Observations of englacial water passages:a fracture-dominated system

Abstract

To test models of the hydraulics and geometry of englacial conduits, 48 holes (3900m 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 (∼70˚), narrow openings (∼40mm) and slow water-flow speeds (∼10mms–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.

Cryo‐hydrologic warming: A potential mechanism for rapid thermal response of ice sheets

“…In this paper we propose a mechanism for warming induced by englacial water in the ablation zones of glaciers and ice sheets. Englacial water flows through a complex network of crevasses, fractures, moulins (vertical conduits of 10–100 m depth through which melt water drains) and conduits that constitute the CHS [ Fountain and Walder , 1998; Fountain et al , 2005]. The occurrence of water in the CHS during the melt season implies that its temperature is at or above the pressure melting point.…”

Channelized, distributed, and disconnected: subglacial drainage under a valley glacier in the Yukon

“…The drilling process itself as well as borehole camera investigation provides additional information on englacial connections (Fountain et al, 2005;Harper et al, 2010). 37 % of all the boreholes drained completely or partially during the drilling process, as did 39 % of those in the cross-glacier lines marked as blue symbols in Fig.…”

“…Werder et al, 2013), still fail to reproduce direct borehole observations of subglacial conditions . These include the existence of disconnected areas that show no signs of flow-related changes in water pressure (Hodge, 1979;Engelhardt et al, 1978;Murray and Clarke, 1995;Hoffman et al, 2016), the development of widespread areas of high water pressure during winter Harper et al, 2005;Ryser et al, 2014a;Wright et al, 2016), large pressure gradients over short distances (Murray and Clarke, 1995;Iken and Truffer, 1997;Fudge et al, 2008;Andrews et al, 2014), sudden reorganizations of the drainage system (Gordon et al, 1998;Kavanaugh and Clarke, 2000), high spatial heterogeneity, boreholes exhibiting anti-correlated temporal pressure variations (Murray and Clarke, 1995;Gordon et al, 1998;Andrews et al, 2014;Lefeuvre et al, 2015;Ryser et al, 2014a), and englacial conduits (Fountain and Walder, 1998;Nienow et al, 1998b;Gordon et al, 1998;Fountain et al, 2005;Harper et al, 2010).…”

Greenland ice sheet hydrology

“…However, field studies have shown that these theoretical models of conduit flow may not conform to reality. Boreholes drilled in Storgläciaren, Sweden, predominantly intersect hydraulically connected englacial fracture-like features that are smaller, and with slower water velocities, than traditional conduits, suggesting that englacial water is transported through an interconnected network of fractures rather than large conduits (Fountain et al, 2005). Further field studies are needed to modify theoretical models of englacial drainage.…”