Alaska Volcano Observatory

Summary 

• Seismic, ground deformation, and satellite data from Mount Spurr indicate that the low-level unrest first detected by the Alaska Volcano Observatory (AVO) in the spring of 2024 is ongoing. 
• The elevated rate of small earthquakes at the volcano has been mostly steady since April 2024. The largest magnitude earthquake to date was a M2.3. 
• Ground deformation measured with a local network of GNSS receivers has indicated steady movement upward and outward since March 2024.
• A small lake formed in the summit crater of Mount Spurr in early summer 2024 from melting ice. The lake has grown slightly over the summer, but no other changes in the lake or the nearby steam vents have been observed.  
• Together, these observations suggest that a new batch of magma has been emplaced beneath the volcano. The rate of activity indicates that the probability of an eruption in the near future is low.   

Current Observations 

The increase in seismic activity was first noted in April 2024 when the seismic monitoring stations on Mount Spurr were repaired following a months-long outage. AVO has located over 900 earthquakes this year to date that cluster in two areas, one at depths of 0 – 6 miles (0 – 10 km) beneath the volcano, and a second at depths of 12 – 22 miles (20 – 35 km) southeast of the Crater Peak vent (https://avo.alaska.edu/image/view/196118). The largest of these earthquakes is a magnitude M2.3 that occurred on October 6, 2024. The rate (~20 per week) and size of the earthquakes detected has not changed significantly since April 2024. The current increase in earthquake activity has some similarities to past episodes of increased earthquake activity at Mount Spurr. These periods include August 1991 to June 1992 that preceded the 1992 eruptions and 2004 to 2006 when increased earthquake activity accompanied an episode of heating at the summit of Mount Spurr that melted a substantial portion of the ice cap. 

Ground deformation measured with Global Navigation Satellite System (GNSS) stations on the flanks of the volcano started in March 2024 and has maintained a steady rate consistent with ongoing inflation of the volcano. At the stations closest to the deformation source, AVO has recorded ~1.6 inches (4 cm) of horizontal movement since the beginning of this deformation episode. Preliminary modeling suggests pressurization (due to magma/fluid inflow or gas exsolution) between 2 – 3 miles (3 – 5 km) depth and about 2 miles (3 – 4 km) west of Mount Spurr. Satellite radar data spanning September 2023 to September 2024 further confirm the GNSS-detected deformation around the volcano. 

Seismic unrest and ground deformation has been accompanied by the formation of a small lake in the summit crater of Mount Spurr in early summer 2024. The lake first appeared between May 15 and June 15 and was well documented during a June 23 overflight (https://avo.alaska.edu/image/view/195469) when it had an area of about 1 acre (~3800 square meters or roughly the size of a football field). The crater lake grew marginally over the summer to a diameter of around 280 feet (85 meters) and an area of approximately 1.4 acres through small collapses and melt of glacial ice inside the crater (https://avo.alaska.edu/image/view/196117). The lake is partially covered by ice and remains blue-green in color. Active steaming from summit area steam vents called fumaroles is visible along and above the northeastern lake shore and crater wall, and from a pit in the ice on the northeast crater rim. The vigor of steaming has not visibly changed over this current period of unrest and remains similar to observations from recent years. No volcanic mudflows (also called lahars) or other signs of significant ice and snow melt have been observed in the summit region or in Crater Peak. The last time a crater lake formed at the summit of Mount Spurr was during seismic unrest and a likely intrusion of magma in 2004 that did not lead to an eruption.  

The June 23 overflight also monitored gas emissions from the volcano and detected low levels of sulfur dioxide and carbon dioxide. The measured compositions are similar to background levels measured in previous years. Deep intrusion of magma is sometimes associated with anomalously high volcanic carbon dioxide emissions, but no such anomaly was detected during the overflight.  

Current Monitoring 

AVO field engineers completed several rounds of critical network maintenance at Spurr during the 2024 field season. The work focused on improving wintertime operation and continuity of real-time data streams from monitoring stations.  Mount Spurr is monitored by a local seismic network, GNSS ground deformation stations, infrasound sensors, and a webcam. Remote sensing data including satellite imagery of surface changes and ash and gas emissions, regional infrasound sensors, and lightning data are also used to detect unrest and eruptions at the volcano.