Glacier crevasses: Observations, models, and mass balance implications

Abstract

We review the findings of approximately 60 years of in situ and remote sensing studies of glacier crevasses, as well as the three broad classes of numerical models now employed to simulate crevasse fracture. The relatively new insight that mixed-mode fracture in local stress equilibrium, rather than downstream advection alone, can introduce nontrivial curvature to crevasse geometry may merit the reinterpretation of some key historical observation studies. In the past three decades, there have been tremendous advances in the spatial resolution of satellite imagery, as well as fully automated algorithms capable of tracking crevasse displacements between repeat images. Despite considerable advances in developing fully transient three-dimensional ice flow models over the past two decades, both the zero stress and linear elastic fracture mechanics crevasse models have remained fundamentally unchanged over this time. In the past decade, however, multidimensional and transient formulations of the continuum damage mechanics approach to simulating ice fracture have emerged. The combination of employing damage mechanics to represent slow upstream deterioration of ice strength and fracture mechanics to represent rapid failure at downstream termini holds promise for implementation in large-scale ice sheet models. Finally, given the broad interest in the sea level rise implications of recent and future cryospheric change, we provide a synthesis of 10 mechanisms by which crevasses can influence glacier mass balance. Field ObservationsBy virtue of providing relatively easy access to a glacier's interior, crevasses can be an asset to observational glaciologists, permitting, for example, the efficient examination of glacier stratigraphy. Annual accumulation

Flow and structure in a dendritic glacier with bedrock steps

“…Crevasse fields are mainly in response to the average bulk stress field, and when travelling through different stress regimes they can become rotated, or close to form crevasse traces. In addition, local discontinuities can also result in specific stress patterns and resulting local crevasses (Meier and others, 1974;Glasser and others, 1998;Hambrey and Lawson, 2000;Colgan and others, 2016). On Shackleton Glacier, expected crevasse patterns included: (i) arcuate upward and transverse crevasses in longitudinal extensional zones that correspond to increases in flow speed upstream of icefalls and in the narrowing trunk valley; (ii) longitudinal crevasses and active splaying crevasses indicating lateral extension at the base of the upper icefalls; (iii) marginal short splaying crevasses with angles of 45°in uniform velocity regions of the main trunk; (iv) upward splaying longer crevasses where the trunk enters the narrowing valley and marginal shear becomes high and compressive; and (v) some chevron and en echelon crevasses in rotating marginal bends in the upper and middle regions of the main trunk.…”

“…This results in a relatively deep trunk valley as evidenced by the steep exposed valley walls. Tributary centreline depths are based on visual interpretation of the broad shallow icefall with séracs, in combination with maximum crevasse depths from the creep relation and measurements in temperate glaciers, and from the stability of a free standing ice cliff (Cuffey and Paterson, 2010;Colgan and others, 2016). See Section 3.1.4 for verification of all chosen scenarios.…”

An Intensive Observation of Calving at Helheim Glacier, East Greenland

“…Colgan et al (2016) present an extensive review of the formation of crevasses, including basal crevasses and hydrofracturing. Observations of calving at Helheim Glacier using stereo photogrammetry suggest that a basal crevasse may be a key ingredient in establishing the onset and location of calving (James et al, 2014).…”

Basal conditions at Engabreen, Norway, inferred from surface measurements and inverse modelling

“…Crevassing is another key process to lowering the viscosity of the ice through the delivery of meltwater to the bed and the fracturing/damage of the ice (e.g. Borstad and others, 2012;Colgan and others, 2015;Lüthi and others, 2015). Meltwater has easy access to the lower part of the ice column through crevasses, where it can lower the viscosity through cryohydrologic warming and hydraulic weakening of the ice, as the meltwater 564 Solgaard and others: Engabreen refreezes and latent heat is released.…”