USGS Volcano Notice - DOI-USGS-AVO-2025-02-07T01:17:45+00:00

Summary

• Volcanic unrest continues at Mount Spurr, an ice- and snow-covered volcano located on the west side of Cook Inlet approximately 75 miles (120 km) west of Anchorage. The most likely cause is new magma beneath the volcano.
• The duration (10 months) and nature of the unrest suggest that an eruption is possible. The most likely site of an eruption is the Crater Peak vent, which erupted in 1992 and 1953. It is less likely that an eruption would occur from Spurr summit, which last erupted several thousand years ago. Past Crater Peak eruptions were often explosive, and far-traveled ash clouds and ashfall can be expected if an eruption occurs.
• We expect to see additional seismic activity, gas emissions, and surface heating, as well as changes to surface deformation prior to an eruption, if one were to occur. Such stronger unrest may provide days to a few weeks of additional warning, but that is not certain.
• AVO is undertaking repairs to the monitoring network this week to improve data return. The current data flow allows us to track activity and detect changes that would precede an eruption. An observation and gas measurement flight is scheduled for February 7. 

Observations and background

An increase in the number of earthquakes underneath Mount Spurr was first observed in April 2024 and continues. The rate of earthquakes has increased from an average of 30 per week from April to early October to a rate of 125 per week from early October to now. AVO has located over 2700 earthquakes during the unrest episode thus far. The largest of these earthquakes is a magnitude 2.9 that occurred on January 2, 2025.

Plot showing timeline of current unrest: https://avo.alaska.edu/image/view/196314

During the unrest episode, earthquakes have clustered at two depths: 0–6 miles (0–10 km) and 12–22 miles (20–35 km) beneath the volcano. Recently, a higher proportion of the earthquakes have occurred in the shallower zone. Shallow quakes are occurring underneath both vents of the volcano, Spurr summit and Crater Peak, though there has been a recent increase in the number of earthquakes under Crater Peak.

Map showing locations of earthquakes under Mount Spurr: https://avo.alaska.edu/image/view/196313

Starting at about the same time as the increase in earthquakes in April, we have detected steady surface deformation (“inflation”) using Global Navigation Satellite System (GNSS) stations on the flanks of the volcano. The total movement away from the volcano to date is about ~2.4 inches (~6 cm) at the closest GNSS station. Preliminary 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’s summit. Satellite radar data confirm the GNSS-detected uplift. This inflation may be caused by new magma, fluids, or gases.

In early summer 2024, a small lake appeared in the crater at Spurr summit consistent with a modest increase in heat flow. The lake has grown slowly to an area of approximately 5 acres through small collapses and melting of ice inside the crater. The lake is partially covered by ice and remains blue-green in color. Active steaming from summit area fumaroles continues and has not changed over this current period of unrest and remains similar to observations from recent years. Unlike at the summit, we have seen no significant surface changes at Crater Peak.

Two gas-measurement flights, on June 23 and December 18, detected low levels of sulfur dioxide and carbon dioxide gas that are similar to background levels measured in previous years. An additional measurement is planned for February 7.

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.  Winter weather can affect data transmission from our remote monitoring sites, and we continue to perform maintenance to mitigate these effects and ensure continual data flow.

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 brief, explosive, and produced columns of ash that rose up to 65,000 feet (20 km) above sea level and deposited minor ashfall in south-central Alaska (up to ¼ inch or 6 mm). The last known eruption from the summit of Mount Spurr was more than 5,000 years ago. In 2004, Mount Spurr experienced an episode of increased seismicity, surface uplift, and heating that melted a large hole in the summit ice cap and generated debris flows but no eruption occurred. Primary hazards during future eruptions include far-traveled ash clouds, ashfall, pyroclastic flows, and lahars or mudflows that could inundate drainages all sides of the volcano, but primarily on the south and east flanks. 

Interpretations and Hazards

The current unrest at Mount Spurr strongly suggests that new magma has intruded into the crust beneath the volcano. Based on our understanding of past eruptions and our analysis of the current episode of unrest, AVO considers the following future scenarios possible:

1)    Failed eruption. No eruption occurs as magma does not reach the surface. Earthquake activity, ground deformation, and surface heating slowly decrease over several weeks or months.

2)    Eruption of Crater Peak similar to 1953 and 1992. Unrest continues to escalate as magma moves towards the surface, culminating in an eruption that is like the ones that occurred in 1953 and 1992. One or more explosive events lasting one or a few hours would produce ash clouds carried downwind for hundred of miles, and the uninhabited area around Mount Spurr would be inundated by pyroclastic flows, mudflows (lahars), and ballistic showers.

3)    Eruption of Spurr summit. An eruption from the summit vent of Mount Spurr could occur, though there have been none in historical times. Such an eruption would likely be explosive and may also form lava flows. A summit eruption also would likely melt large volumes of glacial ice, which could lead to lahars and other hydrologic hazards.

Based on all available monitoring data, AVO regards scenarios one (no eruption) and two (eruption of Crater Peak) as equally likely at this time. Scenario 3 is considered less likely.

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 further increase in the number of earthquakes, onset of sustained seismic tremor, 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 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.  

AVO will continue to monitor the volcano closely. New data and observations may lead us to change our assessment. Any changes would be announced in a subsequent Information Release.

For more information, please see the following websites:

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

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

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

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

Forecasts of ashfall: http://www.weather.gov/afc