Initiation of a major calving event on the Bowdoin Glacier captured by UAV photogrammetry

Abstract

Abstract. In this paper, we analyse the calving activity of the Bowdoin Glacier, north-western Greenland, in 2015 by combining satellite images, UAV (unmanned aerial vehicle) photogrammetry and ice flow modelling. In particular, a highresolution displacement field is inferred from UAV orthoimages taken immediately before and after the initiation of a large fracture, which induced a major calving event. A detailed analysis of the strain rate field allows us to accurately map the path taken by the opening crack. Modelling results reveal (i) that the crack was more than half-thickness deep, filled with water and getting irreversibly deeper when it was captured by the UAV and (ii) that the crack initiated in an area of high horizontal shear caused by a local basal bump immediately behind the current calving front. The asymmetry of the bed at the front explains the systematic calving pattern observed in May and July-August 2015. As a corollary, we infer that the calving front of the Bowdoin Glacier is currently stabilized by this bedrock bump and might enter into an unstable mode and retreat rapidly if the glacier keeps thinning in the coming years. Beyond this outcome, our study demonstrates that the combination of UAV photogrammetry and ice flow modelling is a promising tool to horizontally and vertically track the propagation of fractures responsible for large calving events.

High-Endurance UAV for Monitoring Calving Glaciers: Application to the Inglefield Bredning and Eqip Sermia, Greenland

“…On the other hand, Farquhar glacier exhibits a dual regime at the front, namely fast flow in the western section and very slow motion in the eastern part within ∼1 km from the glacier's margin (Figure 5, bottom panels). This pattern is similar to the one reported at Bowdoin glacier (Jouvet et al, 2017) and is expected to produce high horizontal shear and damage ice in agreement with the highly crevassed texture shown by the ortho-image (Figure 1). Following Jouvet et al (2017), it is plausible that the slow ice flow region reflects a shallower bedrock in the eastern part, however, no information on the bedrock is currently available to verify or refute this hypothesis.…”

“…• Autonomous UAV surveys over long distances (up to 180 km) and during long duration (up to ∼3 h) for mapping up to four calving glacier termini located more than 25 km away from the UAV operator or ∼50 km 2 of a single glacier, which is several times larger than in any other glacier area mapped by UAV in former studies (Ryan et al, 2015;Jouvet et al, 2017;Chudley et al, 2019). • Overcoming adverse conditions often associated with polar environments, such as (i) the roughness of the terrain for take-off and landing in confined areas; (ii) the occurrence of katabatic winds of up to 15 m/s; (iii) the steep inclination angle of the magnetic field in high latitudes, which causes a weak horizontal vector for measuring magnetic North with a compass; (iv) cold temperatures (∼ 0 • C), which might reduce the battery capacity.…”

“…Template matching is a well-established method for deriving glacier velocities from terrestrial (e.g., Ahn and Box, 2010;Messerli and Grinsted, 2015;Schwalbe and Maas, 2017), UAV (e.g., Ryan et al, 2015;Gindraux et al, 2017;Jouvet et al, 2017) or satellite (Sakakibara and Sugiyama, 2018) imageries. Here we used the Matlab toolbox ImGRAFT (http://imgraft.glaciology.…”

“…• tidewater glacier ice flow and iceberg calving (Ryan et al, 2015;Jouvet et al, 2017;Chudley et al, 2019), • surface ice motion of mountain glaciers (Immerzeel et al, 2014;Gindraux et al, 2017), • glacial structures (Tonkin et al, 2016;Ely et al, 2017;Jones et al, 2018), • distribution of organic matter (Hodson et al, 2007;Stibal et al, 2017;Ryan et al, 2018), • spatial albedo patterns (Ryan et al, 2017Podgorny et al, 2018), • supraglacial drainage networks (Rippin et al, 2015), • ice surface melt (Bash et al, 2018).…”

“…In this paper, we detail an open-source, low-cost, fixed-wing UAV designed for monitoring glacial processes similar to the one presented in Ryan et al (2015), Jouvet et al (2017), Chudley et al (2019), , but specifically optimized for flight endurance to survey remote areas. We demonstrate the potential of our platform with 21 long-distance surveys over six fast-flowing glaciers of the Inglefield Bredning, northwest Greenland, and Eqip Sermia, west Greenland.…”