The cavity is located at the bottom of Thwaites Glacier in West Antarctica.
Scientists have found a "cavity" melted in the ice that occupies roughly two-thirds the surface area of Manhattan, prompting the space agency say its existence "signals" the ice sheet's "rapid decay". It is big enough to have contained 14 billion tonnes of ice, and most of that ice melted over the last three years.
Yet the huge size and fast-moving growth rate of the hole in Thwaites was called both "disturbing" and "surprising" by researchers.
"Thanks to a new generation of satellites, we can finally see the detail". "As more heat and water get under the glacier, it melts faster", said Pietro Milillo of JPL.
Once gone, surrounding glaciers will have no obstacle in their path, speeding up their melting and the potential release of enough water to raise sea levels by as much as 2.4m.
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.
There's no way to monitor Antarctic glaciers from ground level over the long term.
"We are discovering different mechanisms of retreat". The research has shown that Thwaites Glacier is peeling off from the bedrock beneath it, meaning more of the glacier's base is exposed to warming waters. The disappearance of the ice mass would cause sea levels to rise by about two feet as well as making surrounding glaciers more likely to melt rapidly-which could cause an eight foot rise.
The glacier has been coming unstuck from a ridge in the bedrock at a steady rate of about 0.6 to 0.8 kilometers a year since 1992.
Meanwhile, "on the eastern side of the glacier, the grounding-line retreat proceeds through small channels, maybe a kilometer [0.6 miles] wide, like fingers reaching beneath the glacier to melt it from below", Milillo said.
The glacier isn't retreating uniformly.
Researchers hope the new findings will help others preparing for fieldwork in the area better understand the ice-ocean interactions. 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. Hopefully, the upcoming worldwide collaboration will help researchers piece together the different systems at work under and around the glacier, the researchers said.