Surface and Englacial Drainage of Glaciers and Ice Sheets

Abstract

Supraglacial drainage occurs wherever snowpack, firn, or ice at the glacier surface is at the pressure melting point and supplied with additional energy, thereby generating melt water. Energy sources vary, but net radiation is usually the dominant source, although inputs of rainwater can also provide large volumes of surface runoff. The surface melt water is routed through the snowpack, firn, and across the glacier surface according to the local hydraulic gradient. In general, routing of water through snow and firn is slow (10 −4 –10 −5 m s −1 ), contributing to a significant lag between melt water production and runoff at the glacier snout, whereas flow across exposed ice surfaces is typically 3–5 orders of magnitude faster. Under certain conditions where parts of the snowpack, firn, and/or ice surface are below the pressure melting point, the melt water will refreeze. Otherwise, the melt water will be routed supraglacially to the glacier margin unless intersected by a pathway from the glacier surface to the glacier interior. Such pathways include crevasses and moulins, and in temperate glaciers, microscale englacial veins. Flow rates through the englacial system vary considerably according to the hydraulic efficiency of the route taken. The routing of melt waters through both supraglacial and englacial drainage systems therefore affects the runoff response of an ice mass to rain and melt water inputs. During the course of a melt season, the efficiency of routing through both systems evolves, thereby altering the runoff response time to input variations.

Possible interactions between bacterial diversity, microbial activity and supraglacial hydrology of cryoconite holes in Svalbard

“…Second, supraglacial drainage networks generally evolve downglacier, with the proportion of smaller feeder channels gradually reducing relative to that of larger trunk channels, as the former merge into the latter. Thus, other things being equal, the greater the upglacier drainage 'fetch' above a sample site, the more discrete and less widespread the local drainage will be (Hodgkins, 1997;Nienow and Hubbard, 2005). As AB has a considerably longer fetch than ML or VB (Figure 1), it follows that the supraglacial drainage system is likely to be more discretely organized into fewer, larger channels in the area concerned.…”

Recent Advances in Our Understanding of the Role of Meltwater in the Greenland Ice Sheet System

“…In west Greenland, Poinar et al [52] observed a moulin density of 0.02 km −2 between 1500-and 1600-m elevations which compared with 12 km −2 at lower (0-1100 m) elevations [51]. This reduction in moulin density ensures that at high elevations, meltwaters are often transported considerable distances from the source of meltwater generation to the point of input to the englacial drainage system [34].…”

“…While storage of waters within the firn aquifer has only recently been revealed, the visible ponding of water in extensive supraglacial lakes has been known for decades [33,34] and their large size and the ready availability of satellite data has seen a marked increase in research on supraglacial lake development and drainage. These data reveal that lakes form seasonally in depressions in both the ablation and lower accumulation zones of the ice sheet [35], with their locations controlled by the underlying subglacial topography [36] or basal friction [37] thereby ensuring that they typically reform in the same location each year given sufficient surface meltwater.…”

Flow Routing for Delineating Supraglacial Meltwater Channel Networks

“…This method assumes an impermeable surface with no storage and requires that sinks (low elevation pixels surrounded by higher elevation pixels) be leveled to force flow routing from drainage boundary to catchment outlet [39]. This processing step is problematic in ice surfaces, however, where surface water drains via moulins (sinks on the ice surface) to the englacial hydrological system [39][40][41]. Yang et al (2015) [34] and Rippin et al (2015) [4] both concluded that flow routing overestimates hydrological network extent for this reason.…”