Plate Tectonics, Volcanoes &
Earthquakes!
What is Plate
 Theory of Plate Tectonics=
Tectonics?
chunks of the lithosphere are
constantly moving slowly b/c
of convection currents in the
mantle
 Plate= sections/chunks of the
Earth’s lithosphere
 Mvmt of the plates causes
earthquakes, volcanoes, mtn
ranges, rift valleys, midocean ridges, deep-ocean
trenches
Evidence that  Alfred Wegener (1910) was
proves PT
the 1st to suggest that Earth’s
theory?
surface moves based on 3
things:
1) continents look like puzzle
pieces
Proved
 Pangaea= Wegener’s
continents
supercontinent
HAD moved,
2) Fossils of the same
but not HOW.
Explained
HOW
continents
moved and
proved
Wegener’s
Theory
organism spread across the
continents
3) Found warm weather
fossils where it is really cold
& vice versa
 Wegener’s idea was rejected
b/c he could show continents
HAD moved, but not HOW
they moved
 1960 technological
advancements led to:
4) sea floor spreading=
magma erupts on the ocean
floor, hardens into rock
then erupts again
 pushes the ocean floor
apart/makes the ocean
bigger
 creates a mid-ocean ridge=
under H2O mtns
 pushes continents away
from e@ other
5) subduction zones= where
What are
plate
boundaries?
one plate sinks under
another plate b/c it is
denser—oceanic plate
always sinks
 creates a deep ocean
trench= deep under H2O
canyon
* continents move SLOWLY! 124 cm/yr
* ocean floor renews itself every
200 million yrs
(glued in chart)
Additional notes:
 Tectonic plate boundaries=
where one plate touches
another plate
 1a= runs down the middle
of the Atlantic Ocean
 1b= Great Rift Valley in E.
Africa
 2a= Cascade Mtns in
Oregon & Washington (Mt.
St. Helens, Mt. Ranier, Mt.
What is a
volcano?
How does PT
cause
volcanoes?
Olympia), mtns in New
Zealand
 2b= Indonesian Islands
 2c= Himalaya Mtns where
India meets Eurasia & The
Alps in Europe
 3= San Andreas Fault in
CA where Pacific Plate &
North American Plate slide
by e@ other
 Volcano= a weak spot in the
crust that creates & destroys
things and looks like a pimple
& firework and is extremely
beautiful
 Magma= melted rock
INSIDE a volcano
 Lava= melted rock
OUTSIDE a volcano
 Plates colliding cracks the
crust so magma can escape
(subduction zones only!)
 @ rift valleys and sea-floor
What is a “hot
spot”
volcano?
What are the
parts of a
volcano?
(structure)
spreading b/c the crust is
getting pulled apart, getting
weaker in the middle and
magma can erupt through
the thinner crust
 Hot Spot Volcano= a volcano
that forms in the middle of a
tectonic plate, NOT near a
boundary
1) magma chamber= a pool of
magma at the bottom of the
volcano
2) pipe= the long tube that
magma travels through
during an eruption
3) vent= the opening at the top
of a volcano where magma
becomes lava
4) crater= bowl shape that
surrounds the vent
5) side vent= a vent on the side
of a volcano; optional! Can
have several or none at all!
What causes a
volcano to
erupt?
What are the
 Gases trapped in magma
expand and create pressure!
 Pressure pushes magma up
& out
 Amt of silica in the magma
determines the type of
eruption:
1) Quiet Eruption: LOW silica
magma that is thin &
runny! Lava flows easily,
like a river
2) Explosive Eruption: HIGH
silica magma that is thick &
sticky! It plugs the vent and
causes great pressure to
build up. BOOMER!
 Pyroclastic flow= mixture
of hot, poison gases, ash,
cinders & bombs that
hurtles down the volcano,
killing everything in its
path
 Active= currently erupting or
stages of
volcanic
activity?
What
landforms are
created by
volcanoes?
will erupt soon
 Dormant= “asleep”
“hibernating” can become
active at any time
 Extinct= will never erupt
again…maybe! 
1) shield volcano= a wide,
gently sloping mtn formed
by layer upon layer of thin,
runny lava from quiet
eruptions; Hawaiian
volcanoes & Medicine Lake
in CA (most hot spot
volcanoes)
2) cinder cone volcano= a
steep, cone shaped hill/mtn
formed by layers of cinders,
bombs & ash from
explosive eruptions;
Paricutin in Mexico
(subduction zone volcano)
3) composite volcano= quiet &
explosive eruptions
alternate layers of lava &
ash create TALL volcanic
mtns; Mt. Shasta & Mt. St.
Helens & Mt. Fuji
(subduction zone volcanoes)
4) lava plateau
5) caldera
6) volcanic soil
Intrusion:
Igneous rock
forced among
the bedrock;
younger than
the
surrounding
rock
7) volcanic neck
8) dike
9) sill
10) batholith
11) hot springs= hot! H2O that
forms in pools around
Geothermal
activity=
“Earth
heated”
phenomena
Video notes:
Earth Science:
Volcanoes
DVD notes:
How Earth
Was Made:
Ring of Fire
volcanic areas (stink!)
12) geysers= H2O volcano!eruption of H2O out of the
Earth b/c of heat
 Roman God of Volcanoes is
Vulcan
 1511 volcanoes, 500 active &
60 eruptions/yr
 Pelee, Hawaiian goddess of
volcanoes, erupts volcanoes
when she is angry
 R of F volcanoes are the most
destructive in the world
 A volcano can threaten Earth
for eons, but will eventually
“die”
** Why are Ring of Fire
volcanoes and earthquakes so
destructive?**
 ¾ of all volcanoes & 90% of
EQ’s in the R of F
 25,000 miles around the
Pacific Ocean
 75% of all US volcanoes are
in Alaska
 Strato volcanoes in the R of F
 Have thick, sticky
lava/magma that traps gasses
& causes massive eruptions
 Magma contains hornblende
minerals that only forms in
the presence of H2O
 H2O causes the magma to
form in the first place
 Gases coming from the R of
F volcanoes have C12 in them
 C12 is the remains of
plankton that make up
sediments on the ocean floor
 Subduction carries H2O &
the ocean floor down to a
magma chamber-that’s
What is an
earthquake &
why do they
happen?
where the H2O & the C12
come from!
 R of F EQ’s are thrust or
megathrust quakes-the most
pwrful on earth!
 Thrust EQ’s happen when
rock slides under another
 Thrust EQ’s cause tsunamis
 1500 EQ/month in Alaska!
 14 plates on the planet
 NA moving west 3 inches/yr
 Subduction releases and
enormous amt of energy!
 The Earth is NEVER at rest
 Earthquake= when the earth
shakes & possibly destroys
buildings & such
 Happen b/c stress from plate
mvmts adds energy to rock
 Released energy causes the
shake
 Seismic waves= energy waves
that shake the crust during
(diagram)
What types of
seismic waves
are there?
What types of
an EQ
 Fault line= crack/break in
the crust where rocks slip by
e@ other & build up stress
 Focus= the point
underground where an EQ
begins
 Epicenter= the point on the
surface directly above the
focus
1) P waves= primary/first
waves of an EQ; move like
an accordion
2) S waves= secondary/second
waves; move up,down &
side to side through rock
only
3) Surface wave= P&S waves
on the crust; slowest waves,
but the most destructive;
move in a combo. of P&S
wave mvmts
1) Normal Fault= tension
faults are
there?
stress (pulling) fault;
hanging slips down
(diagram)
2) Reverse Fault=
compression (pushing)
stress fault; makes mtns!;
hanging wall bulges up &
over the footwall
(diagram)
3) Strike-slip fault= shearing
(rubbing) tension; both
sides move against e@
other; NO up or down
mvmt
(diagram)
Video notes
How do
seismologists
monitor &
measure
EQ’s?
 1 million EQ/yr!
 Earth can move 5mm in just
a couple of hrs
 Strongest EQ in US was in
Alaska in 1964
 San Francisco is VERY
prone to EQ’s b/c San
Andreas Fault runs across it
 20-30 EQ’s daily in S.Cali
 4 minutes is a LONG time for
an EQ to shake
 Seismic waves are like ripples
in water
 @ the San Andreas Fault can
put one foot on Pacific Plate
& one foot on NA plate
 EQ’s are NOT predictable!
TOOLS TO MONITOR
1) tilt meter
2) creep meter
3) laser-ranging device
4) GPS (global positioning
system)