Formation of crevasse‐squeeze ridges at Trygghamna, Svalbard

Abstract

Crevasse‐squeeze ridges (CSRs) are landforms that have been unequivocally linked to surge‐type glaciers. The formation of CSRs has been discussed since they were first defined in the mid‐1980s. Here, we describe geometric CSR networks from the terrestrial glacier forefields of two glaciers in Trygghamna, Western Svalbard. No glacier surges have been observed in Trygghamna; however, the presence of the CSRs signifies past surge activity. Detailed geomorphological maps were constructed, and the spatial context of these landforms described. Cross‐sections of several CSRs highlight ridge architecture, structure and relationships to surrounding landforms and sediments. Most CSRs are symmetrical in cross‐profile, orientated perpendicular or oblique to the ice‐flow direction. Like previous investigations, we observe these ridge networks on top of till and flutes. Additionally, we, for the first time, document CSRs deposited directly on non‐glaciogenic subsurfaces, namely, beach gravels and bedrock. Our findings confirm previous CSR formation theories; basal sediments are squeezed into bottom‐up crevasses during surges, which are subsequently transported englacially until surge termination and are finally released by melt out from stagnant ice. Consequently, a network of CSRs is the product of a significant reorganisation and down‐glacier transport of basal sediment, exemplifying how single surges are agents of glacial sediment redistribution. These formation processes are illustrated in a refined schematic model. The results further contemporary understanding of CSRs in terrestrial surge‐type glacier settings and may also apply to landforms and sediments in certain marine settings and palaeoglacial environments.

Ice‐stream shutdown during deglaciation: Evidence from crevasse‐squeeze ridges of the Iceland Ice Sheet

“…The CSRs in this study are slightly smaller in size to those that have been described from other palaeo-ice stream beds, where some CSRs are up to 2 km long and 200 m wide (Cline et al, 2015;Delaney et al, 2018;Kurjanski et al, 2019;Lamsters et al, 2021), but considerably larger than CSRs in front of modern surge-type glaciers, which are typically tens of metres long and <2 m wide (e.g., Kjaer et al, 2008;Lovell et al, 2015;Ben-Yehoshua et al, 2023).…”

“…The massive, homogenous macro-scale appearance of the sediment in both areas suggests that the till was well-mixed and far travelled (Phillips et al, 2018). The vague fissile structures indicate that the sediments were slightly sheared while being deposited, supporting the hypothesis that CSRs form prior to ice stagnation (Bjarnad ottir, 2007;Evans et al, 2016;Ben-Yehoshua et al, 2023).…”

“…Sedimentological work on till within and outside CSRs has not revealed any significant differences between them, except for generally steeper clast fabric within the CSRs, implying common origin (e.g., Sharp, 1985;Christoffersen et al, 2005;Ben-Yehoshua et al, 2023). Therefore, with the available data, we suggest the lower till (f2) in section B3 in Bakkafl oi may have been deposited prior to the formation of the CSRs (Figure 9a).…”

“…with corridor pattern (e.g., Kjaer et al, 2008;Schomacker et al, 2014;Evans et al, 2016;Ben-Yehoshua et al, 2023). In Bakkafl oi, the corridor pattern is not as clear as in Þistilfjörður but sites 1 and 2 could represent a section of one corridor and site 3 another one (see Figure 2a).…”

“…Ridge preservation is largely a result of the passive retreat when the ice stagnates and melts away in situ and/or floatation (e.g., Kamb et al, 1985;Rea & Evans, 2011;Sharp, 1985). CSR networks form by the squeezing of highly deformable subglacial sediments into basal crevasses that form due to high basal water pressures and extensional forces acting on glacier ice during accelerated flow (Evans & Rea, 1999;Rea & Evans, 2011;Sharp, 1985) and transported englacially within the advancing surge margin (Ankerstjerne et al, 2015;Ben-Yehoshua et al, 2023).…”