Volcano Watch: Underneath Kilauea’s new landscape, the magma plumbing keeps working

  • K. Mulliken/USGS photo A view from Sept. 2 of the 2018 Kilauea caldera collapse structures from Kilauea Overlook within Hawaii Volcanoes National Park.

Last week, Hawaii Volcanoes National Park was able to open the Kilauea Overlook to the public for the first time since the lower East Rift Zone eruption and summit collapse in 2018. The viewing location offers a new perspective on the breathtaking summit collapse structures and the major changes those collapses had on Kilauea’s landscape.

From May 16-Aug. 2, 2018, pieces of Kilauea caldera dropped downward in a series of 62 individual collapse events. At the end, the deepest part of Halema‘uma‘u had descended 500 m (1,600 feet); more than enough to fit the Empire State Building. The eastern section of the caldera floor was lowered by 140 m (460 feet), creating a new cliff face in the interior of Kilauea caldera just as high as the caldera cliff face under Kilauea Overlook.

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While these collapses were happening, it was clear the summit would never look the same. Those of us watching at the USGS Hawaiian Volcano Observatory also wondered if the underlying summit magma system would ever behave the same.

Prior to 2018, geophysical data showed a complex system of magma storage chambers under Kilauea summit. One of the most prominent was a shallow chamber (about 1.6 km, or 1 mile, deep) under Kilauea caldera, called the Halema‘uma‘u reservoir. This reservoir was connected to the surface via a conduit that formed the Overlook crater and supplied lava to the summit lava lake.

The first clue about the post-collapse state of the shallow reservoir came in October 2018 when summit tiltmeters picked up a phenomenon called a deflation-inflation event (DI-event). Before the 2018 collapses, DI-events occurred regularly and could be observed from summit tiltmeter records and in the changing lava lake height. Together these data showed that the shallow Halema‘uma‘u reservoir was deflating and re-inflating repeatedly.

While DI-events were clearly observable at Kilauea’s summit, tiltmeters near Pu‘u ‘O‘o recorded similar motions just with a slight time delay. The fact that pressure changes during the deflation and inflation of the summit reservoir could be transmitted so directly to Pu‘u ‘O‘o was an indication of how closely connected the East Rift Zone was to the summit magma system.

It was with a little excitement that the first clear post-eruption DI-event was observed in October 2018. The shape and size of the event was very similar to pre-eruption DI-events, indicating that the shape and size of the shallow Halema‘uma‘u reservoir must not be too different from its pre-eruption state. Furthermore, tiltmeters on the East Rift Zone showed a faint trace of a DI-event just following the October event. This indicated that the close connection between the shallow Halema‘uma‘u reservoir and the East Rift Zone still exists.

Since then, a more in-depth analysis has been done that gives us more clues about the shallow Halema‘uma‘u reservoir.

In a December 2019 article in Science magazine, USGS scientists detailed how deformation data from the intense deflation of the summit magma chambers during the first weeks of the 2018 eruption, together with observations of the descending lava lake, allowed them to calculate the total amount of magma in the Halema‘uma‘u reservoir more precisely than ever before.

Taking into account the natural uncertainty of the data, they found the most likely volume of the reservoir to be just less than 4 cubic km (about 1 cubic mile). Given the collapse volume of 0.8 cubic km (0.2 cubic miles), this means only about 20% of the reservoir was emptied during the 2018 eruption and 80% of the reservoir’s magma is still underneath the summit.

So, while the surface of Kilauea caldera has undergone a major remodel, underneath, the magma plumbing system still works in much the same way it did before.

This is reassuring because it means what we learned about Kilauea’s magma system during the past several decades can still be applied to our current monitoring efforts. It also means we can continue to improve our understanding of the 2018 eruption by using observations we make now.

The 2018 eruption has already provided incredible insights into Kilauea’s structure and behavior, and we look forward to learning even more.

Volcano activity updates

Kilauea Volcano is not erupting. Its USGS Volcano Alert level remains at Normal (https://volcanoes.usgs.gov/vhp/about_alerts.html). Kilauea updates are issued monthly.

Kilauea monitoring data for the month of August show variable but typical rates of seismicity and ground deformation, low rates of sulfur dioxide emissions and only minor geologic changes since the end of eruptive activity in September 2018.

The water lake at the bottom of Halema‘uma‘u continues to slowly expand and deepen. For the most current information about the lake, see https://volcanoes.usgs.gov/volcanoes/kilauea/summit_water_resources.html.

Mauna Loa is not erupting and remains at Volcano Alert Level Advisory. This alert level does not mean an eruption is imminent or progression to eruption from current level of unrest is certain. Mauna Loa updates are issued weekly.

This past week, about 140 small-magnitude earthquakes were recorded beneath the upper-elevations of Mauna Loa; most of these occurred at shallow depths of less than 8 kilometers (about 5 miles).

GPS measurements show long-term slowly increasing summit inflation, consistent with magma supply to the volcano’s shallow storage system. Gas concentrations and fumarole temperatures as measured at Sulphur Cone and the summit remain stable. Webcams show no changes to the landscape.

For more information about current monitoring of Mauna Loa Volcano, visit https://volcanoes.usgs.gov/volcanoes/mauna_loa/monitoring_summary.html.

There were three events with three or more felt reports in the Hawaiian Islands during the past week: a M2.9 earthquake 1 km (0 mi) east-southeast of Pahala at 30 km (19 mi) depth at 5:09 p.m. Sept. 1, a M2.6 earthquake 4 km (2 mi) west-southwest of Volcano at 0 km (0 mi) depth at 6:15 p.m. Aug. 27 and a M2.1 earthquake 9 km (5 mi) south of Waikoloa at 28 km (17 mi) depth at 12:51 p.m. Aug. 27.

HVO continues to closely monitor Kilauea and Mauna Loa for any signs of increased activity.

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Visit HVO’s website for past Volcano Watch articles, Kilauea and Mauna Loa updates, volcano photos, maps, recent earthquake info and more. Email questions to askHVO@usgs.gov.

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

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