The drilling of boreholes through the glacier is achieved by melting ice with a pressurized jet of hot water (e.g. Gillet, 1975; Iken et al., 1977). In principle, the method entails that water drawn from a supraglacial stream, water-filled crevasse or a pit dug into the soaked snowpack is heated to near the boiling point with a unit consisting of a water circulation coil and a burner and subsequently pumped with a pressure of up to 100 bar through a high-pressure hose into a drill stem. The drill stem is a heat-insulated, double-walled steel tube, typically between 1.5 and 3 m long, which ends in a nozzle having an inside diameter of a few millimetres. The hot water jet ejected from the nozzle melts away the ice in front of it at the base of the lengthening borehole.
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