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Notes Test 3 3.26.13.docx

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University of Miami
GEG 120
Peter Muller

Divergence () spreading as magma wells up from the asthenosphere and new crust is created as at mid oceanic ridge Convergence (-->>> lava) often accompanied by rock fragments and explosive gases -Geographic distribution -Mid-oceanic ridges that trigger seafloor spreading -subduction at convergent plate boundaries -elsewhere (e.g.) Hawaii -State of activity -Active (erupted in recorder history) -Dormant (no known eruption, but signs of recent activity) -Extinct (no signs of life; heavily weathered and eroded) (sea mounts are undersea volcanoes) Lava and landforms -Extruded magma (lava) Varying viscosity (range of flows: motor oil>> thick porridge) Explosiveness (depends on gas content) Airborne solidification after explosion (formation of pyroclastics) Volcanic bombs (largest, boulder sized projectiles) Volcanic cinders (gravel>> baseball sized coarser fragments) Volcanic ash (smallest gravity-controlled fragments) Volcanic dust(finest particles, mostly aerosols) Shaping of lava landforms thickness of flow qualities of surface being covered nature of magma opening vent at top of crust pipe-shaped vents that form mountains lengthy cracks: FISSURE ERUPTIONS Fissure Eruptions -Releases magma to form lava that extends in sheets across the surface -Often forms plateau - Columbia Plateau in Washington, Oregon and Idaho (basalt): Volcanic Mountains -Towering-mountain form most dramatic: (Mt. Fuji, Mt. Vesuvius, Mt. Kilimanjaro) -Most other volcanoes are less impressive in size and shape -Four Categories of volcanic landforms 1. Composite Volcanoes 2. Lava Domes 3. Cinder Cones 4. Shield Volcanoes Composite Volcanoes -Structural Characteristics -Especially associated with subduction zones -Layered with alternating strata of lavas and compacted pyroclastics -During eruptions, materials stay close to crater: steep conical shape -Notoriously dangerous -Unpredictable eruptions -Hazards of lava, pyroclastics, and gases Hazards of Composite Volcanoes -Lahars Abruptly melted snowcaps trigger high-s[
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