Mexico’s Popocatepetl volcano rumbled to life again this 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.

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.