USGS Volcano Notice - DOI-USGS-AVO-2025-07-29T20:13:49+00:00

Summary

• Monitoring data show that the shallow magma intrusion beneath Mount Spurr has stalled, but that magma deeper below the volcano may still be active.
• The likelihood of an eruption is low but remains above background levels. We expect increases in seismic activity, gas emissions, surface deformation, and surface heating prior to an eruption, if one were to occur.

Recent observations

• Earthquakes: The rate of shallow earthquakes (less than 10 km, or 6 miles, below sea level) beneath Mount Spurr remains elevated and has fluctuated week-to-week. The overall trend has decreased since peaking in late December 2024. There is some regional seismicity currently occurring near Mount Spurr that is non-volcanic related to glacial activity at Pothole Glacier 10–15 km (6–9 miles) to the west.

  Small, deep earthquakes (greater than 6 miles, or 10 km, below sea level) continue at a low rate. The rate remains higher than what was observed in the several years before 2024. Rates like what is occurring now have been observed during other periods, including following the previous magma intrusion in 2004–2005.

   

• Gas emissions: Gas compositions and emissions rates from the summit crater of Mount Spurr and the Crater Peak flank vent have not changed significantly in recent months based on the most recent gas measurement flight on June 11, ongoing satellite monitoring of SO₂, and continuous gas measurements from a new sensor AVO installed on the rim of Crater Peak on June 19.

  CO₂ emissions from both vents remain above background levels. However similar values were reported with unrest in 2004–2006, when the volcano did not erupt. Over the last month, the continuous gas monitoring station on Crater Peak has detected CO₂ levels up to 19,000 parts per million.

  Likewise, SO₂ values at the summit remain above background, with a few weak signals observed over the past two months in satellite imagery. No SO₂ has been detected from Crater Peak. These measurements are also similar to 2004–2006 observations.

   

• Ground deformation: The upward and outward ground motion (inflation) observed in GNSS (GPS) and satellite-based radar (InSAR) data beginning in January 2024 stopped in mid-March 2025. The inflation that was observed is consistent with a volume increase in the shallow crust (about 2 km/1.2 miles below sea level) beneath the summit.

   

• Surface changes: No major surface changes have been observed at Mount Spurr summit or Crater Peak in recent months. Collapse of snow and ice into the summit crater has continued with an overall drop in the level of the lake, which remains mostly snow-and-ice covered. Webcam and satellite images have observed minor steaming from Mount Spurr summit in clear views over the past couple months, but this is weaker than during Spring 2025. Slight steaming from a fumarole within Crater Peak has only rarely been observed.

Interpretations and Hazards

Over the past several months, shallow seismic activity and visible signs of unrest, such as ice melt and other surface changes, have shown slowly decreasing trends, and ground deformation has not occurred since March. Taken together, these data show that the ascent of magma to shallow levels beneath the volcano’s summit region from January 2024 to March 2025 has stalled. Continuing low levels of gas emissions from the summit are consistent with degassing of this shallow magma body.

The continuing deeper earthquakes, coupled with ongoing degassing of CO₂ at the Crater Peak vent, suggest that a magma body may have also intruded under Crater Peak at deeper levels in the crust – possibly at 20 km (12 miles) below sea level. While there is no evidence that this deeper magma will rise up towards the surface and erupt, we continue to watch for signs that it might do so.

As was the case at Mount Spurr during the 2004–2006 unrest, most intrusions do not reach the surface. Fluctuating magma ascent, rates of seismic activity, and degassing are common at volcanoes and have occurred during past unrest periods with and without eruptions.

We see no sign that magma is continuing to rise into the shallow crust currently; however, renewed magma ascent remains possible. In that case, we anticipate corresponding changes in our monitoring data.

Current Hazards

While the likelihood of an eruption without additional warning is currently low, the volcano poses hazards for recreators on Mount Spurr. High levels of CO₂ detected on the rim of Crater Peak (up to 19,000 parts per million) suggest that hazardous amounts of CO₂ may be present within the crater, but not in local communities. As defined by NIOSH, the IDLH (Immediate Danger to Life and Health) value for CO₂ is 40,000 parts per million. CO₂ is a colorless and odorless gas, and hazardous areas of high CO₂ cannot be detected by sight or smell. Exposure to high concentrations can lead to headaches, dizziness, increased heart rate, difficulty breathing, unconsciousness, and death.

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.  

Livestreams of Mount Spurr are available from a station located approximately 8 miles south of Mount Spurr [Mount Spurr Live Stream (SPCL)] and as viewed from Glen Alps above Anchorage [Mount Spurr Live Stream (ANCG)].

Background information

Read past AVO Information Statements issued during the current unrest here.

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.