Surface ice motion deviating toward the margins during speed‐up events at Gornergletscher, Switzerland

Abstract

[1] High frequency ice flow measurements during speed-up events in Gornergletscher, Switzerland, revealed intriguing ice motion which has never been reported in detail before. During the summer 2005, more than a 100% flow speed increase was observed three times at four GPS stations installed across Gornergletscher. The speed-ups were accompanied by a decimeter scale surface uplift. Two of the events were triggered by intensive surface melt and rainfall, while the third one was due to the outburst of Gornersee, a glacier-dammed lake located 2 km upglacier. An interesting observation was ice motion deviating toward the side margins during the events. As the glacier accelerated, a transverse (cross glacier) velocity component was generated, turning the flow direction away from the central flow line toward the margins. When the glacier decelerated, the transverse velocity component reversed so that the ice flowed back to the azimuth of the initial flow direction. In the most significant case, the trajectory of the survey stake deviated from the original track by 0.2 m in the transverse direction. We hypothesize that the observed lateral ice motion was caused by locally elevated subglacial water pressure. When the ice sole decoupled from the bed at a part of the glacier, a point source of vertical displacement was transmitted to the surface through viscous ice. This caused the transverse as well as vertical surface motion, as observed in ground motion during magma intrusion. The hypothesis was tested with a two-dimensional ice flow model applied to the transverse glacier cross section. The model confirmed that the surface ice would move toward the margins as observed in Gornergletscher, if subglacial water pressure exceeded the ice overburden pressure over a limited part of the bed.Citation: Sugiyama, S., A. Bauder, P. Riesen, and M. Funk (2010), Surface ice motion deviating toward the margins during speed-up events at Gornergletscher, Switzerland,

Greenland ice sheet annual motion insensitive to spatial variations in subglacial hydraulic structure

“…S3, inferred to be in the vicinity of a major drainage pathway (Figure ), experiences large oscillations in diurnal along‐track velocity and vertical displacement, consistent with oscillatory variability in P w . Furthermore, Sugiyama et al [] observe that vertical ice displacement over a basal perturbation can induce a cross‐track displacement at some distance away from the basal perturbation; the southeasterly displacement of S3 during the speedup periods E1–3 mimics this behavior and places S3 to the south of the VPA, in agreement with the hydraulic potential analysis.…”

Subglacial sediment production and snout marginal ice uplift during the late ablation season of a temperate valley glacier

“…If this is sub‐daily hydraulic jacking, it is surprising that it is being observed late in the melt season. Sub‐daily hydraulic jacking, at the scale of decimeters, has been observed early in the melt season of Alpine glaciers (Kulessa et al, ; Sugiyama et al, ) and attributed to the ease with which subglacial pressure can increase in a distributed subglacial system. Sudden increases in the rate of meltwater supply cause the glacier to decouple from its bed (Mair et al, ; Kulessa et al, ), the surface to uplift and the glacier to accelerate (Mair et al, ; Sugiyama and Gudmundsson, ; Sugiyama et al, ).…”

A high-frequency and high-resolution image time series of the Gornergletscher – Swiss Alps – derived from repeated UAV surveys

“…The entire Gornergletscher system (i.e. the terminal tongue and its five tributaries) covers an area of almost 50 km 2 and its mainstream is 12 km long, making it one of the largest European glaciers (Sugiyama et al, 2010). 5…”

“…The Gornergletscher system has been widely studied since the 1970s due to its significant size, its relatively easy access, and because a glacier-dammed lake often threatened the downstream Matter valley with glacier outburst floods (Sugiyama et al, 2010;Werder et al, 2009;Werder et al, 2013). The long history of glaciological studies in this area has shown that the mass balance of the Gornergletscher system was stable from the 1930s to the early 1980s, and significantly dropped since then (Huss et al, 2012).…”

“…Finally, the time-lapse coupled with the Matching Maps is an interesting tool to monitor ice surface velocity and deformation (Ryan et al, 2015;Kraaijenbrink et al, 2016), and in turn ice flow dynamics at the glacier surface. The Matching Maps provide a quantification of the ice velocity at every location on the surface of the glacier, which can be used to calibrate or to validate ice flow models, especially for the Gornergletscher which was extensively used as a modeling benchmark (see for instance 25 (Werder and Funk, 2009;Riesen et al, 2010;Sugiyama et al, 2010;Werder et al, 2013)).…”