Alaska Volcano Observatory

Overview

• Seismic activity and sulfur dioxide (SO₂) emissions from Kupreanof Volcano have increased over the last few months.
• The cause of these increases is likely magmatic intrusion beneath Kupreanof Volcano.
• Data do not suggest an eruption is imminent and further signs of increased unrest would be expected prior to eruption

Earthquake Activity

An increase in seismicity beneath Kupreanof Volcano (https://avo.alaska.edu/volcano/kupreanof) began in February 2026. Multiple pulses of deep (>12 miles or 20 km) low-frequency earthquakes occurred in early February and early March. Shallow earthquake activity increased in early April, including several events with magnitudes greater than 2. The largest events to date occurred on April 12 and 22 and each had a magnitude of 3.1. Seismicity during the second half of April and early May has consisted of intermittent shallow earthquakes, mostly less than magnitude 2.5, along with occasional deep low-frequency events.

AVO does not maintain a local monitoring network at Kupreanof Volcano, and seismicity is therefore detected using regional stations. The closest functioning seismometer is currently located 17 miles (27 km) to the east at Veniaminof Volcano. The lack of a local monitoring network and the limited number of regional stations mean that smaller events (magnitudes less than 2) are often not detected or located, and earthquake locations have relatively large uncertainties.

Gas Emissions

Since April 4, sulfur dioxide (SO₂) emissions from Kupreanof Volcano have been seen in satellite data on 8 occasions with emission rates of ~100 to 1,000 tons per day. While Kupreanof Volcano is known to have persistent gas emissions from a fumarole field active just west of the summit, SO₂ emissions from Kupreanof Volcano have not been seen previously in satellite data. Airborne gas surveys conducted by helicopter in 2019 and 2022 measured less than 100 tons per day. While some volcanic gases can originate from crustal sources such as carbonate rocks or hydrothermal systems, SO₂ is almost always associated with direct degassing from magma.  Collectively these observations suggest an increase to above background levels in volcanic gas emissions, likely due to intrusion of new magma beneath Kupreanof Volcano.

Interpretations and Hazards

The earthquake types and locations, along with the observed SO₂, suggest magma has likely intruded at depth beneath Kupreanof Volcano and has migrated to shallower levels (<3 miles or 5 km), activating a fumarole field at about 5,000 ft elevation west of the summit. Because of this, if eruptive activity does occur, it may be either hydrothermal or magmatic. Intrusions of new magma under volcanoes do not always result in volcanic eruptions. The earthquake activity and gas emissions at Kupreanof Volcano may cease with no eruption occurring. If the magma rises closer to the surface, this will likely lead to increased unrest, such as a change in the rate and style of earthquake activity, surface heating, and increased gas emissions. Therefore, it is very likely that if an eruption were to occur it would be preceded by additional signals that would allow advance warning.