Volcano Watch: Tracking the growth of a new puʻu at Kīlauea, southwest of Halemaʻumaʻu

“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 HVO geologist Natalia Deligne.

Tephra formed by lava fountains during the ongoing Kīlauea summit eruption has created a new puʻu, or hill, southwest of Halemaʻumaʻu Crater and visible from the public viewing areas around Kīlauea summit in Hawaiʻi Volcanoes National Park.

Hawaiian Volcano Observatory has been busy tracking the continued growth of this young geologic feature.

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 now almost a year ago, the development of a new puʻu started in late March and early April.

Hawaiian Volcano Observatory geologists initially 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.

Geologists prior to and after Episode 22 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.

That 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 because of 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 1 foot or less. This takes between a few seconds to several minutes.

Next, a location data point is recorded every second for 4 minutes. The whole transect takes 2 to 3 hours to complete.

Data is processed for corrections once back in the office by using a nearby permanent GPS monitoring station. The final averaged locations at each site have a vertical accuracy on the order of 4 inches or so.

That data allows us to track how the puʻu is growing with time. The original ground surface was taken from high-precision elevation data collected using lidar (light detection and ranging) in 2019.

Hawaiian Volcano Observatory also did a few surveys of the new puʻu using its new helicopter-mounted airborne lidar system, which provides high-resolution three-dimensional topographic scans 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 Hawaiian Volcano Observatory 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 11 feet thick May 31 after Episode 23. At the same site, Episode 24, throughout about 7.5 hours, added an additional 25.6 feet of tephra.

Episode 36 produced an additional 24.6 feet — in just 5 hours!

The puʻu grows the most during high-fountaining episodes that exceed 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.

Hawaiian Volcano Observatory 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

VOLCANO ALERT LEVEL: Watch

Kīlauea has been erupting episodically within the summit caldera since Dec. 23.

Episode 37 lava fountaining happened for 9 hours Nov. 25. The summit is reinflating and glow has been visible intermittently overnight at both vents.

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

WHAT’S NEXT: Another fountaining episode is likely between Dec. 6 and 9.

MAUNA LOA

VOLCANO ALERT LEVEL: Normal

Mauna Loa is not erupting. Seismicity rates returned to long term background levels in late November, similar to seismicity rates during the prior months.

Hawaiian Volcano Observatory’s monthly Mauna Loa update issued earlier this week said a total of 147 magnitude-3+ and smaller earthquakes were detected beneath Mauna Loa’s summit region during the November reporting period, while the prior month had 123.

Modestly higher rates of seismicity were observed from late-October to early November, with 8 to 16 earthquakes per day in early November. Recent seismicity is much lower than unrest prior to the 2022 eruption and has returned to 3 to 6 earthquakes per day.

Data from global positioning system instruments show a slight increase in inflation beneath the summit starting in mid-November. These rates are normal as the volcano recovers from its 2022 eruption and magma replenishes the reservoir system.

Recent data indicate the center of deformation shifted to the southern caldera region, indicating refilling of a south caldera magma chamber.

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

EARTHQUAKES

One earthquake was reported felt in the Hawaiian Islands during the past week:

• MAGNITUDE-3.5 located slightly west of Pāhala at a depth of 20 miles at 6:39 p.m. Nov. 29.

Visit Hawaiian Volcano Observatory’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.