Report on Spurr (United States) — 27 April-3 May 2005
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 27 April-3 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, 27 April-3 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)
During 22-29 April, elevated levels of seismicity continued to be recorded at Spurr. Thermal imagery taken on 25 April revealed that temperatures in the summit melt-pit region were similar to those recorded in September 2004, with values as high as 40 degrees Celsius in scattered patches of exposed rock. The lake in the summit crater continued to be discolored, and there was a strong scent of sulfur in the area, indicating continued gas emission. The summit melt pit was estimated to be approximately 250 m in diameter, and it continued to widen as the summit snow pack collapsed into the lake. No unusual activity was observed in satellite or web camera images during the report week. Mt. 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.