Volcano Watch: Mauna Loa has lessons to teach during quiet times

“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 research geophysicist Ingrid Johanson.

The 2022 Mauna Loa eruption was extraordinary in many ways.

It was the first Mauna Loa eruption in 38 years and the first during the current era of modern instrumentation.

Scientists continue to learn about Mauna Loa monitoring since the 2022 eruption, including subtle recent changes.

The long-term buildup to the 2022 eruption began in 2014, with an increase in seismicity and deformation as measured by Hawaiian Volcano Observatory’s network of global positioning system, or GPS, stations. These indictors fluctuated until 2019, when they began to increase again.

We observed changes in 2021 on a Mauna Loa tiltmeter, representing the first time a volcanic signal was recorded on that instrument.

As explained in a May 6, 2021, “Volcano Watch” article, tiltmeters are particularly sensitive to shallow magma movement. The signal from that tiltmeter was evidence that magma reached a shallow depth in 2021, and it was an important indicator that the buildup to eruption was evolving.

The 2022 eruption began just before midnight Nov. 27, preceded by an hourlong earthquake swarm and rapid summit inflation.

It started in the summit region before moving into Mauna Loa’s Northeast Rift Zone. There, multiple fissures produced lava flows that erupted downslope toward Daniel K. Inouye Highway, also known as Saddle Road.

Seismicity quieted down and deformation during the eruption indicated rapid deflation of Mauna Loa’s magma chambers. Lava flows slowed and the eruption stopped by Dec. 13, 2022.

GPS instruments quickly began to show inflationary motion again following the end of the eruption, presumably as magma rose from deeper in the volcano into the magma chambers depleted during the eruption. This rapid refilling continued for about 6 months before settling into a steadier reinflation pattern.

Recent changes to the reinflation pattern have given us some clues to the current state of the volcano.

The deformation pattern around Mauna Loa’s summit changed in November 2025. Where previous motions indicated reinflation of magma chamber underneath Mokuʻāweoweo, Mauna Loa’s summit caldera, inflation shifted to a body underneath the southwestern portion of the summit region.

This was not the first time this pattern was observed. Deformation seen in 2015 with GPS shifted in a similar way.

Inflation of the southwestern magma chamber continued until late 2016 before switching back to the more central body under Mokuʻāweoweo. This time, deformation switched back much faster; by Dec. 15, 2025, the inflation center was again under the summit caldera.

Interestingly, the 2025 deformation changes were also accompanied by clear changes in tilt at a summit tiltmeter. This was not the case in 2015, when only volcanic deformation was recorded.

The fact that this deformation is detectable on tiltmeters is an indication that magma is still fairly shallow in the volcano — geologically speaking — possibly between 1.25 to 1.8 miles below the surface.

However, there is less seismicity at Mauna Loa than at almost any time during the 8 years of unrest before the 2022 eruption.

That means the deformation we’re seeing is likely passive refilling in the volcano that isn’t stressing the crust in a way that would indicate the volcano is moving toward eruption.

This pattern was observed following the 1975 and 1984 Mauna Loa eruptions as well.

Rapid inflationary deformation was recorded without much seismicity. It wasn’t until earthquakes started again that the volcano clearly began moving toward its next eruption.

The tilt and GPS observations are nonetheless a reminder that Mauna Loa is in a different state now than it was before the 2022 eruption.

Tilt changes provide evidence that magma is still mobile in Mauna Loa, which is an important factor in how unrest might progress in the future.

Buildup to the next eruption might not look the same as it did in 2022. Especially if Mauna Loa returns to producing eruptions more frequently than decades apart, as it did prior to 1984.

The Volcano Alert Level for Mauna Loa is currently at Normal; we expect to see additional changes such as increased seismicity or gas emissions before any future eruption.

Keeping a close eye on the volcanoes even during quiet times can teach important lessons that will inform our interpretations and decisions as conditions change.

VOLCANO ACTIVITY UPDATES

KĪLAUEA volcano

VOLCANO ALERT LEVEL: Watch

Kīlauea has been erupting episodically since Dec. 23, 2024, within its summit caldera.

Episode 42 lava fountaining happened for just less than 10 hours Feb. 15. No unusual activity has been noted along Kīlauea’s East Rift Zone or Southwest Rift Zone.

WHAT’S NEXT? Summit region inflation since the end of Episode 42 indicates another fountaining episode is possible. Preliminary models suggest Episode 43 could occur between March 6 and 16.

MAUNA LOA volcano

VOLCANO ALERT LEVEL: Normal

Mauna Loa is not erupting. Find more about what’s happening at the volcano by checking out the most recent monthly update from Hawaiian Volcano Observatory.

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

EARTHQUAKES

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

• MAGNITUDE-3.2 at 8:52 p.m. Feb. 25 located 6 miles west-southwest of Pāhala.
• MAGNITUDE-3.6 at 2:25 a.m. Feb. 24 located 14 miles west-southwest of Kahaluʻu-Keauhou at a depth of 24 miles.
• MAGNITUDE-4.1 at 8:25 a.m. Feb. 22 located 28 miles southwest of Kekaha, Kauaʻi, at a depth of 7 miles.

Visit the Hawaiian 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.