Report on Spurr (United States) — 15 September-21 September 2004
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 15 September-21 September 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, 15 September-21 September 2004. Smithsonian Institution and US Geological Survey.
61.299°N, 152.251°W; summit elev. 3374 m
All times are local (unless otherwise noted)
Elevated levels of seismicity continue to be recorded, but have not changed significantly from that observed in the past few weeks. During the week ending on 17 September there were about 85 earthquakes located within 30 km of the summit with an average of approximately 12 per day. Observations of the summit during AVO overflights showed no major changes. Spurr remained at Concern Color Code Yellow.
Geologic Background. The summit of Mount Spurr, the highest volcano of the Aleutian 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. Eruptions from Crater Peak in 1953 and 1992 deposited ash on the city of Anchorage.