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The Explosive Volcanic History of Ilopango Caldera, El Salvador

AuthorsSunyé-Puchol, I.; Aguirre-Díaz, Gerardo ; Pedrazzi, Dario ; Dávila-Harris, P.; Miggins, D.P.; Costa, A.; Smith, V. C.; Ortega-Obregón, C.; Pierre, L.; Gutierrez, E.; Hernández, W.
Issue Date7-Jan-2020
AbstractThe Ilopango caldera (IC) is a large active volcano located along the El Salvador Volcanic Arc. Its magmatism is associated to the subduction of the Cocos plate under the Caribbean plate. Despite the surrounding regions being blanketed in thick and widespread pyroclastic deposits, little was known about the number of large eruptions produced by IC, their magnitude and their age. Here we present the results from field mapping, stratigraphic correlation and geochronological analyses, which provide insights into the magnitude and tempo of large explosive eruptions from IC. The results achieved during this investigation are key for future volcanic hazard assessment for the 3 million inhabitants living in the San Salvador Metropolitan area, which is the most populated city in Central America. Based on stratigraphic correlations, geochronologic constraints (40Ar/39Ar and U-Th-Pb ages) and regional tectonic deformation, the complete pyroclastic sequence of IC has been divided into three formations [1]: the Comalapa (1.78 ¿ 1.34 Ma), Altavista (918 - 257 ka) and Tierras Blancas (<57 ka). Each eruption deposit identified was dated by techniques to reconstruct the volcanic history of IC. At least, IC has erupted explosively 13 times since its formation at 1.78 Ma ago. These high number of large eruptions from this volcano-tectonic caldera has been controlled by the El Salvador Fault Zone (ESFZ) [2]. The depth and the high slip-rate of the ESFZ structures assist magma ascent of large volumes of melt, and their eruption produces periodic caldera collapses. The AD 6th century Tierra Blanca Joven (TBJ) was the last explosive eruption of IC, and occurred whilst Mayans populated the region. The TBJ erupted ~30 km3 Dense Rock Equivalent (DRE) of magma [3], and dispersed volcanic ash over Honduras, Guatemala, Nicaragua and the Pacific Ocean. However, the TBJ was significantly smaller than the first eruptions from IC. For example, the pyroclastic density currents (PDC) of the Olocuilta ignimbrite (OI), a caldera forming event at 1.78 Ma, which covers an area of ~3000 km2 with thick pyroclastic density currents (PDC) deposits. Based on the thickness of the deposits of OI (up to 120 m), it is possible that it may have been a supereruption with an erupted volume of ~350 km3 DRE of magma [2].
DescriptionVolcanic and Magmatic Studies Group Conference 2020
Appears in Collections:(Geo3Bcn) Comunicaciones congresos
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