1.nounAn opening in the ground that emits steam and gases due to volcanic activity."2003: Masaya did not offer an opportunity to sample high-temperature fumaroles, but its neighbors, Momotombo and Cerro Negro volcanoes, are noted for their fumarolic activity — L.J. Wardell, P. Delmelle, T. Fischer, J.L. Lewicki, E. Malavassi, J. Stix, W. Strauch, Volcanic gas workshop features state-of-the-art measurement techniques."