A gigantic cavity two-thirds the area of Manhattan and almost 1,000 feet (300 meters) tall has been found growing at the bottom of Thwaites Glacier in West Antarctica.
About the size of Florida, Thwaites Glacier is currently responsible for approximately 4 percent of global sea level rise.
It holds enough ice to raise the world ocean a little over 2 feet (65 centimeters) and backstops neighboring glaciers that would raise sea levels an additional 8 feet (2.4 meters) if all the ice were lost.
The giant cavity is just one of several disturbing discoveries reported in a new NASA-led study of the disintegrating glacier.
Researchers expected to find some gaps between ice and bedrock at Thwaites' bottom where ocean water could flow in and melt the glacier from below.
However, the size and 'explosive growth rate' of the newfound hole surprised them.
NASA says the cavity is big enough to have contained 14 billion tons of ice, and most of that ice melted over the last three years.
'We have suspected for years that Thwaites was not tightly attached to the bedrock beneath it,' said Eric Rignot of the University of California, Irvine, and NASA's Jet Propulsion Laboratory in Pasadena, California. Rignot is a co-author of the new study, which was published today in Science Advances.
'Thanks to a new generation of satellites, we can finally see the detail,' he said.
The findings highlight the need for detailed observations of Antarctic glaciers' undersides in calculating how fast global sea levels will rise in response to climate change, researchers say.
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