November 4, 2013 – Map of the Ash and Tephra fall for Major Volcanic Eruptions in the United States: The map reflects ash and tephra fall for major eruptions from the Long Valley Caldera, Mount St. Helens and Yellowstone. Tephra is fragmental material produced by a volcanic eruption regardless of composition, fragment size or emplacement mechanism. Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground they remain as tephra unless hot enough to fuse together into pyroclastic rock or tuff.
Posted on: Mon, 04 Nov 2013 09:30:25 +0000