(CNN) A massive cavity two-thirds the size of Manhattan has been discovered growing in an Antarctic glacier, signaling rapid ice decay that has shocked scientists.

The huge hole -- measuring almost 1,000 feet (300 meters) tall -- was found growing at an "explosive rate" at the bottom of a glacier in West Antarctica, said NASA's Jet Propulsion Laboratory in a statement Wednesday.

The Thwaites Glacier is around the size of Florida, and the team of NASA-led scientists researching it had expected to find "some gaps" between the ice and bedrock.

The Thwaites Glacier in West Antarctica

"The size and explosive growth rate of the newfound hole, however, surprised them," they said.

The cavity was "big enough to have contained 14 billion tons of ice, and most of that ice melted over the last three years," they added.

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