At first everything was shaken. Earthquakes shook the earth. The first explosions produced a devastating shock wave. Currents of pyroclastic density were created with volcanic materials and gases that traveled between 150 and 200 kilometers per hour and that wiped out everything in their path. In the end, a column of ash almost 50 kilometers high rose and its remains extended 150 kilometers around, may even have reached the poles of the planet. This is how the supereruption of the Ilopango caldera, a volcano in the center of El Salvador, approximately 1,500 years ago. “It was a total catastrophe”, says the volcanologist Gerardo J. Aguirre Díaz, who coordinated an investigation which details for the first time the complete volcanic history of Ilopango and the danger it still represents, as well as the impact it had on the Mayan populations that inhabited that region.
This eruption of the Ilopango caldera has been the strongest explosion that has taken place in Central America in the last 10,000 years. The hypothesis of the multidisciplinary team of Aguirre Díaz, a researcher at the Geosciences Center of the National Autonomous University of Mexico (UNAM), is that this volcanic event was one of the triggers for the disintegration of the Mayans in El Salvador and their eventual migration to the north, from central Guatemala to the Yucatan Peninsula. This demographic flow most likely happened during the classical period, between 100 and 900 AD. Other theories suggest, instead, that many of those settlers eventually returned to El Salvador and southern Guatemala.
The explosion was so strong that it wiped out practically all the vegetation and made the area in the 40 kilometers that surround the volcano uninhabitable. There were lahars, mudslides that advanced at great speed and destroyed everything in their path along rivers and valleys. Agriculture collapsed and took years to recover, several settlements literally disappeared from the map in a matter of days if not hours, trade disappeared, there were probably famines and diseases spread, Aguirre Díaz infers. “If you weren’t asphyxiated by the gases, you were disintegrated by the currents of ash with high temperatures that the volcano expelled,” says the Mexican researcher. Other works, such as that of the American Robert Dull, point out that these natural phenomena were factors that influenced the fall of the southern flank of the Mayan culture and the political rearrangements of the time, such as the rise of Copán, an important Mayan kingdom that was found in what is now Honduras.
The group of researchers – in which the UNAM, the University of Oxford, the Spanish Higher Council for Scientific Research, the Salvadoran Ministry of the Environment and Natural Resources, the United States Oregon State University and the Institute of Volcanology of Italy – also seeks to confirm whether there was a volcanic winter, which is when gases with suspended particles from volcanic emissions form aerosols (gases) that remain suspended in the stratosphere and block sunlight. These blockages could have caused a drop in temperature of between two and three degrees, which could have increased the collapse in the ecosystems of the region affecting humans. The team, funded by the National Council of Science and Technology of Mexico, managed to determine after three years of work that the first major eruption of the volcano was 1.78 million years ago and identified 12 other explosions.
The effects of the supereruption of some 15 centuries ago are still visible. It is known that the entire metropolitan area of San Salvador, about 10 kilometers from the volcano, is built on Tierra Blanca Joven, the white volcanic remains released by Ilopango and the San Salvador volcano. These materials not only covered practically the entire small Central American country, they are also present in Guatemala, Honduras, Nicaragua and Costa Rica.
The caldera is covered by a homonymous lake that measures around 70 square kilometers and its last eruption was in 1879, a relatively short time ago in volcanology, so it is still considered active. The researchers also calculated how recurrent these eruptions have been and, although they have not found a clear pattern, they warn that it still represents a risk for El Salvador and its neighboring countries. “This caldera has had and will continue to have more eruptions, although we cannot know how strong,” says Aguirre Díaz. While the mystery behind what could have been a decisive episode for the Mayan civilization is unraveled, scientists are still on the trail of the secrets and dangers of the Ilopango volcano, one of the greatest colossi in Central America.