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The composite volcano of San Pedro in the arid Atacama desert of northern Chile is one of the world's highest historically active volcanoes. The 6145-m-high basaltic andesite-to-dacitic San Pedro is located to the west of its older twin volcano, 6092-m-high San Pablo. The youngest cone of San Pedro was constructed within a large horseshoe-shaped escarpment left by the collapse of an older edifice, which produced a large debris avalanche to the west, perhaps accompanied by a major pumice eruption. Thick dacitic lava flows with steep-sided fronts mantle the upper portion of the younger cone. The youthful-looking La Poruña scoria cone on the western flank produced an 8-km-long lava flow, but Worner et al. (2000) obtained a surprisingly old Helium surface-exposure age of 103,000 years from a juvenile block of the lava flow. Reports of variable reliability mention historical eruptions of San Pedro in the 19th and 20th centuries.
Summary of Holocene eruption dates and Volcanic Explosivity Indices (VEI).
|Start Date||Stop Date||Eruption Certainty||VEI||Evidence||Activity Area or Unit|
|1960 Dec 2||Unknown||Confirmed||2||Historical Observations|
|1938 Feb||Unknown||Confirmed||2||Historical Observations|
|[ 1923 ]||[ Unknown ]||Uncertain|
|[ 1917 ]||[ Unknown ]||Uncertain|
|[ 1916 ]||[ Unknown ]||Uncertain|
|1911 Sep||Unknown||Confirmed||2||Historical Observations|
|1901 May 25||1901 Aug||Confirmed||2||Historical Observations|
|1891 (?)||Unknown||Confirmed||2||Historical Observations|
|1877 (?)||Unknown||Confirmed||2||Historical Observations|
|[ 1870 ]||[ Unknown ]||Uncertain|
This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.
|Feature Name||Feature Type||Elevation||Latitude||Longitude|
|Poruña, La||Cone||3545 m||21° 53' 0" S||68° 30' 0" W|
|San Pablo||Twin volcano||5334 m||21° 53' 0" S||68° 20' 0" W|
|The composite volcano of San Pedro in the arid Atacama desert of northern Chile is one of the world's highest historically active volcanoes. The 6145-m-high San Pedro (left) is located to the west of its older twin volcano, 6092-m-high San Pablo (center). The youngest cone of San Pedro was constructed within the horseshoe-shaped crater left by the collapse of an older edifice, which produced a large debris avalanche to the west. Reports of variable reliability mention historical eruptions in the 19th and 20th centuries.
Photo by Oscar González-Ferrán (University of Chile).
The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title.
Casertano L, 1963a. Chilean Continent. Catalog of Active Volcanoes of the World and Solfatara Fields, Rome: IAVCEI, 15: 1-55.
de Silva S L, Francis P W, 1991. Volcanoes of the Central Andes. Berlin: Springer-Verlag, 216 p.
Francis P W, Roobol M J, Walker G P L, Cobbold P R, Coward M, 1974. The San Pedro and San Pablo volcanoes of northern Chile and their hot avalanche deposits. Geol Rundschau, 63: 357-388.
Gonzalez-Ferran O, 1995. Volcanes de Chile. Santiago: Instituto Geografico Militar, 635 p.
IAVCEI, 1973-80. Post-Miocene Volcanoes of the World. IAVCEI Data Sheets, Rome: Internatl Assoc Volc Chemistry Earth's Interior..
O'Callaghan L J, Francis P W, 1986. Volcanological and petrological evolution of San Pedro volcano, Provincia El Loa, north Chile. J Geol Soc London, 143: 275-286.
Worner G, Hammerschmidt K, Henjes-Kunst F, Lezaun J, Wilke H, 2000. Geochronology (40Ar/39Ar, K-Ar and He-exposure ages) of Cenozoic magmatic rocks from Northern Chile (18-22° S): implications for magmatism and tectonic evolution of the central Andes. Rev Geol Chile, 27: 205-240.