Transcript Earthquakes and Volcanoes!

Earthquakes and Volcanoes!
Oh my!
Stress
• Stress: a force that acts on rock to
change its shape or volume
• 3 Types of Stress (happens in the crust):
– Tension: pulls on the crust
– Compression: squeezes until folded or
breaks
– Shearing : pushes rocks in opposite
directions
Faults
• Faults: the point where rocks break Ex.
San Andreas fault
• 3 Types of faults:
– Normal faults: form where rocks are angled with
each other; one block or rock lies below the other
– Reverse faults: are like normal faults but move in the
opposite direction
– Strike-slip faults: form when rocks slide past each
other
Faults
Faults: What kind am I?
Earthquake
• Earthquake: shaking & trembling that results
from the movement of rock below Earth’s
surface
• Forces of the plates causes earthquakes.
• Most start in the lithosphere.
• Focus: area beneath the Earth where the stress
occurs & rock breaks
• Epicenter: point on the surface directly above
focus
Seismic Waves
• Seismic waves: vibrations that travel
through Earth carrying energy released
during an earthquake
• Seismic waves carry energy from an
earthquake away from the focus, through
Earth’s interior, and across the surface.
Types of Seismic Waves
• P Waves- compress & expand (back &
forth) the ground like an accordion, can
damage buildings, travels through solids
and liquids
• S Waves- the crust vibrates from side to
side & up and down, shake the ground
back and forth, travels through solids
• Surface Waves- P and S waves that
reach the surface. Move very slowly in a
wavelike motion
Measuring Earthquakes
• Mercalli Scale-based on level of damage (slight
damage, moderate damage, great damage)
• Richter Scale-based on magnitude based on
the size of the earthquake’s seismic waves,
good for small, near-by quakes
• Seismograph- instrument that records the size
of the seismic waves
• Moment Magnitude Scale-estimates total
energy released
seismograph
Volcano
• Volcano: weak spots in the crust where
molten rock (magma) comes to the
surface
• Magma: molten mixture of rock, gases &
water from the mantle
• Volcanoes form when plates converge &
diverge (on land & on ocean floor)
Island Arcs
• Island arc: a string of islands formed by
the volcanoes along a deep ocean trench
(oceanic plates converge) Ex. Japan, New
Zealand
Hot Spot Volcanoes
• Hot spot: an area where material from deep
inside the mantle rises & then melts
• A volcano forms above a hot spot when magma
erupts through the crust & reaches the surface.
Ex. Hawaii
Viscosity
• Viscosity: the resistance of a liquid to
flowing (a property of magma)
– The greater the viscosity, the slower it flows
(ex. honey)
– The lower the viscosity, the faster it flows (Ex.
water)
• Viscosity of Magma depends on: silica
content & temperature
• Silica-compound made of silicon & oxygen
• More silica, higher the viscosity
• Silica produces light colored magma that
is sticky
• Viscosity increases as temperature
decreases
• Pahoehoe (pah Hoh ee hoh ee):fast
moving, hot lava with low viscosity.
Produces lava mass with ripples &
wrinkles when it hardens
• Aa (AH ah): slow moving, cooler lava with
high viscosity. When it hardens, it forms
huge, jagged chunks.
Pahoehoe
Aa
Parts of a Volcano
• Magma chamber-collection of magma
under a volcano
• Pipe-long tube in the ground that connects
the surface to the magma chamber
• Vent-opening that magma exits through
• Lava flow-area covered by lava
• Crater-bowl-shaped area at the top
Types of Eruptions
• Quiet eruptions -magma has low silica
content, high viscosity, slow moving
• Explosive eruptions -magma has high
silica content, low viscosity, fast moving
– Pyroclastic flow-eruption which hurls hot
gases, ash, cinder, and bombs
Volcanic Landforms
• Caldera-huge hole left by the collapse of a
volcano (the magma chamber collapses)
• Volcanic neck-when magma hardens in a
volcanic pipe (soft rock wears way
exposing the hard rock)
• Dike-rock layer forming vertically
• Sill-rock layer forming horizontally
• Batholith-a large body of cooled, exposed
magma
Caldera (Crater Lake) in Iceland
Devil’s Tower in Wyoming