Published on Oct 15, 2018 GREENLAND — This summer, a chunk of ice the size of lower Manhattan broke off of a glacier in Eastern Greenland. It contained 10 billion tons of ice, making the video of the event an insanely shareable capsule of climate change dread. But for NASA scientists, the spectacle created by these massive calving events is really just the final step in a far more worrisome — and less visible — process. That's because glacial melt isn’t just the result of our planet’s warming air. The biggest threat to these glaciers’ continued existence resides deep below the water’s surface.