The Volcanological and Seismological Observatory (OVSICORI) in Costa Rica warned of surging seismic and volcanic activity at Poás Volcano. Volcanologist Geoffroy Avard says current conditions mirror those before the January 5 eruption this year—but with twice as many seismic events. Over the past 24 hours, more than 200 high-frequency earthquakes rattled the volcano.
“Before the January eruption, we saw a similar uptick, but today’s numbers are double,” Avard said. He noted that tremors have grown stronger in recent days, a key sign of escalating volcanic unrest.
OVSICORI’s surveys also reveal moderate ground uplift near the crater and summit, the largest shift since this eruptive cycle began in December 2024. Meanwhile, a MultiGAS station detected a rising sulfur dioxide-to-carbon dioxide ratio at gas vents, hinting at a higher eruption risk.
“The sulfur dioxide output hit 691 tons per day on March 18—a sharp jump from earlier this month,” Avard explained. Satellite data backs this up, showing two major spikes in atmospheric sulfur dioxide: 600 tons in early January and a peak of 844 tons between March 13 and 14, topping last April’s high of 714 tons.
The volcano’s hyperacid lake is also shrinking fast. Though eruptions on March 9 and rain on March 16 briefly raised its level, the water has since dropped sharply. Experts say the lake can no longer trap magmatic gases and heat due to its reduced volume and altered chemistry.
Poás Volcano remains at caution level 3 out of 4. Avard warns that eruptions could soon threaten visitors to Poás Volcano National Park and nearby communities, urging authorities and residents to stay on high alert.
