Study Guide Part II geology lab

Study Guide Part II geology lab - I Volcanoes Viscosity(a...

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I. Volcanoes Viscosity- (a measure of a fluid's resistance to flowing) especially in magma is due to polymerization of silicon and oxygen in the magma. The higher the silica content, the higher the viscosity. Another determining factor in magma viscosity is temperature. The higher the temp, the lower the viscosity. The third factor is water. Water dissolved in magmas has the effect of lowering viscosity. Magma composition and gas content - control whether a volcano will erupt quietly like many Hawaian type basalt volcanoes do, or like the catastrophic silica rich eruption of Mt. St. Helens. 3 types of lava- Basaltic lava- commonly flows over large distances. Rhyolitic lava- has a very high viscosity and never travels far nor fast when extruded as a lava flow onto the surface of the Earth. Highly viscous felsic lava- commonly plugs up the shallow plumbing of volcanoes, preventing gases from escaping. Volcano Hazards- Powerful explosive eruptions drastically alter land and water for tens of kilometers around a volcano. Tiny liquid droplets of sulfuric acid erupted into the stratosphere can change our planet's climate temporarily. Eruptions often force people living near volcanoes to abandon their land and homes, sometimes forever. Terms relating to volcanism- Ash- Volcanic ash consists of rock, mineral, and volcanic glass fragments smaller than 2 mm (0.1 inch) in diameter, which is slightly larger than the size of a pinhead. Tephra- term for fragments of volcanic rock and lava regardless of size that are blasted into the air by explosions or carried upward by hot gases in eruption columns or lava fountains. Air Fall- Ash flow- Pyroclastic Flow- is a ground-hugging avalanche of hot ash, pumice, rock fragments, and volcanic gas that rushes down the side of a volcano Nuee Ardente- Pumice- is a light, porous volcanic rock that forms during explosive eruptions.
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Lahar- Indonesian word for a rapidly flowing mixture of rock debris and water that originates on the slopes of a volcano. Lava Flow- masses of molten rock that pour onto the Earth's surface during an effusive eruption. Lava Dome- are hemispherically shaped lava fountains that form when the upward pressure of magma from the conduit below is in approximate equilibrium with the mass of ponded lava through which it passes.
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