Abstract
ABSTRACTTime-varying elevations near the calving front of Jakobshavn Isbræ, Greenland were observed with a terrestrial radar interferometer (TRI) in June 2015. An ice block with surface dimensions of 1370 m × 290 m calved on 10 June. TRI-generated time series show that ice elevation near the calving front began to increase 65 h prior to the event, and can be fit with a simple block rotation model. We hypothesize that subsurface melting at the base of the floating terminus breaks the gravity-buoyancy equilibrium, leading to slow subsidence and rotation of the block, and its eventual failure.
Highlights
Jakobshavn Isbræ, Greenland’s largest marine-terminating glacier, has doubled in speed as its ice front has retreated tens of km in the last several decades (Joughin and others, 2004, 2008; Rignot and Kanagaratnam, 2006; Howat and others, 2011)
Increases in subsurface melting and calving triggered by warmer ocean water are believed to be important contributors to this process (Holland and others, 2008; Motyka and others, 2011; Enderlin and Howat, 2013; Myers and Ribergaard, 2013; Truffer and Motyka, 2016)
Recent work by Murray and others (2015a, b) cast doubt on this calving criterion. Their data show that the front of Helheim Glacier tipped backwards during a major calving event, which implies that basal crevassing must be considered in calving criteria at least under certain conditions
Summary
Jakobshavn Isbræ, Greenland’s largest marine-terminating glacier, has doubled in speed as its ice front has retreated tens of km in the last several decades (Joughin and others, 2004, 2008; Rignot and Kanagaratnam, 2006; Howat and others, 2011). A finite-element model of stress evolution near the front of marine-terminating glaciers suggests that undercutting of the ice front due to frontal melting near the base is a strong driver of calving (O’Leary and Christoffersen, 2013). A vertical 2-D ice flow model found that crevasse water depth and basal water pressure could have significant effects, while submarine melt undercutting and backstress from ice mélange are less important (Cook and others, 2014). Recent work by Murray and others (2015a, b) cast doubt on this calving criterion Their data show that the front of Helheim Glacier tipped backwards during a major calving event, which implies that basal crevassing must be considered in calving criteria at least under certain conditions. By using photogrammetric time-lapse imagery, Rosenau and others (2013) documented a major calving event at Jakobshavn Isbræ, finding large vertical displacements of the glacier front of order 15 m and lowering of order 8 m at a position 500 m from the calving front 2 d before the calving event, similar to the observations at Helheim Glacier by Murray and others (2015a, b)
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