Volcano Watch — Tracking the growth of a new puʻu at Kīlauea
Tephra formed by lava fountains during the ongoing Kīlauea summit eruption has created a new puʻu (hill) southwest of Halemaʻumaʻu crater. The new puʻu is visible from the public viewing areas around Kīlauea summit in Hawaiʻi Volcanoes National Park. The USGS Hawaiian Volcano Observatory (HVO) has been busy tracking the continued growth of this young geologic feature.
Volcano Watch is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates. This week’s article is by HVO geologist Natalia Deligne.
Tephra is a piece of rock ejected during an eruption, and it includes Pele’s hair. While tephra has been falling on a closed portion of Crater Rim Drive since the current eruption started, the development of a new puʻu started in late March and early April. Initially, HVO geologists informally tracked the accumulation of tephra by photographing the progressive burial of a road sign. By the end of episode 21 on May 11, only an inch or two of the sign remained exposed; clearly this was not going to work for much longer.
Before and after episode 22, geologists established a series of garden stakes, each about 5 feet tall, at regular intervals along the closed road. The intention was to measure how much tephra fell at each location following an episode—similar to how a rain or stream gauge measures rainfall or water level at a particular location. This plan did not work well, either: episode 23 on May 25 buried five of the twelve stakes, and episode 24 on June 4 buried an additional three.
Low-tech methods were failing due to how much the puʻu was growing during lava fountaining episodes. Higher-tech methods required walking transects by foot using a hand-held, high-precision GPS instrument. This was first trialed at a few points after episodes 23 and 24, with complete transects done along then-buried Crater Rim Drive starting after episode 25.
GPS measurements are taken at several locations, including the closest stable location near the peak of the puʻu (the exact location of the peak changes between episodes, and slumping/cracking near the peak can make the very top unsafe). Once the geologist is at a measurement site, the instrument must first see enough satellites (usually between 10 and 20) to have a vertical accuracy of 30 centimeters (1 foot) or less. This takes between a few seconds to several minutes. Next, a location datapoint is recorded every second for 240 seconds (4 minutes).
The whole transect takes 2-3 hours to complete. Once back in the office, the data is processed by using a permanent GPS monitoring station nearby for corrections. The final averaged locations at each site have a vertical accuracy on the order of 10 centimeters (4 inches) or so. The data allows us to track how the puʻu is growing over time. The original ground surface was taken from high-precision elevation data collected using lidar (light detection and ranging) in 2019.
HVO has also done a few surveys of the new puʻu using its new helicopter-mounted airborne lidar system, which provides high-resolution three-dimensional topographic scan of the entire puʻu. This is done about once a month, but processing the data is complex and still ongoing. Unfortunately, attempts to use photogrammetry methods—how HVO tracks elevation changes across the crater floor—have been unsuccessful because the new puʻu’s surface is too uniform and lacks consistent distinguishable features.
The dataset shows how much the new puʻu can grow in just a few hours during lava fountaining episodes. For example, at the location of the now-buried road sign, the tephra deposit was a total of 3.4 meters (11 feet) thick on May 31, 2025, after episode 23. At the same site, episode 24, over about 7½ hours, added an additional 7.8 meters (25.6 feet) of tephra, while episode 36 added an additional 7.5 meters (24.6 feet) in just 5 hours!
The puʻu grows the most during high-fountaining episodes that exceed 300 meters (1,000 feet) in height. When lava fountains are below the rim, it is harder for tephra to make its way out of Halemaʻumaʻu onto the new puʻu. Pele is now building where 17 years ago visitors used to drive around Halemaʻumaʻu from the now-removed Jaggar Museum to the now-gone Halemaʻuamaʻu Overlook. HVO geologists will continue to track the evolution of this new feature on Kīlauea, which serves as a great example of how quickly Hawaiian volcanoes can change their landscape.
Volcano Activity Updates
Kīlauea has been erupting episodically within the summit caldera since December 23, 2024. Its USGS Volcano Alert level is WATCH.
Episode 37 lava fountaining happened for 9 hours on November 25. The summit is reinflating and glow has been visible intermittently overnight at both vents. Another fountaining episode is likely between December 6 and 9. 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.
One earthquake was reported felt in the Hawaiian Islands during the past week: a M3.5 earthquake 1 km (0 mi) W of Pāhala at 32 km (20 mi) depth on November 29 at 6:39 p.m. HST.
HVO continues to closely monitor Kīlauea and Mauna Loa.
Please 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.