Left, border-Lanin volcanic chain Villarica; Villarrica-Lanin volcanic chain. CM: Cordillera El Mocho; H: Huililco; HM: Huelemolles; CB: Caburgua; LB: The Barda R: Relicura; CR: Cerro Redondo; PCH: Pichares; SJ: San Jorge; LZ: Lizan; EA: El Arenal; LA:. La Angostura - doc. Revista Geologica de Chile - right Simplified geological map Lanin - from a 1:50,000 scale map by Lara, in press / in Revista Geologica de Chile - click to enlarge the map.
The top of 3,776 m., and dominant its base of 2,500 m., Lanin is a composite stratocône covering about 220 km ², at an estimated volume of 180 km ³ . A small summital lava dome fed a lava blocks in a northerly direction, there 2,200 years. A post-glacial tuff ring, called Arenal Volcano, is located on the south-west flank. A young lava flow from Lanin covers the deposits of Arenal, and extends south into the lake Paimún.
To the altitude of 2,600 meters, and more visible on the side NO, slope failure coincides with the head of glacial cirques and seems to be the starting point of postglacial basalts.
Its structure can be divided into four different morphological units. The first is an ancient volcano; the three most recent formed the current cone from the Middle to Upper Pleistocene.
Lanin volcanic rocks have a composition that ranges from basalt to andesite and dacite. Effusive eruptive cycles are controlled by a short stay in a shallow magma chamber with a fast and equal evacuation of basalt and dacite. In recent eruptions, outbreaks of viscous magma sealed the main conduit, and induces a lateral drainage of the basalts, and a possible collapse of the upper part of the cone. The process of deterioration is however to be connected to erosion and ice cover of the cone.
Although no historical activity has been recorded since the year 560, the youthful appearance of emissions during the Holocene suggests that the volcano is still active and potentially dangerous. The main danger would be producing lahars in relation to the presence of summit glacier.