USGS Volcanoes: Notices released in the last day.

Lava continues to erupt slowly within the summit crater of Great Sitkin Volcano. Satellite radar imagery confirms slow lava growth over the last 2 weeks. A few small earthquakes were detected at the volcano over the last day. Clouds obscured other satellite and webcam views of the volcano.

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 at Shishaldin Volcano has declined slowly over the last 4 months. Current activity is near background for this volcano, and does not indicate increased likelihood of an eruption. Reflecting these conditions, the Aviation Color Code and Volcano Alert Level are being lowered to GREEN and NORMAL.

The current period of unrest began in August 2025 with increased sulfur dioxide emissions, seismic tremor, and infrasound signals consistent with explosions deep in the vent. This activity peaked between December 2026 and June 2026 with signals consistent with magma rising to shallow levels in the conduit. At no point was lava or eruptive activity observed at the surface. 

The decline in activity observed in the last 4 months is consistent with magma withdrawing to deeper levels under the volcano. Shishaldin Volcano remains an active open-system volcano, with steam and gas emissions, as well as low level seismicity and infrasound still seen. Future eruptions will occur at the volcano, and these can occur with little to no warning.  

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 data to detect eruptions.

To view information about Shishaldin Volcano: https://www.avo.alaska.edu/activity/Shishaldin.php

Overview:

The summit eruption of Kīlauea in Halemaʻumaʻu remains paused. Slow, steady inflation continues at the summit. Based on current deformation trends and assuming magma chamber inflation continues to follow similar patterns to those established during episodes prior to 54, the forecast window for episode 56 fountaining is November 4-7, 2026.

Summit Observations:

Continuous strong orange glow and occasional spatter was seen from both vents last night. Although visibility was somewhat low in webcams due to atmospheric conditions, increases to bright yellow were suggestive of intermittent flames in the combined southwest vent. 

Low-moderate seismic tremor continues with periodic pulses giving way to more continuous tremor yesterday evening. Tremor pulses are typically associated with increased glow and gas emissions. There were four earthquakes recorded at the summit in the past 24 hours, all of which occurred in the southern part of Kaluapele (Kīlauea caldera), with the largest being M2.2.

Summit tiltmeters have recorded an overall positive trend since the end of episode 55, with several small, short-term oscillations. The general pattern remains consistent with post-fountaining re-inflation observed during previous inter-episode pauses. The Uēkahuna tiltmeter (UWD) has recorded an increase of approximately 0.4 microradians in the past 24 hours for a total of 17.8 microradians of tilt recovered since the end of episode 55. 

Sulfur dioxide (SO₂) emission rates during inter-episode pauses typically range from 1,000 to 5,000 tonnes per day. Strong trades this morning are carrying volcanic gases southwest toward Kaʻū.

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:

Following episode 55 on October 17, 2026, summit tiltmeters initially recorded a typical post-fountaining recovery, with a steady upward trend that gradually slowed and was interrupted by several small fluctuations. Tilt has continued to increase slowly following a brief negative trend on October 26. While the there have been minor fluctuations in tilt over the past week, the overall tilt pattern is a slow, steady increase. The fluctuations in tilt rate result in adjustments to the modeled forecast window for episode 56 fountaining, which is now November 4–7, 2026. Given the unusual buildup to episode 55, uncertainty remains as to whether summit deformation will continue to follow a sufficiently consistent pattern to allow for precise forecasting of the next episode.

Kīlauea has been erupting episodically since December 23, 2024, from two primary vents (north and south) within Halemaʻumaʻu at the summit. Lava fountaining episodes generally last less than 12 hours and are separated by pauses of two or more weeks. The buildup to episode 55 differed substantially from previous episodes, with summit tiltmeters recording positive tilt beyond levels typically observed before fountaining, suggesting continued pressurization of the summit magma chamber. This prolonged buildup was punctuated by extended periods of negative or relatively stable tilt, rather than the more consistent upward trends observed before earlier episodes. Episode 55 was also preceded by 39 days of intermittent lava overflows, the longest period of precursory activity recorded before a fountaining episode in the current eruption. During this interval, several short-lived vents opened within Halemaʻumaʻu, and a shallow dike was emplaced beneath Kaluapele.

HVO continues to closely monitor Kīlauea and remains in contact with Hawaiʻi Volcanoes National Park and the Hawaiʻi County Civil Defense Agency regarding eruptive hazards. Kīlauea's 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.

Yellowstone Caldera activity remains at background levels, with 66 located earthquakes in October (largest = M2.0). Deformation measurements indicate no significant uplift or subsidence of the caldera or north caldera rim for the past several months. Giant Geyser, in Upper Geyser Basin, erupted three times in October.

Recent Work and News

Hydrothermal activity in Yellowstone National Park during the month of October included an eruption of Echinus Geyser (Norris Geyser Basin) on October 26.  Giant Geyser (Upper Geyser Basin)—the second tallest geyser in the park—erupted on October 5, 13, and 22.  In addition, the small pool of hot water that formed via collapse in Biscuit Basin after the June 13, 2026, hydrothermal explosion had at least two small eruptions.  Steamboat Geyser, in Norris Geyser Basin, was characterized by minor eruptions and has only had one major eruption thus far in 2026.

Seismicity

During October 2026, the University of Utah Seismograph Stations, responsible for the operation and analysis of the Yellowstone Seismic Network, located 66 earthquakes in the Yellowstone National Park region. The largest event of the month was a micro earthquake of magnitude 2.0 located about 15 miles south of West Thumb, Yellowstone National Park, on October 4 at 5:32 p.m. MDT.

There were no swarms identified during October.

Earthquake activity in Yellowstone is at background levels.

Ground Deformation

Data from continuous GPS stations indicate little net deformation of the caldera or north caldera regions over the past several months.  Subtle variations in ground motion are probably caused by seasonal changes, especially in groundwater conditions.

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