Water Flow through Widespread and Interconnected Void Spaces at Depth in a Temperate Glacier

We present a suite of observations that suggest void spaces within the ice mass of Bench Glacier, Alaska are abundant, interconnected, and may offer an important means for englacial water storage and routing. During Spring of 2003, a grid of boreholes spaced 20 x 20 m were drilled to the bed of Bench Glacier, Chugach Mountains, Alaska. The boreholes extended 180 m to the bed of the glacier and totaled more than 3600 m within the 10⁶ m³ block of temperate ice. Each borehole was inspected by video camera multiple times during a four-week period. These video observations show that open, crevasse-shaped void spaces are common in the lower two thirds of the ice depth. Upward water flow with active refreezing was observed in association with the voids. Eventual upwelling of turbid water demonstrated a connection between the voids and the bed. Slug tests and monitored drilling experiments (presented in detail elsewhere) revealed numerous englacial connections between different boreholes of the grid. For example, during the drilling process changes in water level were observed in the partially-drilled borehole that were coincident with changes in extant boreholes. Together, these observations imply that void spaces in the glacier are widespread and interconnected over many 10s of meters. They do not appear to form an aborescent network of channels. Since the voids are apparently well connected to the bed, they provide an additional dimension to the subglacial hydrological system - a place to store and route water. Hence, englacial voids may be an important component of the glacier drainage system and the linkage between hydrology and sliding dynamics.