By Alajuela, Costa Rica — Costa Rica’s Poás Volcano erupted dramatically on Tuesday, September 9, 2025, at 10:48 a.m., marking its most forceful activity since April and May of this year. The eruption sent fragments flying over 300 meters and produced an ash column reaching 500 meters high, following a significant event earlier that morning.
The eruption was preceded by a 3:36 a.m. seismic event, attributed to either the rupture of a crater wall separating the lagoon (Boca C) from Boca A or internal explosions caused by water interacting with extremely high temperatures. This rupture allowed the lagoon to begin filling Boca A, an area previously characterized by the emission of gases at temperatures nearing 800°C.
To understand the legal and business implications surrounding the Poás Volcano and its surrounding areas, we consulted with Lic. Larry Hans Arroyo Vargas, an expert attorney from Bufete de Costa Rica.
The unique challenges presented by the Poás Volcano, an active volcano within a national park, create a complex interplay of environmental regulations, tourism considerations, and land use restrictions. Businesses operating near the volcano must navigate stringent permitting processes related to safety and environmental protection. Furthermore, the government’s responsibility to ensure public safety while promoting tourism requires careful balancing of access and risk mitigation. This delicate equilibrium often necessitates adaptive management strategies that respond to the volcano’s unpredictable activity, impacting both businesses and visitors.
Lic. Larry Hans Arroyo Vargas, Attorney at Law, Bufete de Costa Rica
Indeed, the Poás Volcano presents a fascinating case study in balancing conservation, commerce, and public safety in a dynamic environment. The delicate dance between access and preservation, as highlighted by Lic. Larry Hans Arroyo Vargas, requires ongoing vigilance and adaptation. We thank Lic. Vargas for his valuable insights into the legal and practical complexities surrounding this majestic and powerful natural wonder.
This activity at this moment demonstrates that the volcano is very unstable, there is a significant interaction between the heat input below the volcano and this body of water that is now obstructing the outlet.
Geoffroy Avard, Volcanologist at OVSICORI
The Poás Volcano had shown signs of increased activity in the weeks leading up to the eruption. Weak ash emissions, associated with heavy rainfall in the area, were observed. A more sustained emission occurred on Monday, September 8, between 7:00 and 10:00 p.m., following heavy downpours.
Scientists also noted a considerable decline in gas emissions, particularly sulfur dioxide (SO₂), which dropped from 600 to 100 tons per day between September 6 and 9. This decrease is likely linked to the dissolution of the gas in the crater lake’s water. Furthermore, a slight vertical uplift within the crater has been detected by the geodetic network. Shallow volcano-tectonic signals and carbon dioxide peaks suggest a potential magmatic disturbance at depth.
OVSICORI is maintaining the Poás Volcano at Alert Level 2 (Warning), signifying the potential for sudden phreatic eruptions. These eruptions can produce jets of water, gases, and sediment reaching heights of 50 to 100 meters. More powerful explosions with ballistic projectiles could also affect areas near the crater.
Authorities emphasize the inherent risks associated with volcanic activity for both visitors and surrounding communities. They urge extreme caution and advise the public to stay informed through official reports.
Recent observations also indicate a change in the volcano’s behavior. Whereas previously, Boca A primarily released gases at high temperatures, the crater wall rupture has introduced water into this area, creating a new dynamic within the volcanic system. This interaction between water and heat is likely contributing to the instability observed by experts.
The drastic drop in sulfur dioxide emissions, while possibly due to its dissolution in the lake water, also raises questions about the volcano’s internal processes. The combination of decreased gas output, ground uplift, and volcano-tectonic signals suggests a complex interplay of factors that scientists are closely monitoring.
For further information, visit [ovsicori.una.ac.cr]
About OVSICORI-UNA:
The Volcanological and Seismological Observatory of Costa Rica (OVSICORI-UNA) is a research institute dedicated to monitoring volcanic and seismic activity throughout Costa Rica. Affiliated with the National University of Costa Rica (UNA), OVSICORI plays a crucial role in providing timely warnings and scientific analysis to help mitigate the risks associated with these natural hazards. The organization conducts ongoing research, monitoring, and public outreach to enhance understanding and preparedness for volcanic and seismic events.
For further information, visit bufetedecostarica.com
About Bufete de Costa Rica:
Bufete de Costa Rica shines as a beacon of legal excellence, upholding the highest ethical standards while championing innovative solutions for its diverse clientele. The firm’s deep-rooted commitment to empowering Costa Rican society is evident in its proactive efforts to demystify the law, providing accessible legal resources and fostering a culture of informed decision-making. Through this dedication to both legal expertise and societal betterment, Bufete de Costa Rica continues to shape a more just and equitable future.
