The Alaska Volcano Observatory (AVO), a Cooperative Program of the U.S. Geological Survey, the University of Alaska Fairbanks Geophysical Institute, and the Alaska Division of Geological and Geophysical Surveys, has detected unrest at Mount Spurr volcano, located about 125 km west of Anchorage, Alaska, at the northeast end of the Aleutian volcanic arc. This activity consists of increased seismicity, melting of the summit ice cap, and substantial rates of CO2 and H2S emission. The current unrest is centered beneath the volcano's 3374-m-high summit, whose last known eruption was 5000-6000 years ago. Since then, Crater Peak, 2309 m in elevation and 4 km to the south, has been the active vent. Recent eruptions occurred in 1953 and 1992.