Report on Spurr (United States) — 28 July-3 August 2004
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 28 July-3 August 2004
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2004. Report on Spurr (United States). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 28 July-3 August 2004. Smithsonian Institution and US Geological Survey.
61.299°N, 152.251°W; summit elev. 3374 m
All times are local (unless otherwise noted)
According to AVO during 22-30 July elevated levels of seismicity continued to be recorded at Spurr, with approximately 10-20 earthquakes occurring daily beneath the summit. The level of activity had remained constant for the previous several weeks. Although this represented a notable increase over background seismicity levels, there was no indication that an eruption was imminent. AVO noted that this type of seismicity often will decline without producing an eruption. Spurr remained at Concern Color Code Yellow.
Geologic Background. The 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 open to the south. The volcano lies 130 km W 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 edifice. The debris avalanche traveled more than 25 km 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, Crater Peak, formed at the breached southern end of the caldera and has been the source of about 40 identified Holocene tephra layers. Spurr's two historical eruptions, from Crater Peak in 1953 and 1992, deposited ash on the city of Anchorage.