Crevasses as Indicators of Surge Dynamics in the Bering Bagley Glacier System, Alaska: Numerical Experiments and Comparison to Image Data Analysis

Abstract

One of the largest sources of uncertainty in sea level rise prediction is glacial acceleration, of which the surge phenomenon is the least understood type. The surge of the Bering Bagley Glacier System (BBGS), Alaska, in 2011–2013 has provided a rare opportunity to study the surge phenomenon in a large and complex glacier system. A surge results in widespread crevassing throughout the glacier system complicating many traditional techniques used to study glacier dynamics. In this paper, we utilize crevassing as a means to investigate the recent BBGS surge through numerical modeling and geostatistical data analysis. Following the principles of structural glaciology, image‐based crevasse characterizations are obtained through geostatistical methods applied to Landsat‐7 data, supplemented by airborne field observations. On the modeling side, a 3‐D full‐Stokes finite element model of the BBGS is developed and applied to investigate ice dynamics and surface structures during the recent surge. A von Mises criterion is adopted to simulate crevassing at the glacier surface, oriented along the axes of maximum principal tensile stress. To facilitate evaluation of model‐ and data‐derived crevasse characteristics, three different comparison methods are introduced. General agreement in the model‐data comparisons indicates that the model has the ability to represent the BBGS system during peak acceleration. The crevasse‐based approach is also employed to optimize the basal sliding parameter and the von Mises stress threshold in the model. Results further indicate that bed topography is an important constraint in modeling the surge process.

Sharp contrasts in observed and modeled crevasse patterns at Greenland's marine terminating glaciers

“…The geometry and prevalence of crevasses are both affected by and affect the stress state and surface mass balance of glaciers, ice shelves, and ice sheets (Colgan et al, 2016). Changes in crevasse geometry and concentration can arise as the result of long-term or rapid changes in stress state, serving as a valuable tool to infer the onset of kinematic change (Colgan et al, 2011;Trantow and Herzfeld, 2018). These changes can also influence the stress state.…”

“…For example, changes in crevassing within lateral shear margins of Antarctic ice streams have the potential to dramatically alter the ability of ice streams to buttress flow from the interior, in turn exerting an important control on ice sheet stability (Borstad et al, 2016;Reese et al, 2018). The impoundment of surface meltwater runoff in crevasses is expected to promote crevasse penetration and assist in the penetration of meltwater to the glacier bed, thereby influencing the englacial and basal stress states (van der Veen, 1998;Stevens et al, 2015;Poinar et al, 2017). Crevasses also increase surface roughness, altering the incidence angle of solar radiation and turbulent energy fluxes, which in turn influence surface melt production (Pfeffer and Bretherton, 1987;Andreas, 2002;Hock, 2005;Cathles et al, 2011;Colgan et al, 2016).…”

Poor performance of a common crevasse model at marine-terminating glaciers

“…The geometry and concentration of crevasses are both affected by and effect the stress state and surface mass balance of glaciers, ice shelves, and ice sheets (Colgan et al, 2016). Changes in crevasse geometry and concentration can arise as the result of long-term or rapid changes in stress state, serving as a valuable tool to infer the onset of kinematic change (Colgan et al, 2011;Trantow and Herzfeld, 2018). These changes can also influence the stress state.…”

Airborne Validation of ICESat-2 ATLAS Data Over Crevassed Surfaces and Other Complex Glacial Environments: Results From Experiments of Laser Altimeter and Kinematic GPS Data Collection From a Helicopter Over a Surging Arctic Glacier (Negribreen, Svalbard)

“…Glacial acceleration is one of the largest sources of uncertainty in sea-level-rise assessment, according to the Fifth Assessment Report (AR5) of the Intergovernmental Panel of Climate Change (IPCC) (Stocker et al, 2013). The different spatial characteristics of crevasse fields, including crevasse spacing, depth and surface roughness, yield information on the deformation characteristics and ice dynamics during glacial acceleration (Herzfeld and Mayer, 1997;Herzfeld, 2000, 2001;Herzfeld et al, 2014;Trantow and Herzfeld, 2018).…”

“…Important concepts in the analysis of ice dynamics, especially for glacial accelerations which lead to heavy crevassing as is the case during a surge, are crevasse provinces and ice-surface roughness. The analysis of crevasse provinces allows study of the deformation characteristics of a glacier during surge and provides information on several aspects of ice dynamics, which can be modeled (Herzfeld and Mayer, 1997;Mayer and Herzfeld, 2000;Herzfeld et al, 2004;Trantow and Herzfeld, 2018). The mathematically easiest way to distinguish crevassity is through calculation of ice-surface roughness (Herzfeld et al, 2014;Trantow and Herzfeld, 2018).…”