Plate Tectonics, Volcanoes &
Earthquakes!
What is Plate
Tectonics?
What evidence
proves PT
Theory?
 Plate Tectonic Theory=
constant slow motion of Earth’s
plates b/c of convection
currents in the mantle
 Plate= pieces of the
lithosphere/Earth’s surfacecrust
 Plates move & change Earth’s
surface
 PT creates volcanoes, mtn
ranges, deep-ocean trenches,
mid-ocean ridges, rift valleys &
earthquakes
 Alfred Wegener (1910) was the
1st to say that Earth’s surface
moves
 Pangaea= Wegener’s
supercontinent; all the
continents together as one
landmass
 He based his idea on 3 facts:
1) continents look like they fit
together like puzzle pieces
Proves the
continents
HAD moved,
but not HOW
Explains HOW
the continents
moved and
proves
Wegener’s
Theory
2) fossils of the same organism
are found on many different
continents that are now far
apart
3) evidence of tropical climates
in the polar region & vice
versa
 Wegener’s idea was rejected b/c
he only proved that the
continents HAD moved, not
HOW they moved
 He died before his idea was
proved (1930)
 1960 technological advances led
to:
4) Sea-Floor Spreading= magma
spreads through cracks in the
ocean floor and turns into
new rock
 Creates a mid-ocean ridge=
under H2O mtn range
 Makes the oceans bigger
and pushes continents apart
5) Subduction Zones= oceanic
crust slides UNDER
How do plates
interact w/e@
other?
(boundaries)
continental crust or another
piece of oceanic crust b/c it is
denser
 Creates a deep ocean trench=
deep under H2O canyon
 The plate that sinks melts into
magma in the mantle
*plates move slowly! 1-24 cm/yr
(glued in diagram)
Notes UNDER diagram:
 Tectonic Plate boundary= the
place where tectonic plates
touch e@ other
 1a: runs down the middle of the
Atlantic Ocean-lrgst one!
 1b: The Great Rift Valley in E.
Africa
 2a: Indonesia Islands in the W.
Pacific
 2b: Cascade Range along the
northwest coast of N. America
(Mt. St. Helens, Mt. Ranier, Mt.
Olympia) & the Andes Mtns on
the west of S. America
What is a
volcano?
How does PT
cause
volcanoes?
What is a Hot
Spot volcano?
 2c: Himalaya mtn range btwn
India & Asia
 3: San Andreas Fault in CA!
 Volcano= a weak spot in the
crust where magma flows out of
a mountain, AKA “Nature’s
Fireworks”
 Magma= molten/liquid rock
INSIDE a volcano
 Lava= molten/liquid rock that
has been spit OUTSIDE a
volcano
 Plates moving makes cracks in
the crust where magma can
come up
 Form @ colliding subduction
boundaries & spreading
boundaries
 Hot spot volcano= a volcano in
the middle of a plate, NOT on a
plate boundary
 Hawaii, in the center of the
Pacific Plate & Yellowstone
National Park, in the center of
the NA plate
What is the
structure of a
volcano?
What causes a
volcano to
erupt?
1) Magma chamber= pool of
magma @ the bottom of a
volcano
2) Pipe= long tube up the center
of a volcano that connects the
chamber to the outside
3) Vent= opening at the top of a
volcano where lava comes out
4) Side vent= opening NOT at
the top of a volcano;
(optional! Can have 0 or
several)
5) Crater= bowl shaped area
around the top vent
 Gases trapped in the magma
expand, creating great
pressure which forces
magma up & out of the vent
 Amt of silica in magma
determines the type of
eruption:
1) Quiet Eruption= LOW silica
magma that is thin & runny
& flows like a river
2) Explosive Eruption= HIGH
What
landforms are
created by
volcanoes?
1)
2)
3)
4)
5)
silica magma that is thick &
sticky so it plugs up the vent
& causes ++++pressure
 Pyroclastic flow= thick,
heavy, giant clouds of ash,
poison gases, cinders &
bombs rushing down the
volcano killing everything in
its path
shield volcano= quiet erupting
volcanoes that create a gently
sloping mtn with layer upon
layer of runny lava; Hawaii
composite volcano= TALL,
layers of lava and ash; Mt.
Fuji in Japan, Mt.St. Helens
in US
cinder cone volcano= formed
by ash, cinders & bomb piles
making steep sided mtns; Mt.
Paricutin
caldera= huge hole created by
the collapse of a volcano;
Crater Lake in Oregon
volcanic neck= made when
magma hardens in the pipe;
Ship Rock in New Mexico
6) dike= magma hardens across
rock layers; around Ship
Rock
7) sill= magma hardens btwn
rock layers; around Ship
Rock
8) batholith= formed when
magma hardens in the magma
chamber to make a HUGE
body of rock; Sierra Nevada
Mtns in CA
9) lava plateau= FLAT areas of
layer upon layer of runny
lava; Columbia Plateau USA
10) volcanic soil= very rich &
fertile! Excellent for growing
plants/crops
11) hot springs= magma heated
H2O that collects in a natural
pool;
12) geysers= “H2O volcano”!
super, magma heated H2O
shooting out of the ground;
Yellowstone National Park
Video notes:
Earth Science:
Volcanoes
DVD Notes:
How Earth
Was Made:
Ring of Fire!
 word “volcano” came from
Vulcan, the Roman God of the
Forge (blacksmith!)
 when magma stops coming into
the magma chamber, the
volcano starts to die
 Greeks believed when Vulcan
was making weapons, the
volcano was erupting
 Subduction zones volcanoes are
the strongest
 1511 volcanoes, 500 active,
approx 60 eruptions/yr
 When rain falls on volcanic ash,
it turns to “concrete” (Mt.
Vesuvius & Pompeii)

**Why are Ring of Fire volcanoes
and earthquakes so destructive?**
 ¾ of all volcanoes & 90% of all
earthquakes occur on the R of F
 Extensive zone of destruction
on Earth
 25,000 miles around the P.
Ocean
 75% of all US volcanoes are in
Alaska
 R of F volcanoes are Strato
volcanos
 High silica lava is thick, like
pnut butter & sticky
 High silica lava traps gas and
causes massive eruptions &
Pyroclastic flows
 Hornblende in the magma
forms in the presence of H2O
which causes rock to melt into
magma and rise
 megathrust earthquake @
subduction zones due to one
plate sliding under the other
 Megathrust quakes create
tsunamis which are highly
destructive!
 R of F shape is determined by
deep-ocean trenches, not the
volcanoes
 14 plates on the planet
 The Earth is NEVER at rest!
What is an
earthquake &
what causes
them?
(diagram)
What type of
seismic waves
are there?
 Earthquake= when the ground
shakes so hard, things
sometimes fall
 Caused by built up rock stress
that is released by plate mvmts
 Compression, tension &
shearing build up stress in
rocks
 Rock stress=stored energy!
 Seismic waves= energy released
during an EQ
 Fault line= crack/break in the
crust where rocks slip by e@
other creating an EQ
 Focus= the point in the
lithosphere where an EQ
happens—where the rock
breaks!
 Epicenter= the point on the
surface directly above the focus
1) P wave= primary/first waves;
moves in & out like an
accordion
2) S waves= secondary waves
(comes next!); move
What is a fault
& what kinds
are there?
up,down,side to side; CAN’T
move through liquids
3) Surface waves= S & P waves
together @ the crust; slower
than other waves BUT are the
most destructive; move in a
combo. of all mvmts
 Fault= where an EQ happens
1) Normal Fault= tension stress
faults (pulling); hanging wall
slips down
(diagram)
2) Reverse Fault= “backwards
normal fault!” compression
stress faults (pushing);
hanging wall pushes over the
foot wall; can form mtns
(diagram)
3) Strike-slip fault= shearing
stress faults (rubbing); both
sides of the fault move against
Video notes
What tools &
scales do
seismologists
use to measure
& monitor
EQ’s?
e@ other
(diagram)
San Andreas Fault!
 Longest recorded EQ was 4
minutes!
 1 mil+ EQ daily!
 EQ’s can NOT be predicted b/c
there are no warning signs
 1965 Alaska EQ lrgst in US
history
 Can’t see most faults b/c they’re
underground
TOOLS: to MONITOR
1) tilt meter
2) creep meter
3) laser-ranging devices
4) GPS (global positioning
system)
SCALES TO MEASURE:
1) Mercalli Scale: from 1 to 12,
ranks the intensity of an EQ
& level of damage
2) Richter Scale: measures the
magnitude of a seismic wave
How do EQ’s
cause damage?
w/ a seismograph; not good
for far away EQ’s, only close
ones
3) Moment Magnitude Scale:
scale of 1 to 10; measures all
aspects of an EQ!
 There has never been a 10 EQ
in recorded history
 Each ranking is 10x bigger than
the ranking b4 it
 The bigger the #, the bigger the
EQ!
 Big #’s=more destruction!
 Most destruction/shaking
occurs close to the epicenter
 Shaking knocks down buildings
& schtuff!
 Amt of damage depends on:
magnitude of the seismic wave,
distance from the epicenter &
quality of buildings (good
quality survives; bad quality
collapses)
 Aftershocks= weaker/smaller
EQ that happens in the SAME
spot after a major EQ; the fault
settling in to its new spot