A shallow intrusion of magma opened a new path beneath the summit of Kīlauea on the night of September 30 to October 1, 2026, even as lava continued to erupt from the north and south vents in Halemaʻumaʻu, according to the USGS Hawaiian Volcano Observatory.
Kīlauea's summit has remained at a high level of pressurization since early September, a condition that typically ends in a lava fountaining episode. Lava has not fountained since episode 54 ended on August 25, though six new vents on and near the northwest wall of Halemaʻumaʻu erupted from September 14–16, producing small lava flows without high fountaining.
Beginning at about 2:00 p.m. HST on September 30, a flurry of earthquakes struck roughly 1 mile (1.5 km) below the active vents. That swarm lasted about six hours and produced more than 30 located events. Seismic activity then migrated northeast around 8:00 p.m. HST, continuing at high rates for nearly eight hours near an area where satellite imagery had shown ground changes between September 11–27.
The largest event, a magnitude 3.4 earthquake about 1 mile (1.4 km) below the surface, occurred at 9:52 p.m. and prompted 30 submitted felt reports. More than 50 earthquakes were detected in the second swarm before activity subsided around 4:00 a.m. HST on October 1, though seismic activity in the region is ongoing.
Tiltmeters recorded extremely rapid changes consistent with crack growth in an east-west orientation near the vent area. The Uēkahuna tiltmeter (UWD) recorded about 40 microradians of inflation. Overflows from the existing vent complex stopped just before the intrusion began, while flames and spatter continued, and overflows resumed once seismicity migrated away.
A monitoring overflight on the morning of October 1 found no anomalously hot areas or obvious new ground cracks, though much of the caldera floor is already cracked from the 2018 summit collapse and later eruptions. Lava was observed deep within the north vent.
Another fountaining event remains possible from the north/south vent complex, HVO said. Lava could also erupt passively from the September 30 intrusion or other crack systems, or magma could intrude new areas, potentially forming new vents. Activity has been confined to the summit for nearly two years, but magma could eventually migrate out of the region with little to no warning, HVO said, adding that there are no signs of that so far.
Kīlauea has erupted episodically within the summit caldera since December 23, 2024, and its USGS Volcano Alert level is WATCH. Mauna Loa is not erupting and remains at NORMAL.