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Eruptive history[edit]

Four major dacitic - rhyolitic eruptions occurred during the late Pleistocene and Holocene, producing pyroclastic flows and tephra that blanketed much of the country.^[2]

The caldera collapsed most recently^[2] sometime between 410 and 535 AD (based on radiocarbon dating of plant life directly related to the eruption),^[3] which produced widespread pyroclastic flows and devastated Mayan cities. The eruption produced about 25 km³ (6.0 cu mi) of tephra (20 times as much as the 1980 eruption of Mount St. Helens), thus rating a 6 on the (VEI) Volcanic Explosivity Index. The "ash-cloud fallout [..] blanketed an area of at least 10,000 square kilometres waist-deep in pumice and ash", which would have stopped all agricultural endeavor in the area for decades.^[4]

Later eruptions formed several lava domes within the lake and near its shore. The only historical eruption, which occurred from December 31, 1879, up to March 26, 1880, produced a lava dome and had a VEI of 3.^[2] The lava dome reached the surface of the lake, forming the islets known as Islas Quemadas.^[5][6]