Presently, fumaroles in the eastern summit crater are the only ongoing activity at San Pedro; a steam plume is barely visible. The fumarole has formed sulfur deposits. Based on measurements made in December 2013, the SO2 output of San Pedro is about . Fumaroles were also reported from the Ojos de San Pedro area south of San Pedro volcano, and a report published in 1894 mentions a smell of sulfur at La Poruña. In addition, seismic activity has been observed at the volcano.