Volcano Watch: Recent intrusions follow pattern of previous events

Since July 2024, activity at Kilauea has been punctuated by two periods of intense unrest, centered on the upper East Rift Zone (ERZ). The periods included hundreds of earthquakes per day and high rates of tilting in the upper ERZ. Monitoring data have shown that the unrest was the result of two intrusions into a region of the ERZ between Pauahi and Makaopuhi Craters.

This is not the first time these areas have experienced intrusions: two similar events occurred in 2007 and 2011, during the era of the Pu‘u‘o‘o eruption. An intrusion is an injection of magma into rock that causes ground deformation and seismicity but does not result in an eruption.

The 2007 Father’s Day intrusion occurred in the ERZ, in a very similar location to the recent intrusions. In fact, the Father’s Day event included a very small eruption, but the majority of the magma transferred into the ERZ did not erupt, so it is more often remembered as an intrusion. This event did not fundamentally change the eruptive vent at Pu‘u‘o‘o, which had been erupting since 1983 and kept doing so until 2018.

In 2011, the Kamoamoa eruption occurred, also on the ERZ and geographically in between where the Father’s Day intrusion happened and Pu‘u‘o‘o, which was the active vent on the ERZ at the time. Kilauea was also erupting in the form of a lava lake in Halema‘uma‘u crater at the summit. Although the level of lava in the summit lake lowered due to the 2011 intrusion, the event did not dramatically alter the location or style of eruptions from Kilauea.

A couple things have changed since the last events on this part of the ERZ. Pu‘u‘o‘o is no longer erupting, and much of the magma that had been stored in the rift was emptied out during the 2018 lower ERZ eruption. This means the rift is not as full as it was during the 2007 and 2011 eruptions. There has also been a vocabulary change for how we talk about this part of the rift.

Previously, the ERZ was divided into upper, middle and lower sections. The “upper” section, or UERZ, is the segment that bends to the north and intersects with the caldera. The UERZ is unique in that there has not been measurable spreading across the rift. Instead, opening occurs on faults oriented at angles similar to the rift trace (generally west-east trending) consistent with the direction of opening in the middle and lower ERZ. Because of this, USGS Hawaiian Volcano Observatory (HVO) scientist Don Swanson suggested referring to the upper section as the “East Rift Connector,” because it connects the “proper” east-trending part of the ERZ to the caldera. These days, you might see either term used, though they refer to the same structure.

On July 22, 2024, a seismic swarm on the UERZ heralded a shift in activity away from the southern Kilauea caldera region. The seismicity and deformation indicated that magma was pushing open an underground crack, oriented at an angle to the connector, but parallel to the main rift. That is, in a similar direction to the 2007 and 2011 events.

Again, on August 20, seismicity in the UERZ and deformation indicated an intrusion into a crack oriented at an angle to the UERZ but parallel to the main rift, but this time slightly to the north of the July intrusion.

These intrusions have been accompanied by steady inflation of the middle ERZ that is ongoing as of September 2024. The center of inflation has moved around, indicating that the storage structure of the rift is not simple. However, all the locations have been up rift of Pu‘u‘o‘o; so far, there has not been evidence of significant amounts of magma traveling past Pu‘u‘o‘o and further down the rift.

Given that the 2007 and 2011 intrusions had a limited effect on the Pu‘u‘o‘o eruption, it is not clear what these recent events might indicate for the future. However, following the 2018 eruptions, HVO worked to build out our monitoring instrument coverage on Kilauea’s ERZ, into areas that had previously been part of the active Pu‘u‘o‘o flow field. We will continue to monitor these instruments closely for any sign of magma migration.

Volcano activity updates

Kilauea is not erupting. Its USGS Volcano Alert level is ADVISORY.

Seismic activity and ground deformation continues at Kilauea’s summit and upper-to-middle East Rift Zone, at slightly reduced rates compared to the previous week. Over the past week, about 300 earthquakes were detected beneath Kilauea’s upper East Rift Zone and about 200 events were detected between Maunaulu and Pu‘u‘o‘o in the middle portion of the East Rift Zone within Hawaii Volcanoes National Park. Over the past week, Kilauea’s summit and middle East Rift Zone continued to show overall slow inflation. Additional pulses of unrest in the upper to middle East Rift Zone are possible and may evolve quickly.

Mauna Loa is not erupting. Its USGS Volcano Alert Level is at NORMAL.

No earthquakes were reported felt in the Hawaiian Islands during the past week.

HVO continues to closely monitor Kilauea and Mauna Loa.

Please visit HVO’s website for past Volcano Watch articles, Kilauea and Mauna Loa updates, volcano photos, maps, recent earthquake information, 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.