USGS Volcano Notice - DOI-USGS-AVO-2025-05-28T15:46:23+00:00

Summary 

• The magma intrusion beneath Mount Spurr has stalled, and the likelihood of an eruption continues to gradually decline. 
• The volcano remains at an elevated state of unrest, and an explosive eruption like those that occurred in 1953 and 1992 is still possible. 
• We expect additional increases in seismic activity, gas emissions, surface deformation, and surface heating prior to an eruption, if one were to occur. These changes may provide days to weeks of warning.

Recent observations 

• Earthquakes: Earthquake activity beneath Mount Spurr remains elevated. Following a steady decline from late March through April, shallow earthquake activity has increased in the past 2 weeks to ~March levels of about 100 events per week. The rate of deep earthquakes (greater than 6 miles, or 10 km, below sea level) continues unchanged, suggesting that magma remains active deep beneath the volcano. 
• Gas: A gas-measurement flight was conducted last week on Friday May 23, which measured gases from both the summit crater of Mount Spurr and the Crater Peak flank vent. Measured emissions were slightly lower, but within the uncertainty bounds of those measured during the last gas flight on April 24. CO₂ values from both vents remain above background levels, but similar values were reported with unrest in 2004-2006, when the volcano did not erupt. Likewise, SO₂ values at the summit are above background, but similar to 2004-2006 observations. No SO₂ was detected from Crater Peak. In addition, satellites have regularly detected low-level SO₂ from Mount Spurr in the past several weeks. 
• Ground deformation: Ground deformation has paused since mid-March, suggesting the shallow magma intrusion has stalled. Recent data from a single station over the past 2 weeks shows radial outward motion from the volcano, but this trend is the result of seasonal environmental effects unrelated to volcanic activity. This is supported by observations from previous years when vertical deformation is related to seasonal changes and not volcanic activity. 
• Surface changes: Snow and ice continue to collapse into the summit crater lake that formed during this period of unrest, and steam emissions within and around the summit crater continue unchanged. There have also been no significant changes to the fumaroles within Crater Peak over the past month.

Interpretations and Hazards 

Over the past month, various monitoring data show no definite trends, which increases the overall uncertainty of eruption. Earthquake activity and gas emissions continue to be above background levels, but activity is not currently uniformly increasing, nor is an explosive eruption a certainty.  

The pause in deformation suggests that the ascent of magma to shallow levels beneath the volcano over the past 17 months has stalled. This intrusion of magma could still lead to an eruption, but gas and earthquake activity do not clearly indicate an unstable or pressurizing system. As was the case at Mount Spurr during the 2004–2006 unrest, most intrusions do not reach the surface to erupt. However, a similar pause occurred in fall 2024, and it remains possible that magma ascent could resume. 

Fluctuating magma ascent, rates of seismic activity and degassing are common at volcanoes and have occurred during past unrest periods with and without eruptions. Such fluctuations make both the timing and outcome of unrest less certain, and it is possible that activity could continue to decline, ending in no eruption, or it could increase again. 

If an eruption were to occur, an explosive eruption like those that occurred in 1953 and 1992 is the most likely outcome. 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, AVO plans 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 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 prior Information Statements on April 17 and March 12.  

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/