Alaska Volcano Observatory

Summary

• During overflights on March 7 and 11, AVO measured significantly elevated volcanic gas emissions from Mount Spurr volcano. Newly reactivated fumaroles (gas vents) were also seen at the volcano’s Crater Peak vent. Elevated earthquake activity and ground deformation continue.
• The increase in gas emissions confirms that new magma has intruded into the Earth’s crust beneath the volcano and indicates that an eruption is likely, but not certain, to occur within the next few weeks or months.
• The most likely outcome of the current unrest is an explosive eruption (or eruptions) like those that occurred in 1953 and 1992. Those eruptions each lasted a few hours and produced ash clouds that were carried downwind for hundreds of miles and minor ashfall (up to about ¼ inch) on southcentral Alaska communities.
• We expect to see further increases in seismic activity, gas emissions, and surface heating prior to an eruption, if one were to occur. Such stronger unrest may provide days to weeks of additional warning.

Recent observations

• During an overflight on Friday, March 7, AVO measured about 450 metric tons per day of SO₂ from the Spurr summit vent (figure). This is an increase from less than 50 metric tons per day SO₂ measured in December 2024.
• AVO also measured increased concentrations of CO₂ at the summit and at the Crater Peak vent, 2 miles (3.5 km) south of the summit. The CO₂ concentrations at Crater Peak were especially high. In the past, such values have been observed prior to eruptions (for example, at Redoubt Volcano in 2009). Preliminary results from a gas flight on March 11 confirm these results.
• Over the last month, AVO has located over 100 earthquakes per week under Mount Spurr (figure). Most earthquakes are shallow (less than 2.5 miles, or 4 km, below sea level). Magnitudes during this time are as large as M2.7 (figure). Over 3400 earthquakes have been located under the volcano since April 2024.
• Ground deformation also continues. The total movement away from the volcano to date is about ~2.6 inches (~6.5 cm) at the closest GNSS (GPS) station. Modeling of the inflation suggests a source around 2 to 3 miles (3 to 5 km) below sea level and about 2 miles (3 to 4 km) west of Mount Spurr summit.
• Collapse of snow and ice into the summit crater lake that formed during this period of unrest continues, along with steam emissions from fumaroles within and around the summit crater. New diffuse steaming from small snow-free spots within Crater Peak was observed beginning on March 6 (photo). These locations have been sporadically snow-free for years, but steaming has not been observed since 2008.

Interpretations and Hazards

The current unrest at Mount Spurr indicates that new magma has intruded into the Earth’s crust beneath the volcano and that the probability of an eruption has increased. It is likely that magma has been accumulating beneath Mount Spurr summit for some months. The recent gas data suggest that a new pathway towards the Crater Peak vent has opened, and that fresh magma may rise and erupt there. Crater Peak is the site of all historical eruptions. The last known eruption from Spurr summit occurred several thousand years ago.

Based on all available monitoring data, AVO regards the following scenarios as possible. We consider scenario 1, explosive eruption(s) like those in 1953 and 1992, as most likely at this time. Scenarios 2 and 3 (smaller eruption, or no eruption) are possible but considered less likely, and the likelihood of a much larger eruption is currently low.

1. Explosive eruption(s) like those in 1953 and 1992: In this scenario, one or more explosive events, each lasting as long as a few hours, would produce ash clouds carried downwind for hundreds of miles and minor (up to about ¼ inch) ashfall over southcentral Alaska. The flanks of Mount Spurr likely would be swept by pyroclastic flows (hot avalanches) and impacted by ballistic showers. Mudflows (lahars) could inundate the upper Chakachatna River valley.  
2. Lava-forming and/or small explosive eruption(s): It is possible that the volcano could erupt less explosively than it did in 1992 and 1953, and produce lava flows, a lava dome, and/or brief explosive eruptions. Such events would have less far-travelled impacts, but lahars (mudflows) in the drainages around the volcano are possible.
3. Failed eruption: If the magma stalls and does not reach the surface, as happened in 2004–2006, we expect to see earthquake activity, ground deformation, gas emissions, and surface heating slowly decrease over several weeks or months.
4. Large explosive eruption: Eruption(s) larger than those in 1992 and 1953 could occur. These would likely result in larger ash clouds, thicker ashfall deposits and greater overall impacts. No such eruptions are known in historical times, and the geologic record suggests these are rare. Therefore, the likelihood of such an event is low.

We cannot assign an exact timeframe for when an eruption will occur, if it does, but the increased gas emissions recorded on March 7 suggest that an eruption may occur in the next few weeks to months. We expect to see additional changes to monitoring data prior to an eruption, if one were to occur, as magma moves closer to the surface. This would include a change in the rate and character of earthquakes, onset of sustained seismic tremor, further increased gas emissions, changes in surface deformation, and melting of snow and ice. In 1992, such changes occurred about three weeks prior to the first eruption.

Should earthquake activity or other monitoring data suggest that an eruption is likely within hours or days, AVO would raise Mount Spurr from its current Aviation Color Code Yellow and Alert Level Advisory to Aviation Color Code Orange or Red and Alert Level Watch or Warning. Alert level definitions can be found here: Alaska Volcano Observatory | Volcano Alert Levels.  

Decreases in earthquake activity, degassing, and surface deformation would make it less likely that the unrest will progress to eruption.

Current Hazards

While we expect additional changes to monitoring data prior to an eruption, it is also possible that an eruption could occur with little or no additional warning. This would be extremely hazardous for recreators on Mount Spurr or near its drainages as well as those overflying the volcano. In addition, CO₂ and SO₂ emissions are currently elevated and may pose a hazard to anyone in low-lying areas around or downwind of the gas vents, such as within the craters atop Crater Peak and Spurr summit. CO₂ is a colorless and odorless gas and hazardous areas of high CO₂ cannot be detected by sight or smell.

Monitoring information

Mount Spurr is monitored by a local seismic network, GNSS ground deformation stations, infrasound sensors, and a web camera. Remote sensing data, including satellite imagery of surface changes and ash and gas emissions, regional web cameras, regional infrasound sensors, and lightning data are also used to detect unrest and eruptions at the volcano.  

At the current level of unrest, we plan to conduct routine overflights to measure gas emissions, evaluate surface changes, and measure ground surface temperatures. We are considering adding additional monitoring instruments in response to the current unrest.

Background information

For more details of the current period of unrest, please refer to the February 6 Information Statement.

The only known historical eruptions from Mount Spurr occurred in 1953 and 1992 from the Crater Peak flank vent located 2 miles (3.5 km) south of the peak’s summit. These eruptions were explosive and produced columns of ash that rose up to 65,000 feet (20 km) above sea level and deposited minor ashfall on southcentral Alaska (up to ¼ inch or 6 mm). The geologic record shows that Crater Peak was also the source of several explosive eruptions over the past few thousand years.

Mount Spurr’s summit vent has not erupted in historical times and there is little preserved geologic evidence of past eruptions for the last 5,000 years. More recent eruptions, if they have occurred, must have been less explosive than Crater Peak and their deposits not as well preserved. A summit eruption could be explosive or could consist only of lava flows. From 2004 to 2006, Spurr summit experienced an episode of increased seismicity, surface uplift, and heating that melted a large hole in the summit ice cover and generated debris flows, but no eruption occurred.

Primary hazards during future eruptions from either vent could include far-traveled airborne ash clouds and ashfall that could be impactful to southcentral Alaska communities. Pyroclastic flows (hot avalanches), and lahars (mudflows) could inundate drainages on all sides of the volcano, but primarily on the south and east flanks, and pose no significant risk to communities.

For more information, please see the following websites:

Mount Spurr activity page at Alaska Volcano Observatory website: https://avo.alaska.edu/volcano/spurr

New AVO Fact Sheet about Mount Spurr: ic098.pdf

USGS information about volcanic ashfall hazards, preparedness, and mitigation measures: http://volcanoes.usgs.gov/ash/

Official forecasts of airborne ash hazard to aircraft: https://www.weather.gov/aawu/

Volcanic Ash Advisories for aircraft: https://www.weather.gov/vaac/

Official warnings of ashfall on communities and mariners: http://www.weather.gov/afc