Abstract
AbstractGlacier basal motion is responsible for the majority of ice flux on fast-flowing glaciers, enables rapid changes in glacier motion and provides the means by which glaciers shape alpine landscapes. In an effort to enhance our understanding of basal motion, we investigate the evolution of glacier velocity and ice-marginal lake stage on Kennicott Glacier, Alaska, during the spring–summer transition, a time when subglacial drainage is undergoing rapid change. A complicated record of > 50 m fill-and-drain sequences on a hydraulically-connected ice-marginal lake likely reflects the punctuated establishment of efficient subglacial drainage as the melt season begins. The rate of change of lake stage generally correlates with diurnal velocity maxima, both in timing and magnitude. At the seasonal scale, the up-glacier progression of enhanced summer basal motion promotes uniformity of daily glacier velocity fluctuations throughout the 10 km study reach, and results in diurnal velocity patterns suggesting increasingly efficient meltwater delivery to and drainage from the subglacial channel system. Our findings suggest the potential of using an ice-marginal lake as a proxy for subglacial water pressure, and show how widespread basal motion affects bulk glacier behavior.
Highlights
Sub-annual glacier surface velocity changes are driven by variable rates of basal motion (Willis, 1995, and references within)
There is less evidence for a link between Donoho Falls Lake (DFL) stage and glacier velocity. This suggests limits to the transfer rate of water between DFL and the subglacial environment, and may indicate that stage rate of change (ROC) is a better proxy for subglacial water pressure than stage itself
Proving that this is the case that requires further study, including field and modeling efforts. Assuming that this notion is correct, we still require a mechanistic explanation for what DFL stage variations indicate about the subglacial hydrologic system. The interpretation of these data is not as straightforward as the moulin study of Andrews and others (2014), but below we present two potential end-member conceptual models for what DFL stage and its ROC may indicate in terms of subglacial hydrology
Summary
Sub-annual glacier surface velocity changes are driven by variable rates of basal motion (Willis, 1995, and references within). Basal motion is possible under the large temperate fractions of the Greenland ice sheet ( 43%) (MacGregor and others, 2016) and Antarctica ( 55%) (Pattyn, 2010), making its understanding important for predicting ice fluxes to the global ocean and sea level rise. Basal motion mediates mass change on valley glaciers, which disproportionately contribute to modern sea level rise (Meier and others, 2007; Gardner and others, 2013; Zemp and others, 2019) and affect downstream water resources (O’Neel and others, 2014; Huss and Hock, 2018; Pritchard, 2019) and habitat quality (Hood and Scott, 2008; Lydersen and others, 2014; O’Neel and others, 2015). Irrespective of the precise physical mechanism involved, as water pressure approaches the ice overburden pressure, basal traction declines and basal motion increases (Nienow and others, 2005)
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