El Chichon, Mexico, 1982

Some 43 active volcanoes in Central America form a belt running from central Mexico through Guatemala, Honduras and Nicaragua to central Costa Rica. These volcanoes are related to northeastward subduction of the Cocos plate beneath the North American place and the Carribean plate.

El Chichon is the most southern and eastern volcano in Mexico, and prior to 1982, was thought to be extinct. Consequently, activity of the volcano was not being monitored and the 1982 eruption was a total surprise (although, with hindsight, local inhabitants had noticed increased earthquake activity for some months prior to the first eruption).

Between March 28th and April 4th, El Chichon erupted violently three times. Pyroclasitc flows and surges destroyed villages within a 7 kilometer radius of the volcano and killed more than 2000 people. The eruptions destroyed the summit dome of El Chichon, leaving a one kilometer wide, 300 meter deep crater. It also produced a total volume of 0.5 cubic kilometers of volcanic debris. Subsequent studies of the volcano showed that it had been frequently and violently active for the past thousand years, with major eruptions every 600 years. An earlier study and attentive appreciation of El Chichon could have given earlier warning to the 1982 eruption!

One thing to note about El Chichon, is that the eruption, although not particularly large in terms of the amount of volcanic ejections, did have significant atmospheric effects and an impact on global climate. The eruption was notable in that large volumes of sulphur dioxide rich aerosols were injected into the lower stratosphere and were dispersed globally, causing brilliant sunrises and sunsets over a large area of Earth and a decrease in the amount of solar radiation reaching the surface. The stratospheric cloud from the 1982 eruption of El Chichon remained detectable until late 1985!

ash and sulphur dioxide clouds above El Chichon after the eruption. The greens show an intensity in aerosols, the blues indicate the spread of the particles.