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| | Earth on Nov 21, 2012

Witnessing the birth of a giant iceberg

Antarctica’s Pine Island Glacier is preparing to spawn a giant iceberg. Scientists have been watching it since late 2011. This post lets you see what they see.

On October 14, 2011, scientists participating in NASA’s IceBridge mission – who were flying over Antarctica’s Pine Island Glacier in a DC-8 research plane – discovered a massive crack, or rift, running about 29 kilometers (18 miles) across the part of the glacier that extends into the Amundsen Sea. This rift marks the imminent birth of a new iceberg. Since then, when they could, scientists have been watching the rift propagate through the glacier. They’re waiting for it to release the iceberg, which they estimate could span 300 to 350 square miles (up to 900 square kilometers). The animation below – released by NASA on October 15, 2012 – shows how the rift in the glacier has been getting longer since scientists first observed it last year.

Germany’s TerraSAR-X satellite recording these images from Oct. 2011 through Sept. 14, 2012. Image Credit: German Aerospace Center.

It’s not just NASA scientists who keep tabs on this rift. Scientists around the world are watching it. The rift was stable for a time but is now growing again. The animation above shows changes in the Pine Island Glacier rift over the past several months. The images came from NASA’s Aqua and Terra spacecraft and the TerraSAR-X satellite operated by the German Aerospace Center.

Pine Island Glacier is what’s known in Antarctica as an ice stream. As snow falls on the Antarctic continent in wintertime, and as ice accumulates, the weight of the ice pushes Antarctic ice streams toward the sea. Wikipedia says:

The area drained by Pine Island Glacier comprises about 10 percent of the West Antarctic Ice Sheet. Satellite measurements have shown that the Pine Island Glacier Basin has a greater net contribution of ice to the sea than any other ice drainage basin in the world and this has increased due to recent acceleration of the ice stream.

So what you’re seeing here is a very natural process, something that’s no doubt been going on in Antarctica throughout time. Pine Island Glacier is Antartica’s fastest-moving ice stream toward the sea. It broke off large icebergs in 2001 and 2007, too. What’s exciting about this rift is that the 2011 IceBridge survey marked the first time such a rift had been measured in great detail from the air. Those measurements let NASA scientists create the cool virtual tour in the video below.

NASA animation via Vimeo.

This virtual “airborne tour” of the rift in Pine Island Glacier was created from images collected during an IceBridge mission flight over the glacier on October 26, 2011. In this animation, the path of the crack stretches roughly 18 miles (30 kilometers) in length. The average width is 240 feet (about 80 meters). The average depth of the icy canyon ranged from 165 to 190 feet deep (50 to 60 meters), with the floor being roughly at the water line of the Amundsen Sea. In the real world, the crack is longer now.

The image below is a still frame from the animation.

This image is a still frame captured from a three-dimensional, virtual flight through the rift in the Pine Island Glacier. Image via NASA.

Scientists say there is a small ice shelf in front of Pine Island Glacier, on the seaward side, toward the Amundsen Sea. Like a cork in a wine bottle, the ice shelf has prevented the glacier from draining straight into the ocean. But the ice shelf has weakened. It has been thinning for some time now. It’s thought that relatively warm ocean water has created a widening cavity under the ice shelf. As the ice shelf that “corked” Pine Island Glacier has thinned, the glacier has flowed faster into the sea.

Bottom line: Antarctica’s Pine Island Glacier is preparing to spawn a giant iceberg. Scientists have been watching it since late 2011. This post contains an animation released in October 2012, showing how the rift is expanding, plus a virtual tour of the rift made in 2011 by NASA’s flying IceBridge mission team.

Sophie Nowicki on Pine Island Glacier: The weak underbelly of West Antarctic Ice Sheet

Pine Island glacier has cracked and will spawn a giant iceberg