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 motion
Moment
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