Geological Hazards and Their Impact_McGeary_Date_031710

Geological Hazards and Their Impact_McGeary_Date_031710 - o...

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Volcanoes Rocks: Green with black rind- mantle rock (crystallized from magma) Black- basalt Tan- andesite Red- scoria/cinder (pyroclast) White- pumice (pyroclast) volcano- mountain formed by products of volcanic eruptions magma- molten (liquid, melted) rock lava- magma that flows on Earth’s surface pyroclasts- exploded magma (ash, cinder, pumice, bombs) What is an active volcano? Any volcano that is likely to erupt again (active) has a source of magma in subsurface) Recurrence interval can be days to hundreds of years How to determine recurrence interval? o Historical activity o Geologic record (date lave flows) 50-60 volcanoes erupt each year (above sea level) Steps to forming a volcano: 1) generation of magma melt a rock
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o increase temperature o drop pressure (decompression melting) **main way**
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Unformatted text preview: o add water (later, water makes it explosive) ← ← Volcanic rocks ← Dark Intermediate Light ←- basalt - andesite - rhyolite ←- low silica - int. silica - high silica ←- low viscosity - int. viscosity - high viscosity ←- low in gas - can be high in gas ←- mostly lava flow - mostly ash ← ← silica-SiO2 ← viscosity-stickiness/ease of flow ←-to get an explosive eruption need high viscosity and gas (H2O vapor) • high viscosity and no gas = no explosive eruption • low viscosity with gas = no explosive eruption • low viscosity and no gas = no explosive eruption ← ←- most explosive volcanoes are located at subduction zones (because their magma has water vapor in it, and tend to have a higher viscosity)...
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Geological Hazards and Their Impact_McGeary_Date_031710 - o...

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