Resurgent Dome A protrusion created within a crater after an eruption, as new magma forces its way up from underneath. You may have seen this term in the newspapers concerning Mt. St. Helens. A light-colored volcanic rock with abundant silica. It is a felsic rock, the extrusive equivalent of granite. Scoria Volcanic rock that has many vesicles but does not qualify as pumice.
Spatter cone A pile of tephra in a small, conic shape which surrounds a volcanic vent.
Tephra A general term used to refer to material thrown out of a volcano through the air. Tuff Volcanic ash compacted and hardened into a rock layer. A clastic sedimentary rock with particles smaller than marbles or as large as boulders. The smallest layer of a sedimentary rock visible to the unaided eye. Varve Two laminations or thin layers deposited due to seasonal sedimentation variation within one year.