Understanding the Eruptive History of Ilamatepec

Mt. Saint Helens’ style eruptions (dangerously explosive) are typical for volcanoes abundant in the countries of Central America. In our study we began to unravel the unknown geological history of violent eruptions of El Salvador’s largest volcano, Ilamatepec (Santa Ana), that last erupted in 2005. Its immediate surroundings include the country’s major economic artery of sugarcane and coffee production, as well as the second and third largest cities of the country; a 25km radius around the volcano is home to nearly half a million people. Historical records and a few scientific inquiries indicate at least 9 moderate to large eruptions since the early 1500’s. We initiated an expedition in March 2011 to collect volcanic deposits found layered in the crater scar of Ilamatepec. Expedition participants included the volcanologists of the geological survey of El Salvador, an undergraduate student team from Buffalo State College, a graduate student from SUNY Buffalo, and the National Tourist Police of El Salvador. Data collected were analyzed using optical microscopy methods, grain size distribution techniques, and scanning electron microscopy. Analysis of a 15-layer sequence indicates a very explosive history characterized by smaller steam eruptions, moderate steam and magma eruptions, and large magmatic eruption. The information learned through this process will allow us to address the hazards that account for potential damage to infrastructure and loss of life to the Salvadoran population by applying our understanding of previous events to future eruptions. This work was conducted in conjunction with the Panamerican Institute of Geography and History