Abstract
Calving glaciers contribute substantially to sea level rise, but they are challenging to represent in models. Fine resolution is required for continental-scale models to accurately resolve calving dynamics and in many cases glacier geometry is too complicated to be adequately reflected by more simplified models. Flowline models are able to resolve flow along the main branch of a glacier, but many of those in current use either ignore tributaries entirely or parameterize their effect using a measure of “equivalent width”. Here we present a simple method to simulate terminus advance and retreat for an interacting network of glacier branches, based on a model extending Nye’s 1953 perfect plastic flow approximation to calving glaciers. We apply the method to case studies of four marine-terminating glaciers: Jakobshavn Isbrae and Helheim Glacier of Greenland, and Columbia and Hubbard Glaciers of Alaska. Given bed topography and upstream elevation history, our method reproduces observed patterns of terminus advance and retreat in all cases, as well as centerline profiles for all branches.
Highlights
The global sea level rise contribution from land ice is large and growing (Rignot et al, 2011; van den Broeke et al, 2016)
Plastic Tidewater Networks In Ultee and Bassis (2016), we extended the perfect plastic approximation of Nye (1951, 1952, 1953) to a centerline model of tidewater glaciers that self-consistently predicts terminus advance and retreat forced with upstream elevation change
The especially simple solution we present here assumes τb = τy, which may not be realistic but has shown promising results when applied to Columbia Glacier (Ultee and Bassis, 2016). τy becomes our single adjustable parameter
Summary
The global sea level rise contribution from land ice is large and growing (Rignot et al, 2011; van den Broeke et al, 2016). Much of the increase in the land ice contribution to sea level rise comes from the dynamic response of marine-terminating glaciers, including those draining the Greenland and Antarctic Ice Sheets (Church et al, 2013; Straneo et al, 2013; Vaughan et al, 2013). Where glaciers drain the large ice sheets, there is often a transition from laterally unconfined ice (width 102 km) to flow through narrow fjords (width ∼ 10 km or smaller). Most of the 199 widest Greenland outlet glaciers studied by Murray et al (2015) do not exceed 3 km in width, and many smaller glaciers less than one kilometer in width are excluded from consideration. The largest glaciers with the greatest potential contribution to sea level rise have the most tributary branches—more than 400 in the case of Hubbard Glacier, Alaska (Kienholz et al, 2015)
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