MEXICO CITY (AP) — Mexico’s Popocatepetl volcano roared back to life this week, belching towering clouds of ash that forced 11 villages to cancel school sessions.
Locals weren’t the only ones keeping a close eye on the towering peak. Every time there is a sigh, twitch, or heave in Popocatepetl, there are dozens of scientists, a network of sensors and cameras, and a room full of powerful equipment monitoring his every move.
The 17,797ft volcano, affectionately nicknamed ‘El Popo’, has been spouting toxic fumes, ash and glowing chunks of rock persistently for nearly 30 years, ever since it awoke from a long slumber in 1994.
The volcano lies 45 miles southeast of Mexico City, but looms much closer to the eastern fringes of the metropolitan area of 22 million people. The city is also threatened by earthquakes and land subsidence, but the volcano is the most visible – and closely watched – potential danger. A severe eruption could cut off air traffic or smother the city in choking ash clouds.
Around its top are six cameras, a thermal imaging device and 12 seismological monitoring stations that operate around the clock, all reporting to an equipment-packed command center in Mexico City.
A total of 13 scientists from a multi-disciplinary team take turns manning the command center around the clock. Being able to warn of an impending ash cloud is essential because people can take precautions. Unlike earthquakes, warning times can be longer for the volcano and in general the peak is more predictable.
Recently, researcher Paulino Alonso made the rounds, checking the readings at the command center run by Mexico’s National Center for Disaster Reduction, known by its initials as Cenapred. It’s a complex task that involves seismographs measuring the internal tremor of the volcano, which could indicate hot rock and gas moving up the vents of the peak.
Gas monitoring in nearby springs and at the summit — and wind patterns that help determine where ash might be blowing — also play a role.
The forces within are so large that they can temporarily distort the peak, so cameras and sensors must monitor the shape of the volcano itself.
How do you explain all of this to 25 million non-experts living within a 62 mile radius who have become so accustomed to living near the volcano?
Authorities came up with the simple idea of a volcano “stop light” with three colors: green for safety, yellow for warning, and red for danger.
For most of the years since the introduction of the red light, it has been stuck at some stage of “yellow”. The mountain calms down sometimes, but not for long. It rarely spews molten lava: it is more of the “explosive” type, pouring hot rocks that tumble down its sides and emitting bursts of gas and ash.
The center also has monitors in other states; Mexico is a country too accustomed to natural disasters.
For example, Mexico’s earthquake early warning system is also based at the command center. Because the city’s ground is so soft – it was built on an ancient lake bed – an earthquake hundreds of miles up the Pacific coast can cause massive destruction in the capital, as was produced in 1985 and 2017.
A system of seismic monitors along the coast sends messages faster than the shock waves of the earthquake. Once the sirens start sounding, it can take Mexico City residents up to half a minute to get to safety, usually on the streets outside.