Volcanoes and Earthquakes

What is a volcano? Weak spot in crust where molten material (magma) comes to the surface

Volcanoes and Plate Boundaries What are plate tectonics? theory which describes the motions of the earth’s crustal plates What causes plate tectonics? convection currents in the mantle Volcanic belts around plate boundaries Ring of Fire Converging plate boundaries Plates come together Diverging plate boundaries Plates seperate

Hot Spot Volcanoes Magma erupts through Earth’s crust Can happen anywhere Yellowstone

Volcanic Eruptions Quiet Eruptions Low-silica, low-viscosity magma Hawaii Explosive Eruptions High-silica, high viscosity Pyroclastic flow Mt. St. Helens

Volcano Life Cycle Active-is erupting or may erupt at any time Dormant- Might become active in future Extinct- dead, unlikely to erupt again

Volcano Energy Energy comes from magma under Earth Hot Springs- groundwater heated by magma and forms pool Geysers- Hot water, steam erupts from ground Geothermal energy- water heated naturally Used to warm houses electricity (steam)

What is an earthquake? Shaking and trembling that results from the movement of rock beneath Earth’s surface

Stress in Earth’s Crust Tension- stretches rock, divergent Compression- Squeezes rock until it folds or breaks, convergent Shearing- rocks move in opposite directions

Faults Normal Faults- diverge, footwall above hanging wall Reverse Faults- Compression, hanging wall above footwall, converge Strike-slip Faults- plates move past each other

Seismic Waves Carry energy from an earthquake away from the focus (center) through Earth’s interior, and across surface

Types of Seismic Waves P waves- first to arrive, longitudinal waves, move in solids and liquids S waves- second to arrive, transverse waves, only in solids Surface waves- ground moves like ocean waves, transverse waves

Seismograph Detects seismic waves Used to map and monitor faults

Damage from Earthquakes Shaking- triggers landslides, avalanches, destroys buildings and water mains Liquefaction- loose, soft soil turns to mud Aftershocks- smaller earthquakes following big earthquake Tsunamis- large wave