Potential for Large Eruptions at Popocatepetl
A reader in Mexico City asked: "It has been said that Popo, in Mexico, is a Stratovolcano that could have a Krakatau type and size of eruption. Should that happen, what would be the consequences for the 20 million people living in nearby Mexico City, not to mention the major city of Puebla which is only 45 Km from the Volcano?"
Popocatepetl is a typical stratovolcano that has shown violent eruptions during its history. Based on our and others' work we have recognized several major events in the last 5000 years: in 822AD, between 400 and 800 BC, and around 3100 BC Popo had huge Plinian eruptions (like the 79AD Vesuvius eruption that destroyed Pompeii) that produced pyroclastic flows all around the volcano to distances of 10 km; thick ash deposits dispersed by W-SW winds towards the Puebla Valley, and years of destructive mudflows (lahars) that filled the Puebla valley. We have found the 822AD lahars burying the lower 1m of the great pyramid of Cholula and filling the Puebla Valley. Clearly the people living in the valley were massively affected, and archaeological evidence suggests that Cholula was abandoned. An even larger eruption occurred about 23,000BC, when the entire south flank of Popo collapsed and/or exploded (like Mt. St. Helens) accompanied by a major Plinian eruption. A similar eruption to those described above, were it to occur today, would have dramatic impacts on the area surrounding Popo. Pyroclastic flows would be of immediate danger to about 10km distance from the volcano, as these flows kill everyone in their path. Ash fallout and deposition would depend on the prevailing wind directions. During winter and spring, they blow towards the east (Puebla Valley), and in the summer and fall they would send most of the ash westward, over Mexico City. For many years after an eruption, mudflows would continue to come down each rainy season (like at Pinatubo). These would likely produce the greatest economic impacts because of their wide-spread distribution, and long duration.
Michael Abrams, Volcanologist
NASA/Jet Propulsion Laboratory