INTRODUCTION
El Chichón is a volcano located in the remote jungles of southern Mexico's Chiapas province, some 670 km ESE of Mexico City and approximately 150 km from the border of Guatemala (17º22’N, 93º14’W). In Spring 1982, the mountain awoke in a violent series of eruptions that killed an estimated 2,000 people.
Due to its limited accessibility, dense vegetation and lack of any features that set it apart from its neighbors, El Chichón had been subjected to scientific study in only limited amounts and was not suspected to be a dangerous volcano until it was too late. Over the last 20 years, study of El Chichón showed that the volcano has been active for the last 220,000 years, with at least six major eruptions over the last 10,000 years. Prior to the 1982 eruption, the last volcanic event occured in 1259 (evidence of this eruption has been observed in ice cores pulled from Greenland's ice sheet.
THE 1982 ERUPTIONS
El Chichón erupted at least ten times between March 29 and April 4, 1982. In the month leading up to the eruptions, several shallow-focus earthquakes hit the area. On March 29, a major eruption shot ash and debris into the air, but it seemed to pose no immediate threat to local inhabitants. The next week saw eight additional minor eruptions, but few were hurt.
On the morning of April 4, however, the mountain turned lethal. A second huge explosion rocked the area, taking the locals completely by surprise. Unlike the previous eruptions, this time a scalding mix of volcanic gas, ash and rocks called a pyroclastic flow sped down the mountainside, levelling everything in its path. El Chichón unleashed two separate pyroclastic flows on the nine villages surrounding the volcano.
The
death toll was placed at 2000 lives -- making it the 13th most deadly volcano in recorded history -- although some deaths have been attributed to drowning following the sudden damming of the Magdelena River by
debris. In addition to the human death toll, thousands of head of livestock were lost.
GEOLOGY
The three major eruptions deposited appreciable amounts of volcaniclastic sediments. Specifically, El Chichón launched tephra and ash derived from a trachyandesitic magma into the troposphere and stratosphere (up to 17 km), producing tephra-fall and pyroclastic surge deposits and pyroclastic flows. The eruption destroyed the dome covering the vent of the volcano, and now a crater lake sits in within the caldera. It is thought that the magma extruded from the volcano originated from subduction of Pacific oceanic crust beneath the North American and Caribbean Plates.
The 1982 eruption of El Chichón is remarkable for two reasons. Firstly, it was one of the first major eruptions recorded using satellite imagery. Secondly, the ash, tephra and gases produced by El Chichón had a higher sulfur dioxide (SO2) content than expected. This caused concern over potential climatic impact, as SO2 is a major cause of acid rain and acts as an atmospheric aerosol. On the whole, there was no recorded global climate change.
Sources:
USGS Mexico Volcanoes and Volcanics -
http://vulcan.wr.usgs.gov/Volcanoes/Mexico/framework.html
El Chicon -
http://users.bendnet.com/bjensen/volcano/centralamerica/mexico-chichon.html
Volcanic Hazards -
http://www.geo.arizona.edu/geo2xx/geo218/UNIT3/lecture11.html
Matson, M., (1984) 1982 El Chichón Volcano Eruptions – A Satellite Perspective,
Journal of Volcanology and Geothermal Research, Vol. 23.
Duffield, W. A., Tilling, R.I., and Canul, R., (1984) Geology of El Chichón Volcano, Chiapas, Mexico,
Journal of Volcanology and Geothermal Research, Vol. 20.
A PowerPoint presentation I made for a Volcanology assignment