Antarctic glacial melting.

In other words, it's one of the most active tectonic areas on Earth.

Antarctica as a whole is home to 25 known active volcanoes, the majority of which are in West Antarctica. With the continent entirely enshrouded in ice, except for brief peeks of coastline bedrock during summer, these volcanoes melt the glaciers from below, creating canals, lakes, and freshwater streams that eventually empty out into the ocean, warming the currents that slowly chip away at the massive ice shelves abutting the coastal regions.

"IPCC author: Antarctica's abrupt glacial melting greatly overestimated.'" By Thomas Richard, Examiner.com, 5/24/15.

H/t: Principia Scientific International.