Antarctica Glacier's Retreat 'Unprecedented'

Like a plug in a leaky dam, little Pine Island Glacier holds back part of the massive West Antarctic Ice Sheet, whose thinning ice is contributing to sea level rise.
In recent decades, Pine Island Glacier's rapid retreat raised fears that the glacier could "collapse," freeing the ice sheet it buffers to flow even more rapidly into the southern seas. The West Antarctic Ice contributes 0.15 to 0.30 millimeters per year to sea level rise.

info. source:
http://www.livescience.com/26290-pine-island-retreat-history.html