Activity Summary: 

Episode 21 ended at 08:34 p.m. HST on Tuesday, May 11, 2025, after ~8 hours of sustained fountaining. The Halema'uma'u eruption is currently paused.

The sustained fountaining phase of episode 21 began at 12:45 p.m. on Sunday, May 11, 2025. Lava fountains and flows erupted primarily from the north vent, and the south vent was largely obscured by the north vent activity. Fountains from the north vent quickly reached estimated heights of more than 500 feet (150 meters).  Lava flows from this episode inundated the near vent and extended more than a km along the north edge of the Halema'um'au crater floor. The sustained fountaining phase was preceded by the onset of small fountain events at 4:30, 5:20 and 8:00 a.m. after which numerous small fountains were observed.  The precursory low-level activity included gas-pistoning and fountains some of which included modest lava pond drainback. 

The end of episode 21 fountaining activity was accompanied by a rapid change in summit tilt from deflation to inflation, along with a rapid decrease in tremor. The Uēkahuna tiltmeter (UWD) recorded approximately 6 microradians of deflationary tilt between the start and end of episode 21 fountaining. 

Kīlauea's current eruption in Halemaʻumaʻu crater within Kaluapele (the summit caldera) began on December 23, 2024. There have now been 21 episodes separated by pauses in activity. All eruptive activity remains within Hawaiʻi Volcanoes National Park. No significant activity has been noted along Kīlauea’s East Rift Zone or Southwest Rift Zone. Current hazards include volcanic gas emissions and windblown volcanic glass (Pele’s hair) and tephra that have impacted Hawaiʻi Volcanoes National Park and nearby communities.

Each episode of Halemaʻumaʻu lava fountaining since December 23, 2024, has continued for13 hours to 8 days and episodes have been separated by pauses in eruptive activity lasting less than 24 hours to 12 days. 

• Timeline of eruption episodes since December 23, 2024: https://www.usgs.gov/volcanoes/kilauea/science/eruption-information 
• The Kīlauea summit livestream video is available here: https://www.youtube.com/usgs/live

No changes have been detected in the East Rift Zone or Southwest Rift Zone. HVO continues to closely monitor Kīlauea and will issue an eruption update tomorrow morning unless there are significant changes before then. 

Kīlauea Volcano Alert Level/Aviation Color Code remain at WATCH/ORANGE. All current and recent activity is within Hawaiʻi Volcanoes National Park.

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 the primary 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/

Additional hazards include Pele's hair and other volcanic fragments from lava fountains. Pele's hair is strands of volcanic glass often produced by lava fountaining activity. Volcanic fragments can fall on the ground within a few hundred yards (meters) of the eruptive vent(s), or downwind of the vent(s). Strong winds may waft light particles, including Pele's hair, to greater distances downwind. Once they are 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 current wind conditions. Residents and visitors should minimize exposure to Pele's hair and other volcanic fragments, which can cause skin and eye irritation. 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 Frequently Asked Questions document developed for the 2022 Mauna Loa eruption includes information about potential health effects of Pele's hair and is available here: https://vog.ivhhn.org/sites/default/files/FAQ_on_air_quality_and_health_during_Mauna_Loa_eruption_v1.6.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.

For discussion of Kīlauea hazards, please see: https://www.usgs.gov/observatories/hawaiian-volcano-observatory/hazards.