March 15, 2006—If you've seen one volcanic plume, you've seen 'em all? Not so, says a new study, which identifies an entirely new type of ash cloud that may also present a new danger.

Normal plumes look like smooth-domed mushroom clouds. But this one, photographed in Ecuador in 2002, has unusual scalloped edges.

Susan Kieffer, a University of Illinois geology professor, believes the cloud, which erupted from Ecuador's Reventador ("one that explodes") volcano, may represent an extreme hazard.

Volcanic clouds can collapse back to Earth in searing, high-speed events called pyroclastic flows. Unlike with normal plumes, the ash from the scalloped cloud must have been unusually heavy, causing it to collapse more rapidly, Kieffer writes in today's issue of the journal Geophysical Research Letters.

Katharine Cashman, a geologist at the University of Oregon, who was not part of the study, compared the plume to "a giant clam from Australia's Great Barrier Reef."

Cashman looks forward to reading Kieffer's study. Until then, she's not convinced that the cloud represents anything more than a new variant on the type of plumes already known to be prone to collapse. Still, she said, "it's a cool photo."

—:Richard A. Lovett

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