Last week's report flagged Mayon's SO₂ spike to 9,028 t/day as the highest of the 2026 eruption. That figure has since been superseded — on 11 July, SO₂ output hit 13,128 tonnes per day, the highest recorded at Mayon in 26 years and only slightly below the levels measured during its 2000 explosive eruption. PHIVOLCS warned explicitly that these levels could signal a shift from effusive to explosive eruptive activity. Alert Level 3 is maintained. Meanwhile Kīlauea's forecast window for Episode 52 opens today, and Piton de la Fournaise has been building for six weeks without releasing.
Mayon's 11 July SO₂ figure of 13,128 t/day put it in company it hasn't kept since 2000 — the year of its last major explosive eruption. PHIVOLCS stated directly that elevated SO₂ "could even lead to an explosive eruption" that could "generate larger and farther-reaching pyroclastic density currents." Alert Level 3 remains in place. Evacuations are ongoing.
🇵🇭 Mayon Alert 3 · Elevated SO₂
Last week's roundup reported 9,028 t/day as the highest SO₂ output of the 2026 eruption. The actual peak was 13,128 t/day on 11 July — confirmed in a PHIVOLCS advisory issued that night, reported by Philippine media on 12–13 July. The 9,028 t/day figure was the 14 July measurement published in the 15 July PHIVOLCS bulletin. Both figures are extreme; the 11 July peak is the critical one.
The full SO₂ escalation sequence at Mayon unfolded as follows. Campaign spectrometry measurements on 9 July recorded 4,569 tonnes per day — already elevated against the 2,300 t/day average for the 2026 eruption. On 10 July, emissions jumped to 7,475 t/day — PHIVOLCS described this as the highest emission from Mayon recorded in the last 16 years. On 11 July, emissions reached 13,128 tonnes per day — the highest in 26 years and, per PHIVOLCS, only slightly below the levels measured during the volcano's most recent major explosive eruption in 2000. PHIVOLCS issued an advisory stating that these levels "could forewarn of further or even a potential shift to explosive eruptive activity." By 14 July SO₂ had moderated to 9,028 t/day, and by 15 July, 398 rockfalls, 10 PDC signals, and 187 volcanic earthquakes — including 43 volcanic tremors lasting 5 to 45 minutes — were recorded in a single day.
VAAC Tokyo continued to issue eruption advisories for Mayon on 15 July (22:04 UTC), 17 July (22:22 UTC), 18 July (06:07 UTC), and 18 July (18:16 UTC). All four advisories noted that volcanic ash was not identifiable in satellite data — the Strombolian and degassing activity has not produced detectable ash columns at altitude as of these reports. Alert Level 3 remains in force with the 6 km Permanent Danger Zone enforced. Lava flows remain at 3.8 km (Basud), 3.2 km (Bonga), and 2.1 km (Mi-isi). PHIVOLCS have not raised the Alert Level to 4, which would indicate an assessment of imminent hazardous explosive eruption — but they have explicitly stated that the current monitoring picture is consistent with a possible transition to explosive activity.
🇺🇸 Kīlauea Advisory · Yellow
Kīlauea Episode 52 opens its forecast window today, 24 July. The most recent HVO daily update, published at 9:10 AM HST on 23 July, places the forecast window for Episode 52 fountains between 25 and 29 July, following the resumption of summit inflation after a one-day pause on 22 July. The south vent is producing strong glow and flaming overnight, the north vent steady glow. HVO confirmed in the same update that Episode 51's final deflationary tilt figure was 14.7 microradians.
Episode 51's precursory sequence is also now fully documented. On the afternoon of 14 July, four overflows occurred at the north vent between 3:00 and 4:00 PM HST — the longest lasting over 30 minutes — before activity paused as inflation levelled off. Two short south vent overflows followed at 2:08 and 2:32 AM HST on 15 July, each lasting less than five minutes. Sustained fountaining began at approximately 8:30 AM HST on 15 July, with the north vent producing peak fountains of approximately 950 feet at around 10:30 AM. The south vent did not fountain throughout Episode 51. The episode ended at 4:46 PM HST. Total lava volume was approximately 5.1 million cubic metres. Tephra fell within the closed area of Hawaiʻi Volcanoes National Park; no populated areas were affected.
HVO's monitoring network remains largely functional, though the SDH tiltmeter continues to be offline pending access across the deep tephra field southwest of the caldera. The V1 camera remains assigned to monitor the localised subsidence feature on the western floor of Halemaʻumaʻu. SO₂ emissions from the summit are varying within a typical inter-episode range of 1,000–5,000 tonnes per day.
🇷🇪 Piton de la Fournaise Vigilance · 6+ weeks
Piton de la Fournaise continues its extended pre-eruptive build-up — now more than six weeks since the dual-source GNSS inflation signal was first confirmed on 15 June. Both summit GNSS stations and far-field GNSS stations continue to record inflation, and elevated CO₂ flux at the PCRN and GITN monitoring stations has been maintained throughout. This is the longest sustained pre-eruptive signal of the entire 2026 eruption cycle, and significantly longer than the precursory periods that preceded any of the four earlier 2026 eruptions. OVPF are monitoring 24 hours a day. The alert level remains at Vigilance. The extended duration of this build-up continues to raise the question of whether a larger event is accumulating — a longer recharge typically allows more magma to gather before the next eruption begins.
📡 What to watch next week
Mayon is the primary monitor. The 13,128 t/day SO₂ peak on 11 July is the most significant data point of the entire 2026 eruption. PHIVOLCS have explicitly flagged the possibility of a transition to explosive activity. Watch daily PHIVOLCS bulletins for any further escalation in SO₂, PDC frequency, or — critically — any change in alert level. A rise to Alert Level 4 would indicate PHIVOLCS have assessed an elevated risk of hazardous explosive eruption. Kīlauea Episode 52 — the forecast window is 25–29 July. Watch for south or north vent overflows as the precursory signal; HVO will raise to Watch/Orange at that point. Piton de la Fournaise — six weeks of build-up without eruption is unprecedented in 2026. Monitor OVPF daily bulletins at ipgp.fr for any seismic swarm beneath the summit, which would be the next escalation before eruption onset.
Iceland — IMO hazard assessment now valid to 30 September. 27.5M m³ and accumulation continuing. Seismicity low, no significant change. Etna — post-Voragine eruption monitoring continues. INGV noting mild ongoing ash emissions and magma movement below surface.