Measuring one of the world's largest glaciers
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During the first summer campaign glacial geophysicists Andy Smith and Julian Scott together with field assistants Rob Smith and Roger Stilwell measured ice flow using Global Positioning Systems (GPS) and drilled into the upper ice layers to determine accumulation and density. Some of the most dramatic fieldwork involved setting off high explosives near the ice surface to measure the time it takes for the resultant acoustic waves to echo from the ice bed 2 km below. This method was particularly effective for detecting water and ‘soft’ sediments that reduce friction between bedrock and ice and enables faster ice flow.
At 95 days on the ice the second summer field season was longer and much more extensive than the first. Julian Scott, glacial geophysicist Robert Bingham, with field assistants Feargal Buckley and Chris Griffiths, increased the area of the first year’s survey and used a range of over-snow radars to investigate subsurface conditions. They also added ‘passive seismics’ to the array of surveying techniques. Where active seismics use artificial signals created by explosives, passive seismics rely on natural ‘icequake’ activity. Icequakes have been observed on many glaciers around the world. Monitoring their frequency and magnitude with high-resolution sensors, reveals how ice flow in a major ice stream such as Pine Island Glacier is controlled by slippage over the bed.
Surveying techniques involved Rob and Feargal driving skidoos, towing a radar transmitter and receiver that stretched over half a kilometre. BAS’s high resolution DEep-LOoking Radar Echo Sounder (DELORES) can not only ‘see’ through the 2 km of ice to the bed, but also pick out ‘internal reflectors’ - layers of equal age which represent one or more discrete snowfall events. These internal layers act as crucial input and control for ice-flow modelling. They collected 1500 km of data during the season crossing the glacier several times.
Using over-snow radar Julian and Chris were able to create an image of the Hudson Mountains subglacial volcano discovered by Hugh Corr and David Vaughan while analysing the 2004-05 airborne data. They also detected a highly reflective internal layer that may contain high amounts of volcanic ash from an eruption about 2000 years ago.
- Pine Island Glacier drains an area of 162, 300 km², two thirds the size of the United Kingdom.
- The glacier was named after the bay into which it flows, which was named after the U.S.S. Pine Island, a ship that carried sea-planes and discovered the bay in 1947. This ship was named after Pine Island off the coast of Lee County, Florida.
- The nearest base is the U.K.'s Rothera Research Station 804 miles away from the centre of Pine Island Glacier.
- The glacier contributes ~ 83 km³ of ice to the sea each year, the largest contribution of any individual ice stream in the world.
- Satellite measurements indicate the glacier thinned by ~ 1.5 m per yr and accelerated by ~ 10% during the 1990s. The speed has continued to increase by approximately 30% in the last decade.