Greenland glacier's rapid melt threatens sea level rise.

Scientists studying Greenland's Petermann Glacier have found that it is melting faster than expected in its most vulnerable region, which could lead to faster and more dramatic levels of sea level rise worldwide. The glacier has been bouncing up and down, dramatically shifting its seafloor moorings in response to the tides, which has carved a large cavern at the base of the glacier and allowed warm water to regularly stretch beneath it. As the glacier lifts and migrates, the water can rush in for over a mile, thinning the ice by as much a 250 feet a year in some places.