More than 90 earthquakes shook a US volcano and triggered a new magma intrusion beneath the summit

The United States Geological Survey recorded 98 earthquakes at the summit of Kīlauea volcano over a 24-hour period. (USGS)More than 90 shallow earthquakes shook the summit of Kīlauea volcano in Hawaii during the 24 hours preceding October 1, coinciding with a magma intrusion beneath the Halemaʻumaʻu crater. The largest quake reached a magnitude of 3.4. The activity was concentrated in the area where an episodic eruption has continued since December 2024, according to the United States Geological Survey. The Hawaiian Volcano Observatory, part of the United States Geological Survey (USGS), located 98 earthquakes beneath the summit region, mainly below Halemaʻumaʻu. Most of the intrusive activity occurred between 8:00 p.m. on September 30 and 3:00 a.m. on October 1, local time, according to the USGS daily update. The intrusion did not produce a new surface lava output, although monitoring detected accelerated ground deformation and sustained activity at the north, south, and west vents. Kīlauea retains the WATCH alert level and the orange aviation code, according to the Hawaiian Volcano Observatory. The official count was 98 shallow earthquakes in 24 hours within the Kīlauea summit region, with the greatest concentration beneath Halemaʻumaʻu. The USGS daily report specified that the movements were located, for the most part, in the western part of the crater and in the northwest sector of Kaluapele, the summit caldera. The sequence began at around 2:00 p.m. on September 30, when instruments recorded a first cluster of quakes at a depth of about 1.5 kilometers beneath the active vents. That first swarm lasted for approximately six hours and accumulated more than 30 located events, according to a weekly report from the Hawaiian Volcano Observatory. Starting at 8:00 p.m., seismicity shifted to the northeast of the vents. The second swarm remained active for nearly eight hours and exceeded 50 detected earthquakes. The USGS indicated that this sector coincided with an area where satellite data had already shown ground modifications between September 11 and 27. The highest-magnitude movement occurred at 9:52 p.m. on September 30. The quake reached a magnitude of 3.4 and occurred at a depth of about 1.4 kilometers, within the group of events located north of the eruptive area. The observatory received 30 reports from people who felt that tremor, according to the USGS. Seismic activity began to decrease after 3:00 a.m. on October 1. The reduction coincided with the stabilization of inflation signals at the summit, although the federal agency noted that earthquakes in the area had not ceased entirely, according to the USGS update. A magnitude 3.4 tremor at a depth of 1.4 kilometers became the strongest seismic event of the day. (U.S. Geological Survey/Handout via REUTERS)Data collected by the monitoring network showed that a shallow magma intrusion advanced beneath the summit during the night between September 30 and October 1. An intrusion describes the movement of magma within the crust without necessarily reaching the surface, according to the Hawaiian Volcano Observatory. The summit tiltmeters began to show rapid variations shortly after 8:00 p.m. The pattern was consistent with the opening or widening of an east-west-oriented fracture in the vicinity of the active vent complex, according to the USGS daily report. The Uēkahuna tiltmeter recorded about 38.5 microradians of inflation between 8:00 p.m. and 3:00 a.m. The USGS corrected the figure after detecting a brief disturbance in the signal associated with the magnitude 3.4 earthquake. After 3:00 a.m., inflation stopped increasing and the number of quakes declined. The institution explained that the intrusive activity was most intense during that overnight interval. The process was accompanied by an increase in volcanic tremor, a seismic signal linked to the movement of fluids and magma, as well as by rapid displacements recorded on equipment installed around the caldera, according to the USGS. Geologists from the Hawaiian Volcano Observatory conducted a monitoring flight during the morning of October 1. Visual and thermal cameras did not identify abnormally hot areas or evident new cracks. The agency clarified that the caldera floor already has numerous fractures from the 2018 summit collapse and from subsequent eruptions and intrusions, according to the USGS. The official report also detected no lava in a new location. That finding does not rule out the possibility that magma could change course beneath the summit, but it establishes that the intrusion recorded overnight did not open a new surface vent at that time, according to the Hawaiian Volcano Observatory. Episode 55 of Kīlauea remains a possibility, but the USGS indicated that it cannot determine whether the magma intrusion will trigger a new phase of lava fountaining. Current eruptive activity remains limited to the summit area, where the eruption began on December 23, 2024. Kīlauea has since alternated between episodes of lava fountaining and pauses of two or more weeks. Those events usually last less than 12 hours. Episode 54 ended on August 25, but the system maintained elevated pressure from early September, accompanied by an increase in small earthquakes beneath the summit, according to the USGS. The agency reported that the north and south vents maintained intermittent lava overflows, spattering, and an intense glow during the night. The west vent also showed glow and flames. No other incandescent areas were detected at the summit, according to the Hawaiian Volcano Observatory update. The north vent produced several overflows on September 30, including one with a small dome-shaped lava fountain. Another overflow lasted more than an hour in the afternoon. The south vent resumed overflow activity after the intrusion lost intensity, according to the USGS. In total, scientists counted at least 10 overflows during and after the main phase of the intrusion. The agency noted that the north and south vents had persistent glow and spattering during the night, while the west showed occasional glow, according to the Hawaiian Volcano Observatory. Activity outside the summit remained low. The USGS detected no significant deformation or anomalous seismicity in the eastern and southwestern rift zones, structures through which magma could move outside the caldera. It also reported no significant changes in sulfur dioxide emissions from those areas. An underground magma intrusion advanced beneath the Halemaʻumaʻu crater without producing a new lava output at the surface. (USGS via AP)The USGS maintains surveillance over four variables: seismicity, ground deformation, gas emissions, and changes at the vents. The federal agency reported that the summit retains elevated pressure, a condition that can sustain the activity of the current vents or favor the advance of magma toward existing fractures. The scenario of a new intrusion remains among the possibilities considered by the observatory. The USGS noted that an intrusion can remain contained beneath the surface or open new vents, and that these changes could occur with limited seismic or deformation signals. The institution maintained the WATCH volcanic alert level and the orange aviation code. That classification indicates that the volcano is exhibiting elevated activity and that there is potential for changes in its eruptive behavior, according to the official scale of the United States Geological Survey. The Hawaiian Volcano Observatory continues to be in contact with Hawaiʻi Volcanoes National Park and the Hawaiʻi County Civil Defense Agency. Authorities will continue to monitor instrumental measurements and aerial observations to detect changes in magma behavior and in access conditions to areas near the caldera. For residents, visitors, and aircraft operators, official USGS updates and national park notices will be the references for following the evolution of Kīlauea. Monitoring will continue to focus on the summit, where data show that eruptive activity and underground pressure remain active.