USGS Volcano Notice - DOI-USGS-HVO-2025-09-29T17:52:38+00:00

Activity Summary:

Episode 33 lava fountaining ended on September 19. Glow from both north and south vents was observed overnight, with nine overflows from the north vent. The summit is reinflating, and models indicate that episode 34 is most likely to start today or tomorrow (September 29 or 30) with small chance of October 1. No significant activity has been noted along Kīlauea’s East Rift Zone or Southwest Rift Zone.

Summit Observations:

Episode 33 lava fountaining ended at 12:08 p.m. HST on Friday, September 19. The UWD tiltmeter shows that the summit has been reinflating since the end of the fountaining episode, with 16 microradians of inflationary tilt. Overnight, HVO webcams showed persistent glow from north vent punctuated by 9 gas piston cycles of overflow and drainback at 9:47 p.m., 2:15 a.m., 4:16 a.m., 5:12 a.m., 6:18 a.m., 6:32 a.m., 7:00 a.m., 7:40 a.m., and 8:14 a.m., each lasting 5-10 minutes.  There was intermittent strong glow from south vent. This morning, the caldera is quiet with a passive outgassing plume rising from the vents. 

Elevated degassing continues from the vent. Average sulfur dioxide (SO₂) emission rates during pauses are typically 1,200 to 1,500 t/d, though emission rates can vary on short time scales. Wind at Sand Hill, just south of Halemaʻumaʻu are blowing from the northeast direction, which suggests that volcanic gas emissions and volcanic material may be distributed southwest across the Ka'u desert within Hawaiʻi Volcanoes National Park.

Strands of volcanic glass known as Pele’s hair are present throughout the summit area of Hawaiʻi Volcanoes National Park and surrounding communities and can be remobilized by wind even after lava fountaining has ceased.

• 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
• Three Kīlauea summit livestream videos 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 pistoning: https://www.usgs.gov/observatories/hvo/news/volcano-watch-so-what-earth-or-least-kilauea-a-gas-piston

Rift Zone Observations:

Rates of seismicity and ground deformation remain very low in the East Rift Zone and Southwest Rift Zone, with no significant earthquake activity in the past 24 hours outside of the summit. Sulfur dioxide (SO₂) emissions from the East Rift Zone remain below the detection limit.

Analysis:

Intermittent precursory overflows with an increasing frequency along with models of reinflation suggest that episode 34 will begin in the next 24-48 hours.  Overflow activity is only occurring at the north vent, but strong glow from the south vent indicates it will probably also erupt in the next episode. 

The current eruption has been characterized by episodic lava fountaining not seen in any eruptions since the 1983–86 episodic fountains at the beginning of the Puʻuʻōʻō eruption. Lava fountains and flows have erupted from two vents within Halemaʻumaʻu crater that we refer to as the north vent and south vent. Each of the previous fountaining episodes lasted from a few hours to over a week and was accompanied by strong deflation of the summit region. Pauses between the lava fountaining episodes have been marked by an immediate switch from deflation to inflation as the magma chamber recharges and repressurizes. Lava fountaining episodes have occurred approximately once per week since the start of the current eruption on December 23, 2024.

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

Hazards:

This episodic eruption is occurring within a closed area of Hawai'i Volcanoes National Park. High levels of volcanic gas—primarily water vapor (H₂O), carbon dioxide (CO₂), and sulfur dioxide (SO₂)—are one major hazard of concern, as this hazard can have far-reaching effects downwind. As SO₂ is continuously released from the summit during an eruption, it will react in the atmosphere to create the visible haze known as vog (volcanic smog) downwind of Kīlauea. SO₂ and vog may cause respiratory and other problems at high concentrations. Further information on vog can be found at https://vog.ivhhn.org/

Another major hazard is fallout of Pele's hair and other volcanic fragments from lava fountains. Pele's hair is strands of volcanic glass often produced by lava fountaining activity that can be carried well over 10 miles (15 kilometers) from the vent. Other hot glassy volcanic fragments (tephra) including volcanic ash, pumice, scoria, and reticulite can fall on the ground within 1–3 miles (1–5 kilometers) of the eruptive vent(s), with the highest concentrations immediately downwind of the vent(s). Various volcanic fragments have fallen on Highway 11 west of Hawai'i Volcanoes National Park at times, depending on wind and eruption conditions. Strong winds may waft light particles, including Pele's hair, to greater distances downwind. Once on the ground, Pele's hair can sometimes cluster and tangle together, giving it the appearance of a tumbleweed. The extent of Pele's hair deposition is dependent on lava fountaining activity and wind conditions. Residents and visitors should minimize exposure to Pele's hair and other glassy volcanic fragments, which can cause skin and eye irritation and can also contaminate catchment water supplies. More information about how Pele's hair, its hazards, and what to do is available here: https://www.usgs.gov/observatories/hvo/news/volcano-watch-recent-lava-fountains-highlight-peles-hair-hazards. A recently updated Frequently Asked Questions document that includes information about potential health effects of Pele's hair is available here: https://vog.ivhhn.org/sites/default/files/PelesHair_FAQs_v2.pdf

Hawaiian 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 also remain around Kīlauea caldera from Halemaʻumaʻu crater wall instability, ground cracking, and rockfalls that can be enhanced by earthquakes within the area closed to the public. 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.