Osorno volcano, Chile

volcano number: 1508-01= (according to Volcanoes of the World, 1994 edition)

summit elevation: 2652 m

location: 41.10°S, 72.493°W

Contents
• Introduction
• Eruptive history
• References

Topographical map of Osorno
(Full picture JPEG: 195K) Note that the lake to the left is Lago Llanquihue and that to the right is Lago Todos los Santos. Map (by Instituto Geográfico Militaar, Chile) supplied by Werner Keller.

Osorno seen from West, with recent cinder cone
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Aerial view of Osorno's western flank, with its glacier-covered summit area and a cinder cone on the lower flank that may have been the source of one of Osorno's most recent historic eruptions (1834-35?). Note older cones and lava fields nearby. Photo by Christian Brellenthin, 12 October 1996.

Lahar deposit at Osorno
(Full picture JPEG: 78K) Aerial view of a lahar deposit on the western flank of Osorno. The deposit which enters Lago Llanquihue was deposited only a few hundred years ago; now it is the site of the small village "Las Cascadas". Photo by Werner Keller.

INTRODUCTION

Osorno is one of Chile's most famous volcanoes, owing to its near perfect symmetry (it is frequently called "the Fuji-yama 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.

Lahar deposit at Osorno
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Another view of the same lahar deposit. Megaclasts up to 3 m in diameter were found scattered between the buildings visible in this photo.

Osorno's W flank with recent lava fields
(Full picture JPEG: 80K) Osorno viewed from the air on 12 October 1996. Summit and western flank, showing lava fields on the lower flanks that are only a few centuries old, some of them possibly historic. Photo by Christian Brellenthin.

Eruptive fissure on the WNW flank
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This is Osorno's WNW flank seen from the air. A spectacular fissure with several craters and cones extends from the snow-covered part of the mountain to below the limit of snow and ice. Photo taken on 12 October 1996 by Christan Brellenthin.

Osorno seen from Puerto Varas
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Western side of Osorno seen from Puerto Varas, on the shore of Lago Llanquihue. This is the characteristic view of the volcano, making the volcano famous as "the Fuji-yama of South America" all over the world. Photo by Werner Keller, January 1991.

Unusual snowmelt at Ocorno
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This photo, taken by Christian Brellenthin in April 1993, shows the upper part of Osorno's cone, seen from the west (?). Note irregular areas of snowmelt below summit; it seems that the rock that lay beneath glacial ice is exposed. It is not known what kind of process lead to this unusual snowmelt (speculations range from large snow avalanches over the effects of the ozon hole to increased fumarolic activity).

Cinder cone cluster on the south flank
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Osorno has many Holocene cinder cones on its flanks, some being the sources of historical eruptions. This photo shows a cluster of youthful cinder cones on the south flank of the volcano, their excellent preservation and extent of vegetation indicating an age of several hundred, at best a few thousand years. A large lava field extending southwestwards from these cones has separated the lakes of Todos los Santos and Llanquihue which before were one great lake. Photo by Werner Keller, January 1996.

Youthful cinder cone on Osorno's south flank
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Large single cinder cone sitting about 300 m east of cone cluster shown on previous image. This cone may be of a slightly lesser age than the latter, judging from less developed vegetation cover. This cone lies at the head of a vast lava field that extends downslope towards the isthmus separating Lago Todos los Santos from Lago Llanquihue. Photo by Werner Keller, January 1996.

Another view of cone on Osorno's south flank
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Another view of the cone shown in previous photo, seen from summit of older cinder cone. More cones predating the one in center are visible in the right background. Photo by Werner Keller, January 1997.