The cover photograph shows vesicles in a pumice sample observed using scanning electron microscopy. These cavities record the exsolution of volatiles while the material was still magma. The sample comes from the eruption of the El Apeadero Member of the Tocomar Volcanic Center, in the Central Puna. Entitled “Glass Sponge,” the image won first prize in the “Microphotography” category of the photography competition organized by the Argentine Geological Association to mark its 80th anniversary. Photograph by Santiago Retamoso.