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. Spurr's two historical eruptions, from Crater Peak in 1953 and 1992, deposited ash on the city of Anchorage.
The 3374-m-high summit of Mount Spurr, the highest volcano of the Aleutain arc, is a large lava dome constructed at the center of a roughly 5-km-wide horseshoe-shaped caldera that is open to the south. The volcano lies 130 km west of Anchorage and NE of Chakachamna Lake. The caldera was formed by a late-Pleistocene or early Holocene debris avalanche and associated pyroclastic flows that destroyed an ancestral Spurr volcano. The debris avalanche traveled more than 25 km to the SE, and the resulting deposit contains blocks as large as 100 m in diameter. Several ice-carved post-caldera cones or lava domes lie in the center of the caldera. The youngest vent, 2309-m-high Crater Peak, formed at the breached southern end of the caldera and has been the source of about 40 identified Holocene tephra layers.
Click the title to read Areal Distribution, Thickness, Mass, Volume, and Grain Size of Tephra-Fall Deposits from the 1992 Eruptions of Crater Peak Vent, Mt. Spurr Volcano, Alaska by Robert G. McGimsey, Christina A. Neal, and Colleen M. Riley
To find out about NASA's Dante II robotic explorer mission to Spurr, click here.
To order a Video of the August 18, 1992 eruption of Spurr, click here.
Look at a current webcam image of Spurr HERE (Courtesy of the Alaska Volcano Observatory)
Sources of Information:
Wood, Charles A. and Kienle, Jurgen, "Volcanoes of North America United States and Canada," Cambridge University Press, New York, 354 pp., 1990; USGS; Alaska Volcano Observatory;