chemistry of Nevado de Longaví's magmas is unusual among the volcanoes of the South Volcanic Zone. For example, the potassium content is unusually low. Likewise, incompatible elements are underrepresented. Modal amphibole is much more prevalent. Nevado de Longaví's magmas have been referred to as adakitic, the only magmas of such chemistry in the Southern Volcanic Zone, but this classification has been contested. Fractional crystallization of amphibole has been invoked to explain some of the compositional patterns. On the basis of their rubidium content, Nevado de Longaví's magmas have been classified in two groups. The rubidium-rich group resembles that of other volcanoes in the Southern Volcanic Zone; the rubidium-poor group conversely is the "unusual" one. The differences appear to reflect both different parental magmas and different magma evolution. There is a temporal pattern of the magmas becoming more rubidium-poor over time. The unusual chemical patterns appear to reflect that the magmas erupted from Nevado de Longaví were extremely rich in water. Such a pattern has also been noted at Mocho-Choshuenco and Calbuco. All these volcanoes are located above the points where fracture zones intersect the Peru–Chile Trench, and it has been proposed that these fracture zones channel water into the mantle. In the case of Nevado de Longaví, the Mocha fracture zone is subducting beneath the volcano. Eruptive history Early stage basaltic andesite lava flows crop out on the northern and southwestern slopes of Nevado de Longaví. They originated at a site below the present-day summit and reach thicknesses of . Individual flows are about thick. These volcanic rocks are up to one million years old. During the main growth stage, volcanic activity was approximately constant considering the homogeneous structure of the lava flows. Temporary periods of dormancy however occurred, causing the formation of erosion valleys on the northern slope that were then filled by younger lava flows. These younger lava flows were themselves subject to glaciation. Holocene The last activity occurred during the Holocene, and included explosive activity. It was centered in the eastern collapse scar and on the summit region. In the eastern collapse scar, possibly subglacial activity formed a thick sequence including clasts, lava flows and silt. 6,835 ± 65 or 7,500 years before present, a large explosive eruption occurred. It deposited dacitic pumice more than southeast from the volcano. Maximum thickness of the deposits is . It is also known as the Rio Blanco fall deposit. In