Costa Rica’s landscape and history are deeply intertwined with its underlying geology. The nation sits atop the highly active Pacific Ring of Fire, which dictates much of its physical character. This geological setting results in a continuous presence of volcanic activity, a defining feature of the central mountain ranges. The cycle of magma generation and surface release has formed a chain of volcanic peaks, providing fertile soil and dramatic scenery.
The Most Recent Confirmed Eruption
The most recent confirmed eruption occurred at Poás Volcano, which exhibited an explosive burst in April 2025. This was a phreatic eruption, where superheated water flashes to steam, causing an explosion of rock, ash, and gas. On April 21, 2025, the eruption sent a plume of ash and debris approximately 2,000 meters above the crater.
The ashfall drifted, affecting several communities, including parts of the capital area. While not a magmatic eruption involving fresh lava, this explosive activity is potent enough to distribute toxic gases and fine ash over a wide area. OVSICORI reported elevated sulfur dioxide emissions, prompting health warnings. Poás remains closely monitored, known for its hyperacid crater lake which contributes to the volatile phreatic activity.
Why Costa Rica Is Volcanically Active
The volcanic nature of Costa Rica is a direct consequence of global plate tectonics at the boundary of two crustal segments. The country is situated along the Central American Volcanic Arc, which forms where the Cocos Plate meets the Caribbean Plate. The oceanic Cocos Plate, lying beneath the Pacific Ocean, is slowly subducting underneath the continental Caribbean Plate.
As the Cocos Plate sinks deeper, heat and pressure cause the rock to release water and melt, forming magma. This molten material rises through faults and fractures in the overriding Caribbean Plate, feeding the chain of volcanoes. This continuous subduction process drives the volcanic system, explaining the existence of nearly 200 volcanic structures, many of which remain active or dormant.
Current Status of Major Volcanoes
While Poás and others have shown recent activity, the volcanic landscape is characterized by constant, low-level unrest rather than continuous major eruptions. Several major volcanic centers are under continuous observation by OVSICORI, including Poás, Rincón de la Vieja, and Turrialba. These three volcanoes frequently maintain a Level 2 Advisory status, indicating elevated activity that requires close monitoring.
This ongoing activity often manifests as acoustic tremors, which are low-frequency seismic signals indicating fluid movement below the surface. Volcanologists track the composition of gas emissions, such as the ratios of carbon dioxide and sulfur dioxide, to gauge changes in the magmatic system. Rincón de la Vieja, located in the northwest, has shown increased seismic activity. Arenal Volcano is currently dormant, with its last magmatic eruption occurring in 2010, but it is tracked for signs of reawakening. The vigilance of OVSICORI ensures that subtle changes in deformation, seismicity, and gas geochemistry are quickly identified to maintain public safety.