Buoyant calving and ice-contact lake evolution at Pasterze Glacier (Austria) in the period 1998–2019

Abstract

Abstract. Rapid growth of proglacial lakes in the current warming climate can pose significant outburst flood hazards, increase rates of ice mass loss, and alter the dynamic state of glaciers. We studied the nature and rate of proglacial lake evolution at Pasterze Glacier (Austria) in the period 1998–2019 using different remote sensing (photogrammetry, laserscanning) and fieldwork-based (GPS, time-lapse photography, geoelectrical resistivity tomography/ERT, and bathymetry) data. Glacier thinning below the spillway level and glacier recession caused flooding of the glacier, initially forming a glacier-lateral to supraglacial lake with subaerial and subaquatic debris-covered dead-ice bodies. The observed lake size increase in 1998–2019 followed an exponential curve (1998: 1900 m2; 2019: 304,000 m2). ERT data from 2015 to 2019 revealed widespread existence of massive dead-ice bodies exceeding 25 m in thickness near the lake shore. Several large-scale and rapidly occurring buoyant calving events were detected in the 48 m deep basin by time-lapse photography, indicating that buoyant calving is a crucial process for fast lake expansion. We identified a sequence of processes: glacier recession into a basin and glacier thinning below spillway-level; glacio-fluvial sedimentation in the glacial-proglacial transition zone covering dead ice; initial formation and accelerating enlargement of a glacier-lateral to supraglacial lake by ablation of glacier ice and debris-covered dead ice forming thermokarst features; increase in hydrostatic disequilibrium leading to destabilization of ice at the lake bottom or at the near-shore causing fracturing, tilting, disintegration or emergence of new icebergs due to buoyant calving; and gradual melting of icebergs along with iceberg capsizing events. We conclude that buoyant calving, previously not reported from the European Alps, might play an important role at alpine glaciers in the future as many glaciers are expected to recede into valley or cirque overdeepenings.

The sedimentological death mask of a dying glacier

“…The terrace deposits abut against the delta topset to the west, and directly against the ice‐marginal lake to the east. The ice‐marginal lake periodically contains large icebergs (Figures 1 and 5C), which Kellerer‐Pirklbauer et al (2021) proposed originate from the lake bottom rather than through subaerial calving at the ice margin.…”

“…Perspective of the ice‐marginal lake and glacier, showing a large number of icebergs. These are sourced from the lake bottom (Kellerer‐Pirklbauer et al, 2021).…”

“…The Pasterze Glacier, in the Großglockner range, is Austria's largest glacier and since the 1852–1856 maximum has attracted detailed geomorphological (Avian et al, 2018; Kellerer‐Pirklbauer et al, 2021) and structural glaciological investigations (Kellerer‐Pirklbauer & Kulmer, 2019). Its recession has been extensively documented by photographs that remind us of glacier recession in a greenhouse world (Lieb, 2004).…”

“…Historically, much effort on the Pasterze Glacier has focussed on its changing volume and area (Gspuring et al, 2004; Paschinger, 1953; Patzelt & Slupetzky, 1970; Seeland, 1883; Wakonigg, 1993; Wakonigg & Lieb, 1996), the geomorphology of its forefield (Kellerer‐Pirklbauer, 2008; Kellerer‐Pirklbauer et al, 2021) or structural glaciology (Herbst & Neubauer, 2000; Kellerer‐Pirklbauer & Kulmer, 2019). The role of dead ice in influencing the architecture of the glacier forefield has long been known (Lagally, 1932), and its presence has more recently been demonstrated in the 2016 forefield via electrical resistivity tomography (Seier et al, 2017).…”

“…This paper thus represented major progress in understanding the spatial relationship between landform types, and the sequential series of four maps, which showed that landforms changed on an annual basis as the result of melting dead ice bodies. Subsequently, Kellerer‐Pirklbauer et al (2021) demonstrated that an ice‐proximal lake (‘sandur lake’ of Avian et al, 2018) was carpeted with ice at the lake bottom, with buoyant calving of the submerged ice margin bringing icebergs to the surface. The sedimentological consequences of this process merit investigation.…”