Mexico City Mexico’s Popocatepetl volcano has come alive again this week, spewing out towering clouds of ash that have forced 11 villages to cancel school sessions.
Residents weren’t the only ones watching the towering summit. Every time there’s a sigh or sob in Popocatepetl, there are dozens of scientists, a network of sensors and cameras, and a room full of powerful equipment watching its every move.
Known affectionately as “El Popo,” the 17,797-foot (5,426-meter) volcano has been spewing toxic fumes, ash and glowing masses of rock continuously for nearly 30 years, since it awoke from a long slumber in 1994.
The volcano is located 45 miles (72 kilometers) southeast of Mexico City, but it looms near the eastern fringes of the metropolitan area of 22 million people. The city also faces threats from earthquakes and sinking soils, but the volcano is the most obvious potential hazard—and the most closely watched. A severe volcanic eruption could cut off air traffic, or suffocate a city in choking clouds of ash.
Flanking its summit are six cameras, a thermal imager and 12 seismograph stations operating 24 hours a day, all backed by an equipment-packed command center in Mexico City.
Thirteen scientists from a multidisciplinary team take turns assigning the command center around the clock. Being able to warn of an impending ash cloud is key, because people can take precautions. Unlike earthquakes, warning times can be longer for a volcano and in general the peaks are more predictable.
One recent day, researcher Paulino Alonso made the rounds, checking the readings at a command post run by Mexico’s National Center for Disaster Prevention, known by its initials as CINAPRED. It’s a complex task that involves seismometers that measure the volcano’s internal vibration, which can indicate hot rock and gases moving upwards in vents at the summit.
Monitoring of gases in nearby springs and at the peak — and wind patterns that help determine where to blow ash — also plays a role.
The forces inside are so great they can temporarily distort the peak, so cameras and sensors must monitor the shape of the volcano.
How do you explain all this to the 25 million non-experts living within a 62-mile (100-kilometer) radius who are used to living near a volcano?
The authorities came up with the simple idea of ”stopping” the volcano with three colors: green for safety, yellow for alert, and red for danger.
In most of the years since the introduction of the stop sign, it has been stuck at some point out of the “yellow”. The mountain sometimes calms down, but not for long. It rarely spews molten lava: instead it is the “explosive” type, raining hot rocks that fall down its sides and emit bursts of gas and ash.
The center also has monitors in other states; Mexico is a country very familiar with natural disasters.
For example, Mexico’s earthquake early warning system is also in the command center. Because the city’s soil is so soft — it was once built on a lake bed — an earthquake hundreds of miles away on the Pacific coast could wreak havoc on the capital, as it did in 1985 and 2017.
The seismic monitoring system along the coast sends messages racing faster than earthquake shock waves. Once the siren starts to go off, it can give Mexico City residents up to half a minute to get to safety, usually on the streets outside.
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