Volcanic ash is composed of fragments of pulverized rock and volcanic glass ejected from a volcano during an eruption. Clouds of ash are blown high into the sky where they are subject to wind and weather patterns. This ash can be sucked into airplane engines and cause engine failure.
Scientists monitor volcanoes and weather to assist in air passenger safety.
Re-creation of an encounter of an airplane with an ash cloud. Courtesy of UAF Geophysical Institute.
Photo of an ash cloud from Cleveland Volcano as seen from the International Space Station. Courtesy of NASA.