View north of Crater Peak, the active vent of Mount Spurr, Alaska, on 26
September 1992. Crater Peak erupted in June, August, and September 1992.
Ash from the August eruption closed Anchorage International Airport.
Behind the small steam plume is Mount Spurr. Mt. Spurr and the peak
visible on the left define the rim of caldera, evacuated by a huge
debris avalanche about 10,000 years ago. Photo courtesy of USGS Cascades
Volcano Observatory.
Mt. Spurr is a stratovolcano in Alaska. It is composed mostly of andesite. The Spurr volcanic complex was built on the remains of an older volcano. The present Mt. Spurr grew in the center of the old caldera. The original volcano was an andesitic stratovolcano. It is about 12 miles (19 km) around. Snow and ice cover the north side. The base of the volcano is covered by thick ashflows and pyroclastic deposits which contain dikes and sills. The upper part of the volcano is mostly andesitic lava flows. The caldera of the older volcano is ~3 by 4 miles (5 by 6 km) wide. The elevation of this caldera is about 9800 ft (3000 m). The caldera is breached to the south. It contains an ice field which feeds glaciers in all directions.
A dome grew in the center of the old volcano's caldera to form the present Spurr. This volcano is mostly covered with ice. The exposed ground around the volcano has fumaroles which are near the boiling point. A small summit crater sometimes melts some of the ice on the volcano. Fumarole activity from this crater was the only activity before 1953. A second cone called Crater Peak grew in the breach of the older volcano. This was the sight of a major ash eruption on July 9, 1953. The most recent eruption of Spurr was in 1992.
Wood, Charles A. and Kienle, Jurgen, "Volcanoes of North America United States and Canada," Cambridge University Press, New York, 354 pp., 1990.
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