The strongest of the year: impacts in the Central Valley and preventive measures underway

San José, Costa Rica | April 21, 2025 — Yesterday, Poás Volcano produced the strongest eruption recorded so far this year, releasing a massive column of ash and gases that reached between 3 and 4 kilometers in height. The event, which occurred at 2:14 p.m., was visible from multiple points in the Central Valley, including cities such as Alajuela, Heredia, Escazú, and San José.

An Active Volcano Under Constant Observation

Poás Volcano, one of the most iconic in Costa Rica, has maintained significant activity over the past few months. Since March 26, Poás Volcano National Park has been closed to the public due to gas emissions, a preventive measure that helped avoid greater risks during Monday’s sudden eruption.

Details of the Eruptive Event

According to the Volcanological and Seismological Observatory of Costa Rica (OVSICORI), the eruption was explosive in nature and occurred without precursor earthquakes, making it impossible to anticipate its magnitude.
The ash cloud, initially deep black, turned white as it rose and was carried by winds toward the southwest, mainly affecting the communities of Sarchí, Grecia, Poás, Naranjo, and surrounding areas.

Official Report from OVSICORI

In its preliminary report, OVSICORI stated that the maximum height reached by the ash column was approximately 4,000 meters above the crater. The institution continues to monitor the volcano closely to assess the possibility of further eruptions or changes in its activity.

Impact on the Population and Environment

Ashfall was reported on roads, homes, and vehicles in nearby cantons, causing respiratory discomfort and reduced visibility in some areas. Additionally, the characteristic sulfur smell was widely perceived in the environment.

Traffic authorities recommended taking extra precautions, as ash can reduce road traction and damage vehicles if proper measures are not taken.

Safety Measures and Recommendations

The National Emergency Commission (CNE) maintains an orange alert for the Poás Volcano National Park area and a green alert for the cantons of Alajuela, Poás, Grecia, Naranjo, Río Cuarto, Zarcero, and Sarchí.

The public is advised to:

• Avoid outdoor activities while ashfall persists.
• Use N95 masks or similar to protect the respiratory system.
• Keep doors and windows closed.
• Avoid using windshield wipers if vehicles have wet ash, to prevent glass damage.

Voices from the Community

Residents of affected areas shared images and videos on social media, showing the impressive volcanic column and the subsequent ashfall over their communities. “It was like watching a movie scene. The sky darkened for a few moments,” said Esteban Vargas, a resident of Sarchí.

Looking Ahead

OVSICORI maintains strict monitoring of Poás Volcano in case of further eruptions. Authorities reiterate that while this is a striking natural event, it is essential to remain calm and follow official instructions to ensure everyone’s safety.

Conclusion

The April 21 eruption reaffirms the importance of scientific monitoring and preventive measures in a geologically active country like Costa Rica. Collaboration between institutions and citizens will be key in the coming days to mitigate any potential additional impacts.

Sources:

• Volcanological and Seismological Observatory of Costa Rica (OVSICORI)
• National Emergency Commission (CNE)
• La Nación
• La Teja
• Ensegundos.com.pa