'Dangerous' Antarctic glacier has massive hole, scientists warn

'Dangerous' Antarctic glacier has massive hole, scientists warn

The hole, which is nearly 1,000 feet tall, was seen during the space agency's study of the disintegrating Thwaites Glacier in West Antarctica, NASA said Wednesday.

NASA believes the cavity is big enough to have contained 14billion tons of ice, most of which melted only in the last three years. What is more, the Thwaites Glacier backstops other ice sheets with the potential to raise sea levels an additional eight feet (2.5m) if all the ice is lost. Scientists expected to find some relatively small gaps between the glacier and bedrock, but were unsettled by the 1,000-foot deep cavity the mission revealed.

Yet the vast size and fast-moving growth rate of the hole in Thwaites was called both "disturbing" and "surprising" by researchers.

"We have suspected for years that Thwaites was not tightly attached to the bedrock beneath it", said Eric Rignot, one of the co-authors of the study.

Scientists spotted the concealed void thanks to a new generation of satellites, Rignot noted.

NASA's Operation IceBridge, launched in 2010, uses ice-penetrating radar to measure the rate of melting in some of the most remote and inhospitable regions in the world. Researchers combined the NASA data with data from Italian and German spaceborne synthetic aperture radars.

"[The size of] a cavity under a glacier plays an important role in melting", said Pietro Milillo, a NASA researcher and study lead author.

When this happens, the grounding line retreats inland, exposing more of a glacier's underside to sea water, increasing the likelihood its melt rate will accelerate. The growing cavity (red mass, center) caused the greatest sinking.

The Thwaites Glacier is now responsible for 4 percent of global sea level rise. The collaboration includes the U.S. National Science Foundation and British National Environmental Research Council.

Thwaites glacier is one of the most hard places on Earth to reach.

"We are discovering different mechanisms of retreat", Milillo said. In essence, this means that the glacier at this spot is exposed to the ebb and flow of the tide, which causes the ice at the grounding line to retreat and advance across a region that's about 2 to 3 miles (3 to 5 km) long.

Civilization's most important glacier has revealed another worrying surprise to scientists. Even with this accelerating retreat, however, melt rates on this side of the glacier are lower than on the western side. The glacier has retreated at a steady rate of about 0.4 to 0.5 miles (0.6 to 0.8 km) annually since 1992, the researchers found. This data also shed some light on another concern about the glacier's grounding line, the point at which the glacier starts to depart from land and float on the sea.

These findings show the complexity of ice-ocean interactions. The melting of this glacier could lead to as much as 10 feet of sea level rise over the next century or so.