]> When dust, sand, snow, and/or spray is raised by the wind to a height of 6 feet or more The bow shock is a discontinuity that forms in the solar wind when the supersonic solar wind encounters the magnetic field of a planet, very similar to the shock wave that forms upstream of an aircraft moving at a supersonic speed. Peleean eruption is characterized by explosions of moderate to extreme violence in which solid or viscous hot fragments of new lava are ejected -- commonly as pyroclastic fallout and pyroclastic flows. These eruptions are usually associated with silicic magmas. Phreatic eruption is an explosion that follows the transformation of groundwater into steam. No incandescent or juvenile material is erupted. Plinian eruptions are characterized by paroxysmal ejection of large volume of ash and pumice as a well-defined eruption column or "jet;" often precedes caldera collapse. The resulting tephra fallout covers an area of more than 500 square kilometers. Weak-to-violent, sporadic, ballistic eruptions of tephra, generally of mederately fluid basaltic or andesitic magma. Moderate to violent ejection of solid or very viscous hot fragments of new lava in short-lived, cannon-like bursts. Ash and fine ash are emitted with gases and ascend to form a cauliflower-like eruption cloud. 5 5 5 5 5 5 5 5 5 5