Calving Seasonality Associated With Melt‐Undercutting and Lake Ice Cover

Abstract

A detailed understanding of calving processes at the lacustrine margins of the Greenland ice sheet is necessary for accurately forecasting its dynamic response to ongoing climate change. However, existing data sets of lacustrine calving are limited to summer seasons and to alpine glaciers. Here, we use an integrated time-lapse and structure-from-motion approach to generate the first continuous year-round volumetric record of calving processes at a lacustrine ice sheet margin. We identify two distinct calving regimes that are associated with melt-undercutting and lake ice cover. We also find that calving rates respond rapidly to sudden lake drainage. Given that lake temperature, lake ice cover, and sudden lake drainages are controlled by air temperature and ice-margin thinning, we suggest that climate change, manifested in lengthening summer seasons, will accelerate rates of mass loss and terminus recession at lacustrine ice-margins in Greenland.Plain Language Summary Lakes situated at the margins of glaciers and ice sheets are important because they promote the detachment of large blocks of ice to form icebergs, a process known as calving. Climate change is increasing the number of lakes at the margins of the Greenland ice sheet, and many of those already present are increasing in size. Consequently, a detailed understanding of lake calving processes is needed to accurately predict the future response of the ice sheet to climate change. This study improves our knowledge of calving processes by using time-lapse cameras to record images of calving activity at a lake located in western Greenland over a continuous 14-month period. We use the images to create 3D models that illustrate how calving processes change through time and find that rates and styles of calving vary seasonally in response to lake-driven undercutting of the ice sheet margin and the presence or absence of lake ice cover. Our results suggest that ice loss via calving activity at the lake edges of the Greenland ice sheet will increase in future as summer seasons lengthen in response to climate change.

Proglacial Lakes Control Glacier Geometry and Behavior During Recession

“…With lake‐terminating glaciers becoming more numerous and larger (e.g., Carrivick & Quincey, 2014), the likely increasing influence of frontal ablation processes must be incorporated into ice dynamics models with account for fluctuating lake levels driven by contributions to the meltwater flux. Future work should also consider the importance of several other mechanisms that could further enhance recession of a lake‐terminating glacier in comparison to a land‐terminating glacier, such as convective warming of the ice by thermal warming of lake water, and wind‐driven wave erosion (Mallalieu et al, 2020).…”

Toward Numerical Modeling of Interactions Between Ice-Marginal Proglacial Lakes and Glaciers

“…Subaqueous melt rates are a key control on the propagation of thermo-erosional notches at the waterline, and thus melt-undercut driven calving losses (Diolaiuti et al, 2006;Röhl, 2006). A recent analysis of glacier calving into an ice-marginal lake found associations between calving style and magnitude with presence/absence of lake ice cover and lake water depth (Mallalieu et al, 2020). Where lakes freeze or have a floating terminus, a buttressing effect (Geirsdottir et al, 2008;Tsutaki et al, 2013;Mallalieu et al, 2020) can be imparted on the glacier, rather like that of an ice mélange in a marine setting.…”

“…Typical triggers for such failure include mechanical breakage of unconsolidated moraine material or lake water pressure (due to water depth) exceeding ice overburden pressure (Tweed and Russell, 1999). Studies on modern glaciers have shown that when an ice-marginal lake drains, a local portion of the adjacent glacier is near-instantaneously de-buttressed promoting calving (e.g., Sugden, 1985;Mallalieu et al, 2020), localized crevassing, and an abrupt increase in horizontal velocity (e.g., Walder et al, 1996;Furuya and Wahr, 2005;Tsutaki et al, 2013). These effects have been detected with in situ measurements using global positioning systems (GPS) (e.g., Walder et al, 2006;Tsutaki et al, 2013), satellite interferometry (e.g., Furuya and Wahr, 2005), or via processing of multiple oblique field photographs (e.g., Mallalieu et al, 2017Mallalieu et al, , 2020.…”

“…Studies on modern glaciers have shown that when an ice-marginal lake drains, a local portion of the adjacent glacier is near-instantaneously de-buttressed promoting calving (e.g., Sugden, 1985;Mallalieu et al, 2020), localized crevassing, and an abrupt increase in horizontal velocity (e.g., Walder et al, 1996;Furuya and Wahr, 2005;Tsutaki et al, 2013). These effects have been detected with in situ measurements using global positioning systems (GPS) (e.g., Walder et al, 2006;Tsutaki et al, 2013), satellite interferometry (e.g., Furuya and Wahr, 2005), or via processing of multiple oblique field photographs (e.g., Mallalieu et al, 2017Mallalieu et al, , 2020. Vertical displacements of an ice surface have been interpreted to signify passage of energetic and pressurized lake water through/ beneath a glacier (e.g., Walder et al, 1996;Anderson et al, 2005;Tsutaki et al, 2013).…”

Greenland-wide inventory of ice marginal lakes using a multi-method approach

“…In spite of focused research on individual ice marginal lakes and regional studies, there is currently a lack of Greenland-wide research into ice marginal lakes. Lake changes have previously been monitored in detail over small areas using in situ measurements 11 and remote sensing 25 , 26 , along with forecast modelling to predict future dynamics 13 . Remote sensing approaches have also proved advantageous for monitoring water bodies over large regions of Greenland, such as spectral indices generation from optical and infrared imagery 27 , classification from radar imagery 28 , and sink detection from Digital Elevation Models (DEMs) 29 .…”