lLAVA DOMES
LAVA DOMES
Volcanic or lava domes are formed by relatively small, bulbous inasses of lava too viscious to flow any great distance, consequently on extrusion the lava piles over and around it's vent. A dome grows largely by expansion from within. As it grows it's outer surface cools and hardens then shatters, spilling loose fragments down it's sides. some domes form craggy knobs or spines over the volcanic vent, whereas other form short, steep-sided lava flows known as "coulees." Volcanic domes commonly occur within the craters or on the flanks of large composite volcanoes. The nearly circular Novarupta Dome that formed during the 1912 erruption of Katmai Volcanoe, Alaska measures 800 feet across, and 200 feet high. The internal structure of this dome defined by layering of lava fanning upward and outward from the center indicates that it grow largely by expansion from within.