Computer Simulations Help Officials Make Decisions About Planet's ÒRiskiest Volcano"

SAN FRANCISCO -- For the first time, the official risk map for the Mexican volcano Popocatepetl, which has shown alarming activity during the past two years, has been designed with input from computer models, rather than based solely on fieldwork.

Public-safety officials in Mexico are making decisions about Popocatepetl, a towering volcano just 40 kilometers from Mexico City, based on a risk map designed using software that simulates volcano activity developed by researchers at the University at Buffalo.

The software can provide public-safety officials with more accurate information than may be available from fieldwork, and is useful particularly when fieldwork or historical data on a volcano is missing.

"This is a huge volcano surrounded by millions of people," explained Michael F. Sheridan, Ph.D., professor and chair of the Department of Geology at the University at Buffalo. "That makes Popocatepetl the riskiest volcano on the planet."

Sheridan developed the simulations with Hugo Delgado, Ph.D., associate researcher at the Geophysical Institute at the National University of Mexico in Mexico City. The risk map was published at the National University by a team of researchers, of which Sheridan was a member.

Sheridan will discuss Popocatepetl during a press conference at the American Geophysical Union meeting to be held at 11 a.m. PST on Wednesday, Dec. 18, in Room 211 in the Moscone Convention Center in San Francisco. He also will participate in a technical session about the volcano from 1:30-4 p.m. PST on Tuesday, Dec. 17.

Located just 40 kilometers from Mexico City and even closer to the city of Puebla (population: 2 million), Popocatepel is one of the largest volcanoes in the world.

It also is the fifth highest mountain in North America, a feature that adds to its catastrophic potential.

Since a series of ash explosions that occurred in December, 1994, the volcano has gone through several stages of varying severity.

Last year, hikers from a prominent mountain-climbing organization scaled the volcano. While they were near the peak, the ash emissions suddenly and dramatically increased, killing five of the hikers.

In October, it seemed as though the volcano had entered a quieter period, but that period was followed by renewed explosions.

"An eruption is not inevitable," Sheridan stated, "but Popocatepetl is like a dusty champagne bottle sitting in a cellar. The activity may seem to be dying out, but the conduit through which gases could escape to the atmosphere is pretty plugged up right now. That allows pressure to build up and, if the underground chamber gets hot enough, the obstruction could be blasted away."

Earlier this month, the volcano began exhibiting tremors and renewed ash emissions marked by intermittent explosions.

"Reports of the end of this eruption have been greatly exaggerated," Sheridan declared.

To determine how imminent an eruption may be, and to track how far and how fast the volcanic flows would travel, safety officials usually rely on estimates, based on extensive fieldwork by geologists.

A key ingredient in making predictions about the nature of volcanic flows is the frequency and nature of past eruptions. But with Popocatepetl, very little information is available.

"One thing about Popocatepetl is that it generally doesn't produce gentle lavas," Sheridan said, "it explodes, and it hasn't had a major explosion since the 16th century."

Much new geologic information about Popocatepetl has been gathered in the past few years by researchers at the National University of Mexico.

That new information easily can be incorporated into the computer models, Sheridan said.

"These models are well-suited for updating because they function like a spreadsheet," he said. "Results from new parameters can be calculated within a few seconds. That's one of the advantages of this kind of model. It's not fixed in space, it's constantly ready to be updated."

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

Using the simulations, the researchers can estimate how fast and how far lava flows from an eruption would travel and in which direction. They feed that data into computer models, from which they can calculate the probability that sliding material will destroy towns and roads. They take into account factors such as turbulence and viscosity of the flow, the coefficient of friction and the flow's starting velocity.

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

"From a management and public-safety point of view, it's really important to have an accurate idea about where the flows will go and how fast," said Sheridan. "Without the aid of computer models, it's frustrating trying to predict where the hot flows would go. And with the computer models, you need less field data because the models simulate flows for areas we haven't visited."

For example, he said, if an evacuation is being considered, the map provides information that allows officials to decide which areas should be evacuated and which areas are safer.

"This map is designed like a bull's eye," Sheridan explained.

Areas of danger are defined by a series of concentric zones, with the most dangerous areas colored red in the center.

Another advantage of the computer models is that because they are probability models, they allow researchers and public-safety officials to assign a level of confidence to their projections.

The models are particularly important, Sheridan said, in countries where governments don't have the resources to spend hundreds of man-years on fieldwork and where volcanoes become active during a short period of time when there haven't been baseline studies.

They also are useful for volcanoes that don't exhibit the typical warning signs that an eruption may be imminent and that might produce an event that never before occurred at that volcano.

This could be the case with Popocateptel, Sheridan explained. For example, one mysterious aspect of the volcano's current periods of activity is that earthquakes, which typically increase preceding a volcanic explosion, have been strangely weak.

"Some of the normal sorts of precursors aren't evident," said Sheridan, citing the explosion that killed the hikers last year. "At that time, there were no precursors indicating that activity was imminent -- the volcano was giving no warning signals. If it had been, the hikers certainly would never have received permission to climb the volcano. That means Popo has a potential to erupt in a surprise attack, making the data from our models all the more valuable."