Although it has seen fewer eruptions in recent weeks, Poás Volcano remains in an active eruption period. According to experts, there is a magma body located at a shallow depth, high degassing, temperatures of up to 700°C, and constant emissions of gases, steam, and ash.
This was confirmed by volcanologist María Martínez of the Volcanological and Seismological Observatory (OVSICORI), who explained that the main indicators point to the presence of magma near the surface.
“When temperatures of 700, 800, or 900 degrees Celsius are detected at Poás Volcano, that tells us that there is a magma body very close to the surface,” the expert explained.
Is the volcano calm?
During May and June, the frequency of phreatic eruptions has decreased, but the volcano has continued to emit gases, steam, and particles. A small ash eruption was recorded early on Tuesday, June 10, confirming that the system remains active.
“From March 23 until today, Poás has maintained eruptive activity. What has changed is the type of eruption: now there is a vigorous release of gases, water vapor, and aerosols, in a more passive and constant manner,” said Martínez.
According to data from Ovsicori and the National Emergency Commission (CNE), thermal sensors mounted on drones measured temperatures of up to 700°C in the hottest part of the crater this week.
In addition to the heat, a high flow of sulfur dioxide (SO₂) has also been observed, reaching 6,000 tons per day, along with ground deformation and the emission of a reddish light visible from the observation deck at night, all of which supports the presence of magma at shallow depths.
“What the human eye sees as a reddish glow at the bottom of the crater is visible radiation. Webcams detect infrared radiation as a very intense white light,” she added.
Can lava emerge?
The volcanologist explained that no lava has yet been observed on the surface, but that does not mean there is no magma nearby. The outcome of this eruptive period is still uncertain.
“There is a potential for magma to reach the surface, either as a lava flow or a lava lake. But it could also cool along the way and remain stagnant without escaping,” he indicated.
The behavior of the magma will depend on several factors, such as its rate of ascent, the loss of gases, the amount of rainfall the area receives, and the energy available to break the surface crust.
Rainfall
Another key factor in the volcano’s activity is the disappearance of the lake, which has not been able to reform despite abundant rainfall. “Rain enters the crater, but the heat flux is so high that the water evaporates very quickly. That’s why we see pools forming at mouth C, but they don’t last long,” Martínez explained.
Although rainwater can absorb some of the heat and contribute to cooling the magma, constant torrential rainfall for weeks would be needed for this to have a real impact.
