Scientists are closely watching Antarctica's fast-flowing Thwaites Glacier, as they say its retreat is expected to speed up within 20 years when it separates from an underwater ridge that is presently holding it back.

Columbia University researchers said scientists are keeping a keen eye on Thwaites Glacier, which drains into west Antarctica's Amundsen Sea, for its potential to raise global sea levels as the planet warms. They noted that neighboring glaciers in the Amundsen region are rapidly thinning rapidly. This includes the Pine Island Glacier and the much larger Getz Ice Shelf.

They said that the new study published in Geophysical Research Letters is the latest to confirm the importance of seafloor topography in predicting how these glaciers will behave in the near future.

Scientists have seen that a rock feature off west Antarctica seems to be slowing the glacier's slide into the sea. The new study now connects that rock feature to a larger ridge, using geophysical data collected during flights over Thwaites Glacier in 2009 under NASA's Ice Bridge campaign.

The authors of the study said the newly discovered ridge is 700 meters tall and has two peaks - one that is now anchoring the glacier and another located farther off shore that held the glacier in place between 55 and 150 years ago.

That scientists have found that Thwaites Glacier is losing its grip on a previously unknown ridge has helped them to understand why the glacier appears to be moving faster than it used to.

A press release issued on the new study noted that in 2009, researchers sent a robot submarine beneath Pine Island Glacier's floating ice tongue and found a ridge that's about half the size of the one off Thwaites Glacier.

Researchers guessed that Pine Island Glacier lifted off that ridge in the 1970s, which allowed warm ocean currents to melt the glacier from below.

Earlier this year, Lamont-Doherty oceanographer Stan Jacobs and colleagues noted in a study in Nature Geoscience that the glacier's ice shelf is now moving 50 percent faster than it was in the early 1990s. Pine Island Glacier is moving into the sea at the rate of 4 kilometers a year - four times faster than the fastest-moving section of Thwaites, according to a press release.

Knowing the ridge is there lets us understand why the wide ice tongue that used to be in front of the glacier has broken up, Lamont-Doherty geophysicist Robin Bell, study co-author, said via press release. We can now predict when the last bit of floating ice will lift off the ridge. We expect more ice will come streaming out of the Thwaites Glacier when this happens.

Bell added that ridges like this one and the one discovered in front of Pine Island Glacier stabilize ice sheets, but can also be a critical part of the destabilizing process.