Volcanic eruption

Lava from the ongoing eruption of Piton de la Fournaise reached the Indian Ocean along the southeastern coast of Réunion Island at approximately 00:20 local time on March 16, according to the Piton de la Fournaise Volcano Observatory (OVPF-IPGP). The lava traveled downslope from the volcano’s southeast flank through the Grand Brûlé lava field before entering the ocean along the island’s coastal margin.
The current eruptive episode began shortly after 10:00 local time on February 13, when volcanologists detected an eruptive fissure opening on the southeast flank of the volcano within the Enclos Fouqué caldera. Lava flows produced by the fissure advanced downslope across the caldera floor and into the Grand Brûlé sector, a coastal region historically affected by lava flows during eruptions originating on this flank of the volcano.
As the eruption progressed, monitoring by the observatory showed the active flow front steadily descending toward the coastal plain. Authorities raised the volcano alert level to phase 2-2 on March 12 after confirming that the advancing lava was approaching the RN2 corridor, prompting precautionary restrictions and the closure of the coastal highway in the affected sector.
Lava reached the RN2 coastal road in the Grand Brûlé sector early on March 13. The first arm of the flow began crossing the roadway at 08:00 local time, followed by a second branch at 09:27. At that time the active front remained approximately 670 m (2 200 feet) from the shoreline.
The RN2 is the primary coastal route connecting communities along the southeastern coastline of Réunion Island. When the road is cut in the Grand Brûlé sector, traffic between the southern and eastern parts of the island must be diverted through longer inland routes.
After crossing the RN2 corridor, the lava continued advancing downslope across the coastal lava field toward the ocean. The progression of the flow remained irregular due to the rugged topography of the Grand Brûlé sector and the vegetation encountered along the flow path, which can locally slow or channel advancing lava.
Lava finally reached the ocean at 00:20 UTC today, producing spectacular visuals and adding to the hazards. When basaltic lava comes into contact with seawater, rapid cooling produces dense steam plumes composed of water vapor, volcanic gases, and fine glass particles generated as the molten rock fragments on contact with the water.
Interaction zones known as laze (lava haze) form when hot lava heats seawater, producing acidic steam that contains hydrochloric acid and fine volcanic glass particles. These plumes can irritate the eyes and respiratory system of people exposed downwind and may reduce visibility near the coastline.
Ocean entry also creates unstable accumulations of newly solidified lava fragments that build outward from the shoreline. Temporary lava deltas form as successive flows pile up and cool, but they remain structurally unstable and can collapse suddenly, producing localized explosions and sending fragments of hot rock and seawater inland.
The interaction between lava and seawater can also generate brief explosive bursts when seawater becomes trapped beneath advancing lava. Rapid steam expansion may fragment the outer crust of the flow, ejecting lava fragments and forming short-lived jets of steam and debris along the entry point.
Air-quality monitoring conducted by Atmo Réunion detected a temporary exceedance of the health alert threshold for sulfur dioxide in the Bourg Murat area on March 16.
SO2 concentrations exceeded the alert level of 500 µg/m³ per hour for three consecutive hours between 10:00 and 13:00 local time, reaching an hourly average of 593 µg/m³ with a peak of 673 µg/m³ before returning to lower levels. A smaller and shorter SO2 spike had also been observed during the night of March 11–12.
Authorities note that air-quality conditions around the volcano can change rapidly during an eruption, depending on volcanic activity and weather conditions. Elevated concentrations of volcanic gases may cause symptoms in sensitive individuals, including coughing, irritation of the eyes or throat, reduced respiratory capacity, or worsening of asthma.
Residents in affected areas are advised to reduce intense outdoor activity and seek medical advice if respiratory or cardiac discomfort occurs.
Piton de la Fournaise is one of the most active shield volcanoes on Earth. Its eruptions are typically effusive and produce basaltic lava flows that can travel long distances downslope from eruptive fissures. Hazards associated with these eruptions are dominated by advancing lava, volcanic gas emissions, unstable ground near active flow fields, and coastal hazards where lava enters the ocean.
Lava flows from eruptions occurring on the volcano’s southeast flank occasionally reach the coastline through the Grand Brûlé sector. The RN2 coastal road crosses this lava field, which has been repeatedly buried by lava during historical eruptions.
A comparable event occurred during the April–May 2007 eruption, when lava flows descended through the Grand Brûlé sector, buried sections of the RN2 coastal road, and eventually entered the Indian Ocean, forming new land along the southeastern coast of Réunion Island.