Researchers have made a shocking discovery under the Pine Island Glacier in Antarctica — an active volcanic heat source, which they say has played a “critical role” in the movement and melting of the glacier.

The scientists were looking at the role the ocean plays in causing glaciers to weaken when the discovery was made.

“We were looking to better understand the role of the ocean in melting the ice shelf,” Assistant Professor Brice Loose of Newport, R.I., a chemical oceanographer and lead author of the paper, said in a statement.