USGS Volcano Notice - DOI-USGS-HVO-2025-04-21T18:08:10+00:00

Activity Summary:

The ongoing Halemaʻumaʻu eruption is paused. On April 20, episode 18 resumed with lava flows erupting from the south vent starting at approximately 7:45 a.m. HST with 4 cycles of flows that ended around 12:44 p.m. HST. Glow continued to be observed from the vents overnight, but there was no noticeable spattering or vent overflows after the cycles ended. Tilt continues to show inflation, and a deflationary signal could accompany lava fountaining or more small lava flows could precede the fountaining phase.

Kīlauea's current eruption in Halemaʻumaʻu crater within Kaluapele (the summit caldera) began on December 23, 2024. There have now been 18 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.

Summit Observations:

Episode 18 resumed at approximately 7:45 a.m. HST on April 20 with lava flows from the south vent being fed by a 6-10 foot (2-3 meter) high fountain. Eruptive activity paused from about 9:30 a.m. to 9:43 a.m. HST when flows resumed from the south vent. This was followed by another oscillation with the eruptive activity diminishing and stopping after 10:30 a.m. HST, which resumed at 10:50 a.m. HST with flows being fed by a 15 foot (5 meter) high dome fountain. Lava flows ceased just after 11:10 a.m. HST, ending the third cycle of activity. Lava flows resumed at 12:22 p.m. HST with low dome fountains and ended at 12:44 p.m. HST. Small gas pistoning events occurred every 3-5 minutes and are superimposed upon longer cycles of activity. Lava flows from the early cycles reached about a third of the way across the crater floor in a narrow band (about 1,500 feet or 500 meters in length). Tilt leveled and tremor increased slightly with the initial onset of eruptive activity. After eruptive activity paused tremor decreased and the summit began inflating again. Glow continued to be observed from the vents overnight, but there was no noticeable spattering or vent overflows after the cycles ended.

The UWD and SDH tiltmeters continue to show inflationary signals that have been persistent since the end of episode 17. As of this morning, UWD has measured approximately 17.5 microradians of inflationary tilt since 9:45 a.m. HST April 9; greater than the inflation at the start of episodes 16 and 17. High fountains as observed from previous episodes are expected when a strong deflationary signal is detected.

Volcanic gas emissions remain elevated and at heightened levels due to lava fountaining. The last sulfur dioxide (SO₂) emission rate measured on April 10 was approximately 1,200 tonnes per day. Typical levels of Sulfur dioxide (SO₂) emission have been about 1,000 tonnes per day during previous pauses. Sulfur dioxide (SO₂) emission rates during earlier fountaining episodes have reached 50,000 tonnes per day. Plume remains a thick white color and continues to blow to the south and southwest. Strong degassing is currently occurring from both vents.

Strands of volcanic glass known as Pele’s hair from previous episodes are still present throughout the summit area of Hawaiʻi Volcanoes National Park and surrounding communities and can be remobilized by wind.

• Timeline of eruption episodes since December 23, 2024: https://www.usgs.gov/volcanoes/kilauea/science/eruption-information 
• Two Kīlauea summit livestream videos are available here: Kīlauea Volcano, Hawaii (West Halemaʻumaʻu crater) v1cam and Kīlauea Volcano, Hawaii (East Halemaʻumaʻu crater)v2cam
• Summit eruption webcams: https://www.usgs.gov/volcanoes/kilauea/summit-webcams 

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. Sulfur dioxide (SO₂) emissions from the East Rift Zone remain below detection limit.

Analysis: 

The current eruption has been characterized by episodic fountaining not seen in any of the other Halemaʻumaʻu eruptions since 2020. Fountains and lava flows have erupted from two vents that we refer to as the north vent and south vent. Each of the previous 17 fountaining episodes lasted from a few hours to over a week and have been accompanied by strong deflation of the summit region. Pauses between the fountaining episodes have been marked by an immediate change from deflation to inflation as the magma chamber recharges and repressurizes.

Analysis of inflationary tilt patterns prior to the onset of each fountaining episode allows a time window of probability for the onset of new episodes to be estimated. These are calculated using both minimum inflation necessary to start a new eruption and the rate of inflation fit to data derived from past eruptive episodes. The precursory activity of episode 18 occurred as forecast on Wednesday April 16 when inflation slightly exceed episode 17 but was followed by continued inflation. The extended time gap between the precursory eruptive activity starting episode 18 and the onset of fountaining differs from the other episodes. Inflation continues and lava flows and fountains could occur at any time. Based upon prior cycles of fountaining and deflation, episode 18 fountaining is likely to be less than 24 hours long.

• Timeline of eruptive episodes since December 23, 2024: https://www.usgs.gov/volcanoes/kilauea/science/eruption-information
• Summit eruption reference map: January 15, 2025—Kīlauea summit eruption reference map | U.S. Geological Survey
• Volcano Watch article about Pele's hair from this eruption: https://www.usgs.gov/observatories/hvo/news/volcano-watch-recent-lava-fountains-highlight-peles-hair-hazards

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.

General Updates: 

The power system that supplies power to the KWcam webcam, the F1cam thermal camera, and the laser rangefinder sustained damage during the high fountaining on March 26, 2025. Both cameras and the rangefinder are currently offline. Other HVO webcams are still functioning and online.

Hazards: 

This episodic eruption is occurring within a closed area of Hawaiʻi 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.