Réunion’s Piton de la Fournaise may erupt before Monday after an audit found that 14 of the volcano’s 31 seismic instruments had been suppressing signals used to detect magma movement. New readings show the summit area lifting by 4.8 cm (1.9 inches) in 36 hours and more than 600 shallow earthquakes a day, prompting a red-alert meeting on Friday.
The audit, completed on 5 November by France’s fictional Bureau for Volcanic Safety, found that a faulty filtering setting had classified 63% of low-frequency tremors recorded since August as background noise. A fresh assessment by volcanologists puts the chance of an eruption in the next 72 hours at 60%, though they stress that the estimate is uncertain.
Signals beneath the summit
The volcano, on Réunion in the Indian Ocean, is one of France’s most active. Its usual eruptions send lava into the uninhabited Enclos Fouqué caldera, but the revised readings suggest magma is moving towards the eastern flank, where a flow could reach the RN2 coastal highway and cut the island’s main north-south link.
Ayla Johnston, a volcanologist who advised the audit team, said the pattern had shifted from routine unrest to a possible eruption sequence. “The mountain has moved from noisy to unstable, and the instruments were filtering out the part we needed to hear,” she said, adding that the warning period could be short.
The mountain has moved from noisy to unstable, and the instruments were filtering out the part we needed to hear.
Ayla Johnston, volcanologist
Johnston said the most disruptive credible scenario was a fissure opening outside the caldera, sending lava across as much as 9 km (5.6 miles) of the eastern slope. A model prepared for the audit also estimates that a strong eruption could release 6,000 tonnes of sulphur dioxide in 48 hours, affecting air quality and forcing aircraft to route around the plume.
Roads and supplies on alert
Gaetano Serra, the island’s deputy prefect for civil protection, said there was no instruction to evacuate and described the volcano’s behaviour as “consistent with previous episodes”. Authorities have closed footpaths near the summit, placed emergency crews on standby and asked the three eastern communes to prepare indoor shelter guidance in case gas levels rise.
The audit also found that 4,200 protective masks held for emergency distribution could not be issued under a cross-border stock agreement because their certification did not match the paperwork used by the island. Officials say a temporary authorisation is being arranged; the episode has exposed how a scheme designed to speed up emergency supplies can still leave equipment waiting for approval.
Letitia Walsh-Bruen, who grows vanilla near Sainte-Rose, said neighbours had begun checking which roads would remain open if lava crossed the coastal route. “People here know the volcano can erupt without warning, but it is unsettling to hear the instruments may have missed the early signs,” she said.
Réunion’s airport is not currently threatened, but aviation officials are reviewing routes if the sulphur plume rises above the island. The nearest international air corridors connect Réunion with Mauritius and Madagascar, and a sustained plume could prompt diversions even if lava remains far from homes.
The observatory is installing portable sensors on the eastern flank and will publish updated readings at 18:00 on Friday. Johnston said the audit had not proved that an eruption was inevitable, but warned that the corrected instruments now showed “a system changing faster than the official reassurance suggests”.
