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Saturday, October 7, 2006
Wave Tracked 8,000 Miles; Alaska Swell Broke Massive Iceberg in Antarctica
By John Fleck
Journal Staff Writer
A massive storm rocked the Gulf of Alaska on Oct. 21, 2005. Six days later, at the other end of the world, a massive Antarctic iceberg broke into pieces.
Following a trail of scientific bread crumbs, a team of scientists has established a connection: a massive wave that traveled more than 8,000 miles across open ocean, shaking the 60-by-20-mile iceberg until it fell apart.
Scientists have long known ocean waves can circle the planet. But this is the first time they have found evidence of such a dramatic effect, according to New Mexico Tech geophysicist Rick Aster, a member of the scientific team that pulled the clues together.
Aster's specialty is seismology the study of how earthquakes, volcanoes and the like rattle our planet. That might seem a far cry from the effects of ocean waves.
But it is not. Ocean waves banging against the shore or rolling across open ocean do, in fact, shake the Earth enough to be detectable on seismic instruments, Aster explained.
That is what Aster and his colleagues saw in their data as the wave passed Pitcairn Island in the South Pacific, two days before it hit the iceberg.
Buoys scattered across the Pacific to measure ocean height also recorded the wave's passage.
But the clinching evidence came from an unusual scientific trick. The scientists installed seismometers on the iceberg itself.
The seismometers are part of a cache of equipment maintained by New Mexico Tech and deployed worldwide. They are designed to measure tiny movements of the Earth's surface, which made it a cinch to measure the rocking and rolling of the floating iceberg, Aster explained.
When the wave left the Gulf of Alaska, it was about 30 feet high, according to a paper by the scientific team published this week in the journal Geophysical Research Letters. By the time it passed Hawaii three days later, it was down to 15 feet.
By the time it reached Antarctica, the wave was small enough that it lifted the giant iceberg only a fraction of an inch, according to the scientists. But the resulting shaking seems nevertheless to have been enough to break up one of the Earth's largest icebergs, they write.