Englacial drainage systems formed by hydrologically driven crevasse propagation

Abstract

Recent work has shown that surface-to-bed drainage systems re-form annually on parts of the Greenland ice sheet and some High Arctic glaciers, leading to speed-up events soon after the onset of summer melt. Surface observations and geophysical data indicate that such systems form by hydrologically driven fracture propagation (herein referred to as ‘hydrofracturing’), although little is known about their characteristics. Using speleological techniques, we have explored and surveyed englacial drainage systems formed by hydrofracturing in glaciers in Svalbard, Nepal and Alaska. In Hansbreen, Svalbard, vertical shafts were followed through ∼60 m of cold ice and ∼10 m of temperate basal ice to a subglacial conduit. Deep hydrofracturing occurred at this site due to a combination of extensional ice flow and abundant surface meltwater at a glacier confluence. The englacial drainage systems in Khumbu Glacier, Nepal, and Matanuska Glacier, Alaska, USA, formed in areas of longitudinal compression and transverse extension and consist of vertical slots that plunge down-glacier at angles of 55° or less. The occurrence of englacial drainages initiated by hydrofracturing in diverse glaciological regimes suggests that it is a very widespread process, and that surface-to-bed drainage can occur wherever high meltwater supply coincides with ice subjected to sufficiently large tensile stresses.

Thermal structure and drainage system of a small valley glacier (Tellbreen, Svalbard), investigated by ground penetrating radar

“…The second mechanism for routing surface meltwater through cold ice is overdeepening of water-filled crevasses, or hydrofracturing (Alley et al, 2005;Benn et al, 2009;Boon and Sharp, 2003;van der Veen, 2007). Hydrofracturing can occur where ice under tensile deviatoric stress coincides with a sufficient water supply.…”

Structure and evolution of the drainage system of a Himalayan debris-covered glacier, and its relationship with patterns of mass loss

“…Clayton, 1964;Kirkbride, 1993;Krüger, 1994;Benn et al, 2001Benn et al, , 2009Benn et al, , 2012Gulley and Benn, 2007;Thompson et al, 2016). The collapse of conduit roofs can expose areas of bare ice at the glacier surface, locally increasing ablation rates.…”

Brief communication: Observations of a glacier outburst flood from Lhotse Glacier, Everest area, Nepal

“…For debris-covered glaciers, the drainage of supraglacial ponds commonly occurs through englacial conduits, which facilitate connections to areas of lower hydraulic potential (Gulley and Benn, 2007). These englacial conduits develop on debris-covered glaciers in the Himalaya through cut-and-closure mechanisms associated with meltwater streams, the exploitation of high-permeability areas that provide alternative pathways to the impermeable glacier ice, and through hydrofracturing processes (Gulley and Benn, 2007;Benn et al, 2009;Gulley et al, 2009a, b).…”

“…For debris-covered glaciers, the drainage of supraglacial ponds commonly occurs through englacial conduits, which facilitate connections to areas of lower hydraulic potential (Gulley and Benn, 2007). These englacial conduits develop on debris-covered glaciers in the Himalaya through cut-and-closure mechanisms associated with meltwater streams, the exploitation of high-permeability areas that provide alternative pathways to the impermeable glacier ice, and through hydrofracturing processes (Gulley and Benn, 2007;Benn et al, 2009; Gulley et al, 2009a, b).During the last half-century, debris-covered glaciers in the Everest region have experienced significant mass loss (e.g., Bolch et al, 2011), which has led to the development of glacial lakes and supraglacial ponds (Benn et al, 2012). Proglacial lakes may develop if the surface gradient of the glacier is gentle (< 2 • ), while steeper gradients (> 2 • ) will help drain these ponds (Quincey et al, 2007).…”