Last month, Poás Volcano, which towers over the Central Valley, north of San José, produced streams of sulfur shooting 160 meters into the air from one of its fumaroles, according to a statement from the Volcanological and Seismological Observatory of Costa Rica (OVSICORI) at Universidad Nacional, in Heredia, north of San José.

Though sulfur streams are “rare” for active volcanoes, the eastern and northeastern sides of Poás’ active crater have been producing streams of gas caused by temperatures reaching 119 to 203 degrees Celsius, the statement said.

The release of these vapors through fumaroles has produced great quantities of sulfur since 2005, and this yellowish-gray gas can be seen easily from the crater’s lookout point, where thousands of tourists arrive each month.

“Though this change has a great academic and aesthetic value, it does not indicate an increase in activity,” the statement said.