The anatomy of an active volcano
Standing at 5,592 meters (18,346 feet), Lascar is a stratovolcano in the Central Volcanic Zone of the Andes. It is composed of andesite and dacite, and is structurally complex, consisting of two main cones and six overlapping craters. Its activity has shifted between the eastern and western cones over its 220,000-year history. Currently, the westernmost crater of the eastern cone is the active center.
Lascar's volcanic activity is driven by the subduction of the Nazca Plate beneath the South American Plate. This process feeds a magma chamber with temperatures estimated between 890–970°C. The volcano has produced a total volume of 30 to 40 cubic kilometers of rock over the last 43,000 years. It has erupted more than 30 times since 1848, with a major eruption in 1993 creating an ash column that reached 23 kilometers high and deposited ash as far away as Buenos Aires, Argentina. This event produced pyroclastic flows that traveled 8.5 kilometers from the summit.
A chemical hotspot
The active crater of Lascar contains hundreds of fumarolic vents that persistently release a plume of gas and water vapor. These fumaroles are classified into two types: low-temperature vents (below 82°C) and high-temperature vents (exceeding 150°C). Some vent temperatures have been measured at over 295°C, with the hottest reaching 385°C.
The gas mixture reveals the volcano's magmatic system. It contains high concentrations of acidic gases like sulfur dioxide (SO2), hydrogen chloride (HCl), and hydrogen fluoride (HF). Lascar is a major source of volcanic sulfur dioxide, releasing between 200 and 2,300 metric tons of sulfur per day. This amounts to roughly 1% of all volcanic sulfur emissions worldwide. The fumaroles also emit carbon dioxide, carbon monoxide, hydrogen sulfide, and trace elements like arsenic and boron. These chemical-rich gases react with the surrounding rock, creating mineral precipitates.