Volcano Watch: Inter-episode rumblings at Kīlauea

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 RCUH geophysicist Maddie Hawk.

Witnessing a volcanic eruption is, for many, a once-in-a-lifetime experience. Hawaiʻi Volcanoes National Park welcomes well over a million visitors from around the world every year, and many of these visitors hope to see lava erupting in person. As enthralling as each eruptive episode is, experts at the USGS Hawaiian Volcano Observatory watch just as closely at what’s happening between episodes.

For Island of Hawaiʻi residents, the recent eruptive episodes at Kaluapele (Kīlauea’s summit caldera) generously offer many chances to view the mesmerizing lava fountains. Opposed to other recent eruption locations like Kīlauea’s East or Southwest Rift Zone, the summit caldera eruptions are accessible to the public. A ride down Crater Rim Drive and a one-mile walk offers one of the best viewing areas near Keanakākoʻi Crater, though other areas along the caldera rim also offer stunning views from farther away.

Prior to the onset of this eruption in December 2024, Island of Hawaiʻi earthquake counts had reached some of the highest levels in recorded history here. Just last summer, some weekly tallies exceeded 2,000 earthquakes across the island. Some of these earthquakes are magma creating new pathways in the volcano, breaking rocks along the way. When magma erupts, this process of rock breaking stops, and earthquake counts dwindle as a result. In the last five months, Island of Hawaiʻi weekly earthquake counts have rarely exceeded 500.

Though there aren’t as many earthquakes around Kīlauea summit during the ongoing eruption, the ground below Kaluapele is not exactly quiet. During an eruptive episode, the roar of lava fountains shows up on seismic data channels as eruptive tremor. It is a constant, loud, unmistakable signal shared across eruptions and it is associated with large volume fluid movement. Though tremor increases with the onset of each fountaining episode, it has not completely disappeared with each pause. The signal is persistent between episodes.
Between fountaining episodes, the persistent tremor can vary in intensity due to the vent geometry, gas emissions, magma depth, and other factors. Recent pauses have exhibited periods of cyclical low frequency pulsing within the tremor often correlated with the rise and fall of lava in the vent. This process of lava filling the vents and then draining, repeatedly, prior to a new eruptive episode has been visible USGS Hawaiian Volcano Observatory livestream cameras.

Pulsing tremor can indicate magma movement and/or gas transfer within the volcanic system, and it has varied in rhythm, duration, and intensity. One example is the cycle leading up to eruptive episode 20. Pulsing began in earnest about nine hours before lava fountaining appeared on May 6, just before 5:30 p.m. HST. Each pulse lasted around 3 minutes, at a rate of about 8 pulses per hour.

However, the pause between episodes 17 and 18 displayed pulses that were closer to 10 minutes long, with only 2-3 occurring every hour. Though pulsing is common immediately before or after an eruptive episode, it is not consistent. Unlike the onset of episode 20, episode 19 began without being immediately preceded by tremor pulsing. Also, we cannot assume that the pulsing ceases during eruptive episodes, as the loud tremor would cover up any weaker signals.

Recognizing seismic patterns, or lack thereof, can contribute to our understanding of what is happening below the surface. Studying these patterns alongside geodetic data (how the Earth contracts and expands with volcanic activity), changes in gas emissions, and changes in magma compositions gives us the best chance to understand the complex volcanic system beneath our feet.

Volcano Activity Updates

Kīlauea has been erupting episodically within the summit caldera since Dec. 23, 2024. Its USGS Volcano Alert level is WATCH.

Episode 22 of the Kīlauea summit eruption in Halemaʻumaʻu crater occurred on May 16, with approximately 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 22 suggests that 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 USGS Volcano Alert Level is at NORMAL.

Two earthquakes were reported felt in the Hawaiian Islands during the past week: a M3.2 earthquake 13 miles WSW of Hāwī at 13 miles depth on May 21 at 2:18 a.m. and a M4.2 earthquake 11 miles SE of Pāhala at 20 miles depth on May 20 at 9:37 a.m.

HVO continues to closely monitor Kīlauea and Mauna Loa.

Visit HVO’s 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.