In the big picture, melting at the surface still drives most of Greenland ice sheet loss, but underwater melting is also important. “[The study] points to the value of understanding a lot of those local details in order to understand what is happening on an ice sheet wide scale,” says Twila Moon, glaciologist at the National Snow & Ice Data Center, who was not involved in the research. Although the 79º North glacier is just one fragment of a massive icey expanse, it’s located at the mouth of a river of ice that drains a fifth of the ice sheet. When the ice tongue is gone, this ice river will flow faster, ejecting its contents into the ocean. All that extra ice would contribute to sea level rise.