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It's The Mystery Bulge Of Oregon

May 8, 2001 By KOMO Staff & News Services

PORTLAND - It's weird, and they're not quite sure what it means.

A significant bulge in the Earth's crust has developed over the past four years near volcanoes in central Oregon, but it's not clear whether it could presage a volcanic eruption, geologists said Tuesday.

The bulge -- 9 to 12 miles across and about 4 inches high -- was detected by satellite radar, said Willie Scott, a United States Geological Survey scientist at the agency's volcano lab in Vancouver, Wash.

"Because it's a volcanic area and there's been a long history of volcanic activity in that part of the Cascades, it's possible it might be magma, or molten rock, moving deep underground," Scott said.

The bulge is located near the Three Sisters, a trio of volcanoes at the center of the Cascade Range in Oregon.

The last major eruption in the Pacific Northwest occurred in May 1980, when Mount St. Helens blew off about 1,300 feet of its top.

Can't Be Seen From Ground

The uplift in Central Oregon is too broad and low to be noticed from the ground.

The USGS scientists discovered the bulge through use of a relatively new technique called satellite radar interferometry, which uses satellite data to create images of the Earth's surface.

Images taken at different times can be used to detect changes of even a few inches in the elevation of the ground.

Scientists have looked across the West for signs of bulges, but this is the first prominent change on record using this technique.

"There's nothing as striking as this one," Scott said. "This is quite a prominent uplift.

"But there's nothing right now that makes us think there's an imminent danger" of an eruption, he said.

Other Indicators

In addition to accelerating uplift, other indicators of an eruption would include earthquakes -- typically swarms of small quakes generated by rock fracturing as magma moves upward -- and large emissions of volcanic gases, such as carbon dioxide.

The Cascades, which run from the California border into British Columbia, contain a number of volcanic peaks.

Mount Hood, Oregon's highest mountain, is believed to have erupted just before the Lewis and Clark expedition reached the mouth of the Columbia River in 1805.

About 7,000 years ago, Mount Mazama exploded south of Bend in an enormous explosion that left behind a caldera that now holds Crater Lake, the deepest lake in North America.

-- Martin Thompson (, May 08, 2001

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