Bering Glacier surge 2011: analysis of laser altimeter data

Abstract

The Bering Glacier–Bagley Icefield system in Alaska is currently surging (2011). Large-scale elevation changes and small-scale elevation-change characteristics are investigated to understand surge progression, especially mass transport from the pre-surge reservoir area to the receiving area and propagation of the kinematic surge wave as manifested in heavy crevassing characteristic of rapid, brittle deformation. This analysis is based on airborne laser altimeter data collected over Bering Glacier in September 2011. Results include the following: (1) Maximal crevasse depth is 60 m, reached in a rift that separates two deformation domains, indicative of two different flow regimes. Otherwise surge crevasse depth reaches 20–30 m. (2) Characteristic parameters of structural provinces are derived by application of geostatistical classification. Parameters include significance and spacing of crevasses, surface roughness and crevasse-edge curvature (indicative of crevasse age). A classification based on these parameters serves to objectively discriminate structural provinces, indicative of surge progression down-glacier and up-glacier. (3) Elevation changes from 2011 and 2010 altimetry show 40–70 m surface lowering in the reservoir area in lower central Bering Glacier and 20–40m thickening near the front in Tashalich arm. Combining elevation changes with results of crevasse profilometry and pattern analysis, the rapid progression of the surge can be mathematically–physically reconstructed.

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

“…This figure also shows the model domain, defined to include the surging parts of the BBGS. The main Bering Glacier is a surge‐type glacier (Post, ); the surge dynamics extends into the Eastern Bagley Ice Field, also named Bagley Ice Valley, as noted in 1995 (Herzfeld & Mayer, ) and observed again in 2011–2013 (Herzfeld, McDonald, Stachura, et al, ; Herzfeld, McDonald, & Weltman, ), while the Western Bagley Ice Field is not affected by the surge process. The neighboring Steller Glacier originates in the Western Bagley Ice Field and shares a medial moraine with the lobe of Bering Glacier.…”

“…Airborne imagery collected in our Fall 2011 campaign to the BBGS (Herzfeld et al, ) is given in Figure , which shows the locations that were most affected by the early‐2011 phase of the surge. The flightpath for our Fall 2011 campaign is marked by the thin black line in Figure b.…”

“…As observed in Herzfeld and Mayer (), Herzfeld (), and (Herzfeld et al, ), the first visible surface expression of the surge's kinematic wave is an occurrence of bidirectional crevasses with sharp edges in regions of high surface slope, indicative of bedrock slope. The reason is that the kinematic force of the surge breaks first at preexisting weaknesses caused by already crevassed ice or over relatively thin ice.…”

“…The 2011-2013 surge in the Bering Bagley Glacier System (BBGS), Alaska, has provided an opportunity for data collection and analysis of the surge phenomenon in a large and complex glacier system (Herzfeld, McDonald, Stachura, et al, 2013;Herzfeld, McDonald, & Weltman, 2013;Trantow & Herzfeld, 2016). The BBGS is one of the largest glacial systems outside of Greenland and Antarctica and the largest temperate surge-type glacier on Earth (Molnia, 2008).…”

Bering Glacier and Bagley Ice Valley surge 2011: crevasse classification as an approach to map deformation stages and surge progression

“…The analysis and classification of crevassed ice surfaces from images collected during the current (2011) surge of the Bering-Bagley glacier system forms a central part of the paper. The vertical component of the surge kinematics can be constrained using analysis of laser altimeter data (Herzfeld and others, 2013).…”