Volcano Watch: Tilt, tremor and lava — remembering Mauna Loa’s 2022 eruption onset

“Volcano Watch” is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.

As people from around the world are captivated by episodic lava fountaining during the ongoing Kīlauea eruption in Halemaʻumaʻu Crater inside the Big Island volcano’s summit caldera, let’s use the current pause and transition our attention back to the details of another recent eruption — Mauna Loa in 2022.

Many residents remember Mauna Loa — the largest active volcano on Earth — roaring awake after decades of slumber with a dynamic summit and Northeast Rift Zone eruption in late 2022.

Geophysical instruments recorded many major, and even subtle, details the night of the 2022 Mauna Loa eruption onset. Here we’ll explore some of these monitoring data observations that give us clues as to what was happening beneath the surface.

Hawaiian Volcano Observatory monitoring networks detected rapid changes in Mauna Loa’s summit area at about 10:20 p.m. Nov. 27, 2022. A swarm of small, shallow earthquakes occurred beneath the caldera and just south of the summit, lasting about an hour.

Tiltmeters at Mauna Loa’s summit began to record significant ground deformation — a sign that magma was moving rapidly toward the surface — at the same time.

A tiltmeter designated MOK and located on the northeast rim of Mokuʻāweoweo, Mauna Loa’s summit caldera, by 10:50 p.m. measured inflationary tilt of more than 100 microradians, pointing downward to the northwest and away from the summit.

That indicated magma was continuing to rise upward from below. Tremor, a seismic signal often associated with magma movement, was also detected just minutes later.

The eruption began at 11:21 p.m.

Webcam imagery confirmed fissures opened within Mokuʻāweoweo and lava was flooding the caldera floor. The MOK tiltmeter showed rapid deflation almost immediately, reflecting that magma from the summit reservoir was spilling out onto the surface.

Meanwhile, another tiltmeter designated SLC and located southwest of the summit — just above Mauna Loa’s Southwest Rift Zone — also began to show dramatic changes.

By early the morning of Nov. 28, the instrument had recorded more than 500 microradians of tilt toward the north and northwest, and, soon after, it went off-scale because the amount of tilting was higher that it was designed to measure.

The magnitude and direction of these readings were puzzling, as they weren’t exactly what would be expected if magma migrated toward the Southwest Rift Zone, but any movement on this tiltmeter was concerning.

Such a scenario could result in lava flows threatening communities downslope, such as Ocean View or others on the South Kona coast.

However, no deformation was seen at a tiltmeter designated BLB farther down the Southwest Rift Zone, suggesting the magma had not continued in that direction.

Instead, eruptive activity shifted northeast, and vents opened along Mauna Loa’s Northeast Rift Zone, feeding lava flows that mostly traveled north-northeast toward the Humuʻula Saddle.

The eruption remained there until its end in mid-December.

The large tilt magnitude measured at the SLC tiltmeter was instead interpreted as a response to the summit reservoir’s extent and draining, not a sign of rift zone intrusion.

Significant deflation was recorded at summit global positioning system stations as the eruption continued.

Between Nov. 27 and Dec. 10, the summit caldera subsided nearly 16 inches, and signal decreased with distance away from the summit. But even sites on Mauna Loa’s flanks measured several inches of subsidence.

Satellite radar imagery from interferometric synthetic aperture radar, or InSAR, showed additional complex patterns of ground movement, which indicate where magma either reached the surface or was very close to the surface.

The effects of the eruption were not limited to just Mauna Loa.

Global positioning system stations on neighboring volcanoes on Hawaiʻi Island, including Kīlauea and Hualālai, recorded small but measurable motion in response to deflation of Mauna Loa during the active 2022 eruption.

Some stations at Kīlauea began migrating northwest — toward Mauna Loa — within a single day of the eruption starting.

This inter-volcano response illustrates how Mauna Loa’s activity can affect stress fields around the island and potentially influence other volcanic systems.

Instruments on Mauna Loa now show low levels of seismicity and only minor inflation near the summit as the volcano recovers from the 2022 eruption and magma replenishes the reservoir system.

Still, we know Mauna Loa will only slumber for so long, and another eruption will occur years or decades into the future.

But the public can rest assured, while Kīlauea continues to erupt with its impressive lava fountains, Hawaiian Volcano Observatory scientists are also continuing to closely monitor and study the now-quiet Mauna Loa behind the scenes as well as other volcanoes in Hawaiʻi and American Samoa.

Volcano Activity Updates

Kīlauea has been erupting episodically within Halemaʻumaʻu Crater inside the summit caldera since Dec. 23, 2024. Its U.S. Geological Survey Volcano Alert Level remains at Watch.

The eruption continued during the past week. Low-level precursory activity of Episode 18 began the evening of April 16, and the 10-hour fountaining phase began the morning of April 22.

Episode 18 fountains from the south vent reached heights more than 600 feet, while minor activity occurred at the north vent. Since the end of Episode 18, the summit region has shown inflation, suggesting 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 U.S. Geological Survey Volcano Alert Level is at Normal.

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

• Magnitude-2.7 earthquake located 1 mile south-southeast of Leilani Estates at a depth of 4 miles at 8:55 p.m. April 17.

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

Visit the 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.