In recent years, Greenland’s ice has been melting more and flowing faster into the sea—a record amount of ice melted from the frozen mass this summer, according to recently released data—and Earth’s rising temperatures are suspected to be the main culprit.

But clues to a new natural contribution to the melt arose when scientists discovered a thin spot in the Earth’s crust under the northeast corner of the Greenland Ice Sheet where heat from Earth’s insides could seep through, scientists will report here this week at a meeting of the American Geophysical Union.

“The behavior of the great ice sheets is an important barometer of global climate change,” said lead scientist Ralph von Frese of Ohio State University. “However, to effectively separate and quantify human impacts on climate change, we must understand the natural impacts too.”