EARTHQUAKES & VOLCANOES
Feb 23, 2016
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