The Blast that Changed World Weather

Crater of El Chichon Volcano, located in southeastern Mexico. (Smithsonian National Museum Global Volcanism Program)

By Jim Andrews, Senior Meteorologist

Apr 3, 2012; 12:51 PM ET

It has been 30 years since El Chichon volcano burst to life in the spring of 1982, unleashing upon the Mexico countryside one of the biggest volcanic eruptions of the 20th century.
In the wake of two powerful blasts, at least 1,900 people were dead and millions of dollars of crops were in ruin.
Even more, the eruption had a measurable impact upon the atmosphere and weather patterns worldwide.
In the lead-up to the catastrophic blasts of March 28 and April 4, increasing earthquakes around long-dormant El Chichon warned of the volcano's awaking, according to Erik Klemetti, writing in his Eruptions blog.
The last major eruption of El Chichon apparently happened in 1350.
On March 28, a 3-hour eruption shot a column of ash 27 km (about 17 miles -- literally stratospheric) above El Chichon. In so doing, the volcano spewed hundreds of millions of tons of ash.
But the worst was still to come and on April 4, El Chichon uncorked an even greater, more voluminous blast, with its ash cloud lofting into the stratosphere, 29 km high.
This eruption sent fiery 360-km/hr (200-mph) pyroclastic flows as many as 8 km (5 miles) from the crater, according to Klemetti. As many as 1,000 people were killed when the pyroclastic flow destroyed the village of Francisco Leon.
But it was apparently the remarkable chemistry of the ash clouds, being abnormally rich in sulfur dioxide, allowed El Chichon to have such a bearing upon weather and climate.
As many as 10 million tons of sulphur dioxide were blasted into the atmosphere, Klemetti said. This was roughly seven times that of Mount St. Helens in 1981, even though eruptive ash output was comparable in volume to the Mexico eruption.
The sulphur dioxide give rise to clouds of particulate matter that were found to have circled the globe within weeks. Although these warmed the stratosphere, the northern hemisphere cooled by 0.4 to 0.6 degrees C (up to 1 degree F), apparently owing to the reflection of solar energy.
One of the strongest bouts of "El Nino" ever recorded began within weeks of the eruption, leading to widespread disruption of weather patterns into 1983. Some scientists have drawn a direct link between the eruption-induced cooling and the El Nino warming of the equatorial Pacific Ocean.
A "silver lining" to the catastrophic eruption was the many colorful sunsets that were witnessed around the world.
El Chichon volcano is located in the southeastern Mexico state of Chiapas, about 80 km (50 miles) south-southwest of Villahermosa.

The Blast that Changed World Weather