Ancient "Supervolcano" Rocked Washington State

Richard A. Lovett
for National Geographic News
February 6, 2007

An ancient "supervolcano" in what is now Washington State spewed steam and billowed ash in amounts that dwarf the eruption of Mount St. Helens in 1980, new research shows.

The blow-up occurred in two major bursts about 3.7 million years ago in the northern Cascade Range, creating flows of searing-hot gas and belching out some 33 cubic miles (137 cubic kilometers) of ash.

It wasn't the first eruption to occur there, said David Tucker, a research associate at Western Washington University. And it wasn't the last either.

The newly discovered mega-eruption brings to six the tally of ancient volcanoes known to have blown in the Cascades, Tucker said.

"We know there were at least some small volcanoes [at the site]," he said.

"We don't know what kind, because they were obliterated. Now they exist merely as little bits of rock."

The blasts, he added, would have killed all life for several miles around and dumped ash over a vast area downwind.

"These are big eruptions—on the small end of what have been called supervolcanoes," Tucker said.

"If something went off like that today, a long way into British Columbia would be severely impacted." (See Washington State map.)

If it happened in the southern end of the Cascades in Oregon, "thick ash would probably fall in the Midwest [U.S.]."

Tucker's research appears in the March/April issue of the Geological Society of America Bulletin.

At Least Six Giant Eruptions

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