Observations of englacial water passages: a fracture-dominated system

To test models of the hydraulics and geometry of englacial conduits, 48 holes (3900 m of ice) were drilled into Storglaciaren, Sweden, in search of conduits. About 79% of the holes intersected a hydraulically connected englacial feature. A video camera was used to examine the features and measure local water-flow rates. Because of the extremely clear ice that surrounded most features, their geometry could not be discerned. Of the remaining features, 80% (36) were fracture-like, 16% (6) were of complex geometry, and 4% (2) exhibited a conduit-like geometry. The fracture-like features exhibited steep plunges (similar to 70 degrees) narrow openings (similar to 40 mm) and slow water-flow speeds (similar to 10 mm s(-1)). We argue that these fracture-like features are indeed englacial fractures of unknown origin. The depth to fractures intersection varied from near the glacier surface to 96% of local ice depth, with a maximum depth of 131 m. Few hydraulically connected fractures exhibited water motion, indicating some preferential flow pathways exist. We found one 'traditional' englacial conduit after an intentional search in a field of moulins. These results suggest that englacial water flow is conveyed through a ubiquitous network of fractures and that conduits are relatively rare.