News & Events

PhD thesis defense: Billy Armstrong

Wednesday, May 10, 2017, 9:00AM - 11:00AM

Speaker

Billy Armstrong

Location:

Benson room 380

Title

Glacier sliding from space: multi-scale remote sensing, geodesy, and numerical modeling to understand glacier mechanics

Abstract

Glacier basal sliding is a poorly understood aspect of glacier mechanics, and its spatial and temporal distribution affects glacier change and the evolution of alpine landscapes. In these studies, we use on-glacier GPS, moderate- and high-resolution optical satellite imagery, and numerical ice flow modeling to investigate the mechanics of glacier sliding across a variety of scales.

First, we employ on-glacier GPS to investigate the intimate link between subglacial water pressure and the rate of glacier sliding in response to the onset of spring melting on Kennicott Glacier, Alaska. We find large diurnal glacier velocity fluctuations during times of high and rising water level on a well-connected ice-marginal lake. The ice surface speedup at an upglacier station is first driven by longitudinal coupling to down-glacier ice, but then evolves to respond to local basal conditions.

We then use high-resolution WorldView satellite imagery to document the spatial pattern of the seasonal evolution of ice surface velocity over the 45 km2 terminal reach of Kennicott Glacier. We develop a numerical ice flow model to explore the distribution of basal sliding required to explain the observed surface speedup. We find the ice surface speedup is insensitive to the exact distribution of basal sliding, which may allow for simpler sliding parameterizations in glacier models.

Finally, we employ Landsat 8 satellite imagery to characterize the spatial patterns of glacier sliding over a 45,000 km2 area covering 64 glacier longitudinal profiles from ice divide to terminus. We find the entire ablation area of glaciers speeds up in a uniform manner, with the speedup magnitude insensitive to winter surface speeds. These patterns of sliding may drive patterns of glacier erosion that leads to the formation of icefalls.