Scientists warned a public hearing in the Azores on Friday that Furnas volcano on São Miguel island could erupt by Monday after a week of shallow earthquakes, rising gas emissions and ground deformation. Their worst-case planning scenario includes ash up to 10 cm (4 inches) deep near the crater and airport closures across the archipelago.
The warning comes from a monitoring network run by TheraNova GeoMetrics, a private company, whose instruments registered 7.8 cm (3.1 inches) of uplift since 31 August. Regional observatory instruments recorded 1.9 cm (0.7 inches) over the same period. Experts say the mismatch is unresolved; nobody at the hearing presented a reliable probability of eruption.
A deadline without a probability
Helena Silva, a volcanologist advising the hearing, said a new cluster of more than 1,200 small earthquakes had moved to depths of 2–4 km (1.2–2.5 miles), while carbon-dioxide readings at two vents had more than doubled since 18 September. “We cannot say an eruption is certain. We can say the signals now fit a shallow magma intrusion, and the time to prepare is measured in hours, not weeks,” she said.
The instruments do not agree on how fast the ground is rising. Silva said the company’s stations used a different calibration method and some stood on unstable ground, but added that conventional sensors might be missing deformation concentrated beneath the caldera. A scientific team will compare readings on Saturday; until then, she said, no single network should be treated as decisive.
A report presented by the company models a high-impact eruption beginning within 72 hours, with a plume reaching 8 km (5 miles) and ash deposits of 2 mm (0.08 inches) in Ponta Delgada, about 30 km (19 miles) west of Furnas. It estimates that 22,000 residents could need temporary relocation if vents open toward populated valleys. The authors called this a planning scenario, not a forecast.
The data are alarming enough to prepare for, but not strong enough to order people out of their homes today.
Helena Silva, volcanologist
Officials resist evacuation calls
Ajla B. Hribar, the regional civil-protection secretary, said officials had raised the alert level and were preparing transport, temporary accommodation and ash masks for 9,600 people in eastern São Miguel. She said there was no order to leave and that the island’s airport would remain open unless ash reached its flight paths. “We will not turn a model into a prediction,” she told the hearing.
That caution angered residents who travelled to Ponta Delgada to listen. Tâmara Meireles-Cruz, who runs a small guesthouse near Furnas, said she had received no direct guidance on whether to move her guests. “If the scientists disagree, tell us what we should do tonight,” she said. The regional authority promised a public briefing at 08:00 on Saturday.
The company’s chief scientist, Santiago J. Alcaraz, defended its network and said its €3.2 million investment (about $3.8 million) had produced the clearest view yet of activity beneath the crater. He rejected claims that its sensors were unreliable, but conceded that the company had not independently replicated the uplift readings. The hearing chair ordered its raw measurements supplied to the regional observatory by midnight.
Furnas last produced a major eruption in 1630, killing hundreds and burying settlements in ash and volcanic debris; most present-day residents live outside the caldera. Scientists stressed that eruptions can be preceded by unrest that subsides without breaking the surface. The Saturday comparison of sensor records is now the next key test, as emergency teams prepare transport and officials urge residents to follow local alerts.
