Tuesday, May 2, 2017

More on the Rift Associated With West Antarctic Ice Shelf

No automatic alt text available.Image of the rift in Pine Island Glacier ice shelf in West Antarctica photographed from the air during a NASA imaging operation in November, 2016.  This is the second rift to form in three years.

In this era of fake news and rampant pseudo-science, as well as science denial, climate scientists have been trying desperately to warn of the disastrous consequences if the West Antarctic ice sheet were to collapse.  For example, based on current computer projection models, such a collapse could lead to a sea level rise of nearly 3 meters (10 feet) which would be enough to inundate major U.S. cities such as New York, Miami and Jacksonville, while displacing 150 million people inhabiting coasts worldwide.

To set the scene: In 2015 a nearly 225 square mile iceberg broke off from Pine Island Glacier. However, it wasn't until climate scientists began testing new imaging processing software that something peculiar was notice in the Landsat 8 images.  That is, a rift was observed in the surfac3e of the ice shelf nearly 20 miles inland. The Landsat marked date was tracked to 2013. Overt 2 years the rift grew until it set the iceberg adrift in late July, early August, 2015.  During this interval a similar rift opened up 6 miles further inland from the first.

To be sure, such rifts usually form at the sides of an ice shelf where ice is thinner and also subject to shearing that rips it asunder. However, this particular rift (shown in the above image) originated at the center of the Pine Island Glacier's ice shelf then propagated to its margins. The implication is that some agent weakened the center of the ice shelf and the most plausible culprit appears to be a crevasse that melted out a bedrock level. This in turn was most likely driven by a warmer ocean.

The observed fact that the rift opened in the bottom of a 'valley' in the shelf  (where the ice had thinned) provides yet another clue the center of the ice shelf is weak. The 'valley' formation is also something the Antarctic researchers had long suspected given ocean water can intrude far inland and remain unseen. This is also associated with the fact the bottom of the West Antarctic ice sheet lies below sea level.

The rift's origin, interestingly, might have remained unseen if not for the fact the images were taken when the Sun was low in the sky. Thus, long shadows were created across the ice and white snow that provided visibility and drew the team's attention to the valley that had formed there.

It needs to be noted that such 'rifting' behavior provides a mechanism for rapid retreat of glaciers.  Indeed, similar subsurface rifting has been observed in the Greenland ice sheet (jokalhlaup) where ocean water has seeped inland along the bedrock and begun to melt the ice from underneath.  Now the Landsat images provide the first strong evidence that the large Antarctic ice shelves respond to changes at the ocean edge like the Greenland ice shelf.

For a more complete look at the relevant research go to:


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