Triggering and drainage mechanisms of the 2004 glacier‐dammed lake outburst in Gornergletscher, Switzerland

Abstract

[ 1 ] To investigate the triggering and the drainage mechanisms of ag lacier-dammed lake outburst, we conducted high-frequency measurements of the ice surface motion in the vicinity of Gornersee, an ice marginal lake on Gornergletscher,S witzerland. During the outburst event in July 2004, the ice surface within ad istance of 400 mf rom the lakeshore moved vertically upward by up to 0.1 m. This vertical surface motion cannot be explained by vertical straining of ice which was measured in one of the boreholes; therefore, we suggest the separation of the glacier sole from the bed was caused by subglacially drained lake water.Our observation indicates that the lake water drained as a sheet-like flow through the space created by the basal separation. The upward surface motion was greater in the region where the ice flotation level was exceeded by the lake level, implying that the ice barrier was breached when the lake water hydraulically connected to the bed and lifted up the glacier.I na ddition to the centimeter-scale vertical ice motion, three survey stakes located within 100 mfrom the lake showed extraordinarily large vertical displacement of 0.5-3.0 ma ssociated with abrupt changes in horizontal flow direction. Ap lausible interpretation is that the marginal ice wedge bent upward because of the buoyancy force generated by the drained water.Such bending is possible if subglacial and englacial fractures formed at about 200 mf rom the glacier margin and acted as ah inge. The newly formed and preexisting englacial fractures probably took the role of inducing englacial water drainage which preceded the outburst.

The Role of Englacial Hydrology in the Filling and Drainage of an Ice‐Dammed Lake, Kaskawulsh Glacier, Yukon, Canada

“…The subglacial volume ( ) at the beginning of the record was 4.0 (1.7–5.6) m and increased to a maximum of 20.8 (14.3–22.6) m on 20 August, three days after the lake level maximum. This lag between peak lake level (i.e., ) and maximum uplift of the shelf (i.e., ) has also been observed during outburst floods at other sites (e.g., Anderson et al, ; Sugiyama et al, ). The highest inferred daily discharge rate from the subaerial and subglacial reservoirs is 65 m s (Figure S3), which occurred on 4 September, though we note that no estimates of subaerial volume are available on 5 and 6 September, after the lake level dipped below the sensor elevation.…”

Ice tectonic deformation during the rapid in situ drainage of a supraglacial lake on the Greenland Ice Sheet

“…This lowering is simultaneous with uplift at GPS NW, GPS SE and GPS NE, suggesting that the water delivered to the bed during rapid discharge did not access the bed beneath GPS SW. Finally, at 03:00 when GPS SW moves north up the bed slope there is a second low magnitude (10 cm) period of uplift exclusive to GPS SW. Sugiyama et al (2008) observed the greatest uplift near to the drainage centre during the subglacial drainage of icemarginal lake Gornersee in Switzerland and we therefore assert, like Das et al (2008), that surface uplift was likely greater near the centre of the lake. The highest-magnitude uplift observed in this study of 0.9 m by GPS NW is the most consistent with the 1.2 m of uplift measured by Das et al. The bed slope underneath GPS NW slopes down towards the north-west (Fig.…”

A viscoelastic Rivlin-Ericksen material model applicable to glacier ice

“…In recent field observations on an Alpine glacier (Gornergletscher, Switzerland), repeated near-reversal of flow, accompanied by reversed displacement direction was observed (Sugiyama et al, 2007(Sugiyama et al, , 2008. The change of motion takes place within a few days during the periodical drainage of a supra-glacial lake, and is possibly related to the unloading and stress redistribution during the rapid drainage.…”