GEOL 1 Lecture Notes - Lecture 19: Rhyolite, Andesite, Basalt
Document Summary
Types of volcanoes and styles of eruption . Rocks are black to dark gary (basalt) Rocks are dark gray to beige in color (andesitic) Silica in melt forms a three-sided pyramid or tetrahedron. Gas cannot easily escape higher viscosity intermediate and felsic magmas. Volcanoes with higher silica magma then erupt explosively. Occurs under continental crust in any setting (continental rift, subduction zone, continental hot-spot) Crust forms quickly, interior cools much more slowly. Cooled and solidified rock is also referred to as lava. Thin flows can travel long distances and cover large areas. Not dangerous to people unless directly in its path. Do not travel as far as basalt. Semi-solid, vesiculated (small holes) basaltic lava fragments. Very small pumice fragments, glass shards or rock fragments. As clouds moves downwind ash fallas out, heaviest particles first, closest to vent. Larger eruptions produce more ash and distribute it further.
