Tolhuaca

Geography & Climate

Tolhuaca is located in Chile, within the Southern Andean Volcanic Arc of the broader South America Volcanic Regions. Situated at 38.31° S, 71.64° W in the Southern Hemisphere, the volcano lies within a temperate climate zone. At 2,739 meters above sea level, Tolhuaca rises above the surrounding terrain into montane or subalpine conditions. The elevation creates distinct ecological zones along its flanks, from forested lower slopes to exposed rocky terrain near the summit. 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

Tolhuaca 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 near Tolhuaca, 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

Tolhuaca has 4 recorded eruptions in the geological database, spanning from 5857 BCE to 4000 BCE. The most powerful recorded event was a severe eruption capable of regional ash fall and pyroclastic flows in 4885 BCE, reaching VEI 3 on the Volcanic Explosivity Index. Notable eruptions include 4885 BCE (VEI 3), 5371 BCE (VEI 3), 5857 BCE (VEI 3). These eruptions span roughly 1,857 years of volcanic history.

Significance

With a maximum recorded VEI of 3, Tolhuaca has produced eruptions capable of generating pyroclastic flows and significant ash fall in the surrounding area. While not among the largest eruptions globally, VEI 3 events pose serious hazards to local populations and can disrupt regional air travel.

GVP Reference Summary

Tolhuaca (or Tolguaca) is a late-Pleistocene to Holocene stratovolcano located immediately NW of Lonquimay volcano. A NW-SE zone of aligned summit craters is youngest to the NW. Another group of vents cutting the south and east flanks is oriented SW-NE, parallel to the zone of flank vents on Lonquimay, and is of post-glacial age (Moreno and Gardeweg 1989). Reports of eruptions in 1876 and on 7 January 1933 are not confirmed; the latter date probably refers to an eruption of Lonquimay or Llaima (Petit-Breuilh 1994, pers. comm.). Polanco et al. (2000) stated that explosive activity consisted of three VEI 3-4 eruptions between 8050 and 6590 BP. The Pemehue volcanic trend on the NW flank was noted by Naranjo (pers. comm. 2010) in Melosh et al. (2012) as having post-glacial lava flows dated at less than 6,000 years old. Only fumarolic activity has occurred from this basaltic-andesitic volcano during historical time. Fumaroles and hot springs are common across the NW flank where there is an active geothermal reservoir (Melosh et al., 2012).

— Smithsonian Institution, Global Volcanism Program