Volcano Watch — Watching a new puʻu take shape on Kīlauea
Volcano Watch, a weekly briefing from the U.S. Geological Survey’s Hawaiian Volcano Observatory (HVO) team and collaborators, provides updates on ongoing activity. This week’s piece is authored by HVO geologist Natalia Deligne.
Tephra refers to rock fragments expelled during eruptions, including Pele’s hair. Since the current eruption began, tephra has been settling on a closed stretch of Crater Rim Drive, while observers noted the birth of a fresh puʻu (a volcanic cone) beginning in late March into early April. Early efforts to gauge tephra buildup involved photographing the progressively buried road sign. By the end of episode 21 (May 11), only a sliver of the sign remained visible, signaling that this method would soon fail.
To improve measurements, the team placed a line of roughly 5‑foot-tall garden stakes along the closed road before and after episode 22, intended to record tephra deposition at each point after an eruption. This approach resembled how rain gauges or stream gauges track rainfall or water levels. Yet, it proved inadequate: episode 23 (May 25) buried five of the twelve stakes, and episode 24 (June 4) covered three more.
Growing lava activity outpaced these low-tech methods. Higher-tech options required moving along transects on foot with a high‑precision GPS device. After episodes 23 and 24, a few test transects were run, and full transects along the then-buried Crater Rim Drive were completed after episode 25.
GPS measurements take at several sites, including the closest stable point near the puʻu’s summit (the top location shifts between episodes due to slumping and cracking near the peak). At a given site, the instrument must lock onto enough satellites (typically 10–20) to achieve vertical accuracy of 30 centimeters (about 1 foot) or better. Data are collected once per second for 240 seconds (4 minutes) once a satisfactory satellite fix is obtained.
A full transect requires about 2–3 hours. Back in the office, data are corrected using a nearby permanent GPS monitoring station, producing averaged site locations with roughly 10 centimeters (about 4 inches) vertical accuracy. This dataset reveals how the puʻu grows over time. The initial ground surface was mapped with 2019 lidar data (high‑precision elevation measurements) to establish a reference surface.
HVO has also conducted several surveys of the new puʻu with its helicopter‑mounted airborne lidar system, delivering high‑resolution three‑dimensional topographic scans of the entire feature. This work, performed roughly monthly, involves complex data processing. Attempts to use photogrammetry to monitor elevation changes across the crater floor have not been successful so far, largely because the puʻu’s surface is unusually uniform and lacks distinct features to track.
The data illustrate how quickly the puʻu can accumulate tephra during lava‑fountaining episodes. For instance, at the location of the buried road sign, tephra accumulation reached 3.4 meters (11 feet) by May 31, 2025, after episode 23. Episode 24 added about 7.8 meters (25.6 feet) of tephra over roughly 7½ hours, and episode 36 contributed another ~7.5 meters (24.6 feet) in just 5 hours.
Peak growth occurs during high‑fountaining events when lava jets rise above 300 meters (1,000 feet). When fountains stay below the rim, tephra has a harder time traveling from Halemaʻumaʻu to the new puʻu. Pele’s activity now mirrors a landscape once familiar to visitors who drove around Halemaʻumaʻu—from the Jaggar Museum era to the now‑removed overlook. HVO will continue monitoring the evolution of this burgeoning feature on Kīlauea as a striking example of how rapidly Hawaiian volcanoes can reshape their surroundings.
Volcano Activity Updates
Kīlauea has been erupting episodically within the summit caldera since December 23, 2024, with a Volcano Alert Level of WATCH.
Episode 37 featured a 9‑hour lava fountaining event on November 25. The summit shows reinflation, with glow visible intermittently overnight at both vents. A subsequent fountaining episode is anticipated between December 6 and 9. No notable activity has been reported along Kīlauea’s East Rift Zone or Southwest Rift Zone.
Mauna Loa remains non‑eruptive, with the Volcano Alert Level at NORMAL.
During the past week, a felt earthquake occurred in the Hawaiian Islands: a magnitude 3.5 event located 1 km west of Pāhala at a depth of 32 km, felt on November 29 at 6:39 p.m. HST.
HVO will continue to monitor both Kīlauea and Mauna Loa closely.
For more past Volcano Watch articles, Kīlauea and Mauna Loa updates, volcano photos, maps, and recent earthquake information, visit HVO’s website. Questions can be emailed to askHVO@usgs.gov.
