Report on Spurr (United States) — 4 May-10 May 2005
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 4 May-10 May 2005
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2005. Report on Spurr (United States). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 4 May-10 May 2005. Smithsonian Institution and US Geological Survey.
61.299°N, 152.251°W; summit elev. 3374 m
All times are local (unless otherwise noted)
An approximately 500-m-long debris flow emanating from the ice and snow ESE of the summit melt pit was seen from Anchorage and confirmed by an overflight on 2 May. This debris flow is similar in size and location to those observed in July 2004, just prior to first recognition of the summit melt pit. Clear views of the melt pit showed increased steam emanating from recently exposed rock around the lake, which coalesced to form a weak steam plume that rose above the rim of the melt pit. The lake level had decreased since 25 April, indicating outflow of water from the lake which may have coincided with emplacement of the recent debris flow. 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.