shows a pattern of ground uplift
centered about 3 miles (5 km) west of
South Sister volcano in central Oregon.
Each full color band from blue to red represents about 2.8 cm (slightly more than 1 inch)
of ground movement in the direction of the radar satellite. In this case, four concentric color bands
show that the surface moved toward the satellite (mostly upward) by as much as 10 cm (about 4 inches)
sometime between August 1996 and October 2000. No information is available for uncolored areas, where
forest vegetation or other factors hinder the acquisition of useful radar data. A numerical model
places the source of the uplift about 4 miles (7 km) beneath the ground surface. The most likely
cause is magma accumulation in the Earth's crust, a process that has been observed with radar
interferometry at several other volcanoes worldwide. There is no immediate danger of a volcanic
eruption or other hazardous activity. The U.S. Geological Survey, in cooperation with the U.S. Forest Service,
is analyzing additional information and installing new monitoring instruments to determine if the uplift is continuing.
The interferogram was produced by Wicks and others (2001) using radar images from the
European Space Agency's ERS satellites.
Wicks, C. Jr., Dzurisin, D., Ingebritsen, S.E., Thatcher, W., and Lu, Z. (2001) Ground uplift near the Three Sisters volcanic center, central Oregon Cascade Range, detected by satellite radar interferometry, in preparation.
[Graphic,201K,JPG, click to enlarge]
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