D. Chapter 5 - D Chapter 5 Volcanism All processes...

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D. Chapter 5 Volcanism All processes extruding lava, gases, and pyroclastic materials onto the earth’s surface or into the atmosphere. Gases Composition – 50 – 80 % water vapor, nitrogen, sulfur dioxide and hydrogen sulfide (rotten eggs). Traces of other gases. Gas pressure – increases as magma rises, pressure from overlying country rock decreases and contained gases expand. Felsic magmas– high viscosity, inhibit expansion, may explode producing pyroclastic materials (ash). Mafic magmas – low viscosity allows gases to expand and escape easily, quieter eruptions. Lava Flows - Generally not dangerous as they are slow and their direction may be calculated. Special features of a lava flow: Lava tube Pahoehoe Aa Pressure ridges Spatter cones Columnar joints Pillow lava Pyroclastic materials Ash (particles less than 2mm) Ash falls and flows (nuee ardentes) Lapilli (particles 2 to 64 mm) Blocks (particles greater than 64mm) – angular Bombs (particles greater than 64mm) - stream- lined and twisted indicating they cooled
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D. Chapter 5 - D Chapter 5 Volcanism All processes...

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