Ice-marginal lake hydrology and the seasonal dynamical evolution of Kennicott Glacier, Alaska

Abstract

Glacier 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.

Supraglacial River Forcing of Subglacial Water Storage and Diurnal Ice Sheet Motion

“…Differencing supraglacial and proglacial hydrographs, therefore, may characterize subglacial water storage conditions more sensitively than small vertical ice surface elevation changes, which are inherently difficult to detect and have multiple sources of uncertainty (Anderson et al., 2004; Andrews et al., 2018). A discharge input‐output approach (e.g., Armstrong & Anderson, 2020; Bartholomaus et al., 2011, 2008; McGrath et al., 2011), comparing moulin inputs with proglacial outputs, offers an alternate strategy for characterizing subglacial water storage and its link to basal sliding laws. Future studies, for example, could develop discharge‐difference proxies over longer time scales and larger study areas by pairing surface‐routed climate model output (e.g., Smith et al., 2017; Yang et al., 2019) with proglacial discharge records (Rennermalm et al., 2017; van As et al., 2019), to relate net increases/decreases in Δ S to regional ice speed variations.…”

“…Such correlations are typically weak and spatially variable due to a range of factors confounding estimation of basal uplift from ice surface elevation measurements (Andrews et al., 2018; Hoffman et al., 2011). Therefore, it is difficult to infer interactions between surface melting, subglacial water storage, cavity growth, and ice motion for the GrIS, despite previous success on mountain glaciers (e.g., Armstrong & Anderson, 2020; Bartholomaus et al., 2011, 2008)…”

“…We present GPS measurements of horizontal ice surface speed and vertical uplift, and use them to estimate subglacial storage S and rate‐of‐change Δ S , respectively. We also compute alternate proxies for S and Δ S by differencing normalized supraglacial and proglacial discharge hydrographs (adapted from Bartholomaus et al., 2008, 2011; McGrath et al., 2011; Armstrong & Anderson, 2020). We conclude that diurnal cycles in supraglacial river discharge drive ice accelerations through Δ S , confirming that transient water storage and cavity growth are important influences on GrIS subglacial basal pressure and short‐term ice motion.…”

Annual 30 m dataset for glacial lakes in High Mountain Asia from 2008 to 2017

“…Considering that small lakes represent less of a glacial-lake outburst flood (GLOF) risk, they set 0.01 km 2 as the minimum lake size. Ashraf et al (2012) used Landsat-7 Enhanced Thematic Mapper Plus (ETM+) images for the 2000-2001 period to delineate glacial lakes greater than 0.02 km 2 in the Hindukush-Karakoram-Himalaya region of Pakistan.…”

Glacier Image Velocimetry: an open-source toolbox for easy and rapid calculation of high-resolution glacier-velocity fields

“…A team from the University of Minnesota installed 3 automated weather stations and 3 automated ablation stakes near the southern flank of Glaciar Perito Moreno in order to better understand the local conditions of this glacier and construct temperatureindex and energy-balance models for glacier ablation. We installed the automated ablation stakes, based off of designs by Wickert (2014) and Wickert et al (2019), and tested by Saberi et al (2019) and Armstrong and Anderson (2020), for 20 days between the 23rd of February and 14th of March, 2020. In slowly flowing glaciers, ice flow may be largely neglected when considering equipment recovery.…”