Basal crevasses on the Larsen C Ice Shelf, Antarctica: Implications for meltwater ponding and hydrofracture

Abstract

[1] A key mechanism for the rapid collapse of both the Larsen A and B Ice Shelves was meltwater-driven crevasse propagation. Basal crevasses, large-scale structural features within ice shelves, may have contributed to this mechanism in three important ways: i) the shelf surface deforms due to modified buoyancy and gravitational forces above the basal crevasse, creating >10 m deep compressional surface depressions where meltwater can collect, ii) bending stresses from the modified shape drive surface crevassing, with crevasses reaching 40 m in width, on the flanks of the basal-crevasseinduced trough and iii) the ice thickness is substantially reduced, thereby minimizing the propagation distance before a full-thickness rift is created. We examine a basal crevasse (4.5 km in length, $230 m in height), and the corresponding surface features, in the Cabinet Inlet sector of the Larsen C Ice Shelf using a combination of high-resolution (0.5 m) satellite imagery, kinematic GPS and in situ ground penetrating radar. We discuss how basal crevasses may have contributed to the breakup of the Larsen B Ice Shelf by directly controlling the location of meltwater ponding and highlight the presence of similar features on the Amery and Getz Ice Shelves with high-resolution imagery. Citation:

Recent rift formation and impact on the structural integrity of the Brunt Ice Shelf, East Antarctica

“…This caused temporary changes in its alignment with respect to the large-scale stress field, which might explain part of the slowdown. Other studies have suggested that the presence of marine ice can suppress the speed at which rifts propagate, and several ice shelves such as Larsen C and Filchner-Ronne ice shelves contain rifts that terminate in marine ice-rich suture zones (Glasser et al, 2009;Hulbe et al, 2010;McGrath et al, 2012;Jansen et al, 2013;Borstad et al, 2017). However, very few studies have investigated the relationship between rift tip propagation and fracture toughness of ice directly (see for example Rist et al, 2002) and the dynamics of rift tip propagation remains subject to large uncertainties.…”

Complex network of channels beneath an Antarctic ice shelf

“…More recent studies found basal crevasses and channels of various sizes oriented both perpendicular and parallel to the main ice-flow direction at Larsen C, Amery and Getz, Pine Island Glacier, and Fimbul, as well as in Greenland [Luckman et al, 2012;McGrath et al, 2012;Vaughan et al, 2012;Mankoff et al, 2012;Humbert and Steinhage, 2011;Nicholls et al, 2006;Rignot and Steffen, 2008]. The majority of the basal channels reported to date are from ice shelves exposed to ocean waters with a high thermal potential for melting the overlying ice shelf, such as at Pine Island Glacier [Jacobs et al, 2011;Dutrieux et al, 2013].…”

“…The base of an ice shelf is a critical interface; basal roughness in the form of channels influences ice-shelf stability [Gladish et al, 2012;McGrath et al, 2012;Vaughan et al, 2012], affects ocean circulation close to the ice base, and plays an important role in modifying the exchange of heat and mass between the ocean and ice shelf [Stanton et al, 2013]. Mapping of the ice basal topography, in most cases, relies on ice surface elevations from satellite altimetry and the freeboard assumption to calculate ice thickness [Pritchard et al, 2012]; thus, basal topography on spatial scales similar or less than the local ice-shelf thickness remains largely unknown for most ice shelves.…”

Semi-brittle rheology and ice dynamics in DynEarthSol3D

“…Observations have shown that the bending that occurs as ice transitions from resting on land to floating in water (the grounding line) promotes the failure of ice from the bottom up, called basal crevasses, that often appear with characteristic regularity in spacing, persisting within the ice for long distances and eventually promoting the calving of ice (Bindschadler et al, 2011;Glasser and Scambos, 2008;Logan et al, 2013;McGrath et al, 2012;Murray et al, 2015). The main motivation of using DES to understand this phenomenon (or a simplified version thereof) is its rheological flexibility.…”