Mexico's Popocatepetl Volcano Threatens Millions.

Mexico's Popocatepetl volcano, located 45 miles southeast of Mexico City, has been spewing toxic fumes, ash, and lumps of incandescent rock persistently for almost 30 years. The volcano is the most visible potential danger to the city of 22 million people and is closely monitored by a network of sensors, cameras, and scientists. The National Disaster Prevention Center has implemented a volcano "stoplight" system to warn residents of potential danger. The center also monitors earthquakes and other natural disasters in Mexico.