Download Plate motion, earthquakes, and volcanoes

 The main theory believes that there is an uneven
distribution of heat in the mantle, caused by heat from
the core.
 Hot mantle material will rise from near the core and
sink as it reaches near the lithosphere
 This motion of hot rising and cold sinking is known as a
convection cell
 1. Slab Pull
 When ocean lithosphere is being subducted beneath
another plate, if drags the rest of the lithosphere behind
is down as well.
 This slab pull is the downward arm of the convection
cell
 Found at convergent boundaries
 2. Ridge Push
 When oceanic crust is being made at divergent plate
boundaries, it is pushing the oceanic lithosphere away
from the upwards arm of the convection cell
 This motion is found at divergent plate boundaries
 3. Mantle Plume
 The rising mantle materials is the up ward arm of the
convection cell can happen in a single place in the
middle of a plate and create a hot spot/island
 Example: Hawaii
 Shaking of the Earth’s crust
 Caused by a break or shift in the Earth’s crust
 Is it possible for an earthquakes to happen in the
mantle? _______
 Why Not? Mantle is too soft to break or crack
 The energy that is released when the rocks begin to
move is called elastic energy , much like when a rubber
band is stretched and the tension builds up before it is
released
 1. Plate boundaries have earthquakes because there is
two plates rubbing against each other’s rocks, creating
shockwaves through the crust
 2. All other earthquakes will happen at faults, which
are ancient plate boundaries or cracks in the Earth that
show movement once in a while
  Foreshocks Smaller earthquakes that occur before
the earthquakes
 Do these always happen? _________
 How long before the earthquake do foreshocks happen?
Months or days before
 Aftershocks Smaller earthquakes that occur after
the big earthquake
 Why would these cause more damage if they are smaller
than the big earthquake?
 The buildings and foundation were already weakened with
damage from the first hit
 Focus Origin point in
the earth where the
earthquake started
 Waves from this will
travel in all directions
 If the focus is shallow
underground, meaning it
is closer to the surface, it
is more dangerous that
an earthquake that is
deep underground
 Epicenter Location on
the Earth’s surface
directly above the focus
of the earthquake
 Why would we care more
about the epicenter of an
earthquake than the
focus?
 It is where all of our
possessions are located
 The measure of how strong the earthquake is
 Higher numbers means that the earthquake is stronger
 1. Surface Waves Waves that travel along the Earth’s
surface
 Slowest waves, but they are the strongest of all the waves
 Most destructive of the earthquake eaves
 Why? Because these waves travel along the surface, it makes
us vulnerable
 Can travel through solids only
 Primary Waves (AKA P-waves)
 These waves will pull and push the ground underneath
you
 Fastest waves, but not the strongest
 P-waves can travel through solids and liquids
 Least destructive , but these are the first parts of an
earthquake that you feel
 3. Secondary waves (AKA S-waves)
 These waves will cause an up and down motion of the




ground
Strong waves, but second to the surface waves
Slower that p-waves, but faster than surface waves
Fairly destructive, definitely more so than the p-waves
S-waves cannot travel though air or liquids
 **Can these waves travel through the outer core?*** ______
 Seismogram
 Paper record of an
earthquake
 You need 3 of these to
find an earthquake
epicenter
 Seismograph
 Instrument that records
earthquakes
 A mountain that erupts violently, releasing lava, ash,
and other hot crustal materials
 Magma Chamber
Place where magma is
held underground until
eruption
 Conduit (pipeline) 
Lava tube that carries
magma to surface
 Vent  Opening at the
top that releases the
magma
 Crater Depression
surrounding the vent
that is blown off
during eruption
 Pyroclastics 
Molten rock bombs,
ash, and other lava
fragments released
out or off the volcano
 1. At Plate Boundaries
 Convergent boundaries will form more violent and
explosive volcanoes
 At divergent boundaries, the volcanoes are less, violent
and less explosive
 2. At Hot Spots
 When weakened lithosphere has allowed mantle
material to rise through and creates islands in the
middle of some oceans
 If they are on continents, they usually create
supervolcanoes under the surface
 Viscosity the ability to flow
 When things flow fast, they have a high viscosity and the lava
can move up to 50 mph
 When things flow slow, they have low viscosity and the lava
moves as slowly as in inches per hour
 Ash and other aerosols can block out the Sun, making
temperatures to drop on a global scale
 Ash can also combine with rain clouds and produce acid
rain
 Larger pyroclastics called volcanic bombs and will destroy
property upon impact
 Lava flows will burn anything that they come in contact
with until they have cooled enough to become igneous
rock
Cinder Cone
 Shortest on land average
8-10 feet tall
 Made of only
pyroclastics, no lava
flows
 Usually only erupts once
in its life time
 No viscosity
 Violent for a short period
of time
 Lots of gases released
 Example: Yellowstone
Diagram of Cinder Cone
Composite (Cone)
 Tallest volcanoes on land
 Made of lava flows and





pyroclastics
Erupts very violently
Erupts on a scheduled
build up (50-100 years)
High viscosity means a
high silica content to the
lava
High amounts of gases
released
Example: Mt St. Helens
Diagram of Composite
Shield Volcano
 Tallest underwater
 Made of mostly lava
flows and maybe a few
pyroclastics
 Erupts often (daily to
monthly)
 Low viscosity which
means a low silica
content
 Very few gases are
released
 Example: Hawaii
Diagram of Shield