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Exploring a Glacier with Ground-Penetrating Radar

What’s beneath the surface?

Frank Weirich's team takes the ground-penetrating radar out onto the surface of the Exit Glacier.

Frank Weirich’s team takes the ground-penetrating radar out onto the surface of the Exit Glacier.

The glaciers are melting. But exactly how fast are they disappearing? And what processes are going on out of sight, hundreds of feet beneath the ice? Answers to these questions are crucial for scientists hoping to understand the rate and magnitude of climate change.

IIHR Associate Research Engineer Frank Weirich and his research team are conducting a multi-year research project designed to look beneath the ice using ground-penetrating radar. “It’s a very simple idea,” he explains. “All we’re doing is taking the equivalent of atmospheric radar and aiming it down — but changing the frequency.” Ground-penetrating radar uses different frequencies than conventional weather radar, and when configured as a multi-channel radar system, can send and receive multiple frequencies simultaneously, providing data of relatively high resolution from different levels within the glacier.

An Evolving Plumbing System

Weirich, who is also an associate professor of geoscience, has been studying the meltwater tunnels inside the Exit Glacier in Alaska to learn how they affect the rate of glacier melt. “Essentially, it’s a plumbing system that over the course of the summer evolves and gets larger and more complex,” Weirich says. The question is, how much larger, and how quickly?

Ground-penetrating radar is providing some answers. Weirich’s team, which includes PhD candidate Susan Kilgore and several graduate and undergraduate students, has spent three summers studying the Exit Glacier’s meltwater tunnels. In the late spring, the team goes out on the ice with the ground-penetrating radar to create a 3-D image of the tunnels beneath the glacier’s surface.

Frank Weirich (left) and student Phil Kerr check the ground-pentrating radar unit in its reinforced transport sled.

Frank Weirich (left) and student Phil Kerr check the ground-pentrating radar unit in its reinforced transport sled.

As part of the research effort, Weirich designed and constructed equipment to move the radar system safely across the ice. He started with a commercial car-top carrier, which was then heavily reinforced. He added instrument mounts and stabilizers, tow cable systems, and antenna-mounting structures. Researchers tow this radar “sled” over the ice surface using a harness and guide rope system. A carefully calibrated tow wheel connected directly to the radar system measures the distance covered, and a wireless transmitter sends all the data to a computer located nearby but off-ice. The researchers also meticulously guide and track their progress across the ice using a system of straight-line markers to ensure that the lines of data are being consistently collected for repeat surveys, and that data are collected along lines critical to the 3-D subsurface tunnel map the researchers are developing.

As the summer progresses, they also monitor drainage from the glacier using continuous stream discharge monitoring systems. In the fall, the team returns to repeat the radar study and compare the results to the spring data to understand the rate of melting and the tunnel evolution within the massive river of ice. These data are combined with climate data for the site and area to better understand the overall hydrologic processes at work on the glacier.

And the news is not good. “The tunnel system inside is growing at a very rapid rate and causing more melting from the inside out,” Weirich says. “It’s essentially more like swiss cheese than we thought.”

Unseen Dangers

Even though the team does its work during the temperate months, there are still plenty of dangers — such as slipping into crevasses or vertical meltwater shafts, some hundreds of feet deep, which descend from the glacier surface. Weather can also pose real challenges. Sometimes a helicopter delivers the researchers to remote locations on the glacier. On one occasion, the weather closed in before the helicopter could carry them back to safety, so researchers were forced to spend the night on the ice, weathering 40-mile per hour winds — fortunately with tents, thermal sleeping bags, a satellite phone, and five days’ food and water. The next day brought no break in the weather, so the team hiked out, temporarily abandoning their equipment. Two days later, the weather cleared enough to allow the helicopter back in so the team could retrieve their gear.

Processing the data in the lab to create a 3-D image is a long and laborious process requiring three software programs. The team still has more work to complete on the glacier, but Weirich says one result is already clear.

“It’s melting faster than we thought.”

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Last modified on June 25th, 2015
Posted on November 12th, 2013

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