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 HVO geophysicist Ingrid Johanson. 

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This is not the first time these areas have experienced intrusions, two similar events occurred in 2007 and 2011, during the era of the Puʻuʻōʻō 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 Puʻuʻōʻō, 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 Puʻuʻōʻō, which was the active vent on the ERZ at the time. Kīlauea was also erupting in the form of a lava lake in Halemaʻumaʻu 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 Kīlauea.

A couple things have changed since the last events on this part of the ERZ. Puʻuʻōʻō 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 Kīlauea 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 again 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 Puʻuʻōʻō; so far, there has not been evidence of significant amounts of magma traveling past Puʻuʻōʻō and further down the rift.