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, according to the 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]. 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.
If it happened in the southern end of the Cascades in Oregon, "thick ash would probably fall in the Midwest [U.S.].
The first of the two eruptions that rocked the northern Cascades formed a giant crack. When the crack widened, the ground on one side dropped like a trap door swinging down. The section of earth fell more than 3,000 feet (1,000 meters).
Vast quantities of ash then filled the hole, and rivers of ash and superheated air rushed away with enough momentum to flow over surrounding mountains, incinerating everything in their paths.
The second eruption occurred about a hundred thousand years later, when the upper end of the trap door dropped, forming a roughly rectangular crater measuring 5 miles by 2.5 miles (8 kilometers by 4 kilometers).
The best known ancient eruption to have occurred in the Cascades is the one that produced Oregon's Crater Lake, only 7,700 years ago. (Download a wallpaper photo of Crater Lake.)
Compared the Cascades supervolcano event to the eruption of the Indonesian island of Krakatau (or Krakatoa), which exploded in 1883, killing 36,000 people. Actually, Krakatoa was small compared to [the ancient Cascades eruption].
Krakatau ejected approximately 10 cubic miles (25 cubic kilometers) of rock and ash when it blew its top.
The two eruptions described by Tucker involved a total of about 30 cubic miles (130 cubic kilometers) of magma "in a period of probably a day or two [each].
Since then the site has been quiet, as volcanic activity has shifted 15 miles (25 kilometers) southwest, to the present location of 10,778-foot (3,285-meter) Mount Baker, near the city of Bellingham.
No one knows if Mount Baker, or another peak in the Cascades, might someday produce a similar mammoth eruption.
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