In eastern Siberia, a perfect circle of rock contrasts with the surrounding topography. The 6-kilometer- (3.7-mile-) wide ring looks like an impact crater, or the caldera of an extinct volcano, but it is neither. Kondyor Massif was formed by the intrusion of igneous, or volcanic, rock that pushed up through overlying layers of sedimentary rock, some of them laid down more than a billion years ago.
Using data acquired September 13, 2002, this 3-D visualization shows an old lahar (avalanche of volcanic mud) extending from Anyuyskiy Volcano in far eastern Russia.