(One gigaton is a billion tons.) All that ice dumped into the ocean has raised global sea levels by 14 millimeters since 1979, according to the study. The NASA scientists who discovered it think most of the hole formed in just the past three years. This water then pooled between the ice and rock, eroding away the glacier above.
"[The size of] a cavity under a glacier plays an important role in melting", study lead researcher Pietro Milillo, a scientist at the Radar Science and Engineering Section at JPL, said in the statement.
And the subsurface ice erosion has disturbing implications. If the entire glacier melted, the resulting water could raise world ocean levels by more than 2 feet (65 centimeters), the researchers said.
This means the mass of ice - about the size of Florida - can break up and slip into the sea, much faster than projected.
Changes in surface height at Thwaites Glacier's grounding line.
Thwaites Glacier is now responsible for approximately 4 per cent of global sea level rise.
The cavity was seen using NASA's Operation IceBridge, an airborne campaign beginning in 2010 that studies connections between the polar regions and the global climate.
Unlike much of the North Pole, an enormous amount of South Pole ice sits on land.
The discovery is important, because it illustrates that Antarctic ice not only melts at the edges touching the ocean, but also from underneath ice sheets, CBS News notes. It found Antarctica as a whole went from losing about 40 gigatons of ice per year in the 1980s to 252 gigatons per year over the last decade.
Thwaites Glacier alone holds enough ice above sea level to raise sea levels by more than 65cm if it was to melt.
About the size of Florida, Thwaites Glacier is now responsible for approximately 4 percent of global sea level rise.
Scientists spotted the concealed void thanks to a new generation of satellites, Rignot noted. It will begin its field observations later this year. Different processes at various parts of the 100-mile-long (160-kilometer-long) front of the glacier are putting the rates of grounding-line retreat and of ice loss out of sync.
The Thwaites glacier has experienced significant flow acceleration since the 1970s.
Annual ice discharge from this region as a whole has increased 77 per cent since 1973.
CBS News climate and weather contributor Jeff Berardelli reports that the cavity is likely a significant finding because the West Antarctic ice sheet is considered one of the most unstable and vulnerable.