Giant iceberg shakes loose off Antarctica
Copyright 2000, Environmental News Network
Saturday, March 25, 2000
By Lucy Chubb
An enormous iceberg dubbed B15 recently broke off of the Ross Ice Shelf in Antarctica. A smaller iceberg, B16, also came loose and can be seen to the left of B15 in the image above.
One of the largest icebergs ever recorded broke off of Antarctica's Ross Ice Shelf earlier this week and is now flying solo in the Ross Sea.
The immense block of ice — dubbed B15 — is 300 kilometers (186 miles) long and 37 kilometers (23 miles) wide, and is almost the same size of the state of Connecticut.In the 23-year history of the U.S. National Ice Center's iceberg database, no iceberg has been bigger, said Selina Nauman, a NIC scientist. An iceberg named A-22 that calved from the Filchner Ice Shelf in 1987 may have been bigger than B15, but further analysis is required to verify this.
Scientists are not exactly sure how tall B15 is because there is no observational data so far. They estimate that the iceberg towers about 30 meters (98 feet) above the water line and plunges to about 400 meters (1,312 feet) below the surface, said Matthew Lazzara, a senior research specialist at the University of Wisconsin at Madison who has been analyzing the satellite data.
Forecasters from the U.S. National Science Foundation's McMurdo Station in Antarctica were the first to notice the giant breakaway while looking at images transmitted from two polar orbiting satellites. The two satellites, managed by the National Oceanic and Atmospheric Administration, orbit the Earth from pole to pole at an altitude of about 700 kilometers (435 miles).
"Antarctica is a huge, steep continent", said Lazarra. Glacial ice obeys the laws of gravity by flowing down the sides of the land mass and extending into the ocean, forming what are known as ice shelves. Just like glaciers, the ice has a multitude of crevices. Water flows into these fissures, where it freezes and expands, thereby widening the cracks and weakening the ice.
Icebergs like B15 occur when ice at the edge of an ice shelf finally succumbs to the forces of the sea, which include warmer temperatures, currents and tides. The crannies in the ice begin to lengthen and eventually meet to create a floating island of frozen water.
The cracks in the Ross Ice Shelf that now make up part of the perimeter of B15 have been evident and under observation for many months if not years, Lazarra said. But only just last week did the scientists discern the separation of the iceberg from the shelf beginning to take place.
Icebergs B15 and B16 formed in the region of the Ross Ice Shelf indicated by the red arrow.
The calving off of this tremendous iceberg is quite normal, he said. Researchers believe that icebergs like B15 break away from all Antarctic ice shelves every 50 to 100 years as part of their natural cycle of ice loss and regeneration. According to iceberg observation records, the Ross Ice Shelf has been due for a good purge.
"This is probably not a global warming issue at this time," said Lazarra, but scientists will be keeping an eye on this area to see if anymore very large icebergs break free in the near future.
B15 has not yet strayed very far from the Ross shelf. Ocean winds, currents and tides, plus the influence of the rotation of the Earth, work to move icebergs around, said Lazarra.
Whatever the influences, icebergs of this size typically do not move very fast, said Chief Lori Butcher of NIC. "It may take a year or several years to move a couple of miles."
But if the colossal ice chunk strays 200 miles in the wrong direction and at the wrong time, it could interfere with shipping traffic to the NSF's McMurdo research station.
"Shipping to McMurdo is important in January and February," said Lazarra. "It will be interesting to see where this iceberg will be at that time."
In Antarctica, January and February are summer months when the bulk of research takes place at the McMurdo outpost.
But where B15 will go is not clear. The NIC does not make official forecasts for iceberg movement, said Butcher.
Doug MacAyeal, an NSF-supported researcher from the University of Chicago, is at work modeling the potential path of the iceberg, based on the science of iceberg drift dynamics. MacAyeal was not available for comment.
MORE INFORMATION
Iceberg names are derived from the Antarctic quadrant in which they were originally sighted. The quadrants are divided counter-clockwise in the following manner:A = 0 to 90 degrees West longitude (Bellinghausen/Weddell Sea)
B = 90 West to 180 (Amundsen/Eastern Ross Sea)
C = 180 to 90 East (Western Ross Sea/Wilkesland)
D = 90 East to 0 (Amery/Eastern Weddell Sea)
Another iceberg known as B16 also separated from the Ross Ice Shelf this week, said Selina Nauman, a scientist at NIC. It is in close proximity to B15 but it is significantly smaller.
According to calculations performed by colleagues of Matthew Lazarra, the B15 iceberg is so big that, if it melted, the resulting water would be the equivalent of 10 percent of all on-land precipitation for the entire Earth.