Volcano Watch: More than 1,600 earthquakes recorded on Kīlauea since late April

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

Earthquake activity in the upper East Rift Zone, directly southeast of Kaluapele (Kīlauea’s summit caldera), increased around midnight of April 27.

Since then, over 1,600 events have been recorded, most extending from Keanakākoʻi crater southeast towards Pauahi Crater. Most earthquakes have been smaller than magnitude 2, taking place at depths of 1.2-1.8 miles beneath the ground surface.

Patterns of ground motion are consistent with inflation of the two main magma storage regions beneath Kīlauea – Halemaʻumaʻu and South Caldera. These magma bodies, which are long-term features of Kīlauea’s summit plumbing system, began to re-inflate in tandem about a month after the short-lived September 2023 eruption. They then fed the intrusion into the Southwest Rift Zone in late January-early February 2024.

Thousands of earthquakes accompanied that intrusion as magma moved underground to the southwest, where ground deformation was significant enough to cause ground cracks to appear on the surface along the Maunaiki Trail in Hawaiʻi Volcanoes National Park.

Since the Southwest Rift Zone intrusion earlier this year, instruments have once again been showing signs of Kīlauea’s shallow magma plumbing system refilling. The Sand Hill tiltmeter, which is sensitive to the deeper South Caldera magma reservoir of Kīlauea, has shown steady inflationary tilt since early February. Data indicate that the South Caldera reservoir has regained the volume of magma that it lost during the recent intrusion, such that pressurization levels are now similar to pre-intrusion levels.

The Uēkahuna tiltmeter is more sensitive to the Halemaʻumaʻu reservoir, which has been the source for recent summit eruptions. The Uēkahuna tiltmeter has shown slower inflation than SDH over the past few months, which implies that the South Caldera reservoir continues to be the main focus of magmatic recharge.

During the long-lived Puʻuʻōʻō eruption, earthquake activity in the upper East Rift Zone of Kīlauea sometimes occurred along with increased rates of tilt at Kīlauea summit; this indicated that the summit magma reservoirs were becoming increasingly pressurized. When the 2008-2018 summit lava lake was active in Halemaʻumaʻu, this increased pressurization was visible as a rise in the level of the lava lake, with its level acting like a barometer of the underlying Halemaʻumaʻu magma chamber.

The current increases in the number of earthquakes (particularly in the upper East Rift Zone) and rates of ground inflation are showing us that Kīlauea’s magma storage system is becoming primed for its next event. One potential outcome could be another significant intrusion – when magma moves into a new area within the volcano but fails to erupt on the surface – such as what occurred along the Southwest Rift Zone during late January/early February of this year. Another potential outcome could be another eruption, either inside or outside the caldera.

The eruptions within Kaluapele over the past several years have been preceded by about an hour of rapidly occurring earthquakes and greatly increased rates of ground deformation in the summit region as magma makes its way to the surface. An eruption outside of the caldera, along one of the rift zones, would likewise be preceded by rapidly occurring earthquakes, along with greatly increased rates of ground deformation in the region of magma movement outside the summit region.

USGS Hawaiian Volcano Observatory staff are closely monitoring and do not currently see signs of such magma movement in the dense network of monitoring instruments on Kīlauea; currently activity is confined to the upper East Rift Zone and summit only.

Though Kaluapele has been home to the last few years of eruptions, pit craters and lava flows in the upper East Rift Zone are evidence of a long history of magma moving along this rift zone pathway. Most recently, in November 1979, a brief one-day eruption occurred in and near Pauahi Crater; it was preceded by two months of 200-800 earthquakes occurring daily, along with inflation at the summit region.

Currently, there are no signs that an eruption is imminent; however, Kīlauea monitoring data indicate that magma is once again accumulating and pressurizing in the long-lived magma bodies beneath Kīlauea’s summit. How that pressure is released remains to be seen – the USGS Hawaiian Volcano Observatory is closely monitoring multiple datasets for clues.