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\begin{document}

\title{Borehole-based characterization of deep crevasses at a Greenlandic
outlet glacier}



\author[1,1]{Bryn Hubbard}%
\author[2,2]{Poul Christoffersen}%
\author[1,1]{Samuel Huckerby Doyle}%
\author[3,3]{Thomas Russell Chudley}%
\author[4,4]{Marion Heidi Bougamont}%
\author[2,2]{Robert Law}%
\author[5,5]{Charlotte Schoonman}%
\affil[1]{Aberystwyth University}%
\affil[2]{University of Cambridge}%
\affil[3]{Scott Polar Research Institute}%
\affil[4]{Cambridge University}%
\affil[5]{Alfred-Wegener-Institut}%


\vspace{-1em}



  
  \date{May 26, 2024}


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\begin{abstract}
Optical televiewer borehole logging within a crevassed region of
fast-moving Store Glacier, Greenland, revealed the presence of 35
high-angle planes that cut across the background primary stratification.
These planes were composed of a bubble-free layer of refrozen ice, most
of which hosted thin laminae of bubble-rich `last frozen' ice,
consistent with the planes being the traces of former open crevasses.
Several such last-frozen laminae were observed in four traces,
suggesting multiple episodes of crevasse reactivation. The frequency of
crevasse traces generally decreased with depth, with the deepest
detectable trace being 265 m below the surface. This is consistent with
the extent of the warmer-than-modelled englacial ice layer in the area,
which extends from the surface to a depth of \textasciitilde{}400 m.
Crevasse trace orientation was strongly clustered around a dip of 63\selectlanguage{ngerman}°
and a strike that was offset by 71° from orthogonal to the local
direction of principal extending strain. The traces' antecedent
crevasses were therefore interpreted to have originated upglacier,
probably \textasciitilde{}8 km distant involving mixed-mode (I and III)
formation. We conclude that deep crevassing is pervasive across Store
Glacier, and therefore also at all dynamically similar outlet glaciers.
Once healed, their traces represent planes of weakness subject to
reactivation during their subsequent advection through the glacier.
Given their depth, it is highly likely that such traces - particularly
those formed downglacier - survive surface ablation to reach the glacier
terminus, where they may represent foci for fracture and iceberg
calving.%
\end{abstract}\selectlanguage{ngerman}%



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\emph{AGU Advances}

Supporting Information for

\textbf{Borehole-based characterization of deep crevasses at a
Greenlandic outlet glacier}

Bryn Hubbard1, Poul Christoffersen2, Samuel H. Doyle1, Thomas R.
Chudley2, Charlotte M. Schoonman2, Robert Law2, Marion Bougamont2

1Centre for Glaciology, Department of Geography and Earth Sciences,
Aberystwyth University, Aberystwyth, UK. 2Scott Polar Research
Institute, University of Cambridge, Cambridge, UK.

\textbf{Contents of this file}

Figure S1 Caption for Figure S1 Caption for Movie S1





Figure S1. Full depth temperature profiles for BH18c showing measured
englacial temperatures (red dots) and modelled temperatures (black
dots). The depth axis extends from the ice surface (at 0 m) to the
glacier bed at \textasciitilde{}949 m.

{\label{figure-s1.-full-depth-temperature-profiles-for-bh18c-showing-measured-englacial-temperatures-red-dots-and-modelled-temperatures-black-dots.-the-depth-axis-extends-from-the-ice-surface-at-0-m-to-the-glacier-bed-at-949-m.}}

Movie S1. Video of a surface meltwater channel \textasciitilde{}15 cm
across that has exploited and revealed a crevasse trace cropping out at
the surface of Store Glacier. Note the clear, bubble-free ice bounding
the mm-thick central bubble-rich lamina, similar to that imaged by our
OPTV log of BH18c (see Figure 3 of main text).

{\label{movie-s1.-video-of-a-surface-meltwater-channel-15-cm-across-that-has-exploited-and-revealed-a-crevasse-trace-cropping-out-at-the-surface-of-store-glacier.-note-the-clear-bubble-free-ice-bounding-the-mm-thick-central-bubble-rich-lamina-similar-to-that-imaged-by-our-optv-log-of-bh18c-see-figure-3-of-main-text.}}

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