Englacial water distribution in a temperate glacier from surface and borehole radar velocity analysis

We have obtained common offset, common midpoint (CMP) and borehole vertical (VRP) ground-penetrating radar profiles chose to the margin of Falljokull, a small, steep temperate valley glacier situated in southeast Iceland. Vel ocity analysis of CMP and VRP surveys provided a four-layered velocity mode l. This model was verified by comparison between the depths of englacial re flectors and water channels seen in borehole video, and from the depths of boreholes drilled to the bed. In the absence of sediment within the glacier ice, radar velocity is inversely proportional to water content. Using mixt ure models developed by Paren and Looyenga, the variation of water content with depth was determined from the radar velocity profile. At the glacier s urface the calculated water content is 0.23-0.34% (velocity 0.166 m ns(-1)) , which rises sharply to 3.0-4.1% (velocity 0.149 m ns(-1)) at 28 m depth, interpreted to be the level of the piezometric surface. Below the piezometr ic surface the water content drops slowly to 2.4-3.3% (velocity 0.152 m ns( -1)) until similar to 102 m depth where it falls to 0.09-0.14% (velocity 0. 167 m ns(-1)). The water content of the ice then remains low to the glacier bed at about 112 m. These results suggest storage of a substantial volume of water within the glacier ice, which has significant implications for gla cier hydrology, ice rheology and interpretations of both radar and seismic surveys.