Volcano Watch: What lurks beneath; learning from lava ooze outs

“Volcano Watch” is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates. Today’s article is by Hawaiian Volcano Observatory geologist Kendra Lynn.

Halemaʻumaʻu has progressively filled since 2020 by lava from several eruptions at the summit of the Big Island’s Kīlauea volcano, and it continues to accumulate new lava with each successive fountaining episode of the ongoing eruption that began Dec. 23, 2024.

Let’s dive beneath the solidified crust on the crater floor to explore the complicated mix of molten material below.

Kīlauea has had six summit eruptions inside Kaluapele, the summit caldera, during the past 4 years:

• 2020–21 (5 months).
• 2021–22 (1.25 years).
• January to March 2023 (3 months).
• June 2023 (1.5 weeks).
• September 2023 (1 week).
• Ongoing 2024–25 eruption (5 months so far).

Each of these eruptions filled the area that collapsed in 2018, and lava now reaches more than 1,394 feet deep — for comparison, the Empire State Building in New York City is 1,250 feet tall.

During many of these eruptions, Hawaiian Volcano Observatory field crews documented “ooze outs” — where lava squeezes out from underneath the solidified surface crust onto the floor of the crater, usually in places far away from where eruptive vents are located.

These ooze outs tell us that despite the solid crust at the surface, some portions of the interior have remained molten, even in the periods between eruptions.

During the earlier eruptions, field crews had limited access to sample the lava in Halemaʻumaʻu because of vents being located deep inside the collapsed area of Kaluapele.

As the surface of the crater, and thus the elevation of the vents, rose and expanded laterally through time with every eruption since 2020, safe opportunities to sample lava flows became possible.

With permission and coordination from Hawaiʻi Volcanoes National Park, Hawaiian Volcano Observatory field crews recently were able to directly sample the lava ooze outs for the first time since 2020.

As part of observatory’s agreement with the national park, Hawaiian Volcano Observatory staff are typically available at the Volcano House and Wahinekapu (Steaming Bluff) overlooks during overflight missions when conditions are safe for sampling to answer questions about our work and field operations.

The location of ooze outs are documented with photographs and thermal images.

Thermal images are used to create a thermal map, which often show the ooze outs occurring on the eastern side of Halema‘uma‘u, far from active surface flows being fed by lava fountains.

These different types of lava flows can be seen from public overlooks at many points around Kaluapele in Hawai‘i Volcanoes National Park — sometimes even during periods between the eruptive episodes.

Ooze out lavas are spiny pāhoehoe: they have a rough surface texture compared to fresher pāhoehoe fed by hot lava fountains.

These spiny flows are more viscous, meaning they flow more slowly, because they had time to cool. They also have lower gas contents, meaning they are denser, and analysis in the laboratory shows they also are rich in crystal.

The most common mineral in Hawaiian eruptions is olivine, which is green, but other minerals are found in lavas that had more time to cool, such as white plagioclase and dark green/brown pyroxene.

The ooze out lavas collected from Halemaʻumaʻu are dominated by clots of plagioclase and pyroxene with minor amounts of small — less than 0.02 of an inch — olivine crystals.

Ooze outs also contain larger — 0.04 to 0.08 of an inch — olivine crystals that were recycled from previous eruptions or episodes.

Originally, these larger crystals were formed in the magma reservoirs underneath Kaluapele. They were erupted in one of the previous lava lakes and then re-erupted in a recent ooze out.

We know these crystals had this complex history because of careful laboratory work by two University of Hawai‘i at Hilo undergraduate students examining samples from the January to March 2023 and June 2023 Halemaʻumaʻu eruptions.

Their work documented minerals found in those eruptions, and they identified lake-recycled minerals through chemical and textural analysis, similar to what we see in the recent ooze outs.

Additional clues will come from comparing the recent ooze out samples to rock core drilled from the Kīlauea Iki lava lake in the 1960s and 1970s.

Studies on these found that the lava lake interior, fed by 17 episodes during the 1959 Kīlauea Iki eruption, took decades to cool, resulting in crystallization of a variety of minerals.

Each eruptive episode of the ongoing summit eruption, and successful sampling mission, provides further insights into how Halemaʻumaʻu is evolving and helps us understand eruptive behavior of Kīlauea.

Volcano Activity Updates

Kīlauea has been erupting episodically within the volcano’s summit caldera since Dec. 23, 2024. Its U.S. Geological Survey Volcano Alert Level remains at Watch.

Episode 21 of the Kīlauea summit eruption inside Halemaʻumaʻu Crater occurred May 11, with about 8 hours of fountaining primarily from the north vent. Strong glow visible in both the north and south vents and summit region inflation since the end of Episode 21 suggests another episode is possible.

Sulfur dioxide emission rates are elevated in the summit region during active eruption episodes.

No unusual activity has been noted along Kīlauea’s East Rift Zone or Southwest Rift Zone.

Mauna Loa is not erupting. Its U.S. Geological Survey Volcano Alert Volcano Alert Level is at Normal.

Three earthquakes were reported felt in the Hawaiian Islands during the past week:

• MAGNITUDE 2.8 located 14 miles south-southeast of Waimea at a depth of 8 miles at 11:08 p.m. May 14.
• MAGNITUDE 3.3 located 9 miles west-southwest of Kailua-Kona at a depth of 3 miles at 12:16 a.m. May 14.
• MAGNITUDE 3.6 located 14 miles east-southeast of Leilani Estates at a depth of 26 miles at 8:01 a.m. May 13.

Hawaiian Volcano Observatory continues to closely monitor Kīlauea and Mauna Loa.

Visit the volcano observatory website for past “Volcano Watch” articles, Kīlauea and Mauna Loa updates, volcano photos, maps, recent earthquake information and more. Email questions to askHVO@usgs.gov.