EARTHQUAKES & VOLCANOES

EARTHQUAKES

• Vibrations in the ground that result from movement along breaks in Earth’s lithosphere called faults

WHERE DO EARTHQUAKES OCCUR?

• Most earthquakes occur along plate boundaries

TYPES OF FAULTS• Normal• forces pull two blocks of rock

apart• ex. divergent plate boundary

• Reverse• forces push two blocks of rock

together• ex. convergent plate boundary

• Strike-Slip• two blocks of rock slide

horizontally past each other• ex. transform plate boundary

EARTHQUAKE EPICENTER

• Seismic Waves - Energy that travels as vibrations on and in the Earth

• Focus – where seismic waves originate and where rocks first move along the fault

• Epicenter - location on the Earth’s surface where the seismic waves originated

TYPES OF SEISMIC WAVES• Primary (P) Waves• move in a push-pull motion like

a spring• fastest-moving waves and the

first waves you feel

• Secondary (S) Waves• move in an up-and-down

motion• slower than P waves• do not travel through liquid

• Surface Waves• travel only on Earth’s surface in

a rolling motion• most destructive

STUDYING EARTHQUAKES

• Seismologist – scientist that studies earthquakes

• Seismometer – instrument used to measure and record ground motion

• Earthquake Scales:

Richter Scale measures ground motionMoment Magnitude Scale

measures total amount of energy released by an earthquake

Modified Mercalli Scale

measures and describes damage resulting from an earthquake

VOLCANOES

• A vent in Earth’s crust through which molten rock (magma) flows• Once magma reaches the surface it is called lava

FORMATION OF VOLCANOES

• Most volcanoes form at plate boundaries• Convergent• as one plate subducts

beneath another the rock melts and rises to the surface

• Divergent• As the plates separate

magma rises through the vent in Earth’s crust and forms new crust • ex. sea-floor spreading

HOT SPOTS

• Volcanoes not associated with plate boundaries• convection currents in the

mantle rise magma to the surface

• as plates move over the hot spot island chains are formed

• The oldest island is the farthest away from the hot spot• ex. Hawaiian Islands

TYPES OF VOLCANOES• Shield Volcano• large, with gentle slopes• form along divergent

boundaries or hot spots

• Composite Volcano• large and steep-sided resulting

from explosive eruptions• form along convergent

boundaries

• Cinder Cone• Small, steep-sided

VOLCANIC ERUPTIONS

• Quiet Eruptions• magma has a low

viscosity (low silica content)

• Violent Eruptions• magma has a high

viscosity (high silica content)

EFFECTS OF VOLCANIC ERUPTIONS

• Pyroclastic Flow• fast-moving avalanches of hot gas, ash, and rock that can

reach speeds of up to 100 km/h and temperatures of up to 1000 °C

• Lava Flows

• Ash Fall

• Mudflows