Mexico’s Popocatepetl volcano, some 40 miles outside Mexico City, has entered a heightened phase of activity. The mountain has been spewing towering clouds of ash and steam since mid-April, putting local residents on alert.
Sheridan has been studying Popocatepetl for years. After the volcano’s last significant eruption, in December 2000, he and a team of researchers developed a map showing which communities around the volcano could be threatened by mud flows during a major event.
Q: Why is Popocatepetl considered one of the world’s most dangerous volcanoes?
The great danger that ‘Popo’ presents is that there is a dense population in an area that potentially could be affected by a really big eruption. They say more than 25 million people live in and around Mexico City. Since the end of the last Ice Age (14,000 years ago) there have been five really large eruptions of Popo.
The oldest of these big eruptions sent blocks the size of a person’s fist to the middle of Mexico City. The most recent big eruption resulted in mudflows that inundated a large pre-Hispanic city near where the city of Puebla sits today.
However, such a large event would give distinctive precursor signals prior to an eruption that the civil protection authorities and scientists in the region could detect.
Q: Is the threat of a major eruption high?
A: It has been more than 1,100 years since an eruption that seriously affected human habitation.
In the back of my mind is the fact that these volcanoes are more or less continuously accumulating gas and liquid in a subterranean chamber. The longer the material is sitting down there, the longer the volcano is in ‘repose,’ and the bigger the eruption that could be expected.
Q: Does Popocatepetl’s current behavior indicate that a large eruption may be about to occur?
A: Most forecasts are based on observation of the behavior of a volcano. We know how Popocatepetl behaved before it began erupting in 1994, and how it behaved in 2000, when it had a significant eruption.
It’s behaving like that now. There was a report from CENAPRED yesterday that said there have been some mud flows already.
Q: Is the risk map you developed in 2001 still useful today?
A: There hasn’t been enough research done at this volcano yet to make what you would call a definitive hazard map.
What we did in 2000 was use computers to simulate two different categories of events that we thought would be possible, small- and intermediate-sized. The map we published provides basic information on mud flows, which are important to consider.
Q: What can people do to prepare for a disaster?
A: If the imminent threat is a mud flow, the idea is to go to high ground. The surface of the mud flows themselves might be three feet or 10 feet or 15 feet above the channel that they flow in. So the way to be safe is to have a pathway from your house to somewhat higher ground nearby, somewhere you can go to in 10 or 15 minutes.
An alternative is that the government will come in and evacuate people if they feel that it’s severely dangerous. People should also have food and medical supplies available in case they become isolated for a few days.