A week dominated by the wait for Kīlauea Episode 48. The forecast window opened on 24 May and has been repeatedly pushed back by irregular deflation-inflation events at the summit — a pattern HVO have noted is capable of delaying onset. As of the 28 May daily update, the window is Thursday to Saturday 28–30 May and the tiltmeter has recovered nearly all the 15.6 microradians lost during Episode 47. Meanwhile Piton de la Fournaise is stirring again after a brief geochemically quiet phase, and Mayon continues to slowly extend its Mi-isi flow.
Episode 48 has been teased all week. Inflation hit 15.1 microradians on 25 May — within touching distance of the 15.6 lost in Episode 47 — then the summit switched abruptly to deflation on the afternoon of 25 May. Inflation returned on 26 May noon. Then another deflation wobble. These irregular DI events are a known feature of the current eruptive system, and HVO say they can delay but not prevent the next episode. Both vents are glowing brightly with flames visible overnight. It is imminent.
🇺🇸 Kīlauea Advisory · Yellow
The week began with summit reinflation tracking steadily following Episode 47's end on 15 May. By 25 May the UWD tiltmeter had tracked 15.1 microradians of inflationary tilt — slightly less than the 15.6 microradians of deflationary tilt recorded during Episode 47, suggesting the system was very close to the threshold needed to trigger fountaining. At 4:00 PM HST on 25 May, inflation switched abruptly to deflation, pushing HVO's Episode 48 forecast window out from 25–26 May to 27–29 May. Summit inflation returned on 26 May at noon. Further irregular deflation resumed later that week, with HVO's 28 May update noting 15.1 microradians total accumulated reinflation and a forecast window of Thursday 28 to Saturday 30 May. As of publication, no precursory overflows have occurred and Episode 48 has not yet begun.
Throughout the week, bright glow and flames were visible overnight from both eruptive vents — the most active inter-episode vent activity seen during the current repose period. HVO noted on 25 May that SO₂ emissions from the summit during the pause were varying within a typical range of 1,000–5,000 tonnes per day, with a measurement of approximately 2,000 tonnes per day recorded on 22 May. A M6.0 earthquake on the west side of the island on 22 May at 9:46 PM HST caused a small instrumental offset in the tiltmeter data but had no apparent impact on volcanic activity at Kīlauea or Mauna Loa — HVO confirmed this explicitly in an Information Statement issued that night. The earthquake occurred at a depth of 22 km south of Hōnaunau-Nāpōʻopoʻo and was caused by stress from bending of the oceanic plate under the weight of the islands, not by volcanic processes. Minor structural damage and rockslides were reported in South Kona.
🇷🇪 Piton de la Fournaise Alert 2-2 · Stirring
A significant shift in Piton de la Fournaise's monitoring data this week. As reported last week, both summit and far-field GNSS stations had gone quiet — the most genuinely inter-eruptive state the system had been in since before the January 2026 eruption began. That changed on 27 May. The OVPF preliminary bulletin for 27 May, published early on 28 May, reports that the summit area GNSS stations are once again recording inflation — a sign of pressurisation of a shallow source. This is the first return of summit inflation since the end of the fourth 2026 eruption on 12 April, after a period of approximately six weeks when neither shallow nor deep sources showed geodetic signals.
The far-field GNSS stations are not yet recording particular signals, suggesting the deep source remains quiet for now — the reactivation is currently confined to the shallow system. Geochemically, SO₂ and H₂S at the summit are still at background levels below 0.1 ppmv, and the CO₂ flux at the PCRN monitoring station continues its decreasing trend. This combination — shallow inflation returning while geochemistry remains quiet — is consistent with the early stages of a shallow recharge cycle rather than imminent eruption. But given Piton's 2026 tempo of four eruptions in under four months, this shallow signal is worth tracking closely. OVPF continue to monitor 24 hours a day.
🇵🇭 Mayon Alert 3 · 143+ days
Mayon's effusive eruption ground through its 143rd consecutive day this week without meaningful change in alert status, but with a notable measurement: the Mi-isi Gully lava flow extended a further 100 metres to reach 1.8 km by 24 May. This is the second consecutive weekly advance in the Mi-isi drainage — it stood at 1.3 km at the start of May, reached 1.6 km last week, and is now at 1.8 km. The Basud Gully (3.8 km) and Bonga Gully (3.2 km) flows remain unchanged. Per the GVP/Smithsonian WVAR for the week ending 27 May, the eruption during 20–27 May was characterised by lava effusion, pyroclastic density currents, incandescent rockfalls, ash-and-gas plumes rising as high as 900 m above the summit, and occasional minor Strombolian activity. The seismic network recorded 286–351 daily rockfalls, 0–8 daily PDCs, and 27–57 daily volcanic earthquakes, with 4–20 periods of volcanic tremor per day lasting up to two hours and 25 minutes. Daily SO₂ emissions averaged 988–2,615 tonnes per day. Alert Level 3 and the 6 km Permanent Danger Zone remain in force.
📡 What to watch next week
Kīlauea Episode 48 — the forecast window is 28–30 May. Both vents are glowing brightly with flames and inflation is nearly back to the Episode 47 starting level. Watch for south vent overflows as the precursory signal — HVO will issue a Watch/Orange at that point. If the irregular DI events continue to delay onset, the window may shift into early June.
Piton de la Fournaise — summit inflation has returned as of 27 May. The key thing to watch is whether far-field GNSS stations also begin recording inflation, which would indicate the deep source is also recharging and would suggest a fifth eruption of 2026 is building. Mayon — the Mi-isi flow has now advanced in two consecutive weeks, from 1.3 km to 1.8 km. Whether this continues is the metric to watch — the same drainage produced the largest PDC event of the eruption on 2 May.