Popocatepetl is one of Mexico's most active volcanoes. After almost 50 years of dormancy, "Popo" came back to life in 1994 and has since then been producing powerful explosions at irregular intervals. In the past centuries before European invasions, large eruptions produced giant mud flows that have buried Atzteque settlements, even entire pyramids. The glacier clad smoking volcano towers to 5426 m 70 km SE of Mexico City to form North America's 2nd-highest volcano.