Hawaiian Volcano Update: Kīlauea Summit Eruption’s Episode 55 & New Fissure - October 21, 2026
Episode 55 of Kīlauea’s ongoing summit eruption finally arrived on Saturday, October 17, more than 7 weeks after episode 54. When it finally arrived after 21 hours of continous overflows peaking out of all 3 vents, it also broke open a small new fissure on the northwest caldera floor, not far from the north vent where the main fountain later grew up to 720 feet or 220 meters high, sending lava across the landscape that covered the new fissure along with 75% of Halemaʻumaʻu crater floor. Although only vigorously active for about 5.7 hours, about 7 million cubic meters of lava were erupted, the largest output and eruption rate since episode 43 in early March, when double fountains were last active.
The small new fissure opened in a similar location to the 6 vents at the base of the northwest caldera wall which erupted from September 14 to 16, which we preliminarily refer to as episode 54A following the naming conventions used during the Puʻuʻōʻō eruption. That first delay to episode 55 came 3 weeks after episode 54, and 2 weeks before the September 30 to October 1 intrusion in a similar area beneath the north caldera wall. However, there have been no signs of reactivation of any of the 3. Rather, the previous recharge pattern typical between episodes appears to be underway with no interruptions through its first 4 days, although tiltmeters show signs of a slowdown today. According to the USGS Hawaiian Volcano Observatory, while “there is uncertainty in whether future episodes will return to the regular, predictable patterns that allowed them to be forecast with reasonable precision,” based on ground-tilt data “the preliminary forecast is for episode 56 to occur between October 28 and November 5, 2026.”
Trade winds from the north-northeast were dominant during the episode, across which an estimated 50,000 tonnes of SO2 were released along with significant tephra. Fortunately, the great majority of the tephra remained below 8,000 feet or 2,400 meters above sea level, falling into the closed area of Hawaiʻi Volcanoes National Park, even as the main emissions plume topped out at 25,000 feet or 7,500 meters above sea level. Since the end of the episode, both vents continue to emit roughly 1,000 to 5,000 tonnes of SO2 per day, which combined with the episode 55 output continues to linger over Hawaiʻi Island. When trade winds blow, emissions can be carried substantial distances across the south side of the island including the Kaʻū district still recovering from Hurricane Lala, wrapping around to the Kona coast as reflected by today’s air quality readings. Light winds from Thursday through the weekend further increase the possibility of vog in nearby communities. Both during and between episodes, vog and tephra remain the most common hazards for island residents, and the usual precautions and preparations apply, especially for those with respiratory sensitivities – more information at https://vog.ivhhn.org/.
Earthquakes have slowed under Kīlauea summit following episode 55, largely returning to recent patterns. That includes persistent south flank activity and deep quakes under Kīlauea and Maunaloa summits, as well as the hotspot feeder zone beneath Pāhala. Several quakes clustered towards the end of episode 55, near the vent area and recent intrusion site, highlighted by a magnitude 2.1. As usual, we summarize the monitoring signals, imagery, and reports available courtesy of the USGS Hawaiian Volcano Observatory as well as our broader community, annotating the presentation on-screen and discussing live viewer questions as we go.
