2-D representation of 360-degree borehole images from about 34 and 80 meters deep showing several identified crevasse traces
These images show several identified crevasse traces from depths of approximately 34 meters (left) and approximately 80 meters (right) in the core. In this 2-D representation of the 360-degree borehole image, the traces are identifiable as distinct sinusoids cutting other (horizontal) ice layers at a high-angle; in 3-D space they are steeply-dipping planes. The layers are formed of bright (bubble-rich) laminae, enveloped on each side by centimeter-thick layers of dark (bubble-poor) ice. These are interpreted as the freezing of water filling a several cm thick crack in the ice, with air expelled on freezing accumulating in the central zone. Credit: Hubbard et al. [2021], Figure 3ab
Source: AGU Advances

Newly available optical technology has provided the first direct observations of crevasse traces in a borehole drilled in the Store Glacier, a fast-moving outlet glacier of the Greenland Ice Sheet. Hubbard et al. [2021] have recognized these traces as distinctive zones of steeply inclined layers with bubble-rich and bubble-free ice zones. These features are explained as crevasses that opened, filled with water, then refroze, sometimes occurring repeatedly in the same place. What is surprising is that these crevasse traces are observed up to 265 meters deep in the borehole, while increased ice temperatures suggest that water and the heat it carries are penetrating up to 400 meters, deeper than previously assumed. An implication of this discovery is that such deep crevasse traces can survive advection to the ice front and be an important determiner of patterns of ice calving and rifting.

Citation: Hubbard, B., Christoffersen, P., Doyle, S. H., Chudley, T. R., Schoonman, C. M., Law, R., & Bougamont, M. [2021]. Borehole-based characterization of deep mixed-mode crevasses at a Greenlandic outlet glacier. AGU Advances, 2, e2020AV000291. https://doi.org/10.1029/2020AV000291

—Susan Trumbore, Editor-in-Chief, AGU Advances

Text © 2021. The authors. CC BY-NC-ND 3.0
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