USGS Volcano Notice - DOI-USGS-AVO-2025-04-17T14:25:55+00:00

Summary

• Shallow earthquake activity underneath Mount Spurr remains elevated, though it has declined slightly over the past month. Ground deformation has also slowed over the past three weeks.
• AVO has been unable to measure volcanic gases via airplane or helicopter since March 21 due to poor weather. Satellites have not detected SO₂ from Mount Spurr since April 3, most likely due to cloudy weather.
• Based on the recent modest changes in monitoring data and the inability to measure gas for the last month, the outcome of the current unrest is less certain. When weather conditions become more favorable, collection of new gas data will help us improve this assessment.
• Overall, the likelihood of an eruption has decreased from March, but the volcano remains at an elevated level of unrest and an explosive eruption (or eruptions) like those that occurred in 1953 and 1992 is still possible.
• We expect to see 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

• The last gas-measurement flight was on March 21; poor weather has prevented flights since that time. Analysis of the data from three flights in March suggests emission rates of about 1000 metric tons per day CO₂ from Crater Peak. This value is high, but similar values were reported in 2004, when the volcano did not erupt. No SO₂ was detected from Crater Peak. At the summit, measurements from the March flights show several hundred metric tons per day of CO₂ and SO₂. These values are also similar to what was measured in 2004–2006.  
• Satellite detections of SO₂ occurred on 7 occasions in mid-March and early April and were broadly consistent with airborne measurements. No satellite SO₂ detections have been made since April 3. This may be due to cloudy weather limiting satellite views, or alternatively, could reflect a decrease in degassing.
• Over the last month, AVO has located about 60 to 80 earthquakes per week under Mount Spurr (time-series figure and map). The rate of shallow earthquakes (less than 2.5 miles, or 4 km, below sea level) is lower than in January and February. However, the rate of deep earthquakes (greater than 6 miles, or 10 km, below sea level) has been fairly constant, suggesting that magma remains active deep beneath the volcano.
• Ground deformation, or inflation, as measured by GNSS (GPS) has slowed or paused since about March 19. A similar pause occurred in Fall 2024.  
• 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. There have been no significant changes to the fumaroles within Crater Peak over the past month.

Interpretations and Hazards

The modest changes in monitoring data over the past month suggest that the likelihood of an eruption has decreased, and the inability to measure gas has made it more difficult to assess the current state of the volcano. However, the current level of unrest remains above background, monitoring data show the presence of magma under the volcano, and an eruption is still possible. If an eruption were to occur, an explosive eruption (or eruptions) like those that occurred in 1953 and 1992 is the most likely outcome.

Fluctuating rates of seismic activity and other monitoring data have occurred during past unrest periods, for example before the eruption of Redoubt Volcano in 2009. Such fluctuations make the outcome of the unrest less certain, and it is possible that the unrest could continue to decline, ending in no eruption, or it could increase again (see illustration).

We cannot assign an exact timeframe for when an eruption will occur, if it does. We expect to see additional changes to monitoring data prior to an eruption, 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 the Aviation Color Code and Alert Level for Mount Spurr. Alert level definitions can be found here: Alaska Volcano Observatory | Volcano Alert Levels. 

Current Hazards

While the likelihood of an eruption without additional warning is currently low, the volcano poses hazards for recreators on Mount Spurr. Elevated CO₂ and SO₂ concentrations may exist in low-lying areas around or downwind of the gas vents, such as within the craters atop Crater Peak and Spurr summit (but not in local communities). 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 (GPS) ground deformation stations, infrasound sensors, and web cameras. 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.  

At the current level of unrest, we plan to conduct routine overflights when weather permits to measure gas emissions, evaluate surface changes, and measure ground surface temperatures. We also plan to add additional monitoring instruments in response to the current unrest.

A new livestream of Mount Spurr, as viewed from Glen Alps, is available here: Mount Spurr Live Stream (ANCG).

Background information

For more details of the current period of unrest, please refer to the March 12 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 those from 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. Short-lived seismic swarms under Mount Spurr also occurred in 1979, 1982, and 1989 but did not result in eruption.

Primary hazards during future eruptions from either vent are ashfall that could be impactful to southcentral Alaska communities and airborne ash clouds that could temporarily disrupt air travel within Alaska and for thousands of miles downwind. 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

2025 AVO Fact Sheet about Mount Spurr: ic098.pdf

US Geological Survey information about volcanic ashfall hazards, impacts, preparedness, and mitigation measures: http://volcanoes.usgs.gov/ash/

If an eruption occurs:

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

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

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