When it comes to a giant Antarctic glacier, what you don’t want is a chunk of ice with a gaping hole in it. That is, however, our reality: On Wednesday, NASA announced that there’s a cavity growing rapidly at the bottom of Thwaites Glacier. While the Florida-sized body of dense ice is located in one of the most difficult places to reach on Earth, it will have a global reach when it melts.

Described by NASA as “disturbing,” the cavity is almost 1,000 feet tall and about two-thirds the size of Manhattan. The team behind its discovery write in Science Advances that the size of the cavity means it once contained 14 billion tons of ice. Most of that ice has probably melted over the past three years, contributing to the planet’s overall sea level rise. Scientists already suspect that the Thwaites Glacier is responsible for approximately 4 percent of global sea level rise, and now it’ll likely be blamed for more.

Rising seas expose coastlines to greater risks of flooding and erosion, endangering the people and wildlife that live there. When seawater reaches inland, it can contaminate agricultural soil and destroy the habitats of fish, birds, and plants. Sea levels have steadily rose over the past century, and as the glaciers melt, the rate at which they rise increases. Despite its massive cavity, Thwaites Glacier still contains enough ice to raise the world ocean by a little over 2 feet. If its neighboring glaciers also melt, the sea level will rise by an additional 8 feet.

Though they suspected for years that Thwaites wasn’t attached tightly to the bedrock beneath it, the team behind this study weren’t able to investigate in detail until now. Advancements in satellite technology revealed the cavity as well as the fact that an ice shelf near it melted at a rate of more than 650 feet per year between 2014 and 2017.

The cavity is under the glacier on its western side, the side farther away from the West Antarctic Peninsula. NASA

NASA reports that the colossal cavity is under the main trunk of the glacier on its western side, and the glacier is becoming unstuck from a ridge in the bedrock at a steady rate of 0.4 to 0.5 miles a year since 1993. What’s not steady is the cavity’s “extremely high” melt rate, which depends on the changing size of the cavity itself: As more heat and water get under the glacier, the faster it erodes.

Unfortunately, the newfound presence of the cavity also indicates that previous models probably underestimated how fast Thwaites is losing ice. Usually, mathematical models of ice sheets use a fixed shape to represent a cavity, but the shifting dynamics of Thwaites’ cavity make it obvious that scientists need to better understand how these change and grow. Understanding exactly how — and how fast — this glacier is melting away will, hopefully, help us prevent others from doing the same before it’s too late.