Earth Sciences 1022A/B Lecture Notes - Lecture 2: Northwestern United States, Shield Volcano, Magma Chamber
14 Jan 2016
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Document Summary
Volcanic eruptions occur where magma reaches earth"s surface, often from gas buildup. Materials extruded: hot, runny mafic lava tends to flow quietly downhill while cooler, viscous felsic magma tens to erupt violently, with pyroclastic material. Two lava types: hot: runny pahoehoe with a surface resembling coils of, cooler: blocky aa, viscous rope. Pillow lavas form underwater as lave repeatedly breaks through quenched tube ends (called black sand in hawaii) Pyroclastic material ranges from fine ash to large bombs and blocks (bombs are shaped like footballs) Nu e ardentes (pyroclastic flows) of devastating hot glowing clouds of ash and gas (very hot cloud of ash and gas) Lahars of pyroclastic (wet ash flow) mixed with rain, ice and snow. Volcanic structures: commonly cone-shaped mountains with a small crater at the top or a larger caldera (>1 km across) after magma chamber drains, rim and sides cave in. **illustration: sequence of events that formed crater lake, oregon**
