© Provided by San Diego Union Tribune A plume of ash and steam rises from the Popocatepetl volcano near Mexico City in June 2019. ( A plume of ash and steam rises from the Popocatepetl volcano near Mexico City in June 2019. ( (Marco Ugarte / Associated Press)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 volcano is 45 miles southeast of Mexico City, but lies much closer to the eastern fringes of the larger metropolitan area of 22 million people. Authorities came up with the simple idea of a volcano warning “stoplight” with three colors: green for safe, yellow for alert and red for danger.