December 21 Eruption of Volcano Near Mexico City is Prelude to A Dangerous Phase, Say Scientists

Conditions Mirror Those at Mount St. Helens Immediately Preceding Eruption

Release Date: December 23, 1994 This content is archived.


BUFFALO, N.Y. -- University at Buffalo volcanologists, who have been studying Popocatepetl, a towering volcano just 40 kilometers from Mexico City, said that its eruption on Wednesday, Dec. 21, is a sign that it is entering a dangerous phase.

"The chamber is loaded" is how Michael Sheridan, Ph.D., volcanologist and chair of the UB Department of Geology, describes the volcano's status.

Sheridan and colleague Hugo Delgado, Ph.D., associate researcher at the Geophysical Institute at the National University of Mexico in Mexico City, have jointly developed the first three-dimensional computerized models of Popocatepetl that simulate the reach of potential eruptive phenomena.

One of the largest volcanoes in the world, it also is the fourth highest mountain in North America, a feature that adds to its catastrophic potential.

Sheridan said that this latest eruption, which has blown ash into the city of Puebla, (population: 2,000,000) and nearby villages, bears similarity to small ash explosions that shortly preceded the catastrophic Mount St. Helens eruption in 1980.

"Ash came out of Mount St. Helens in April 1980, just a month before it finally blew," said Sheridan.

"This is just a first puff," Sheridan predicted of Popocatepetl. "It means that other premonitory signs that have been observed, such as increases in seismic activity and in the emission of gases from the volcano imply that magma is moving up into the volcano."

He noted that while any one of these signs by themselves is not a sufficient cause for alarm, together they indicate that the volcano is in a very dangerous phase.

If the conduit (feeding system that leads to the surface) of the volcano fills up with magma, Sheridan explained, it could cause a lateral bulge that could lead to structural collapse of the cone. Such events have occurred three times in Popocatapetl's history, the last happening several thousand years ago.

"Using our models, we can see where the movement of various types of materials, ranging from hot, pyroclastic flows to cold mudflows will be focused," said Sheridan.

Developed by digitizing paper maps of the area, the colorful, computerized simulations show the volcano and the surrounding area, with towns, villages and roads superimposed on it.

Using computerized simulation models, the researchers can estimate how fast and how far flows from an eruption would travel. They feed that data into computer models, which in turn calculate the probability that sliding material will destroy towns and roads.

Because it is essentially a topographical map that has been digitized, the three-dimensional simulation also shows the precise contours of the land in relief. The image can be manipulated in any direction in real-time so that eruptions on any side are visible in three dimensions.

"The model shows you the same views you would see if you were flying over the volcano," said Sheridan.

"With a large-scale eruption, almost all the cities on the screen are in danger," said Delgado.

While there have been no reports yet of damage or casualties from the latest Popocatepetl eruption, the scientists noted that even fallen ash can be dangerous.

"If a layer of ash spreads through towns and villages, and then there is a heavy rainfall, there can be mudflows and floods," explained Delgado. He noted that more fatalities are due to secondary effects like mudflows than to eruptions themselves.

The simulations are particularly helpful in effectively communicating risk to public officials.

"Officials can understand what they see on the screen with a very simple explanation," said Sheridan. "They can understand the value of using this animation to explain to villagers what could happen during an eruption, and what they would need to do to save themselves."

He added that the simplicity of the animation overcomes the difficulty of communicating public-safety programs to people living in small towns near the volcano, some of whom may not be able to read.

This marks the first time that the computer simulation models will be put to use for public-safety planning. Delgado will be using the results of the simulations in his position as an advisor to the Secretaria de Governacion, a department of the Mexican government that functions like the Department of Interior, and which is responsible for issues like monitoring volcanoes and proposing evacuation plans when necessary.

The simulations were developed under initial funding from the National Science Foundation.

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