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Water is at the heart of the dynamic behavior of glaciers. Water located beneath a glacier is believed to "lubricate" its movement toward the sea. How glaciers melt and move is likely to have a major impact on sea levels.
It thus came as an apparent surprise to researchers when they discovered a system of deep cracks in the ice of Alaska's Bench Glacier. Some of the cracks extended 80 meters from the glacier's bottom and held considerable amounts of water. The researchers theorized that water pressure below the glacier and stress from the glacier's enormous weight could have produced the cracks, and in turn the cracks allowed the glacier to absorb a sudden inflow of water from melting of the ice or from rain. This "sponge-like" activity might prevent the glacier from sliding even more as water floods the soil and rock beneath the glacier. But, under certain conditions the cracks might suddenly drain, sending water into the area beneath the glacier, and thus sending the glacier sliding along even faster.
The researchers drilled holes through the glacier's roughly 200 meters of ice. From the various cracks they hit, the researchers concluded that the cracks held enough water to cover the entire "bed" beneath the glacier with 10 cm [roughly 4"] of water. This is rather significant. Other research has indicated that just 4 cm of water can increase the pace of glacial movement by a factor of five.
The research can be found at http://www.nature.com/nature/journal/v467/n7315/full/nature09398.html.