GEOL 2207 Lecture Notes - Pyroclastic Fall, Gravitational Collapse, Mafic
Document Summary
Glass is a non-crystalline or amorphous, metastable solid formed by quenching a melt: cools so fast that a regular crystal lattice cannot form. As magma rise, they: crystallize, exsolve volatiles: volatiles (gases) dissolved exsolved. Explain what lava flows, fire fountains, lava bombs and volcanic ash are and how they form: magma is generated by melting of existing rock, primary processes, effusive: Outer crust cools and solidifies insulating the molten interior. Gravitational collapse of lava flows/domes (block and ash flows: explosive: Pyroclastic fall: widespread distribution of ash, 10"s of kms. Ballistics proximal to vent: secondary processes. Explain what controls volcanic explosivity: volcanic eruptions: effusive and explosive, effusive: outpouring of molten magma from the vent lavas, explosive: gas driven violent eruptions pyroclastic deposits key to explosive volcanism: gas content + melt viscosity. Magmas produce bubbles, bubbles expand as magma rises, foaming. Gas escapes, pressure released = safe: felsic high gas content + gooey explosive eruptions. Gas kept under increasing pressure = dangerous.
