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 CompositionMafic Lava- low viscosity- Heavier elements (magnesium
and iron)- Usually quiet eruptions
Felsic Lava- High viscosity
-Lighter elements (silicon, oxygen, aluminum, potassium)
- Explosive eruptions
Types of VolcanosVolcanoes 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