A Magnitude 2.9 Four Kilometres From Furnas Adds a São Miguel Volcano to the Azores Alert List, and the Warning Expires in Eight Days

At 16:41 local time on Tuesday, a magnitude 2.9 earthquake struck about four kilometres west-south-west of Furnas, on São Miguel. It was felt at maximum intensity V on the Modified Mercalli scale in the parish of Furnas itself, which is enough to wake people, rattle windows and move small objects. Three hours later, the Centro de Informação e Vigilância Sismovulcânica dos Açores (Azores Seismovolcanic Information and Surveillance Centre, CIVISA) raised the volcanic alert level for the Furnas volcano to V1.

The alert is the second rung of a six-level scale, and it comes with something the Azores' three other standing volcanic alerts do not have: an expiry date. CIVISA said the alert will run for a period of eight days, unless there is new information in the meantime.

What actually happened on Tuesday

CIVISA's account is short and precise. From 11:47 on 8 September it recorded an increase in seismic activity at the Furnas volcano. Every event registered up to the time of the notice was low in magnitude. Two were felt.

• 13:44. Magnitude 2.5, epicentre about four kilometres west of Furnas. Felt at maximum intensity III/IV in Furnas, in the municipality of Povoação.
• 16:41. Magnitude 2.9, epicentre about four kilometres west-south-west of Furnas. Felt at maximum intensity V in the parish of Furnas.

The second event reached well beyond the valley. CIVISA logged intensity IV at Ribeira Quente and Povoação, in the Povoação municipality, and at Ponta Garça and Ribeira Seca, in Vila Franca do Campo. It logged III/IV at Ribeira das Tainhas in Vila Franca do Campo, at Salga in Nordeste, and at Lomba da Maia, Maia and São Brás in Ribeira Grande. It logged III at Água d'Alto, in Vila Franca do Campo. That is four of São Miguel's six municipalities feeling a magnitude 2.9.

What V1 means, in CIVISA's own words

The Azores volcanic alert scale does not begin at zero danger and end at eruption in the way a colour-coded warning does. It describes the state of a volcanic system. V0 is a system at rest with normal activity. V1, the level Furnas is now at, describes a system in metastable equilibrium with weak activity, slightly above reference levels, of tectonic, hydrothermal and/or magmatic origin.

The rungs above it are worth reading, because the difference between them is the whole point of the scale:

• V2: a system in a phase of instability, with moderate activity clearly above reference levels.
• V3: a system in a phase of reactivation, with high activity frankly above reference levels and evidence that suggests or confirms magmatic influence.
• V4: a system in a pre-eruptive phase, with activity at a critical level and a real possibility of eruption to be considered.
• V5: eruption in progress.

There is a detail in the Furnas notice that is easy to miss and worth holding on to. For the Terceira and São Jorge alerts, CIVISA's standing texts state plainly that the elevated activity is the result of a deep magmatic intrusion process. The Furnas notice makes no such claim. It says the seismic activity is slightly above reference levels, that the events are low in magnitude, and nothing more. On this scale, "magmatic influence" is a V3 descriptor, not a V1 one.

The Azores now have four volcanic systems on alert

Furnas joins a board that was already occupied. As of Tuesday night, CIVISA lists four volcanic systems across three islands at alert level V1:

• Vulcão das Furnas, São Miguel. V1 since September 2026. Its alert history has exactly one line in it: 2026.09.08, raised to V1.
• Vulcão de Santa Bárbara, Terceira. V1 since July 2026, at the end of a four-year sequence: raised to V2 on 30 July 2022, to V3 on 26 June 2024, lowered to V2 on 4 December 2024, raised to V3 again on 5 November 2025, lowered to V2 on 4 February 2026, and lowered to V1 on 8 July 2026.
• Sistema Vulcânico Fissural Oeste da Terceira (Western Terceira Fissural Volcanic System). V1 since July 2026, having been raised to V1 in June 2024, to V2 in October 2025, to V3 on 24 November 2025, and stepped back down through V2 in February 2026.
• Sistema Fissural Vulcânico das Manadas (Manadas Fissural Volcanic System), São Jorge. V1 since 6 March 2024, and at some level of alert continuously since 19 March 2022.

Two things follow from that list. The first is that a V1 in the Azores is an ordinary administrative state rather than an emergency. São Jorge has been at V1 for two and a half years, and Terceira's two systems have spent most of the past four years above V0 without an eruption.

The second is the speed at which the scale can move when it does. In March 2022, São Jorge went to V2 on the 19th, to V3 on the 20th and to V4 on the 23rd. Four days from the first notice to a pre-eruptive classification. That is why CIVISA's language about what can happen "at any moment" appears at every level of the scale, including the calmest one.

The eight-day clock is the unusual part

The Terceira and São Jorge alert levels were set and lowered by the Gabinete de Crise, the crisis cabinet that convenes to assess Azorean seismovolcanic activity, and they are open-ended: they stand until the cabinet moves them. The Furnas alert was raised by CIVISA itself on Tuesday evening, and it carries a self-limiting term of eight days.

That is not a softer warning. It is a different instrument. An eight-day alert is what a monitoring body issues when a swarm has begun and it does not yet know whether it is dealing with a short tectonic episode or the start of something that needs the crisis cabinet. If the seismicity fades, the alert lapses on its own around 16 September. If it does not, the next notice will say so.

What residents and visitors should actually do

CIVISA's standing advice at V1 across all four systems is the same single line: follow the preventive measures indicated by the civil protection authorities. There is no evacuation, no exclusion zone and no restriction attached to a V1.

For anyone in or heading to the Furnas valley, the practical points are these:

• Alerts are published at civisa.pt. Felt-earthquake notices and alert changes both go up there, with the time, magnitude, epicentre and the intensity recorded in each locality. It is the primary source, not a summary of one.
• Intensity V is a felt-shaking measure, not a damage measure. It describes what people experienced in Furnas, not what happened to the buildings. CIVISA reported no damage in its notices.
• Furnas is a hydrothermal area with fumaroles, boiling springs and thin, hot ground in places. The marked walkways exist because the ground beside them is not safe to stand on. Those markings matter more, not less, during a period of elevated seismicity.
• The alert is a state, not a forecast. V1 does not mean an eruption is expected. It means the system is no longer at its baseline and is being watched more closely.

The Azores live with this permanently. The archipelago has spent the past few years working through what that costs, from an infrasound network built to hear eruptions on the other side of the planet to a centenary marked with an evacuation drill for a hundred children. In July, it was Pico's turn; that alert is no longer on the board. On Tuesday it was São Miguel's, in the one valley on the island where the volcano is not an abstraction but the reason the water steams.