What happens if Delaware-sized iceberg breaks off Antarctica?

NASA is keeping a close eye on a 70-mile-long rift in an Antarctica ice shelf that could produce a massive iceberg and indirectly lead to rising sea levels.

The crack in the Larsen C Ice Shelf is more than 300 feet wide and about a third of mile deep, according to the agency. Once the crack goes all the way across, it could produce an iceberg the size of Delaware.

Ice shelves are permanent floating sheets of ice that connect to a landmass, according to the National Snow and Ice Data Center.

Most of the world's ice shelves hug the coast of Antarctica. The Larsen C shelf is on the Antarctic Peninsula, the portion of the continent that juts out toward South America.

What would happen to the iceberg?

If the iceberg did break off, it wouldn't contribute to sea level rise since it's already floating, said Ted Scambos, a scientist with the data center. If a chunk of ice that big did drop into the sea, it would raise sea levels about one-sixteenth of an inch, he said.

However, once that iceberg breaks off, land ice that had been blocked by the berg would plop into the sea. It's that ice that would raise sea levels, NASA scientist Thomas P. Wagner said.

"Ice shelves serve a critical role in buttressing ice that's on land," he said.

Once the iceberg sheared off, it would float along the coast of Antarctica, then head out into the Southern Ocean.

"As it moved north, ocean temperatures both at the surface and at the base of the berg would begin to thin it and erode it from the edges," Scambos said. It would eventually break apart into smaller chunks that would melt into the ocean.

Ice shelf collapses are not uncommon

When a shelf collapses, the ice behind it speeds toward the ocean, where it can contribute to a rise in sea level, according to NASA. Scientists say recent ice shelf collapses in the Arctic and Antarctica are related to climate change, due to warmer air and water temperatures, the data center said.

In the past 30 years, a series of unusual ice shelf collapses have been seen on the Antarctic Peninsula, the data center reported: "Although it is not unusual for ice shelves to calve large icebergs, that process normally takes months to years, as cracks slowly form in the ice."

The collapses in previous years have happened over a period of weeks, leaving a soup of chunky ice and small icebergs. An ice shelf near Larsen C fell apart in 2002 after a similar crack.

There's been a large-scale destabilization of the Larsen C Ice Shelf recently, Wagner said, which has implications for global climate change. "Its a natural laboratory for understanding how the rest of Antarctica might behave," he said.

Scientists to brave stormy seas for 90-day trip around Antarctica

How are these massive cracks discovered?

Scientists taking part in NASA's annual Operation IceBridge mission to measure changes in the polar ice and sea discovered the latest crack last month, according to the agency.

Operation IceBridge employs the most precise instruments to fly over Antarctica, NASA scientist John Sonntag told  The Christian Science Monitor.

The mission studies the Arctic and the Antarctic, the most remote place on earth, NASA said.

"Why do we do this?" NASA Deputy Administrator Dava Newman asked in a social media presentation. "It's critically important for all of us, all of humanity, especially looking at sea rise and climate change."