“Kīlauea summit magma system is in a complex balance of magmatic pressure and strength of the surrounding rocks.” This balance has been described for more than a year as a repeating summit process: fast deflation during lava fountaining in Halemaʻumaʻu, followed by reinflation during pauses. The current summit eruption has been characterized by episodic activity from two vents, with models indicating that the shallow Halemaʻumaʻu magma chamber depressurizes rapidly during high-effusion fountaining episodes and then recovers towards a threshold that commonly precedes an episode. The process has been regular enough to allow short-term prediction on the basis of deformation and tremors.
Within this familiar cycle, two longer-term trends have been monitored through the modeling of the summit GPS network. The modeled pressurization that reached in the shallow chamber before each new fountaining event has been increasing, while the modeled pressurization in the deeper south caldera magma chamber has been decreasing since the eruption began in late 2024. The increasing shallow pressurization has been associated with a higher effusion rate, which has been described as about twice Kīlauea’s magma supply rate.
Until mid-January, the plumbing system that links the vents to the shallow reservoir had been remarkably steady, with very few earthquakes. Following the end of episode 40 on January 12, there were periodic swarms of very small earthquakes that began to occur beneath Halemaʻumaʻu and the south caldera area, typically at depths of 1.5-4 km (1-2.5 miles). These earthquakes were typically smaller than magnitude 1, and the locations of the earthquakes were spread out, rather than being concentrated in a line that would define a single new crack or conduit. Some of these swarms were accompanied by small deflationary steps that interrupted the inflationary tilt trend.
This combination of a continued overall inflation between swarms, together with a short-lived deflation synchronous with small earthquakes, indicates a summit area where pressure is still building while stress is adjusting in small increments. In this context, the swarms of inflation have been interpreted as an indication of a change in conditions without necessarily indicating that magma has established a new, organized channel to the surface.
Episode 41 offered another look at how the system is operating during the current episode. The fountaining episode began on January 24 and lasted for 8 hours and 18 minutes, with estimated maximum fount heights of 460-480 m and a maximum effusion rate of 1050 cubic yards (800 cubic meters) per second. An estimated 14 million cubic yards (11 million cubic meters) of lava covered 80-85% of the Halemaʻumaʻu crater floor, and the Uēkahuna tiltmeter recorded about 31 microradians of deflationary tilt during the episode, as expected for rapid drawdown of shallow storage. The run-up included precursory overflows and a brief swarm during a sharp deflation step, after which inflation resumed and returned to the amount lost in the previous episode, which fits with the episodic pattern of activity as described for the eruption.
The key difference relevant to the new swarms is again the episode 30 event, where a brief vent opened in the southwest wall of Halemaʻumaʻu. In this event, earthquakes were strongly grouped around the magma pathway to the surface, and deformation patterns suggested magma intrusion into a new region. In the summit swarms of the past few weeks, the scattered points and small, transient deformation changes have not indicated this characteristic of concentrated crack growth. Eruptions in older summit and rift zone episodes give insight into what is possible under sustained pressure and its effects on eruption style.
Previous episodic eruption sequences at Puʻuʻōʻō (1983) and Maunaulu (1969) transitioned after their fountaining episodes, and summit activity has included transitions into the Southwest Rift Zone, such as the 1919 transition to the Maunaiki eruption. Current monitoring capabilities now include these possibilities with dense seismic, deformation, gas, and thermal coverage; one indicator of the recent summit pause was a measured summit sulfur dioxide emission rate of 1550 tons per day, consistent with previous pauses and significantly lower than fountaining rates.
For the viewer, the essential engineering-scale observation is that the process is being influenced by measurable pressure changes in two interrelated magma storage areas and the surrounding rock. The recent eruption swarms have introduced a new dynamic to this process one of small, rapid changes without yet indicating the focused signals that accompanied the opening of a new vent in 2025 or the more substantial deformation transfers that were seen during the emplacement of a dike beneath Kaluapele in June 2024.
