NASA scientists fear that a growing crack in the Nansen Ice Shelf may cause it to break free from the Antarctic coast and form a massive iceberg more than twice the size of Manhattan.

"Over the course of two years, a small crack grew large enough to spread across nearly the entire width of the Nansen Ice Shelf," NASA said in a post last week.

Ice shelves are thick plates of coastline ice that float over the ocean. This particular one, Nansen, measures about 20 miles wide and 30 miles long.

A team of scientists first noticed the crack in 2013, but two NASA scientists Christine Dow and Ryan Walker discovered in December 2015 that the crack had grown substantially. Dow and Walker were visiting the ice shelf to install GPS stations on it to track how it was affected by tides. When they flew over the area, they realized that it was no longer a small crack.

Christine Dow captured this image of the Nansen Ice Shelf via helicopter in December 2015. Photo credit: Christine Dow / NASA Earth Observatory

Satellite images taken when Dow and Walker returned confirmed what they saw on the ground.

In 2013, NASA scientists noticed a small crack in the Nansen Ice Shelf. Photo credit: NASA Earth Observatory

 

By December 2015, satellite imagery showed that the crack stretched across nearly the entire length of the shelf. Photo credit: NASA Earth Observatory

"There’s a huge crack, miles long and sometimes over a hundred yards wide, which runs more or less parallel to the front of the ice shelf," Walker wrote in a post in December 2015. "Over the winter, the sea surface freezes and traps small icebergs in the crack, producing a fascinatingly broken icescape."

Antarctic winter is now setting in, and, as of this month, satellite imagery indicated the ice shelf was still attached. Though winter may not be enough to prevent the shelf from collapsing.

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"Even in winter, strong winds can prevent the water beyond the shelf from freezing, so it is unclear whether the front will separate soon or hang on like a loose tooth," NASA said.

Although the ice shelf's collapse may sound catastrophic, IFLScience noted, there are two points worth considering:

"Firstly, ice shelves make up around 75 percent of the Antarctic coastline, and their total combined area is equivalent to 1.56 million square kilometers (603,000 square miles). If all of Nansen collapses, it will reduce Antarctica’s ice shelf coverage by just 0.1 percent.

Nansen doesn’t even register as a 'major' ice shelf, with those such as Ross, at around 472,000 square kilometers (182,000 square miles), dwarfing it. The Ross Ice Shelf partly collapsed at the end of the last ice age around 10,000 years ago, when a colossal chunk 280,000 square kilometers (108,000 square miles) in size fell into the sea over 1,500 years. That’s 360 times the size of Manhattan Island, by the way.

Secondly, these ice shelves may be anchored to the land, but they do not actually significantly contribute to sea level rise—after all, they’re already floating on the sea. So the collapse of Nansen by itself won’t cause much harm, per se.

However, ice shelves like Nansen do act as vast barricades for glaciers behind them. When an ice shelf is removed, glaciers begin to tumble into the sea at surprisingly fast speeds—sometimes moving ten times faster than normal—and these will definitely cause the sea level to rise. So in effect, man-made climate change is breaking Antarctica’s huge ice dams.

And while ice shelves have historically broken off and often reformed, ScienceAlert said the trend is alarming:

"Several iconic ice-shelf disintegrations, such as the Serson Ice Shelf in northern Canada, have been linked to increasing temperatures.

And the rate of ice shelf loss has also been speeding up. Over the past 20 years, Antarctica's Larsen ice shelves has pretty much decreased significantly, losing 75 percent of its area.

The icebergs produced by these types of events don't just pose threats to boats that get in their way, but also to marine life—such as the 150,000 penguins that died at the start of this year when an iceberg blocked their path to the sea, cutting off their food supply."

NASA researchers want to keep studying the ice shelves to better understand why they collapse and how to prevent it. Dow is already planning a trip with other researchers to study the crack this summer.

“I’m really interested to see whether this feature is occurring because of the topography around the ice shelf, or whether it was initially created by surface water flowing into a small ice surface crack,” she said. “We’re planning an intensive survey of this feature in the coming years and will hopefully get a handle on the causes.”

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