Semester of Graduation

Summer 2018

Degree

Master of Science (MS)

Department

Geology and Geophysics

Document Type

Thesis

Abstract

Glacial outburst floods are difficult to predict and threaten human life. These events are characterized by rapid draining of glacier-dammed lakes via the sub/englacial hydraulic network to the proglacial stream. The glacier-dammed lake on Gornergletscher in Switzerland, which fills and drains each summer, provides an opportunity to study this hazard. For three drainages (2004, 2006, and 2007), icequakes (IQ) are tracked as well as on-ice GPS movement. The seasonal seismic networks had 8 – 24 three-component stations and apertures of about 300 – 400 m on the glacier surface. The seasonal GPS arrays contained 4 – 8 GPS antennae on the glacier surface with spacings of 100 – 1,000 m. Using Rayleigh wave coherence surface IQ location, 2924, 7822, and 3782 IQs were located, in 2004, 2006, and 2007, respectively. The GPS data were smoothed using a nonparametric protocol, with average station velocities of 10 – 90 mm/day. In 2006, strains were calculated using five stations within 500 m of the lake, co-located with the seismic network. In 2007, strains were calculated using seven stations that were not co-located within the seismic network.

In 2006, there was no obvious increase in GPS speeds with slow (~21 days), supraglacial lake drainage. However, when drainage was subglacial as in 2007 (sub/englacial over ~11 days), GPS speed increased over 100% (6 to 13 cm/day). This speed increase is evidence for basal sliding induced by subglacial drainage. In general, when the strain increases on the principle extension axis that aligns with the crevasse opening direction, IQs are more prolific. A diurnal signal in both IQ occurrence and surface strain is observed, with peak strain occurring in the mid- to late-afternoon (15:00 – 19:00 local) across the study area in 2006. This time-shift in strain and spatiotemporal dependence of IQs is interpreted to be caused by diurnal variations in melt-induced sliding. This analysis highlights crevasse formation on short time scales where glacier flow is controlled by sliding variations in response to water input into the subglacial drainage system. Coupled seismic and GPS monitoring can thus make a key contribution to our understanding of brittle deformation and crevassing of glacier ice.

Glacial outburst floods are difficult to predict and threaten human life. These events are characterized by rapid draining of glacier-dammed lakes via the sub/englacial hydraulic network to the proglacial stream. The glacier-dammed lake on Gornergletscher in Switzerland, which fills and drains each summer, provides an opportunity to study this hazard. For three drainages (2004, 2006, and 2007), icequakes (IQ) are tracked as well as on-ice GPS movement. The seasonal seismic networks had 8 – 24 three-component stations and apertures of about 300 – 400 m on the glacier surface. The seasonal GPS arrays contained 4 – 8 GPS antennae on the glacier surface with spacings of 100 – 1,000 m. Using Rayleigh wave coherence surface IQ location, 2924, 7822, and 3782 IQs were located, in 2004, 2006, and 2007, respectively. The GPS data were smoothed using a nonparametric protocol, with average station velocities of 10 – 90 mm/day. In 2006, strains were calculated using five stations within 500 m of the lake, co-located with the seismic network. In 2007, strains were calculated using seven stations that were not co-located within the seismic network.

In 2006, there was no obvious increase in GPS speeds with slow (~21 days), supraglacial lake drainage. However, when drainage was subglacial as in 2007 (sub/englacial over ~11 days), GPS speed increased over 100% (6 to 13 cm/day). This speed increase is evidence for basal sliding induced by subglacial drainage. In general, when the strain increases on the principle extension axis that aligns with the crevasse opening direction, IQs are more prolific. A diurnal signal in both IQ occurrence and surface strain is observed, with peak strain occurring in the mid- to late-afternoon (15:00 – 19:00 local) across the study area in 2006. This time-shift in strain and spatiotemporal dependence of IQs is interpreted to be caused by diurnal variations in melt-induced sliding. This analysis highlights crevasse formation on short time scales where glacier flow is controlled by sliding variations in response to water input into the subglacial drainage system. Coupled seismic and GPS monitoring can thus make a key contribution to our understanding of brittle deformation and crevassing of glacier ice.

Date

6-6-2018

Committee Chair

Luttrell, Karen

DOI

10.31390/gradschool_theses.4748

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