GEOL 1303 Lecture Notes - Lecture 4: Pumice, Lava Dome, Lapilli
Document Summary
Volcanoes as geosystems: depths 100 km plus within asthenosphere each at least 1300 c rocks. Thus asthenosphere identified as main source of magma. 1. volcanism is a fundamental tectonic process in the construction of earth"s. 2. volcanic eruptions are a major natural hazard for human society. 3. lavas from volcanoes provide geologists with samples from which they can infer properties of earth"s interior. The major intrusive igneous rocks are granite (felsic), diorite (intermediate), and gabbro (mafic). The major extrusive counterparts are rhyolite (felsic), andesite (intermediate), and most common of all basalt (mafic). Variations due to differences in chemical composition, gas content, and temperature. Higher silica content and lower temperature lavas are more viscous . The more gas in lava, the more violent is the eruption. Dark in color; erupts at 1000 to 1200 c; high temperature and low silica content; extremely fluid can flow downhill fast and far. Flood basalts: examples are columbia plateau of oregon and washington states.
