Elevated levels of seismicity continued to be recorded at Spurr during 29 October to 2 November. An earthquake swarm on 4 November consisted of as many as 10 shallow earthquakes per hour during a 6- to 7-hour period. After that, the level of seismicity declined to an average of 0-2 earthquakes per hour. Airborne measurements of volcanic gas from the volcano on 29 and 30 October indicated no significant change in the amount of carbon dioxide or sulfur-bearing gases compared to previous measurements in September. No unusual activity was observed on satellite or web-camera images. Spurr remained at Concern Color Code Yellow.

Geological Summary. The summit of Mount Spurr 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.

Source: US Geological Survey Alaska Volcano Observatory (AVO)