Threatening 22 million people, Mexico’s Popocatepetl is a very closely watched volcano

MEXICO CITY — Mexico’s Popocatepetl volcano rumbled to life again this past week, belching out towering clouds of ash that forced 11 villages to cancel school sessions.

The residents weren’t the only ones keeping a close eye on the towering peak. Every time there is a sigh, tic or heave in Popocatepetl, there are dozens of scientists, a network of sensors and cameras, and a roomful of powerful equipment watching its every move.

Marco Ugarte, Associated Press

A plume of ash and steam rises from the Popocatepetl volcano, as seen from Mexico City, on June 19, 2019. Popocatepetl has rumbled to life again, spewing out towering clouds of ash that forced 11 villages to cancel school sessions. 

The 17,797-foot volcano, known affectionately as “El Popo,” has been spewing toxic fumes, ash and lumps of incandescent rock persistently for almost 30 years, since it awakened from a long slumber in 1994.

The volcano is 45 miles southeast of Mexico City, but looms much closer to the eastern fringes of the metropolitan area of 22 million people. The city also faces threats from earthquakes and sinking soil, but the volcano is the most visible potential danger — and the most closely watched. A severe eruption could cut off air traffic, or smother the city in clouds of choking ash.

Volcanic ashes are especially dangerous for aviation, not only because they reduce visibility but because they can act as an abrasive, damaging an aircraft’s wings and fuselage.

Mexico City’s two main airports temporarily shut down operations on Saturday due to ash spewing from the volcano. The city’s Benito Juarez International airport suspended operations from 4:25 to 10 a.m. local time, resuming operations after removing volcanic ashes, checking the runways and verifying favorable wind conditions, the airport said on Twitter. Felipe Angeles airport, located north of Mexico City and operated by the military, suspended operations for five hours starting about 6 a.m.

Popocatepetl’s explosions registered in the early hours of Saturday were more intense than in recent days, but authorities — who keep a close eye on the active volcano — are maintaining the threat at an intermediate level.

Ringed around the volcano’s summit are six cameras, a thermal imaging device and 12 seismological monitoring stations that operate 24 hours a day, all reporting back to an equipment-filled command center in Mexico City.

A total of 13 scientists from a multidisciplinary team take turns staffing 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 the volcano and in general the peak is more predictable.

Marco Ugarte, Associated Press

Paulino Alonso Rivera, who works at the National Center for Disaster Prevention of Mexico, gives an interview as he monitors the Popocatépetl volcano from Mexico City on Feb. 8.

On a recent day, researcher Paulino Alonso made the rounds, checking the readings at the command center run by Mexico’s National Disaster Prevention Center, known by its initials as Cenapred. It is a complex task that involves seismographs that measure the volcano’s internal trembling, which could indicate hot rock and gas moving up the vents in the peak.

Monitoring gases in nearby springs and at the peak — and wind patterns that help determine where the ash could be blown — also play a role.

The forces inside are so great that they can temporarily deform the peak, so cameras and sensors must monitor the very shape of the volcano.

How do you explain all of this to 25 million non-experts living within a 62-mile radius who have grown so used to living near the volcano?

Authorities came up with the simple idea of a volcano “stoplight” with three colors: green for safety, yellow for alert and red for danger.

For most of the years since the stoplight was introduced, it has been stuck at some stage of “yellow.” The mountain sometimes quiets down, but not for long. It seldom shoots up molten lava: instead it’s more the “explosive” type, showering out hot rocks that tumble down its flanks and emitting bursts of gas and ash.

The center also has monitors in other states; Mexico is a country all too familiar with natural disasters.

For example, Mexico’s earthquake early alert system is also based at the command center. Because the city’s soil is so soft — it was built on a former lake bed — a quake hundreds of miles away on the Pacific coast can cause huge destruction in the capital, as happened in 1985 and 2017.

A system of seismic monitors along the coast sends messages that race faster than the quake’s shock waves. Once the sirens start blaring, it can give Mexico City residents up to half a minute to get to safety, usually on the streets outside.