GEOL 1001 Chapter : Chapter 12 Outline
Document Summary
Factors influencing eruptive style: flow (effusive) or blow (explosive): effusive eruptions- productive lava flows. Controls on eruptive style: viscosity (fig. 5. 2: composition (sio2, temperature, amount of gas- gas pressure0 greater p favors explosive style. Pahoehoe basalt with a glassy, ropy texture. Forms when extremely hot basalt forma a skin. With flow, the skin is rolled into ropy ridges and furrows. A"a"- basalt that solidifies with a jagged, sharp, angular texture. A"a" forms when hot flowing basalt cools and thickens. With flow, lava crumbles into shards and fragments. Lava tube- insulated conduit for lava flow. Columnar jointing- solidified flows may contract with vertical fractures that are hexagonal in across section. Pillow basalt- rounded blobs of basalt that form underwater due to lava cooling instantly. The pillow surface is cracked, quenched glass. Higher si)2 makes andesitic lavas viscous: unlike basalt, they do not flow rapidly. Isteas, they mound around the vent and flow slowly. Andesitic lava flows remain close to the vent.
