USGS Volcanoes: Notices released in the last day.

Lava continues to erupt slowly within the summit crater of Great Sitkin Volcano, with satellite-based radar showing continued growth of the south lobe of the lava dome. A few small earthquakes were detected in the past day. Slightly elevated surface temperatures observed in satellite views.

The current eruption began in July 2021. Since then, lava flows have 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 continues with elevated seismic activity with small earthquakes and tremor detected over the past day. Steam emissions could be seen in web camera views over the past day. No activity observed in 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 summit eruption of Kīlauea in Halemaʻumaʻu is paused following lava fountaining in episode 55 on October 17, 2026. Summit tiltmeter data showed re-inflation began immediately following the end of episode 55 and steady, slow inflation is continuing. Assuming magma chamber inflation has returned to the pattern established in the past, the preliminary forecast for episode 56 fountaining to occur is between October 29 and November 5, 2026. 

Summit Observations:

Glow was again observed overnight from both vents in Halema'uma'u with weak intermittent glow from the north vent and strong continuous glow from the west vent. No glow was visible from the south vent, which was covered in a layer of tephra during episode 55. 

Continuous, low-level seismic tremor has been present over the past day, which is typical during inter-episode pauses. Two earthquakes were recorded in the summit area in the past 24 hours. 

Steady inflationary tilt continued over the past 24 hours. The UWD tiltmeter has recovered at total of 10.8 microradians of inflationary tilt since the end of episode 55. Deflationary tilt measured at a summit tiltmeter at Uēkahuna (UWD) totaled 21 microradians during episode 55. Post-fountaining tilt patterns have been similar to those seen prior to episode 54.

During inter-episode pauses, the sulfur dioxide (SO₂) emission rate from the summit typically varies between 1,000 to 5,000 tonnes per day. Winds are forecast from the northeast, which are pushing the gas plume to the southwest over the Kaʻū Desert this morning.  

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. No significant ground deformation was recorded in either rift zone.

Analysis:

Initial magma chamber reinflation followed the normal, predictable pattern seen after most fountain episodes. Inflation remains steady with the rate of inflation slowing gradually, which is the normal pattern during the start of repose periods between fountains.  Based on modeling of the inflationary tilt observed at summit tiltmeters, the preliminary forecast is for episode 56 to occur between October 29 and November 5, 2026. However, given the differences in the run-up to episode 55, there is uncertainty in whether inflation will remain regular and predictable allowing forecasts with reasonable precision. 

Kīlauea has been erupting episodically between December 23, 2024, and August 25, 2026, from two vents (north and south) in Halema‘uma‘u at the summit. Lava fountaining episodes generally lasted for less than 12 hours and were separated by pauses of two or more weeks. The onset of episode 55 departed from the pattern established from previous episodes, with summit tiltmeters recording inflationary tilt indicating additional pressurization of the summit magma chamber beyond levels typically seen before fountaining. The prolonged period of inflationary tilt was not steady, being marked by extended periods of irregular deflationary tilt or no tilt. The episode was also preceded by 39 days of intermittent overflows, a record for the length of precursory activity prior to fountaining. During this prolonged interval, a series of short-lived vents opened within Halemaʻumaʻu and a shallow dike was emplaced beneath Kaluapele. 

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. Kīlauea volcano alert level and aviation color code remain at ADVISORY/YELLOW. 

Summary of episode 55:

A detailed account of episode 55 is given in the HVO Daily Update for October 17: https://volcanoes.usgs.gov/hans-public/notice/DOI-USGS-HVO-2026-10-17T15:47:29+00:00  

• Episode 55 of the ongoing Halemaʻumaʻu eruption began at 3:19 a.m. HST on October 17 and ended abruptly at 9:03 a.m. HST on the same day.
• The maximum lava fountain height was approximately 720 feet (220 meters) above ground level from the north vent. The south and west vents never fountained during this episode but did produce overflows prior to the fountaining episode.
• The maximum plume height was approximately 25,000 (7,500 meters) above mean sea level. 
• Tephra fall was restricted mostly to the closed area of Hawaiʻi Volcanoes National Park, southwest of the active Halemaʻumaʻu vents.  

Other notices related to episode 55:

• VAN VONA issued at end of eruption: USGS Volcano Notice - DOI-USGS-HVO-2026-10-17T19:04:00+00:00
• VAN VONA issued at peak fountain heights: USGS Volcano Notice - DOI-USGS-HVO-2026-10-17T14:51:56+00:00
• VAN VONA issued at onset of episode 55 fountaining:  USGS Volcano Notice - DOI-USGS-HVO-2026-10-17T13:25:52+00:00
• NOTE: Changes in the fountain activity have also been posted here: https://www.usgs.gov/observatories/hvo/observatory-messages

Hazards:

Eruptive activity since December 2024 has been occurring within a closed area of Hawai'i Volcanoes National Park. However, recent intrusions highlight that the location of eruptive activity could change. Intrusions can also be hazardous with potential to cause earthquakes, ground cracks, and small landslides. The primary hazards at Kīlauea due to eruptive activity and/or intrusions are:

• 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/ and https://vog.ivhhn.org/sites/default/files/PelesHair_FAQs_v2.pdf 
• Lava flows: Hawaiian lava flows generally advance slowly downslope but destroy everything in their paths. Lava flows that erupt within Halemaʻumaʻu remain confined to the crater, including those during the eruption that started in December 2024. However, intrusive activity could result in lava flows outside of Halemaʻumaʻu. Hazards associated with active or recent lava flows include hot and glassy (sharp) surfaces that can cause serious burns, abrasions, and lacerations upon contact with unprotected or exposed skin; uneven and rough terrain can lead to falls and other injuries; hot temperatures that can cause heat exhaustion or dehydration, or in heavy rain can produce steamy ground-fog that can be acidic, severely limiting visibility and sometimes causing difficulty breathing.
• Earthquakes and ground cracks: Shallow magma movement and eruptions can produce minor to severe ground fractures and subsidence features. These ground cracks can continue to widen and offset as magma migration continues, may have unstable overhanging edges, and should be avoided. Other significant hazards exist around Kīlauea caldera from Halemaʻumaʻu crater wall instability, ground cracking, and rockfalls that can be enhanced by earthquakes.

Additionally, 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.

Small plumes of discolored water were seen in the ocean above Ahyi on October 16 and 21 this past week. Discolored greenish water was visible drifting several hundred meters from the summit of Ahyi. These plumes are likely associated with degassing and hydrothermal activity at the summit of the underwater volcano. No notable activity was detected in distal geophysical monitoring data over the past week. 

Eruptive activity at Ahyi seamount may present a hazard to mariners in the water above and near the volcano. The summit has shallowed over the course of previous eruptions to 180 feet (55 m) below sea level, but the lack of local real-time data means we are unable to forecast or warn of impending eruptions. We will continue to monitor satellite and distal hydroacoustic data for additional evidence for, or escalation of, volcanic activity.

NORTHERN MARIANAS VOLCANOES
No signs of unrest were detected at any Northern Mariana Island volcanoes besides Ahyi Seamount 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.