Photograph by R. P. Hobblitt, U.S. Geological Survey. Photograph by Maurice and Katia Krafft. Pyroclastic fallout consists of particles that have been ejected from vents and have travelled through the atmosphere before falling to earth or into water. Fallout ash can also be derived from elutriation of ash the boils up from pyroclastic flows as they travel across the land. Transport of pyroclastic fallout material is by ballistic trajectory and by turbulent suspension.
Energy is supplied initially to fragments by the eruption and later by wind.
Tephra falling from above characteristically drapes over the landscape. Pre-historic ash fall layers that blanket earlier topography. Oshima Island, Japan. Photograph by Fisher. Troubles with Long-Distant Pyroclastic Fallout Lessons learned at Mount St. Helens, Mt. Pinatubo and many other eruptions are that it is difficult to clean up after the fall of just a few centimeters of ash, and that ash in the atmosphere severely damages jet engines , thereby endangering the lives of passengers.