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Lecture 5

Earth Rocks Lecture 5.docx

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Department
Earth Sciences
Course
Earth Sciences 1022A/B
Professor
Stephen R Hicock
Semester
Winter

Description
Volcanoes Chapter 4  Vocanic Gases • Build up of gas in the magma chamber • Gas and magma have to break through and “spill” out of volcanoes • Lava will flow from the sides of the volcano and beyond  “molasses in January” • Feeds the lava to the surface “Pipe” o All starts by gas build up  Materials Extruded Lava Flows: • Hotter, runny pahoehoe (ropy) • Cooler, viscous aa (blocky) • Pillow lavas form under water pyroclastic material ranges from fine ash to large  bombs. • Nuee ardentes (very hot cloud of ash & gas); lahars (wet ash flow) • Hot, runny mafic lava tends to flow quietly downhill while cooler, viscous felsic  magma tends to erupt violently, with pyroclastic material; two lava types: • Hot, runny pahoehoe with a surface resembling coils of rope, and cooler, blocky aa • Pillow lavas form underwater as lava repeatedly breaks through quenched tube ends • pyroclastic material ranges from dust and ash to streamlined bombs and large blocks • nuée ardentes (pyroclastic flows) of devastating hot glowing clouds of ash and gas • Lahars of pyroclastics mixed with rain, ice, and snow • Pahoehoe crystalizes on the top, but the lava still flows underneath  • Aa, red hot  • Pillow Lavas: individual tooths that have solidified  • After the erruptions are over you find a lot of black sand, intermediate between ash  and other stuff o Volcanic bomb, looks like football or rugby ball, goes through the air  • Nuee Ardente, Mt. St. Helens 1980, incandescent volcano, 34 years ago in  Washington state  • St. Pierre Martinique 1902, locked up in a dungeon, force 
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