USGS Volcanoes: Notices released in the last day.

Lava continues to slowly erupt within the summit crater at Great Sitkin Volcano. Cloudy conditions obscured satellite and webcam views of the volcano throughout the week. Seismic activity remains low, with the detection of occasional small volcanic earthquakes and seismic signals from small rockfalls within the crater.

The current lava eruption began in July 2021 and has filled most of the summit crater and advanced into the valleys below. There have been no explosions at Great Sitkin Volcano since an event in May 2021. The volcano is monitored using local seismic and infrasound sensors, satellite data, and web cameras, and regional infrasound and lightning networks. 

Signs of volcanic unrest at Shishaldin Volcano continue. Seismic and infrasound activity remains elevated, with numerous small earthquakes, frequent infrasound detections, and periods of volcanic tremor being observed throughout the week. Minor steaming was also consistently observed in daytime webcam views, and sulfur dioxide emissions were seen in satellite data most days. Barely elevated surface temperatures, probably related to the gas plume, were also seen occasionally at the volcano's summit in satellite views.

Shishaldin Volcano is monitored by local seismic and infrasound sensors, web cameras, and a telemetered geodetic network. In addition to the local monitoring network, the Alaska Volcano Observatory uses nearby geophysical networks, regional infrasound and lightning data, and satellite data to monitor the volcano. 

A small explosion occurred Sunday evening (February 22) at Semisopochnoi volcano and was detected by seismic and infrasound sensors on Semisopochnoi Island. Weather conditions were cloudy at the time, and no eruption cloud or deposits were detected subsequently in satellite or webcam data. Seismicity quickly returned to background levels, and no additional activity has been detected. This unheralded event posed little hazard, as it was localized to Mount Young, which last erupted in 2023. The north cone of Mount Young—the likely source of the explosion—hosts a crater lake and has vigorous fumaroles that produce a small gas plume. The Aviation Color Code and Volcano Alert Level at the volcano were not changed following this event and remain at GREEN and NORMAL.  

Semisopochnoi is monitored by a local seismic and infrasound network, local web cameras, regional lightning and infrasound sensors, and satellite data.   

Activity Update: All volcanoes in the Cascade Range of Oregon and Washington are at normal background activity levels. These include Mount Baker, Glacier Peak, Mount Rainier, Mount St. Helens, and Mount Adams in Washington State and Mount Hood, Mount Jefferson, Three Sisters, Newberry, and Crater Lake in Oregon.

Past Week Observations: Small earthquakes were detected at Mount Rainier, Mount St. Helens, and the Three Sisters region during the past week. Field crews repaired a monitoring station at Mount St. Helens. All monitoring data are consistent with background activity levels in the Cascade Range.

Activity Summary:

The Halemaʻumaʻu eruption of Kīlauea is paused. Episode 42 ended February 15 at 11:38 p.m. HST. Preliminary models suggest the likely forecast window for the onset of episode 43 lava fountaining is March 6-16.

No significant activity has been noted along Kīlauea’s East Rift Zone or Southwest Rift Zone.

A recap of episode 42 can be found in this Status Report.

Significant changes in activity between Daily Updates are posted here: https://www.usgs.gov/observatories/hvo/observatory-messages

Summit Observations:

Little-to-no glow could be seen from the vents last night. This morning, both vents remain quiet and emitting steady gas plumes. Low seismic tremor continues at the summit, punctuated by more energetic bursts every 5-10 minutes. These bursts have been associated with brief increases in gas emission and increases in glow from the vents at night. There were two earthquakes less than M1.0 located in the summit region in the past 24 hours.

Summit tiltmeters began recording mild deflation early yesterday morning, and this trend continue throughout the day. The UWD tiltmeter has recorded recovery of nearly 17.6 microradians of inflationary tilt since the end of episode 42, with about 0.2 microradians of net deflation over the past 24 hours.

Sulfur dioxide (SO₂) emission rates from the summit have been averaging 1000-1500 t/d, typical of these eruptive pauses. This morning, due to weak southerly winds, gas is rising slowly from the vents and blanketing the caldera and surrounding areas.
 

Rift Zone Observations:

Rates of seismicity and ground deformation remain very low in the East Rift Zone and Southwest Rift Zone. SO₂ emissions from the East Rift Zone remain below the detection limit.

Analysis:

The initial rapid rebound of tilt and glow from both vents indicate that another fountaining episode is likely. The overall inflationary trend has been interrupted by periods of no inflation or slight deflation recorded across all four summit tiltmeters that may impact the onset of episode 43 fountaining. Periods of weak deflation or no inflation have not been common in the early stages of repose between fountaining episodes. These changes in tilt rate are not predictable and create uncertainty in modeling the onset of episode 43 fountaining. Preliminary models suggest the forecast window for the start of episode 43 fountaining is likely between March 6 and March 16. Additional data are needed to more accurately determine the forecast window.

Kīlauea has been erupting episodically since December 23, 2024, primarily from two vents (north and south) in Halema‘uma‘u. Eruptive episodes, which generally last for less than 12 hours, are separated by pauses that can be as long as over two weeks.

HVO continues to closely monitor Kīlauea and is in contact with Hawai‘i Volcanoes National Park and the Hawai‘i County Civil Defense Agency about eruptive hazards.

Please see the Hawaiʻi Volcanoes National Park website for visitor information: https://www.nps.gov/havo/index.htm

Recap of episode 41:

A recap of episode 42 can be found in this Status Report.

Resources:

The following links provide more information about the current eruption that began on December 23, 2024:

• Eruption resources, including the most recent map and a timeline of eruption episodes since December 23, 2024: https://www.usgs.gov/volcanoes/kilauea/science/eruption-information
• Short messages tracking the evolution of the fountains and eruptive activity can be found here: https://www.usgs.gov/observatories/hvo/observatory-messages 
• Three Kīlauea summit livestream videos that show eruptive lava fountains are available here: https://www.youtube.com/@usgs/streams
• Note: The V3 camera is experiencing data issues and we have ordered a new camera to replace it following episode 42.
• Summit eruption webcams: https://www.usgs.gov/volcanoes/kilauea/summit-webcams
• Volcano Watch article on gas pistons: https://www.usgs.gov/observatories/hvo/news/volcano-watch-so-what-earth-or-least-kilauea-a-gas-piston

Hazards:

This episodic eruption is occurring within a closed area of Hawai'i Volcanoes National Park.

• Volcanic Gas: high levels of volcanic gas—primarily water vapor (H2O), carbon dioxide (CO2), and sulfur dioxide (SO2)—are continually released during an eruption. Emissions can remain locally hazardous in the areas immediately downwind of the vents, even when the vents are not actively erupting. SO2 reacts in the atmosphere to create vog (volcanic air pollution) downwind. SO2 and vog may cause respiratory and other problems at high concentrations. Further information on vog can be found at https://vog.ivhhn.org/
• Tephra: small glassy volcanic fragments—volcanic ash, pumice, scoria, Pele’s hair and reticulite—are created by the lava fountains. A combination of fountaining dynamics and wind conditions determines where tephra fall may occur for any given eruption episode. Larger particles fall near the vents while light particles may be wafted greater distances. These particles may be remobilized during windy conditions following recent eruptive episodes. Residents and visitors should minimize exposure to these fragments, which can cause skin, eye, and respiratory irritation. More information and guidance on tephra fall hazards is available at https://seagrant.soest.hawaii.edu/resource-and-guidance-for-volcanic-tephra-fall/
• Lava flows: lava on the floor of Halemaʻumaʻu crater and the southwest side of Kaluapele, Kīlauea's summit caldera, remains hot and may slowly move in the days immediately following an eruptive episode.

Other significant hazards exist around Kīlauea caldera from Halemaʻumaʻu crater wall instability, ground cracking, and rockfalls that can be enhanced by earthquakes. Close to the vents, the tephra material on the crater rim is prone to cracking, slumping, and small landslides that sometimes expose hot and molten material within. This underscores the extremely hazardous nature of Kīlauea's caldera rim surrounding Halemaʻumaʻu crater, an area that has been closed to the public since late 2007.

No signs of significant unrest were observed in satellite data or geophysical data. The last visible plume of discolored seawater was observed on January 9. Distant underwater pressure sensors near Wake Island (1,410 miles east of Ahyi) have also not detected any activity from the direction of Ahyi seamount for several weeks. Due to the apparent absence of activity, and the lack of local monitoring stations near Ahyi Seamount, the Aviation Color Code and Volcano Alert Level were lowered to UNASSIGNED on February 24. 

There are no local monitoring stations near Ahyi seamount, which limits our ability to detect and characterize volcanic unrest there. We will continue to monitor satellite and distal hydroacoustic data for additional evidence for, or escalation of, volcanic activity.

NORTHERN MARIANAS VOLCANOES
No definitive signs of unrest were detected at any other Northern Mariana Island volcanoes during the past week. 

Monitoring of Northern Mariana Islands Volcanoes

Northern Mariana Island volcanoes are monitored using seismo-acoustic sensors on Saipan, and by examining satellite imagery. We also use distant seismic stations in Guam and Chichijima, Japan, and hydroacoustic data from Wake Island, when available. 

This level of monitoring can detect significant volcanic activity in the CNMI but cannot provide advanced warning of eruptions.

Due to a lack of geophysical monitoring on any of the volcanic islands, the following volcanoes have alert levels of UNASSIGNED: Anatahan, Sarigan, Farallon de Pajaros, Supply Reef, Maug, Asuncion, Agrigan, Pagan, Almagan, and Guguan.