This Week
in Fire

This week's new story is Poás in Costa Rica — a volcano that spent most of 2026 in low-level warning status and then had a very active April. Four eruptions in the month, the most significant of which was driven not by a fresh magmatic pulse but by a structural collapse of the crater wall on 10 April that exposed a new fumarolic field and pushed the hyper-acidic lake three metres upward. OVSICORI say the system has not returned to pre-collapse levels of stability. Two further eruptions on 27 and 28 April confirm this. Meanwhile Kīlauea is steadily building toward Episode 46, forecast for next week.

🇨🇷 Poás Alert 2 · Warning

Poás has been in low-level eruption throughout 2026, with continuous activity since at least January characterised by long-period seismicity, background tremor, and intermittent gas-and-steam emissions from Laguna Caliente. The system was already at Alert Level 2 (Warning) when the month's most significant event occurred. At 2244 on 10 April a section of the inner western crater wall — a 23-metre-high stretch along the crater floor — collapsed into Laguna Caliente. According to OVSICORI volcanologist Geoffroy Avard, this was not a typical explosive eruption driven by fresh magma but a structural failure of hydrothermally altered wall rock, which had accumulated a thermal anomaly since 2022 before being progressively buried under tephra from the 2024 and 2025 eruptions.

The collapse caused rapid decompression of gases trapped beneath the surface at the newly exposed fumarolic field, producing a gas-and-ash plume that caused minor ashfall and a pronounced sulfur odour in Grecia, 17 km to the southwest, and in neighbouring San Pedro. The crater lake rose by as much as three metres during the event. The sequence lasted approximately two minutes based on seismic data and was followed by a period of sustained tremor associated with continuous gas emissions at the newly exposed fumarolic field. OVSICORI reported no significant crustal deformation before or after the collapse, and no major changes in seismicity — consistent with a hydrothermal rather than magmatic trigger. Avard noted that monitoring data did not suggest Poás was entering a deeper magmatic phase like the one seen during the escalation of 2025.

However, the system clearly did not settle after the 10 April event. A short eruption at 1206 on 17 April ejected an ash plume 500 m above the crater rim and a steam-and-gas plume reaching 2 km above the rim. Further minor eruptions were recorded at 2318 on 19 April and 2024 on 20 April, both unobserved due to darkness. Most significantly, OVSICORI's 30 April weekly report confirms that background tremor has undergone a spectral shift toward lower frequencies since 10 April — a process that intensified around 19 April and remained through the eruptions of 27 and 28 April. OVSICORI interpret this as a transition to system dynamics dominated by fluid movement at depth. Two eruptions on 27 April at 3:00 PM and 28 April at 3:00 AM, each with an acoustic magnitude of around 3.5, are the most recent events recorded. The Alert Level remains at 2 — Warning — on OVSICORI's four-level scale, with aviation at Yellow.

🇺🇸 Kīlauea Advisory · Yellow

Kīlauea remains at Advisory/Yellow following the end of Episode 45 on 23 April. Both vents continue to glow on webcams overnight, with the south vent producing consistent glow and occasional flames, and the north vent producing more intermittent glow. Tilt has been steadily building back since the 16 microradians of deflationary tilt recorded during Episode 45. As of HVO's 30 April daily update — the most recent at time of writing — the forecast window for Episode 46 is Tuesday 5 May to Saturday 9 May, based on summit tiltmeter data. This window will be refined as inflation progresses.

Episode 45, which occurred on 23 April, lasted approximately 8.5 hours from 1:34 AM to 10:01 AM HST, with peak north vent fountain heights of approximately 300 metres reached around 3:00 AM. HVO's post-episode thermal overflight mapped a single channelised lava flow extending from the north vent, splitting into branching channels across the crater floor with individual lobes extending northeast and southeast. North-to-northeast winds during the episode directed tephra and gases south and southwest — no significant community tephra impact was reported, in contrast to Episodes 43 and 44. The eruption cycle from Halemaʻumaʻu has now produced 45 episodes of lava fountaining since 23 December 2024.

🇷🇪 Piton de la Fournaise Alert 2-2 · Recharging

Piton de la Fournaise remains in its inter-eruptive recharge phase following the end of its fourth 2026 eruption on 12 April. As reported last week, brief low-amplitude tremor returned on 19 April before fading by 20 April. As of the latest OVPF bulletins, summit GNSS stations continue to record inflation — a sign of pressurisation of a shallow source — while far-field stations show no particular signals. Deep seismicity at approximately 6 km below sea level west of the summit persists. The system has produced four eruptions in 2026 with relatively short pauses between events, and is clearly in a sustained active phase. The tempo of activity so far — January, February–March, late March to April, and early April — suggests another event before the end of May is plausible.

🇵🇭 Mayon Alert 3 · 115+ days

Mayon's effusive eruption continues without significant change. Now more than 115 consecutive days into the eruption that began in January 2026, the most recent available data — from the GVP/Smithsonian WVAR for the week ending 15 April (sourced from PHIVOLCS) — shows continued lava effusion, pyroclastic density currents, incandescent rockfalls, and ash plumes rising 200–1,000 m above the summit daily. Daily SO₂ emissions averaged 1,536–2,428 tonnes per day during 8–14 April. Lava flow lengths remain unchanged at 3.8 km (Basud), 3.2 km (Bonga), and 1.3 km (Mi-isi). Alert Level 3 remains in force with a 6 km permanent danger zone. There is no indication of an imminent change in eruptive behaviour.