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Largest Existing Iceberg Is Born

April 03, 2000

A massive iceberg has broken off of the Ross Ice Shelf in Antarctica that is about the size of Connecticut or twice the size of Delaware, about 4,250 square miles (11,000 square kilometers). The iceberg, the largest currently known to exist, broke free from the Antarctic's Ross Ice Shelf around March 20 and is expected to bounce up against the main ice shelf for several days before drifting out to sea. Identified as B-15 by the National Ice Center, it measures 183 miles long (295 kilometers) and about 25 miles wide (37 kilometers). It extends about 900 feet below the surface and rises about 120 feet (30 meters) above the ocean.

This image from NOAA's polar-orbiting satellite shows the iceberg's merging as it breaks awau from the Ross Ice Shelf in Antartica.(Courtesy: National Oceanic and Atmospheric Administration and the University of Wisconsin at Madison.)

The iceberg was 'calved', or broke off from, the main ice sheet about 200 miles east of the National Science Foundation's (NSF) McMurdo Station as measured from its western edge. Among the largest ever observed, its size is eclipsed by an iceberg that was spotted in 1955 about 150 miles west of Scott Island inside the Antarctic Circle by the U.S.S. Glacier, the US Navy's most powerful icebreaker at the time. That iceberg was reported as 60 miles wide by 208 miles long, or about 12,000 square miles (31,000 square kilometers). McMurdo Station is the largest of three U.S. Antarctic stations and serves as a "gateway" for field teams studying astronomy, atmospheric sciences, biology, earth science, environmental science, geology, glaciology, marine biology, oceanography and geophysics.

This high-resolution radar map of Antarctica took just 18 days to complete. The red arrow points to the Ross Ice Shelf and the Ross Sea.(Courtesy: NASA and Ohio State University. As seen from the Canadian satelite RADARSAT in October 1999.

NSF reported on March 31 that the iceberg has created new icebergs by bumping into the ice shelf. According to Dr. Ted Scambos, a polar scientist working at the National Snow and Ice Data Center at the University of Colorado, it appears that the berg has collided with an adjacent section of the Ross Ice Shelf, just to the east and broke off a new berg. Satellite pictures show that four new icebergs have broken off from the Ross Ice Shelf to the immediate east of B-15, as a result of the larger iceberg's collisions against the main ice sheet. Still, Dr. Scambos explains, the iceberg itself is likely to break into smaller pieces as it bounces up against the ice shelf and drifts around the Antarctic waters.

"The B-15 berg will probably knock around the Antarctic for several years, staying within the zone of sea ice, and drifting generally westward around the continent," Dr. Scambos said, indicating that at some point the iceberg will drift northward into eastward-trending currents of the Southern Ocean. "It will not be hard to avoid this berg," he concludes.

Taken March 31, this satellite photograph shows four new icebergs(indicated by the red arrows) east of B-15, most likely the result of the larger iceberg bumping up against the iceshelf in that area..(Courtesy: NOAA and the University of Wisconsin at Madison.)

However, Dr. Scambos warns that the iceberg may disrupt vital shipments to the McMurdo base which relies on a brief spring period when the sea ice usually disappears. This allows the ships to come in to re-supply the base. "If the berg positions itself in front of McMurdo, there is a good chance that the sea ice will thicken to the point where it doesnÃt break up, perhaps not for years," he said. The US program would have to re-think how to keep the base open, and what activities it could support, in that case. According to NSF spokesman Peter West, there are many factors that would determine how fast an iceberg may drift, including such conditions as wind, the iceberg's depth into the ocean, its reach into the air, and water currents. "It is a possibility that this iceberg could affect McMurdo's shipping lanes by this October," West said. "It's just too early to tell, and many things can happen."

This iceberg, referred to as B-10 by the National Ice Center, is of the tabular variety as is the B-15 iceberg that recently broke off from the Ross Ice Shelf. Reaching 700-800 feet into the ocean and rising 100 feet into the air, B-10 is as big as Rhode Island and has become a hazard in the shipping lanes between the southern tip of South America and Antarctica(Courtesy: National Science Foundation)

B-15 was formed from glacial ice moving off the Antarctic continent and calved along pre-existing cracks in the Ross Ice Shelf near Roosevelt Island. The calving of the iceberg essentially moves the northern boundary of the ice shelf about 25 miles to the south, a loss that would normally take the ice shelf as long as 50-100 years to replace. According to information provided the NSF, cracks in the Antarctic ice shelf have been closely observed by scientists since satellite remote sensing has become available and they are of particular interest to scientists studying the potential effects of global warming. However, this iceberg is not considered a result of global warming and it is believed to be "part of a normal process in which the ice sheet maintains a balance between constant growth and periodic losses."

Did you know...?

Icebergs are virtually indestructible other than by natural deterioration. In theory, it would take about 1,900 tons of TNT to breakup up an average sized North Atlantic iceberg (about 70,000 cubic feet). To melt such an iceberg, it would require the combustion of nearly 2.4 million gallons of gasoline. Just think about how much it would take to break up or melt the B-15 iceberg!

The largest icebergs come from the Antarctic, where they are also called "ice islands." But, the tallest icebergs come from the North Atlantic. The tallest iceberg ever recorded was 550 feet high, about the size of the National Monument in Washington, DC. Antarctic icebergs are tabular -- flat and layered -- whereas the North Atlantic icebergs have a more jagged appearance.

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