Congratulations Jeremy Stock, MS!

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Jeremy Stock successfully defended his MS thesis, “Modeled Patterns of Crevassing Induced by Supraglacial Lake Drainage in Western Greenland”, and turned in a very nice dissertation this May. Congratulations, Jeremy!

Abstract:

The Greenland Ice Sheet is expected to contribute substantially to global sea level rise over the next century in response to climate change. As increasing volumes of surface meltwater are delivered to the glacier bed via moulins during supraglacial lake drainage events, it has been hypothesized that new crevasses may form upflow, causing a cascade of lake drainages. This upflow expansion could alter ice sheet dynamics, leading to ice sheet instability and even greater sea level rise contributions. To investigate this hypothesis, we applied an analytical ice-flow model (Gudmundsson, 2008) to calculate surface strain rates and infer the pattern of crevassing induced by a modeled rapidly drained lake. We calibrate the model using data collected during a lake drainage event in the summer of 2011 in the Pakitsoq region of Western Greenland. The patterns and extent of crevassing we see in our model results are highly dependent on the bed topography, basal sliding ratio, dimensions of the slipperiness patch, and the seasonal timing of the drainage event. Our model results show evidence of considerable crevassing occurring within 3-5.5 km upstream of the modeled lake drainage, with crevassing enhanced by a factor of 5-6 within a 3 km radius of the rapidly drained lake. Because lakes in this area are spaced by roughly 2-4 km, our results support the hypothesis for cascading lake drainage. This research improves our understanding of how meltwater may affect ice sheet dynamics, which are a major factor in how much the Greenland Ice Sheet will contribute to sea level rise in the future.

G. H. Gudmundsson. Analytical solutions for the surface response to small amplitude perturbations in boundary data in the shallow-ice-stream approximation. The Cryosphere, 2(2):77–93, 2008. http://doi.org/10.5194/tc-2-77-2008

Modeled Patterns of Crevassing Induced by Supraglacial Lake Drainage in Western Greenland

A few figure excerpts:

Figure 2.12: Flow chart of the data inputs (colored blocks), required parameters (gray circles), and outputs (white circles) produced by the analytical perturbation model (Gudmundsson, 2008). The model outputs are responses to basal perturbations and represent changes to the mean surface elevation (s), mean longitudinal velocity (u), mean transverse velocity (v), and mean vertical velocity (w).
Figure 4.1: Most likely new crevasse locations in response to supraglacial lake drainage. Model results when the study area is centered around lakes 55, 52, 44, 64, 59, and 54. Lake 52 is always shown as a bold circle. Supraglacial lakes are shown as black circles, with the lakes involved in the drainage event outlined twice (Morriss et al., 2013) and GPS stations shown as black triangles (Andrews et al., 2014). The colors indicate where all 3 theoretical strain rate thresholds are exceeded (deep red), 2 thresholds are exceeded (red), 1 threshold is exceeded (orange), and no thresholds are exceeded (tan). The concentric circles are separated by 1 km. We used constant values for mean slip ratio ( ̄C), time (t), and the amplitude of the basal slipperiness patch (Ac) across all tests shown. The diameter of the basal slipperiness patch (Dc) is scaled relative to mean ice thickness ( ̄h) in each location.

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