caldera - a crater larger than five miles in diameter formed by collapse of the ground or volcano into an underground cavity formed by the ejection of an equivalent amount of pyroclastic material. Some calderas are more than 40 miles in diameter.
cinder - a rough-surfaced pyroclastic fragment baseball to nut size, formed directly from magma and explosively ejected to the surface. It is gaseous and therefore many bubbles (vesicles) form within the viscous material. Synonymous with scoria.
cinder cone - a volcano formed by cinders that pile up around an active vent.
cross beds - a bed of layered laminations (very thin layers) truncated by other layers across eroded edges within a larger layer, or within an assemblage of layers.
dome - a dome-shaped protrustion of solidified magma formed by slow extrusion of highly viscous magma located on the side of, or within, the crater of a volcano.
ejecta - Pyroclastic material explosively ejected from a volcano.
fallout - Acumumlation of pyroclastic material that falls from the sky.
fumarole - a vent from which gases form magma - or steam created by hot magma-heating water-escape into the atmosphere.
hydrovolcanic eruption - an explosion or eruption caused by sudden expansion of water when mixed with magma.
Bibliography
Out of the Crater: Chronicles of a Volcanologist, Richard V. Fisher, Princeton University Press, 1999
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