Polythermal Glacier Hydrology: A Review

Abstract

[1] The manner by which meltwater drains through a glacier is critical to ice dynamics, runoff characteristics, and water quality. However, much of the contemporary knowledge relating to glacier hydrology has been based upon, and conditioned by, understanding gleaned from temperate valley glaciers. Globally, a significant proportion of glaciers and ice sheets exhibit nontemperate thermal regimes. The recent, growing concern over the future response of polar glaciers and ice sheets to forecasts of a warming climate and lengthening summer melt season necessitates recognition of the hydrological processes in these nontemperate ice masses. It is therefore timely to present an accessible review of the scientific progress in glacial hydrology where nontemperate conditions are dominant. This review provides an appraisal of the glaciological literature from nontemperate glaciers, examining supraglacial, englacial, and subglacial environments in sequence and their role in hydrological processes within glacierized catchments. In particular, the variability and complexity in glacier thermal regimes are discussed, illustrating how a unified model of drainage architecture is likely to remain elusive due to structural controls on the presence of water. Cold ice near glacier surfaces may reduce meltwater flux into the glacier interior, but observations suggest that the transient thermal layer of near surface ice holds a hydrological role as a depth-limited aquifer. Englacial flowpaths may arise from the deep incision of supraglacial streams or the propagation of hydrofractures, forms which are readily able to handle varied meltwater discharge or act as locations for water storage, and result in spatially discrete delivery of water to the subglacial environment. The influence of such drainage routes on seasonal meltwater release is explored, with reference to summer season upwellings and winter icing formation. Moreover, clear analogies emerge between nontemperate valley glacier and ice sheet hydrology, the discussion of which indicates how persistent reassessment of our conceptualization of glacier drainage systems is required. There is a clear emphasis that continued, integrated endeavors focused on process glaciology at nontemperate glaciers are a scientific imperative to augmenting the existing body of research centered on ice mass hydrology.

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

“…Several theoretical models of the likely hydraulic structure of subglacial drainage systems have been proposed and all have some support from field evidence, although primarily at valley glaciers [2,4]. These drainage systems can be classified in to two broad categories: hydraulically 'efficient' (or 'channelised') and 'inefficient' (or 'distributed') systems, which are distinguished by the geometry of their passageways and thus the ease of water flow.…”

“…The importance of meltwater to glacial systems, and downstream regions affected by the meltwater, has long been recognised and comprehensive research has investigated temperate alpine glacier hydrology [2,3] and more recently High Arctic polythermal glacier hydrology [4]. Prior to the twenty-first century however, the hydrology of the GrIS had received little attention, with the exception of reports in the Rapport Grønlands Geologiske Undersøgelse [5] which remain largely unused by the research community, and studies at Jakobshavn Isbrae [6].…”

Flow Routing for Delineating Supraglacial Meltwater Channel Networks

“…Relatively little is known about the characteristics of these channel networks and their controls, in part because of a dearth of data on their form and behavior through space and time [21,22]. Most data pertaining to supraglacial channel form and process come from spatially and temporally limited field studies carried out in the 1970s-1980s [1,9,[23][24][25][26][27][28].…”

An investigation of the thermomechanical features of Laohugou Glacier No. 12 on Qilian Shan, western China, using a two-dimensional first-order flow-band ice flow model

“…The temperature distribution of a glacier primarily controls the ice rheology, englacial hydrology, and basal sliding conditions (Blatter and Hutter, 1991;Irvine-Fynn et al, 2011;Schäfer et al, 2014). A good understanding of the glacier thermal conditions is important for predicting glacier response to climate change Gilbert et al, 2015), improving glacier hazard analysis (Gilbert et al, 2012), and reconstructing past climate histories (Vincent et al, 2007;Gilbert et al, 2010).…”