Global Volcanism Program | Image GVP-10030
Major pyroclastic-flow deposits of the April 3 and 4 El Chichón eruptions formed natural dams blocking the Magdalena-Ostuacán river. The tephra dam seen here, located about 4.5 km WSW of the crater, produced a lake that eventually reached 5 km in length and had a volume of several million cubic meters. It failed catastrophically about 7 weeks after the end of the eruption (May 26), causing a massive lahar with temperatures to 82° C that destroyed a bridge and damaged a hydroelectric site, killing one worker.
Photo by Servando De la Cruz-Reyna, 1982 (Universidad Nacional Autónoma de México).