The NASA-led team were surprised by the size of the cavity, which once contained 14 billion tons of ice.
'As more heat and water get under the glacier, it melts faster'.
According to the readings, the hidden void is but one ice casualty among a "complex pattern of retreat and ice melt" that's taking place at Thwaites Glacier, sectors of which are retreating by as much as 800 metres (2,625 ft) every year.
The new data, revealed by ice-penetrating radar aboard aircraft flying over Antarctica, point to a previously underestimated method of glacial collapse that scientists' models don't adequately factor in.
The icy monster "backstops neighbouring glaciers that would raise sea levels an additional 8 feet (2.4 metres) if all the ice were lost", Nasa warned.
"Understanding the details of how the ocean melts away this glacier is essential to project its impact on sea level rise in the coming decades", added Rignot. However, huge quantities of this colossal ice cube have melted away over the past three years as a result of climate change, contributing to around 4 percent of global sea level rise.
While Thwaites is certainly a hard place to reach, a five-year expedition by the International Thwaites Glacier Collaboration to study the glacier will begin this summer.
Last year, the National Science Foundation and Britain's Natural Environment Research Council launched a joint programme called the International Thwaites Glacier Collaboration to study the unstable glacier and its role in sea levels.
Different processes at various parts of the 160-kilometer-long front of the glacier are putting the rates of grounding line retreat and of ice loss out of sync, NASA said. In that region, the rate of grounding-line retreat doubled from about 0.4 miles (0.6 kilometers) a year from 1992 to 2011 to 0.8 miles (1.2 kilometers) a year from 2011 to 2017.
Thwaites Glacier, curiously, isn't melting in a uniform way.
Researchers hope these new findings will help other scientists better understand the connection between the weather and glaciers.