Volcanoes Forms when magma reaches the Earths surface and erupts as lava or ash

Volcano Formation -Melting occurs in asthenosphere -Magma is lava underground -Magma is less dense than surrounding rock -rises to lithosphere and creates cracks in the solid rock -cracks are how magma reaches surface

Plate Boundaries Eruptions on plate boundaries that separate, collide, or are hot spots

Convergent Plate Boundaries -most volcanoes are at plate boundaries around the Pacific at subduction zones - this is the Ring of Fire

Divergent Plate Boundaries Mostly unnoticed b/c they occur under water - One major divergent boundary that is above water is the East African Rift Valley

Hot Spots Balloon like plume Usually NOT near plate boundaries Stationary (non moving) Creates island chains in the ocean (Hawaii)

Lava -Magma that has reached the surface Viscosity -measure of a fluids RESISTANCE to flow - low viscosity flows more easily (water) than high viscosity (molasses) - viscosity decreases as temp increases

Chemical Composition Mafic Lava - low viscosity - Heavier elements (magnesium and iron) - Usually quiet eruptions Felsic Lava - High viscosity -Lighter elements (silicon, oxygen, aluminum, potassium) - Explosive eruptions

Volcanoes are classified by their size, shape, and mineral type Types of Volcanos Volcanoes are classified by their size, shape, and mineral type Composite Cone - form at convergent boundaries - explosive eruptions - large, steep shape 1000’s of meters wide - composed of ash and lava - pyroclastic flows- a fast-moving current of hot gas and rock

Shield Cone -fluid lava erupts, travels far - broad, wide, flat shape - gas poor -composed of lava -quiet eruption Cinder Cone -high temp - gas rich - mafic -explosive, ejects cinders -smaller 100’s meter range - short eruption cycles - composed of ash