El Chichón, Active volcano in Francisco León, Mexico

El Chichón is an active stratovolcano in Francisco León, north-western Chiapas, built from alternating layers of lava and ash with a complex of domes and a tuff ring. Its 1982 eruption destroyed the summit dome and left a 1-km-wide, 300-m-deep crater whose flat floor holds a bright white, acidic crater lake ringed by steep, gullied inner walls.

El Chichón was first identified as a volcano in 1928 by the German geologist Friedrich Karl Gustav Müllerried; before that it was studied only as a possible geothermal energy source. Its 1982 eruption, the largest volcanic disaster in modern Mexican history, came after more than 600 years without a major event. Earthquakes were felt through 1980 and 1981 and geologists hazard-mapped the region, but monitoring activity was not increased.

Locals in Chiapas, Tabasco and southern Veracruz call the volcano Chichonal rather than El Chichón. Zoque residents reported feeling the ground tremble from November 1981, months before the 28 March 1982 eruption, and say the volcano also erupted in 1850, a date geologists dispute.

Access to the volcano follows unpaved roads that can become slippery or impassable depending on weather conditions. Those approaching the crater should prepare for steep climbs and loose rocks underfoot.

The released sulfur dioxide reached the stratosphere and caused reddish twilights on several continents in the following months. Pilots reported unusual lighting conditions during flights over the Atlantic and Pacific oceans.