The Pine Island Glacier in Antarctica is poised to shed a 300-square-mile chunk of ice. NASA discovered an 18-mile crack in the glacier in October 2011, during Operation IceBridge. This will be the southern continent’s largest contribution so far to global sea-level rise, according to researchers. The chunk of ice is expected to break off in the coming months, bringing the glacier to its farthest point of retreat since NASA started observing it in the 1940s. Pictured here, a DC-8 turns over Pine Island Bay while it maps the glacier.