Close-up image of the crack spreading across the ice shelf of Antarctica’s Pine Island Glacier. See more photos. (NASA/DMS)

NASA researchers flying low over Antarctica’s vast, frozen landscape recently stumbled across a rare event in progress: the calving of a massive iceberg from one of Antarctica’s largest and fastest-moving glaciers. The scientists, who were taking part in NASA’s “Operation IceBridge,” were able to fly a follow-up mission above the Pine Island Glacier to gather unprecedented airborne measurements of an ongoing iceberg calving event. Typically, scientists can only learn of such events after they take place.

Since 2009, NASA scientists have been flying research aircraft loaded with sophisticated sensing equipment above Antarctic and Arctic ice, providing crucial data on ice sheet dynamics. This data is of great interest to the climate science community, considering the massive sea level rise that would occur if land-based ice sheets were to rapidly melt in coming decades.

Numerous studies have been published in the past several years that have raised alarms about the accelerating pace of ice loss in West Antarctica and Greenland. Operation IceBridge is meant to fill data gaps caused by a lag between two different ice-tracking satellites, thereby keeping data flowing to inform ongoing studies.

According to NASA, the last significant Pine Island Glacier calving event took place in 2001. It’s estimated that this one, an 18-mile long crack in the ice that was first spotted on Oct. 14 by a NASA DC-8 crew, probably began to form back in early October. Pine Island Glacier terminates in the sea, and has an “ice tongue” that juts out into the water. This makes the ice vulnerable to melting due to both rising air and water temperatures, although this calving event may have been a largely natural occurrence.

Video: NASA Operation IceBridge discovers massive crack in ice shelf.

Here’s how NASA describes the event in a blog post on the agency’s website:

Pine Island is one of the largest and fastest-moving glaciers in Antarctica. It has captured scientists’ attention for years because of the rate at which its ice is thinning. The ice shelf thins, the grounding line retreats and the speed of the glacier increases. As it sits on bedrock below sea level -- West Antarctica is the last place with such so-called “marine glaciers” -- and drains about 10 percent of the West Antarctica ice sheet, scientists are concerned about the impact Pine Island’s continued thinning will have on sea level.

Ice shelves naturally calve icebergs to shed ice that flows from the landmass to the sea. However, given Pine Island’s prominence as a target of study for glaciologists, the crack is at the very least an interesting observation.

“It’s part of a natural cycle, but it’s still very interesting and impressive to see up close,” said IceBridge project scientist Michael Studinger. “It looks like a significant part of the ice shelf is ready to break off.”

The NASA team found that the rift had a diameter as large as 820 feet at its widest point, and that once it breaks free and becomes an iceberg, it will have about 340 square miles of surface area - larger than New York City. The iceberg will have a total thickness of about 1,600 feet, most of it found underneath the water. After the iceberg breaks off, the Pine Island Glacier’s ice shelf will have receded farther than at any point since the 1940s, when this location was first mapped.

Research shows that the ice sheets of Greenland and Antarctica are melting at an accelerating pace, and may soon become the biggest contributor to sea level rise. If current rates of ice loss were to continue, sea level could rise by as much as a meter or more before the end of this century, according to this Climate Central story.