PSU Team Takes on Thwaites

News

By Katie Oberthaler
Winter 2010

Find a half-kilometer-long cable. Walk 15 feet. Dig a hole in the ground. Secure a large pole compacted in a bucket into the opening. Repeat 24 more times. Find three more cables, and begin again.

Then, using the propane-driven automatic fence post pounder you’ve brought, drill a 30 meter hole in the ground. Pack with explosives. Detonate. Repeat, repeat, repeat.

Did I mention you’ll have to fly to Antarctica first?

Add in chilling -60ºF, winds and snow as far as the eye can see, and you have Knut Christianson and Rebecca Boon’s winter break. Christianson and Boon, Pennsylvania State University graduate students, are part of a six-person team from PSU that began stationing in a remote camp on Thwaites glacier in November and will conduct research there for two months.

The team will repeat these labor-intensive seismic measures using the devices, called geophones, which record the time between the surface explosion and reverberation back to the ice’s surface. From the recordings, the team can determine the geological makeup below the bedrock and how it might interact with the glacier.

The team’s bustling activity above the ice mirrors the glacial movement below Thwaites, dubbed the “weak underbelly” of the West Antarctica Ice Sheet (WAIS). The area of Thwaites the team is studying sits in part on a 50km “wedge” of land. The grounding line - the point which separates the ice forming solid ground from the ice shelf floating in the surrounding ocean water – rests on this ridge. If the ice retreats just slightly beyond this line, warmer water from the coast could circulate near the ice, which would accelerate its break up and ultimately contribute to increased sea level.

Glaciers like Thwaites and its neighbor, Pine Island Glacier, that drain into basins resting below sea level remain vulnerable to faster retreat. Thwaites’ drainage basin lies approximately 2 kilometers below sea level. Together, Thwaites and Pine Island account for five percent of the West Antarctica Ice Sheet’s yearly drainage.

The glacier’s relatively small floating ice shelf which surrounds its deep catchment makes it further susceptible to these effects. Only a small amount of ice shelf melting and grounding line retreat would need to occur to catalyze a large-scale break-up.

This expedition completes a three-year campaign by the team on Thwaites to refine this poorly-understood phenomenon. Between the first and second seasons, the team measured a 1 to 1.6 percent acceleration of Thwaites. Beyond this observation, the glacier's stability remains undetermined.

“We really don’t have a good handle on it,” said Christianson.

The team has improved their research setup to increase their understanding and simplify logistics. This year, they will use wireless GPS sensors, which are not as cumbersome to move. They also created "shop boxes" which separate the recording system in the geophones from the glacier’s dynamic system and ensures that recording begins exactly at the time of detonation. In addition to the geophones, the team will deploy 40 GPS devices this year that will monitor the glacier’s movement. They will also fly a tight grid of radar over the ridge. An aggregate of data collection systems will allow the team to measure the change in topography on a small scale and the change in ice flow over ridges. The team cannot approach the ridge directly due to the deep and dangerous crevasses surrounding the grounding line.

“They could eat planes,” Christianson notes of the crevasses, which often remain invisible beneath snowfall.

Christianson has accompanied the team for the past two field seasons, but Boon will be braving these traps for the first time. She'll need those planes to stay in tact, though, when she analyzes the radar data, or "picks the bed," to determine the bedrocks' topography. Joining her and Christianson on the survey from PSU are Sridhar Anandakrishnan, Don Voigt, Luke Zoet, and Leo Peters. They'll all endure a hefty work-out for the next two months moving geophones, but untangling all those half-kilometer cables will also unravel Thwaites' complexity.