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.
