Elevated levels of seismicity continued to be recorded at Mt. Spurr during 25 February to 4 March. No activity was observed in satellite and web-camera images. AVO staff observed that the "ice cauldron" at the volcano (a collapse feature in the ice possibly caused by increased volcanic heat) had continued to grow since its first sighting in August 2004. Continued heat flux was indicated by vigorously upwelling water in the "melt pit lake" (the nearly ice free lake at the bottom of the "ice cauldron"), rapid melting of ice and snow that had fallen into the melt pit lake, and minor steaming from rock surfaces and small melt pits in the vicinity of the summit dome and Crater Peak cone, 3 km S of Spurr's summit. According to AVO, both Spurr and Crater Peak were emitting volcanic gases, including carbon dioxide, sulfur dioxide, and hydrogen sulfide, which may be hazardous to recreational visitors. Mt. 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)