Research on Black Rapids Glacier

Black Rapids Glacier is a surge-type glacier in the central Alaska Range with a long and interesting history of scientific research, dating back to the last surge in 1936-37. There is some evidence suggests that it should surge again soon, but the ice dynamics over the past 10 years do not support this. Perhaps the latest earthquake might have change that. The glacier has been studied closely since the 1970s, with projects continuing today. The bulk of my thesis research was completed here.

The goal of my research was to develop a new seismic method for studying how the basal properties of glaciers change temporally, and use that technique to better understand spring speed-up events on Black Rapids Glacier. To do this, we repeated seismic shots every day (or sometime more frequently) without moving the geophone or source locations. In this way, we imaged the same region of the bed over time to detect changes. It worked out pretty well. The vast majority of seismic records were virtually identical, though anomalies were found that correlated with the timing of fast motion events on the glacier. Each of the three motion events we observed through surveying were caused by the sudden draining of large lakes on the margins of the glacier. As this water reached the bed, it caused an overpressurization of the subglacial hydraulic system and essentially floated the ice locally, causing it to slide rapidly. The anomalous reflections we observed were caused by a change in the material properties of the till layer beneath the ice. As the conduit system began to lift the ice, it began to bear more of the glacier's weight, meaning that most of the rest of the bed felt as if the glacier suddenly got lighter. Here, the till matrix expanded elastically, causing a decrease in saturation as new pore space was created. This sudden drop in saturation was exactly the mechanism needed to explain the seismic changes. Once the conduit water pressure dropped, the glacier weight redistributed as normal, causing the seismic anomalies to disappear and reflections to return exactly to their normal state. We observed this switch to occur as rapidly as 45 minutes in one case.

I hope to add a lot more information as time permits.