surface area of and a height above base level of , Nevado de Longaví has a volume of about . The basement beneath the volcano is formed by the volcaniclastic Cura-Mallín Formation of Eocene–Miocene age, Miocene plutons and the lavic-breccia Pliocene-Pleistocene Cola de Zorro formation. This last formation was identified as forming a deeply eroded volcano in the Cordón de Villalobos south of Nevado de Longaví. This volcano south of Nevado de Longaví is known as Villalobos. The emplacement of this formation was facilitated by a decrease in the compressional stress that had affected the region prior to the Pliocene. Some isolated monogenetic volcanic centres can be found southeast of Nevado de Longaví. Aside from Villalobos, this includes Resago and Loma Blanca. The first and the last are of Pleistocene age, based on their preservation. Resago is post-glacial. The last two centres appear to be related to a geological lineament that flanks the eastern slopes of Nevado de Longaví. A glacier is found on the southern slope, between 1989 and 2017 glacier cover has decreased by over 95% with less than of glacier cover remaining. Previous glaciation is also supported by the presence of glacial striations on lava flows and of lahar deposits. The Rio Blanco originates on the southeastern slope of Nevado de Longaví, within the collapse scar. It turns south and west around the volcano in a fishhook pattern. The Estero Martinez and Quebrada Los Bueyes rivers also originate on Nevado de Longaví, on the western and southern flank respectively. They are both tributaries of the Rio Blanco. The Achibueno River also originates on the eastern flank of Nevado de Longaví in a lake of the same name. It flows first northeastward and then turns around the volcano. Composition Nevado de Longaví has chiefly erupted andesite, which forms about 80% of the volcano. Smaller amounts of basalt and dacite were also erupted by the volcano, the former in the early stages of activity and as basaltic andesite inclusions, the latter during the Holocene. Early stage rocks contain phenocrysts of clinopyroxene, olivine and plagioclase. Mainstage rocks in addition contain amphibole and orthopyroxene. In the Holocene rocks, apatite, iron and titanium oxides and sulfides have been found. Aside from minerals, gabbro and mafic rocks form enclaves. Granite xenoliths are also found. Unlike these granites, the gabbros appear to be cumulates considering their chemical similarity to Nevado de Longaví rocks. The