Volcanoes & Earthquakes
 Plates rubbing against e@ other
causes EQ’s-ALL plate boundary
create EQ’s b/c they are moving!
 Spreading apart allows magma to
come up b/c it thins the
crust=volcano
 Subduction also creates volcanoes
b/c it weakens the crust
What is the
CONVERGENT: strongest, most
strength of
destructive volcanoes & EQ’s (5-10
volcanoes & EQ’s rank) @ subduction zones
at each plate
 Cont. vs. Cont.= EQ’s only b/c it
boundary?
doesn’t weaken the crust
How do plate
tectonics cause
volcanoes &
earthquakes?
DIVERGENT: weakest volcanoes &
EQ’s (1-5 rank) b/c they are shallow
What is a
volcano?
TRANSFORM: EQ’s only! No
volcanoes b/c no weak spots! Medium
sized (4-8 rank)
 Volcano= a beautiful, scary
mountain that shoots lava from a
weak spot in the crust while
creating and destroying at the
same time
What are the
different types of
volcano and on
which boundary
does each form?
SHIELD VOLCANO:
 Made of layers upon layers of
thin, runny lava
 Wide-based, gentle-sloped mtnNOT steep
 Can be very tall and wide
 Form at divergent boundaries &
hot spots= a weakness away from
a plate boundary
 EX: Hawaiian volcanoes &
Iceland
(diagram)
CINDERCONE VOLCANO:
 Made of piles of ash, cinders &
bombs=magma the hardens in the
air
 Very steep, narrow-based hills or
short mtns
 Most common type of volcano
 Usually erupt only once
 Form @ subduction zones &
divergent boundaries & hot spots
 EX: Paricutin in Mexico
(diagram)
COMPOSITE VOLCANO:
 TALL, cone-shaped mtns
 Made of alternating layers of ash
& lava
 Most destructive & dangerous
kind!
 Big BOOMERS!
 Can be dormant for 100’s of yrs
b4 erupting
 aka “Stratovolcano”
 EX: Mt. St. Helens, Mt. Fuji, Mt.
Vesuvius, Mt. Shasta, Mt.Ranier
 Form along subduction zones
only!
(diagram)
Why does a
volcano erupt?
What did I learn
from the video,
EyeWitness
Volcano?
& the video field
 Gases trapped in magma
 Gases push magma up the
volcano b/c they expand as they
rise causing more pressure
 Expanding gases exerting
pressure=BOOM!
 Volcanoes create & destroy @ the
same time!
 Kilauea is a hot spot volcano that
has been erupting since 1983
 People believe volcanic sand has
healing properties
trip!
What is the
difference btwn
quiet & explosive
eruptions?
 More lava flows on Earth than
H2O goes over Niagara Falls
 Volcanoes create “earthquake”
like ground mvmts
 More volcanoes under water than
on land
 Magma at a colliding boundary is
hotter
 Animals act weird before an
earthquake or eruption
 Ashes can black out the sun
 1 in 10 EQ occur in Japan
 250+ eruptions e@ yr!
 ≈500 active volcanoes
 Only 600 volcano bunnies left in
Mexico…short ears!
 Gems, gold & crystals form in
volcanic areas
 Volcanic soil is very fertile &
GREAT for farming
 An eruption can last hrs, days,
weeks, months, years, decades!
Depend on the volcano itself!
1) Quiet Eruption:
 LOW silica magma
 Thin & runny magma/lava
 Shield volcano eruptions-
2)




What is an
earthquake (EQ)?
“blub, blub!”
 “Lava river” type lava
 Can flow 6- mph
 Pretty, Hawaiian volcanoes
Explosive Eruption:
HIGH silica magma
Thick, sticky, plugs the volcano
like a cork
Does NOT flow
Pyroclastic flow= HOT!!! ash,
poison gas, bombs, smoke, etc.
speeding down the side of an
erupting volcano…150+mph!
3)
 Earthquake= crust shaking b/c of
the release of built up stress along
a fault line near a plate boundary.
 Several 1000 e@ day
 Most are too weak to feel
 Strong one can destroy entire
cities!
 Most begin ≈100 kms below the
surface
 Focus= the point underground
where an EQ starts
 Epicenter= the point on the
surface directly above the focus
(diagram)
What is a fault?
What is a seismic
wave?
 Fault (fault line)= a break in the
crust where stress builds in rocks;
where an EQ happens
 3 types of fault line:
1) Normal fault= tension (pulling)
stress fault
 Foot wall does NOT move“plants its foot and stays
put!”
 Hanging wall falls down the
footwall
2) Reverse fault= compression
(pushing) stress fault
 Hanging wall moves up & over
the footwall
3) Strike-slip fault= shearing
(slipping) stress fault
 NO hanging wall or foot wall
 The only fault you can see on
the surface
 NO up or down mvmt on either
side of the fault b/c there is no
hanging or foot wall
 Seismic wave= energy wave
released by an EQ’s focus
 3 types of seismic wave:
1) P wave= travels through solids
& liquids
P
 “ rimary”/FIRST waves
 Move in & out like an
accordion…like a punch!
2) S wave= can’t move through
liquid, only solid rock
S
What did I learn
from the video,
“Earth Science:
EQs”?
 “ econdary”/second wave
 Move side to side & up/down
3) Surface wave= P&S waves
joined up on the surface
 Roll like ocean waves
 Slowest but most destructive
waves
 Lrgst EQ in North America was
in Alaska 1964
 People have recorded EQ for yrs
 Worst EQs @ subduction zones
 Seismograph=records the seismic
waves/EQ
 San Andreas fault has 10,000+
EQs/yr
 30+ small EQ’s daily in the world
 CAN’T predict an EQ!
 Vibrations move in ALL
directions-circular mvmt
 Engineers build buildings to
withstand EQs
 Epicenter gets the strongest
shaking & most damage
 Seismic waves lose energy as they
move away from the focus
How do EQ’s
1) SHAKING:
cause
 Poorly built buildings fall down
damage/disasters?
b/c the shaking is pwrfl
 Roads & bridges can collapse b/c
the ground moves
 Can make trees fall down &
fracture gas & H2O mains
causing floods & fires
 Can cause landslides &
avalanches
 Aftershock= a smaller EQ in the
EXACT same spot following a
large EQ…can knock down
weakened structures
2) Liquefaction= water rising b/c of
the shaking & making the ground
mud…buildings sink & fall apart;
happens in loose, sandy soil w/ lots
of groundwater
3) Tsunami= a large ocean wave
(100ft+ tall) caused by an EQ @ a
subduction zone-deep ocean trench
 nonsubducting plate bends on
the other plate and flicks up
 can reach up to 3 miles inland
 80% are in the R of F
 each wave has less power than
the one before it, but does
more damage b/c of the debris
in the water from the first
wave
What tools &
TOOLS:
scales do
1) seismograph= machine that
seismologists use
records seismic waves on a
to measure EQ’s?
seismogram (diagram)
2) tilt meter
3) creep meter
4) laser-ranging device
5) GPS satellites