Red Alert issued following eruption at Poás volcano, Costa Rica
A Red Alert was issued for Poás Volcano National Park in Costa Rica on Wednesday, April 23, 2025, after a series of eruptions produced ash plumes reaching up to 4 500 m (15 000 feet) above the crater. Ashfall was reported in several surrounding areas, prompting Orange Alerts in Grecia and Sarchí, and Yellow Alerts in Alajuela, Poás, Naranjo, Río Cuarto, and Zarcero due to increased volcanic hazards.
Eruption at the Poas Volcano, Costa Rica at 14:14 LT on April 21, 2025. Image credit: OVISCORI-UNA
A powerful eruption occurred at Poás Volcano at 14:14 local time on Monday, April 21, 2025, initially sending an ash column approximately 2 000 m (6 500 feet) above the crater.
Later observations by the Volcanological and Seismological Observatory of Costa Rica (OVSICORI) reported the ash plume reaching up to 4.5 km (15 000 feet) above the crater.
The eruption, which lasted approximately 10 minutes, was preceded by a 7-hour period of very low seismic activity. Following the initial explosion, Poás continued to emit ash and volcanic gases throughout the afternoon while seismicity gradually returned to pre-eruptive levels by the evening hours.
Eruptive activity at Poás Volcano persisted through Tuesday, April 22, culminating in a significant eruption at approximately 05:15 local time on Wednesday, April 23. This event produced an ash plume that rose 3.5 km (11 480 feet) above the crater. Multiple eruptions have been recorded since.
The Costa Rican National Emergency Commission (CNE) declared a Red Alert for Poás Volcano National Park on Wednesday, April 23. Under the Red Alert, entry to Poás Volcano National Park is strictly prohibited.
Authorities warn of extreme hazards such as ballistic blocks, high-concentration gas emissions, and rapid ash accumulation that can collapse structures and overwhelm emergency responders. All roads towards the park have been closed along with all park facilities indefinitely, urging tourists and park staff to heed the ban.
Ash fall was reported in multiple areas in the surrounding region, including San Luis de Grecia, Alajuela, and Belen, along with Palmares.
The volcano remains under Alert Level 3 on a 4 level scale. The Aviation Color Code remains Orange.
Grecia and Sarchí were put under Orange alerts, while Río Cuarto, Zarcero, Naranjo, Poás, and Alajuela were placed under Yellow due to broader ash and gas dispersion as well as elevated lahar risk.
For areas under the Orange alert, especially the Toro Amarillo district of Sarchí, officials remind people of the increased threat of lahars—dangerous volcanic mudflows that can occur when heavy rainfall mixes with accumulated ash and debris.
Heavy rainfall over the volcano could result in large volumes of ash and debris being discharged down the Desagüe, Anono, Gorrión, and Agrio rivers, endangering the communities along the rivers. Residents are told not to approach or drink from the waterways until conditions stabilize.
For areas under Yellow alert, residents and tourists alike should expect intermittent ashfall and volatile gas concentrations as wind patterns shift. Authorities advised citizens in the surrounding regions to wear masks (ideally N95-grade) and seal doors and windows with damp cloths, and limit time outdoors.
People with asthma and other respiratory conditions would be especially susceptible to the ashfall and volcanic emissions. Local health clinics have been advised to prepare for increased patient visits related to ash inhalation and irritation.
A lasting eruptive phase of the Poás volcano can have a detrimental impact on the local economy as the number of tourists goes into decline. In 2017, the volcano’s eruptive phase closed off the area for more than a year, causing significant losses to the local communities who heavily rely on tourism for their livelihood.
Poás is one of Costa Rica’s most active volcanoes, featuring three craters aligned north-south. It is a basaltic-to-dacitic stratovolcano easily accessible from San José.
A north-south fissure extends to its northern flank, forming the Congo stratovolcano and several lake-filled maars. The southern crater lake, Botos, last erupted approximately 7 500 years ago. The northern lake, Laguna Caliente, is highly acidic and has been the site of frequent phreatic and phreatomagmatic eruptions since 1828, often producing geyser-like water ejections.
References:
1 Costa Rica Declares Red Alert for Poás Volcano Amid Increased Eruptions – The Tico Times – April 24, 2025
2 Red Alert Declared at Poás Volcano – U.S. embassy in Costa Rica – April 23, 2025
3 Poas geological summary – GVP – Accessed April 25, 2025
I am an Assistant Editor and Severe Weather & Science Journalist at The Watchers, specializing in real-time severe weather coverage, geophysical event reporting, and research-driven scientific analysis. You can reach me at rishav(at)watchers(.)news.
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