volcano number: 1508-01= (according to Volcanoes of the World, 1994 edition)
summit elevation: 2652 m
location: 41.10°S, 72.493°W

Introduction

Osorno is one of Chile's most famous volcanoes, owing to its near perfect symmetry (it is frequently called "the Fujiyama of South America") and its scenic location above the lakes Todos los Santos and Llanquihue. Although there have been no eruptions of this volcano since the mid-19th century, Osorno is a very youthful volcano, and fumarolic activity is still occurring at some points on its summit crater rim. Numerous cinder cones and lava flows on its flanks show an excellent state of preservation, implying that they have formed only during the past centuries to millennia. Historical records mention eruptive activity through the 1860's.
The rocks of Osorno are basaltic, thus contrasting with the more evolved products (andesites) of neighboring Calbuco. Some of Osorno's flank eruptions have produced vast lava fields which extended into the plains around the volcano. One such lava field forms a large portion of the isthmus now separating Lago Todos los Santos from Lago Llanquihue. One of the most recent eruptions from Osorno, that of 1834-1835 (which was witnessed and described by Charles Darwin) originated from one or more vents on the SSW flank and produced a lava flow.
The record of historical eruptions and the presence of many youthful (Holocene) features on Osorno, together with the presence of a large icecap in the upper part of the mountain make this a potentially very dangerous volcano. (...)

References

Casertano L (1962) La actividad volcanica en Chile durante 1961. Boletín de la Universidad de Chile, No. 30 (June 1962): 40-45.
López-Escobar L, Parada M, Moreno H, Frey FA & Hickey-Vargas RL (1992) A contribution to the petrogenesis of Osorno and Calbuco volcanoes, Southern Andes (41°00'-41°30'S): comparative study. Revistia Geológica de Chile vol. 19: 211-226.
Stone JB (1930) Two active volcanoes of Chile. The Volcano Letter No. 284 (5 June 1930). All issues of the Volcano Letter were re-printed in 1987 by the Smithsonian Institution.
Stone JB (1935) The volcanoes of Southern Chile. Zeitschrift für Vulkanologie vol. 16: 81-97.

Extracted from Werner Keller's and Boris Behnke's Chile's Volcanoes