Kīlauea gave a silent warning a year before its 2018 eruption

Volcanoes change the world with heat, pressure, and movement. Their power feels sudden, yet the build-up often begins quietly. Scientists now understand Kīlauea Volcano in this deeper way.

Its dramatic 2018 eruption heated the ground, reshaped communities, and shook Hawai‘i Island with thousands of quakes. But the path toward that event started long before the first lava surged across the landscape.

Kīlauea shifted before the eruption

Researchers studying Kīlauea found that the volcano shifted almost a year before the eruption. Magma usually rises from the mantle into two summit reservoirs.

During this period, that pathway changed. Flow between the reservoirs weakened and pressure gathered below the East Rift Zone.

Sin-Mei Wu is an assistant professor in the Department of Earth Sciences in the UH Mānoa School of Ocean and Earth Science and Technology (SOEST).

“Our hypothesis is that a blockage formed between the volcano’s two summit magma reservoirs, impeding the flow, and pressure began to build beneath Kīlauea’s East Rift Zone,” said Professor Wu.

Seismic velocity records supported this early shift. Shallow crust above the deeper reservoir slowed seismic waves. That slowdown matched long periods of inflation, which pointed to rising pressure within the system.

Unusual behavior in the crater

The lava lake inside Halema‘uma‘u crater dropped by about 30 meters while deeper pressure stayed steady. The mismatch suggested a clogged system.

“It remains unclear whether the unusual behavior we identified was a singular event or part of a recurring pattern that could influence future eruptions,” noted Professor Wu.

Seismic data revealed a long decline in wave speeds along the southern rim of the caldera. That zone sits above the deeper reservoir.

The decline suggested pressurization spreading upward year after year. Researchers linked this to ongoing mantle input beginning around 2013.

Pressure building deep

GPS readings showed steady inflation across the summit. These results matched deeper signals from the velocity data.

The system absorbed new magma, yet the shallow reservoir did not rise as expected. This gap pointed to a blockage that trapped pressure in the deeper regions.

The shallow crust near Pu‘u‘ō‘ō later experienced rising pressure. Seismic waves sped up in that zone.

Wave speed increases when cracks close under stress. This change suggested that magma pushed sideways toward the rift zone.

Magma moving sideways

The researchers proposed that magma shifted from the summit into the horizontal dike system. This sideways path lasted for months.

Pressure increased beneath Pu‘u‘ō‘ō. Cracks sealed under stress, and seismic waves traveled faster.

The pattern continued until a magnitude 5 earthquake struck the volcano’s flank. That quake likely opened the blocked connection between the reservoirs.

Increased pressure then surged upward and disturbed the summit for months. These shifts marked the final stage before the 2018 eruption.

Listening with waves

Researchers monitored Kīlauea using seismic noise created by ocean waves. This method works even without clear earthquakes.

“The ocean provides a constant supply of seismic energy, allowing us to track the status of Kīlauea’s magma plumbing system over time, even when there are no noticeable earthquakes or ground deformation,” explained Professor Wu.

Changes in wave travel times revealed stress patterns inside the volcano. Cracks opened or closed depending on pressure.

Wave paths shifted with each small movement. This approach captured a quiet record of the volcano’s inner pulse.

Kīlauea’s quiet eruption signals

As months passed, the deeper reservoir continued to inflate. The shallow reservoir remained under-supplied. The imbalance grew.

Data showed a stronger mantle input between 2015 and 2017. The deeper reservoir accepted this new supply, but the blockage kept it from rising.

These long signals explain the later surge. When the blockage loosened, pressure rose into the shallow system. That surge disrupted the summit and prepared the volcano for major activity.

Gradual changes add up

The study gives a new view of magma transport. It shows how deep changes build over years.

These changes do not always appear at the surface. Instead, they hide in pressure shifts, crack behavior, and wave travel times.

By tracking these subtle patterns, scientists can understand how magma chooses new paths. They can also learn how blockages form and release.

These insights help explain eruptions that seem sudden but grow from long internal shifts.

Eruption insights from Kīlauea

“As a UH Mānoa faculty member dedicated to understanding Kīlauea, my goal is to contribute to volcanic hazard mitigation and support the safety of Hawaiʻi’s residents,” said Professor Wu.

This work strengthens that goal. It shows how careful monitoring can reveal slow, silent signals. It also shows why eruptions require long study.

The volcano speaks through pressure, cracks, and waves. Scientists now hear those messages with growing clarity.

The study is published in the journal AGU Advances.

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