Ground Uplift Near South Sister Volcano,
Central Oregon Cascade Range

This radar interferogram 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.