Alaskan Storm Plays Role of Butterfly for Antarctica

B-15 Iceberg pre-breakup

hide captionThe B-15 iceberg is the large, coke-bottle-shaped iceberg toward the lower right. Last year, it broke off from the Ross Ice Shelf and began drifting out to sea.

NASA
B-15 on October 28, 2005

hide captionThe B-15 broke into pieces October 28, 2005. This image was taken one week later.

NASA

A scientist named Edward Lorenz once mused that a butterfly flapping its wings could cause a storm half-way around the world.

A storm in Alaska recently played the role of the butterfly for an iceberg located at the South Pole.

The Antarctic B-15 iceberg broke into pieces in October 2005, but scientists didn't know what caused the ice shift. But two researchers recently discovered the ice shift originated about 8,000 miles away –- in the Gulf of Alaska.

When B-15 broke off the Ross Ice Shelf in March 2000, two geologists from the University of Chicago and Northwestern University decided to track it using a seismometer, the device used to measure earthquakes. A year after installing the device, they began to analyze the data.

"The first thing we saw were signals from the great tsunami that devastated parts of the Indian Ocean back in December of 2004," says researcher Doug MacAyeal. "It was telling that we were able to see this event come into Antarctic waters and rock the icebergs."

McKale and his colleagues were more interested in what happened on October 27, 2005, the day the iceberg suddenly broke apart into a number of smaller pieces. The breakup didn't make sense to MacAyeal.

"We said to ourselves 'What in the world would make this darn iceberg break up on October 27, a day of roughly nothing going on,'" he says.

Using the seismometer, MacAyeal and his colleagues discovered that the iceberg had been hit by a series of waves 13,500 km away. They drew a line on a map that was about 8,000 miles away from B15 and wound up in the Gulf of Alaska.

"And lo and behold, there was a very fierce intense onset of winter storm in exactly the place our science had predicted the waves had come from," MacAyeal says.

He asked a colleague who makes surfing forecasts to determine how big the waves from this storm would have been.

"The wave heights for the storm were above 45 feet," MacAyeal says. "So these were monstrous waves."

By the time the waves traveled from the Gulf of Alaska to Antarctica, they were just a powerful swell. MacAyeal thinks the waves caused the iceberg to repeatedly pound the seabed, causing the great explosion.

MacAyeal notes that some climate forecasts predict more powerful storms as a result of global warming. He says that the B-15 story is evidence that those storms could hasten the breakup of other icesheets in Antarctica.

His findings are reported in the latest issue of Geophysical Research Letters.

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