San Jose

Geography & Climate

San Jose is located in Chile-Argentina, within the Southern Andean Volcanic Arc of the broader South America Volcanic Regions. Situated at 33.79° S, 69.89° W in the Southern Hemisphere, the volcano lies within a subtropical climate zone. At 6,070 meters above sea level, San Jose reaches well into the permanent snow and ice zone. Glaciers and snowpack on the upper slopes create the potential for lahars — destructive volcanic mudflows — during eruptions, as heat rapidly melts ice and snow. The volcanic landform is characterized as a composite, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

San Jose sits in a subduction zone, where one tectonic plate dives beneath another, creating intense heat and pressure that generates magma. Subduction zones are responsible for many of the world's most explosive volcanoes and deadliest eruptions. For communities in Chile-Argentina near San Jose, this tectonic setting means the volcano is capable of producing powerful explosive eruptions, pyroclastic flows, and lahars that can threaten populated areas within tens of kilometers of the summit. The dominant rock type is andesite / basaltic andesite, a dark, fine-grained volcanic rock that forms from rapidly cooling, low-viscosity lava. Basaltic eruptions tend to be less explosive and produce fluid lava flows that can travel long distances. While less immediately dangerous than explosive eruptions, basaltic lava flows can destroy structures and infrastructure in their path, and volcanic gases released during these eruptions can affect air quality over a wide area.

Eruption History Summary

San Jose has 7 recorded eruptions in the geological database, spanning from 1822 CE to 1960 CE. The most powerful recorded event was an explosive event producing ash plumes up to several kilometers in 1960 CE, reaching VEI 2 on the Volcanic Explosivity Index. This eruption frequency indicates a moderately active volcanic system with periodic reawakenings. The most recent eruption in 1960 CE places this volcano within the modern era of volcanological observation.

Significance

With 7 recorded eruptions on file, San Jose has enough documented activity to help scientists identify patterns in its eruptive behavior. Given its recent activity, San Jose is closely monitored by geological survey organizations to provide early warning of future unrest.

GVP Reference Summary

Volcán San José lies along the Chile-Argentina border at the southern end of a volcano group that includes the Pleistocene volcanoes of Marmolejo and Espíritu Santo. The glaciated 6070-m-high Marmolejo stratovolcano is truncated by a 4-km-wide caldera, breached to the NW, that has been the source of a massive debris avalanche. San José is a 5856-m-high stratovolcano of Pleistocene-Holocene age with a broad 2 km x 0.5 km summit region containing overlapping and nested craters, pyroclastic cones, and blocky lava flows. Volcán la Engorda and Volcán Plantat, located SW of Marmolejo and NW of San Jose, have also been active during the Holocene. An 8-km-long lava flow traveled to the SW from the 1-km-wide summit crater of Espíritu Santo volcano, which overlaps the southern slope of Marmolejo. Mild phreatomagmatic eruptions were recorded from San José in the 19th and 20th centuries.

— Smithsonian Institution, Global Volcanism Program