(BIVN) – Episode 23 in the ongoing Kīlauea eruption remains in a “precursory activity” phase, and scientists have noted a change in the rate of inflation at the summit. 

The USGS Hawaiian Volcano Observatory says a notable decrease in the rate of summit inflation since Wednesday “has likely delayed the onset of sustained fountaining compared to previous episodes.” The Observatory says sustained fountaining could begin at any time through the weekend. 

USGS: “A USGS Hawaiian Volcano Observatory geologist uses an FTIR (Fourier transform infrared spectrometer) to measure the chemical composition of volcanic gas during cycles of spattering and seismic tremor at the active vent at Kīlauea summit on May 22, 2025.” (USGS photo by M. Patrick)

From the USGS HVO on Saturday morning:

Strong glow and intermittent spatter was visible in both vents overnight with occasional flames seen in the north vent. This is similar to activity seen in the lead up to previous sustained fountaining episodes. Although activity is expected to increase before the onset of sustained fountains, there is no way to estimate the duration of precursory activity.

The rate of summit inflation has slowed significantly, with tiltmeters at Uēkahuna (UWD) and Sandhill (SDH) recording a total of 1 microradian of inflation since Wednesday. Small variations in summit tilt rates are not uncommon, but this represents a departure from previous inter-episode trends. Total inflationary tilt recorded at UWD is just under 10 microradians since the end of episode 22 on May 16. Low level tremor continues beneath Halemaʻumaʻu crater.

The average sulfur dioxide (SO2) emission rate remains around 1,200 tonnes per day (t/d), similar to rates recorded during prior pauses.

USGS: “This reference map depicts the Kīlauea summit eruption within Halema‘uma‘u crater that began on December 23, 2024. As of this posting on May 21, the eruption continues episodically. Most of the map data included here were collected during a Hawaiian Volcano Observatory helicopter overflight on May 14, between episodes 21 and 22; for this reason, the provided statistics only reflect the first twenty-one episodes of the eruption.”

Analysis: 

The current eruption has been characterized by episodic fountaining not seen in any eruptions since the 1983-86 episodic fountains at the beginning of the Puʻuʻōʻō eruption. Fountains and lava flows have erupted from two vents within Halema’um’a’u crater that we refer to as the north vent and south vent. Each of the previous fountaining episodes lasted from a few hours to over a week and have been accompanied by strong deflation of the summit region. Pauses between the fountaining episodes have been marked by an immediate change from deflation to inflation as the magma chamber recharges and repressurizes.

Episode 22 ended on May 16. The rapid rebound of tilt at the end of episode 22 from deflation to inflation, along with persistent strong glow from the vents, indicates that magma remains shallow in both the north and south conduits. The notable decrease in the rate of summit inflation, recorded on all summit tiltmeters, has likely delayed the onset of sustained fountaining compared to previous episodes. Although current rates of inflation are low, renewed fountaining activity may occur at any time through the weekend. Estimates of fountaining onset will be refined as more data become available.

HVO continues to closely monitor Kīlauea and is in contact with Hawai‘i Volcanoes National Park and the Hawai‘i County Civil Defense Agency about eruptive hazards.