MEXICO CITY — Mexico’s Popocatepetl volcano rumbled to life again this week, belching out towering clouds of ash that forced 11 villages to cancel school sessions.
But the residents were not the only ones who kept a watchful eye on this towering peak. There are scientists and powerful tools watching every tic, sigh or heave from Popocatepetl.
The 17,797-foot (5,426-meter) 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 (72 kilometers) southeast of Mexico City, but looms much closer to the eastern fringes of the metropolitan area of 22 million people. Although the city faces other threats, including earthquakes and sinking land, the volcano remains the biggest and most obvious. A severe eruption could cut off air traffic, or smother the city in clouds of choking ash.
Ringed around its 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 multi-disciplinary team take turns manning the command center around the clock. Being able to warn of an impending ash cloud is key, because people can take precautions. The warning time for a volcano can last longer than an earthquake, and the peak of the eruption is generally more predictable.
On an occasion, Paulino Alono, a researcher, checked the data at Mexico’s National Disaster Prevention Center (Conapred), a command center that is run by the Mexican National Disaster Prevention Center. Seismographs are used to measure internal volcano trembling. This could be a sign of hot gas and rock moving upwards from the top vents.
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 within the volcano are so strong that they may temporarily alter the shape, which is why cameras and sensors need to monitor its very shape.
How do you explain all of this to 25 million non-experts living within a 62-mile (100-kilometer) 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.
The stoplight has been on “yellow” for most years. The mountain will sometimes calm down but it won’t last long. The mountain is not a molten-lava volcano, but more of an “explosive”, hurling hot stones that fall down its sides and emitting gas and ash.
The command center has also monitors located in other states. Mexico, a nation that is all too familiar with disasters, keeps a close eye on the situation.
For example, Mexico’s earthquake early alert system is also based at the command center. The soil in Mexico City is soft, having been built on an old lakebed. A quake on the Pacific Coast hundreds of miles from the capital can have devastating effects in the capital.
A system of seismic monitors along the coast sends messages that race faster than the quake’s shock waves, and can give Mexico City residents up to a half minute of warning once the sirens start blaring, to get to safety, usually on the streets outside.
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