USGS Volcanoes: Notices released in the last day.

Slow lava effusion continues within the Great Sitkin summit crater. Over the past day, seismic data recorded rockfalls from the growing lava dome. No significant activity was observed in cloudy web camera and satellite views.  

The current lava eruption began in July 2021 and, since then, has filled most of the summit crater and advanced into 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, webcams, and regional infrasound and lightning networks.

Unrest persists at Shishaldin Volcano, with seismic and infrasound activity remaining elevated over the past day. No significant activity was observed in cloudy web camera and satellite views.  

Local seismic and infrasound sensors, web cameras, and a geodetic network are used to monitor Shishaldin Volcano. In addition to the local monitoring network, AVO uses nearby geophysical networks, regional infrasound and lightning data, and satellite images to detect eruptions. 

Overview:

The eruption at the summit of Kīlauea is currently paused. The forecast window for episode 46, based on tilt data, suggests that lava fountaining will occur again sometime between Tuesday, May 5 and Friday, May 8. This window may be adjusted based on continuing observations.

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

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

Summit Observations:

Consistent glow was observed from the south vent on webcams overnight, and intermittently from the north vent. Both vents, especially the south vent, produced occasional bursts of large flames, likely caused by the ignition of volcanic gases escaping the vent.

Seismic tremor at the summit continued to ease slightly over the past day. Tremor pulses have weakened and become less defined, but earthquake activity remains elevated. There were 25 small earthquakes recorded across the summit in the past day, located within Halemaʻumaʻu crater. All 25 earthquakes were less than 2.0M and were shallow, less than 3 miles (5 km) depth. The largest earthquake within Kilauea summit was 1.95M at 0.5km depth. Similar, small earthquake swarms have been concentrated under the caldera for the past month. 

During episode 45, the Uēkahuna tiltmeter (UWD) recorded about 16.0 microradians of deflationary tilt. Currently, UWD is recording positive tilt at a more rapid rate than the previous two days. Since the end of episode 45, UWD has recorded a total of 11.0 microradians of inflationary tilt. Fluctuations in tilt are normal during eruptive pauses.

With the eruption now paused, the SO₂ emission rate is likely varying within a typical range of 1,000 to 5,000 tonnes per day. 

Rift Zone Observations:

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

Analysis:

The rapid return of inflationary tilt and strong glow from both Halemaʻumaʻu eruptive vents indicates that another lava fountaining episode is likely. The current forecast window is based on data from summit tiltmeters and suggests that episode 46 will occur between Tuesday, May 5 and Friday, May 8. This window may be adjusted based on changes to the rate of summit inflation as measured by summit tiltmeters.

Kīlauea has been erupting episodically since December 23, 2024, from two vents (north and south) in Halema‘uma‘u. Lava fountaining episodes, which generally last for less than 12 hours, are separated by pauses that can be longer than three 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 45:

Episode 45 of the ongoing Halemaʻumaʻu eruption began at 1:34 a.m. HST on April 23 and ended at 10:01 a.m. on the same day. Lava fountaining occurred from the north vent and reached a maximum height of 900 feet (270 meters). Prevailing winds were from the north and northeast, and no significant tephra fallout was reported at visitor areas of Hawai'i Volcanoes National Park or on county roads. However, small particles were reported in communities farther downwind to the southwest. 

A full summary of episode 45 can be found in a Status Report here: https://volcanoes.usgs.gov/hans-public/notice/DOI-USGS-HVO-2026-04-23T19:07:34+00:00

Resources:

NOTE: HVO’s monitoring network is mostly recovered from recent power- and storm-related outages. Several summit stations, including the SDH tiltmeter, will remain offline until we are able to re-establish access across the deep tephra field south of the caldera.

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 lava fountains and eruptive activity can be found here: https://www.usgs.gov/observatories/hvo/observatory-messages
• Three Kīlauea summit livestream cameras that show eruptive lava fountains are available here: https://www.youtube.com/@usgs/streams
• 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 eruptive 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.

Summary

Yellowstone Caldera activity remains at background levels, with 97 located earthquakes in April (largest = M2.5). Deformation measurements indicate no significant uplift or subsidence of the caldera or north caldera rim since January 2026.

Recent Work and News

Echinus Geyser, in Norris Geyser Basin, reawakened from a several-year slumber in February, with about 40 eruptions that month, but the geyser had only four eruptions in April.  At Black Diamond Pool in Biscuit Basin (site of a hydrothermal explosion in 2024), two eruptions were recorded during the month by acoustic, seismic, and temperature measurements, occurring on April 28 and 29.  The latter event was the largest recorded since monitoring instruments were installed in the area during summer 2025.  In April, geologists visited the park to conduct field investigations of geyser activity.  Planned field work in May includes deployment of ground deformation equipment, geochemical sampling, and reconnaissance work for new monitoring stations.  The biennial Yellowstone Volcano Observatory coordination meeting will also take place in May.

Seismicity

During April 2026, the University of Utah Seismograph Stations, responsible for the operation and analysis of the Yellowstone Seismic Network, located 97 earthquakes in the Yellowstone National Park region. The largest event of the month was a microearthquake of magnitude 2.5 located about 16 miles south-southeast of Mammoth Hot Springs in Yellowstone National Park on April 14 at 2:13 a.m. MDT.

April seismicity in Yellowstone was marked by a swarm of 16 earthquakes that occurred approximately 16 miles south-southeast of Mammoth Hot Springs in Yellowstone National Park during April 13–14. The largest earthquake in the sequence was also the largest in April (described above).

Earthquake activity in Yellowstone is at background levels.

Ground Deformation

Continuous GPS stations indicate that the uplift that started in July 2025 on the north caldera rim ceased by mid-January 2026.  In Yellowstone Caldera, continuous GPS data recorded little net change since December.  This is the first winter since 2015–2016 with no caldera subsidence, suggesting a subtle change in the style of caldera deformation.

An example of GPS data can be found at http://www.unavco.org/instrumentation/networks/status/pbo/data/NRWY (click on Static Plots / Cleaned)