In a special information statement on 6 February, the Alaska Volcano Observatory (AVO) reported that unrest at Spurr continued and was likely caused by new magma beneath the volcano. The nature of the unrest and the 10-month duration suggested that an eruption remained a possibility. The most likely vent location would be at Crater Peak, which erupted in 1953 and 1992; less likely would be the summit vent, which erupted several thousand years ago. The rate of earthquakes increased from an average of 30 per week during April into early October to a rate of 125 per week from early October to 6 February. More than 2,700 earthquakes were located during the unrest episode thus far and the largest was a M 2.9 that occurred on 2 January 2, 2025. Earthquakes were clustered at two depth ranges, 0-10 km and 12-22 km, beneath both the summit and Crater Peak, though there was a recent increase in the number of earthquakes under Crater Peak.

Increased seismicity was accompanied by around 6 cm of inflation detected by the Global Navigation Satellite System (GNSS) stations on the flanks and satellite data. Modeling indicated that the inflation source was located 3-5 km below sea level and 3-4 km W of the summit. A small lake appeared in the summer crater in the early part of the summer in 2024. The lake had grown to an area of about 5 acres. Active steaming from summit area fumaroles has not changed over the current period of unrest and is similar to observations from recent years. There were no significant surface changes at Crater Peak. Instruments aboard gas measurement flights on 23 June and 18 December 2024, and 7 February 2025, detected low levels of sulfur dioxide and carbon dioxide, similar to background levels measured in previous years. The Volcano Alert Level remained at Advisory (the second lowest level on a four-level scale) and the Aviation Color Code remained at Yellow (the second lowest level on a four-color scale).

Geological Summary. Mount Spurr is the closest volcano to Anchorage, Alaska (130 km W) and just NE of Chakachamna Lake. The summit is a large lava dome at the center of a roughly 5-km-wide amphitheater open to the south formed by a late-Pleistocene or early Holocene debris avalanche and associated pyroclastic flows that destroyed an older 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-collapse cones or lava domes are present. The youngest vent, Crater Peak, formed at the southern end of the amphitheater and has been the source of about 40 identified Holocene tephra layers. Eruptions from Crater Peak in 1953 and 1992 deposited ash in Anchorage.

Source: US Geological Survey Alaska Volcano Observatory (AVO)