1. Ch 13-Volcanoes What causes most volcanoes?
Movement of tectonic plates
Magma-liquid rock produced under Earth’s surface
Temp of rock rises above melting pt of the minerals the rock is composed of, rock melts
Enough pressure is removed from the rock, melting pt will decrease and rock will melt
Addition of fluids, such as water, may decrease the melting pt of some minerals in the rock and cause rock to melt

2. Volcanism
Any activity that includes the movement of magma toward or onto Earth’s surface
Magma rises upward through the crust cuz the magma is less dense than surrounding rock
Lava-magma that flows onto Earth’s surface
Vent-opening that lava flows through
Volcano-vent or fissure in Earth’s surface through which magma and gases are expelled

3. Major Volcanic Zones Where do they occur?
Convergent and divergent boundaries of tectonic plates
Pacific Ring of Fire
Subduction Zones-one tectonic plate moves under another
Oceanic to oceanic, continental to oceanic
Mid Ocean Ridges-largest amount of magma comes to surface
Plates pull apart magma flows upward along rift zone
Fissures-cracks through which lava flows to Earth’s surface
Hot spots-volcanically active area of Earth’s surface
Areas of volcanism w/in interiors of lithosphere plates

4. Intrusive Activity
Magma intrudes overlying rock, magma that doesn’t reach Earth’s surface cools and solidifies inside crust
Plutons-igneous rock
Dikes-small tabular plutons
Batholithes-large plutons

5. Sec 2-Volcanic Eruptions
Types of magma
Mafic-magma or rock that is rich in magnesium and iron, dark
Felsic-magma or rock rich in light colored silicate materials
Mafic-oceanic crust
Felsic and mafic-continental crust

6. Types of Eruptions
Viscosity-resistance to flow, of magma affects force w/ which particular volcano will erupt
Mafic-runny lava, low viscosity, quiet eruptions
Felsic-sticky lava, high viscosity, explosive eruptions
Quiet eruptions
Oceanic eruptions, mafic magma. Low viscosity=gases escape so volcanoes are quiet
Lava flows
Lava cools rapidly, crust forms and lava continues to flow, it forms rock=pahoehoe
Crust deforms rapidly, forms wrinkles, surface breaks into jagged chunks=aa
Blocky lava-high viscosity, produces large chunks, and lava continues to flow

7. Explosive Eruptions
Felsic lavas of continental volcanoes-cooler and stickier
Large amounts of trapped gases-CO2 and water vapor
Explodes and throws pyroclastic material into air
Pyroclastic material-fragments of rock that form during volcanic eruption

8. Types of Pyroclastic Material
Volcanic ash-less than 2 mm in diameter
Volcanic dust-volcanic ash less than .25 mm in diameter
Lapilli-large pyroclastic particles, less than 64 mm
Volcanic bombs-large clots of lava, red hot when thrown out
Volcanic blocks-largest pyroclastic material, form from solid rock blasted from vent

9. Types of Volcanoes
Crater-funnel shaped pit at top of volcanic vent, forms when materials are blown out
Types of cones
Shield Volcanoes-broad at base, sloping sides, wide area, quiet eruptions
Cinder Cones-steep slopes, explosion eruptions, made up of pyroclastic material
Composite volcanoes-alternating layers of hardened lava flows and pyroclastic material

10. Volcanic Eruptions
Calderas-large circular depression, forms when magma chamber below volcano partially empties, causes ground to sink
Krakatau in Indonesia
Predicting Volcanic Eruptions
Earthquake activity-most important sign is changes in earthquake activity around volcano
Patterns in activity-upward movement of magma beneath the surface, causes surface of volcano to bulge outward before eruption