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Pumice Raft From Undersea Eruption In The South Pacific
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Pumice Raft From Undersea Eruption In The South Pacific

August 17, 2012
On August 13, 2012 the Moderate Resolution Imaging Spectroradiometer (MODIS) flew over the South Pacific Ocean and captured a curious true-color image. Although at first glance this white and blue image seems to be a study of clouds against ocean, a closer looks reveals that in the lower left corner of the image, the apparently white “cloud” is tinged with gray and lies in in long tendrils across the surface of the ocean. These swirls are not clouds – they are floating pumice.

A raft of floating pumice was noticed in the South Pacific Ocean as early as August 1, and visited by an ocean going vessel that was traveling along a chain of underwater volcanoes between Auckland and Raoul Island, New Zealand on August 9 and 10. But the source of the eruption was not readily apparent. Several local volcanoes, including Monowai, located north of the raft, had recently erupted – but no known eruption correlated with the appearance of the pumice in the ocean. Using a combination of seismology and satellite imagery, scientists were able to discover the origin of the pumice – Havre Seamount in the Kermadec Islands.

Seismologists identified a cluster of earthquakes in this region on July 17 and 18. Ranging in magnitude from 4.0 and 4.8, they were consistent with magma rising in a volcano prior to eruption. Volcanologist Erik Klemetti and NASA visualizer Robert Simmon then examined a month’s worth of MODIS images from the Aqua and Terra satellits and found ash stained water, gray pumice and a volcanic plume over the seamount on July 19, 2012. Night time imagery suggested that the eruption may have begun on July 18.

By July 21, the eruption appeared to have waned, leaving behind the dense rafts of pumice. Winds and currents spread the pumice into a series of twisted filaments, spread over an area about 450 by 250 kilometers (280 by 160 miles) as of August 13.

Credits: Jeff Schmaltz, MODIS Land Rapid Response Team, NASA GSFC


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