USGS Volcanoes: Notices released in the last day.

Lava continues to slowly erupt within the summit crater at Great Sitkin Volcano. Minor lava dome growth and rockfalls down the east and south sides of the lava field continue. Satellite and webcam views were cloudy throughout the week. Seismic activity remains low, with 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.

Volcanic unrest at Shishaldin Volcano continues. Seismic and infrasound activity remain elevated, with numerous small earthquakes, frequent infrasound signals, and volcanic tremor recorded throughout the week. Minor steaming from the summit was visible in webcam images when conditions were clear. Elevated sulfur dioxide gas emissions were detected in satellite data most days this week.

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.

Slow lava effusion continues within the Great Sitkin summit crater. Over the past day, seismic data recorded rockfalls from the growing lava dome. Web camera and satellite views were cloudy.  

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. Satellite and web camera views of the volcano were obscured by clouds.  

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. 

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 and Mount St. Helens during the past week. All monitoring data are consistent with background activity levels in the Cascade Range. Several staff participated this week in outreach and execution of a large lahar evacuation drill in the Puyallup River Valley near Mount Rainier.

Overview:

Episode 45 of lava fountaining in Halemaʻumaʻu at the summit of Kīlauea began at 1:34 a.m. HST on April 23, after two days of precursory activity, and ended at 10:01 a.m. HST the same day. The eruption is currently paused. 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 

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:

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. No significant tephra fallout was reported at visitor areas of Hawai'i Volcanoes National Park or on county roads, but small particles were reported in communities farther downwind to the southwest. 

Overnight, glow was visible from both eruptive vents, with the south vent producing occasional flames. Lava flows on the Halemaʻumaʻu crater floor remained incandescent and continued to slowly spread towards the east through yesterday and slowing down overnight. Incandescence on the crater floor for several more days.

Seismic tremor continues during the current pause, with bursts of tremor every 1–10 minutes that are typical after the end of fountaining and are likely associated with gas pistoning cycles in the eruptive vents. Earthquake activity at the summit during and after episode 45 has been low; with seven small earthquakes recorded in the past day.

The Uēkahuna tiltmeter (UWD) recorded about 16.0 microradians of deflationary tilt during episode 45. Since the end of fountaining, summit inflation has resumed, with the same tiltmeter recording about 3 microradians of inflationary tilt as of this morning. 

Emissions during episode 45 were likely similar to those measured during episode 44, when HVO was able to measure a sulfur dioxide (SO₂) emission rate of 208,000 tonnes per day during lava fountaining. With the eruption now paused, the SO₂ emission rate is likely now 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. At this time, there is not enough information to develop a detailed forecast window for the next episode.

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

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.

Activity Summary: 

• Episode 45 of the ongoing Halemaʻumaʻu eruption ended abruptly at 10:01 a.m. HST on April 23, 2026, after 8.5 hours of continuous lava fountaining. The eruption is currently paused.
• No significant tephra fallout was reported at visitor areas of Hawaiʻi Volcanoes National Park or on county roads. Winds blew the plume to the south at low altitudes and to the southwest at higher altitudes, with minor amounts of ash fall reported in the community of Pāhala located about 20 miles (32 kilometers) to the southwest of the eruptive vents in Halemaʻumaʻu.

Episode 45 Chronology:

Episode 45 of lava fountaining in Halemaʻumaʻu at the summit of Kīlauea began at 1:34 a.m. on April 23 and stopped at 10.01 a.m. HST the same day, after 8.5 hours of continuous lava fountaining from the north vent. The south vent never fountained during this episode, but it displayed periodic gas jetting and flames. The highest peak of instantaneous effusion rate of just over 390 cubic yards (300 cubic meters) per second occurred around 3:00 a.m. HST on April 23. Episode 45 saw an average effusion rate of 220 cubic yards (170 cubic meters) per second, with an estimated 6.8 million cubic yards (5.2 million cubic meters) of lava erupted and covering about 50% of the Halemaʻumaʻu crater floor. The Uēkahuna tiltmeter (UWD) recorded about 16.0 microradians of deflationary tilt during episode 45.

Episode 45 lava fountaining began at 1:34 a.m. HST on April 23, 2026, just over two days after the onset of precursory lava overflows on the evening of April 20. There were only 3 precursory overflows until about 9:30 p.m. when a series of overflows began from the south vent, accompanied by low dome fountaining. At 1:00 a.m. activity picked up at the north vent, with low fountaining. Over the next half hour, activity continued to increase at the north vent, while decreasing at the south vent. At 1:34, a sharp increase in seismic tremor and deflationary tilt at summit tiltmeters marked the start of the high fountaining episode. North vent fountains grew steadily until their peak at 3:00 a.m. HST. The main body of the fountains reached heights of at least 700 ft (220 meters), however wispy trails at the top of the fountain occasionally reached above 1000ft (300 meters). After their peak, fountain height gradually decreased and were about 330 feet (100 meters) high just before the episode ended abruptly at 10:01 a.m. HST.  

The lava fountain produced significant heat and ash, feeding a plume that reached a maximum height of about 20,000 feet (6,000 meters) above sea level. North to northeastern winds directed the plume and tephra fall to the south and southwest of Halemaʻumaʻu. At 3:22 a.m., the National Weather Service issued an ashfall advisory for communities in the south of the Big Island that has been cancelled with the end of the episode. No significant tephra fallout was reported at visitor areas of Hawai'i Volcanoes National Park or on county roads, but some Pele's hair and fine ash was reported falling in communities at the southern end of the island. 

Earthquake activity during episode 45 was minor, and did not include a repeat of the seismicity observed at the end of episode 44. Levels of seismic tremor rose and fell with fountaining and are now at typical levels for eruption pause. 

Resources:

• Additional short messages during episodes: https://www.usgs.gov/observatories/hvo/observatory-messages   
• Timeline of eruptive episodes since December 23, 2024: https://www.usgs.gov/volcanoes/kilauea/science/eruption-information 
• Three Kīlauea summit livestream videos: https://www.youtube.com/@usgs/streams 
• Report tephra fall: https://hawaiiash.science/report_form 
• Hawaiʻi Volcanoes National Park Information https://www.nps.gov/havo/planyourvisit/conditions.htm
• County of Hawaii Hazard Impact Map: https://www.arcgis.com/apps/dashboards/5865229bcba74020992b372ef18b6f17

Hazard Analysis: 

• Volcanic Gas: Water vapor (H₂O), carbon dioxide (CO₂), and sulfur dioxide (SO₂) are continuously released during an eruption. SO₂ reacts in the atmosphere to create the visible haze known as vog (volcanic smog) downwind, which may cause respiratory and other problems. 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 the links below:
  • https://seagrant.soest.hawaii.edu/resource-and-guidance-for-volcanic-tephra-fall/  
  • https://vog.ivhhn.org/sites/default/files/PelesHair_FAQs_v2.pdf

• Lava flows: Generally advance slowly downslope, and during this eruption flows have been confined to Halemaʻumaʻu crater and the southwest side of Kaluapele, Kīlauea's summit caldera. 

  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.

Episode 45 of the ongoing Halemaʻumaʻu eruption ended abruptly at 10:01 a.m. HST on April 23, 2026, after 8.5 hours of continuous lava fountaining. Due to reduced ground and aviation hazards, the USGS is dropping the Volcano Alert Level from WATCH to ADVISORY and the Aviation Color Code from ORANGE to YELLOW.  Additional details on this eruptive episode will be provided in the next official report.

• All eruptive vents and lava flows are confined to Halemaʻumaʻu crater within Hawaiʻi Volcanoes National Park. Tephra fall from volcanic ash clouds is greatest within 3 miles (5 km) of the vents, lighter ash and Pele's Hair may stay suspended for large distances from the vents.
• Timeline of eruptive episodes since December 23, 2024: https://www.usgs.gov/volcanoes/kilauea/science/eruption-information 
• Three Kīlauea summit livestream videos are available here: https://www.youtube.com/@usgs/streams 
• Additional short updates shared during the episode can be found here: https://www.usgs.gov/observatories/hvo/observatory-messages 

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

Monitoring of Northern Mariana Islands Volcanoes

Typhoon Sinlaku has caused extensive destruction to the infrastructure on the island of Saipan. All data feeds from seismic and acoustic sensors on the island are now unavailable, and there are no ground-based instruments to detect significant explosive activity in the region, should it occur. It is unclear when connections to these sensors will be restored.

The USGS will continue to monitor satellite images and distant hydroacoustic and seismic sensors for any signs of volcanic activity in the CNMI. This level of monitoring can detect significant volcanic activity but cannot provide advance 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.