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