Scientists got their first up-close look at what’s eating away part of Antarctica’s Thwaites ice shelf, nicknamed the Doomsday Glacier because of its massive melt and sea rise potential, and it’s both good and bad news.

Using a 13-foot pencil-shaped robot that swam under the grounding line where ice first juts over the sea, scientists saw a shimmery critical point in Thwaites’ chaotic breakup, “where it’s melting so quickly there, there’s just material streaming out of the glacier,” said robot creator and polar scientist Britney Schmidt of Cornell University.

Before, scientists had no observations from this critical but hard-to-reach point on Thwaites. But with the robot named Icefin lowered down a slender 1,925-foot (587-meter) hole, they saw how important crevasses are in the fracturing of the ice, which takes the heaviest toll on the glacier, even more than melting. “That’s how the glacier is falling apart. It’s not thinning and going away. It shatters,” said Schmidt, lead author of one of two studies in Wednesday’s journal Nature.

The work comes out of a massive $50 million multi-year international research effort to better understand the widest glacier in the world. The Florida-sized glacier has gotten the nickname the “Doomsday Glacier” because of how much ice it has and how much seas could rise if it all melts — more than 2 feet (65 centimeters), though that’s expected take hundreds of years.

The melting of Thwaites is dominated by what’s happening underneath, where warmer water nibbles at the bottom, something called basal melting, said Peter Davis, an oceanographer at British Antarctic Survey who is a lead author of one of the studies.