their behavior is a key control on the overall ice-sheet mass balance. Understanding the response of the ice sheet in a warming climate requires a thorough understanding of the internal dynamics of ice streams, in addition to the relevant ice/atmosphere and ice/ocean interactions in the region. The basal environment of the ice streams and of many glaciers is a key scientific interest, including conditions, mainly basal sliding, that lead to fast flow of the ice. To obtain direct data on the deep basal glacial conditions, emplacements of instruments are enabled by fast hot-water drilling of access boreholes (Engelhardt and Kamb, 1997); and to obtain data on the nature of the ice near the bed, borehole video cameras have been deployed to acquire extensive video images (Behar and others, 2001; Carsey and others, 2002). The purpose of this paper is to present a review of the full range of original video recordings from the basal ice of Kamb Ice Stream (KIS). Direct observations at the ice-stream bed are a crucial complement to modeling efforts predicting future scenarios in a warming climate. West Antarctic ice sheet The West Antarctic ice sheet (WAIS) is drained to the Ross Sea, the Weddell Sea and the Amundsen Sea by ten large ice streams and several glaciers of various sizes. The overall balance of the ice mass depends on the dynamics of the ice streams that move at a speed 10–100 times faster than the surrounding ice sheet. The dynamics of the ice is controlled for the most part by processes that are active at the base of the ice. Is the ice frozen to the bed or is it at the pressuremelting point? Is the ice underlain by a layer of watersaturated till or by bedrock? Is the water pressure at the bed high or low? Is the ice mostly deforming or sliding over its bed? Is the geothermal flux normal or unusually high? Various ice/bed interactions control the velocity of the ice and so ultimately the balance of the ice mass. Is the ice sheet increasing or shrinking; is it in stable condition or is it destined to collapse (Kamb, 1990; Vogel and others, 2005)?