Volcanic history of El Chichon Volcano (Chiapas, Mexico) during the Holocene, and its impact on human activity

Before its devastating eruption in 1982, El Chichon Volcano was little know n and did not appear on any listings of hazardous volcanoes. Subsequent geo logic studies, based on stratigraphic and radiocarbon investigations, showe d that at least three explosive eruptions had occurred previously at this v olcano. In this paper, we present the result of recent studies on the strat igraphy of the volcano and new radiocarbon ages which show that at least 11 eruptions have taken place at El Chichon in the past 8000 years. Explosive events, most of them producing block-and-ash flow and surge deposits, occu rred around 550, 900, 1250, 1500, 1600, 1900, 2000, 2500, 3100, 3700 and 77 00 years BP. The juvenile products of these eruptions have a trachyandesiti c composition with similar degree of evolution, as evidenced from their SiO 2 abundance and depletion in MgO, CaO, TiO2, as well as trace and rare eart h elements. This suggests segregation of olivine and orthopyroxene from the melt. Since human settlements in southeast Mexico and Central America can be traced as far back as approximately 2500 years BP, most of these events probably affected human activity. In fact, there are reports of pottery sha rds and other artifacts in deposits from the eruption of 1250 BP. Pottery f ragments in deposits of an eruption that took place 2500 BP are also report ed in this paper. Thus, the impact of the volcano on human activities has b een frequent, with most of the repose intervals lasting between 100 to 600 years. The impact of the eruptions was probably of greater than local exten t, because airfall tephra could reach distant sites and possibly even affec t weather. The eruptive history of El Chichon also offers clues in the inve stigation of the Maya civilization. Several researchers have considered the volcano as an important factor in the answer to some intriguing questions such as the extensive use of volcanic ash in Late Classic Maya ceramics or, of greater importance, the causes of the collapse of the Classic Maya civi lization.