Plate Tectonics, Volcanoes &
Earthquakes!
What is Plate
Tectonics?
What evidence
PROVES PT
theory?
Showed the
 Plate Tectonic Theory= pieces
of Earth’s surface are moving
b/c of convection currents in the
mantle
 Tectonic plates= pieces of the
lithosphere/crust that move;
continental plates move land &
oceanic plates move oceans
 Plate mvmt creates
earthquakes, volcanoes, mtns,
deep-ocean trenches & midocean ridges
 Alfred Wegener (1910) was the
1st to suggest that continents
move
 Pangaea= Wegener’s
supercontinent…all lands
smushed together!
 Wegener suggested continental
drift based on:
1) continents look like puzzle
pieces
2) fossils of the same organism
continents
HAD moved,
but not HOW
Showed HOW
the continents
moved and
proved
Wegener’s
Theory
found on different continents
3) found evidence of tropical
plants in the polar regions &
evidence of glaciers in Africa
 Wegener’s idea was rejected b/c
he could prove continents HAD
moved, but not HOW they
moved
 He died w/ nobody believing
him
 Technological advances in the
1960’s led to:
4) Sea-floor spreading: molten
rock/magma comes up in a
crack in the ocean floor &
spreads the floor apart, which
moves the continents apart;
continually adds rock to the
ocean floor
o Creates a mid-ocean ridge=
underwater mtn range
o Oceans get bigger
o Pushes the continents away
from e@ other
5) Subduction= ocean floor dives
under continental crust into
the mantle
 Deep-ocean trench= under
H2O canyon formed when
ocean crust meets
continental crust
**Sea-floor Spreading +
Subduction proved Wegener’s
idea!
What are plate (glued in chart)
boundaries?
Additional notes:
o Tectonic plate boundaries=
where the plates meet and
subduction or sea-floor
spreading happens
o 1a: mid-ocean ridge runs down
the middle of the Atlantic
Ocean
o 1b: Great Rift Valley in E.
Africa
o 2a: Indonesian Islands in the
Pacific Ocean & New Zealand
o 2b: Cascade Mtns in
northwestern N. America (Mt.
What are
volcanoes?
How does PT
cause
volcanoes?
What are Hot
Spot
volcanoes?
St. Helens, Mt. Olympia, Mt.
Ranier); Andes Mtns along the
west coast of S. America
o 2c: Himalaya Mountains btwn
India & Eurasia & The Alps in
Europe
o 3: San Andreas Fault btwn the
N. American & Pacific plates
* volcano= a destructive/creative
force that is an Earth-made
firework; a weak spot in the crust
* magma= melted rock INSIDE a
volcano
* lava= liquid rock OUTSIDE a
volcano
 The crust weakens @ a
spreading or colliding boundary
creating cracks that magma can
escape through
 Hot Spot Volcanoes= a volcano
that lies in the middle of a plate
NOT near the edge of a plate
 EX: Hawaii on the Pacific Plate
& Yellowstone National Park in
the USA on the NA plate
What are the
parts of a
volcano?
Why do
volcanoes
erupt?
1) magma chamber= pool of
magma under a volcano
2) Crater= bowl shaped hole at
the top of a volcano
3) Pipe= long tube that connects
the magma chamber to the
outside; magma flows up this
tube
4) Side vent= an opening on the
side of a volcano that magma
escapes from
5) Vent= an opening on top of a
volcano that lets magma out
 Dissolved gases are under great
pressure
 Pressure pushes magma up &
out
 Amt of silica in magma
determines the force of an
eruption:
1) quiet eruption: LOW silica,
thin & runny magma/lava
that runs down the volcano in
a river
2) explosive eruption: HIGH
What are the
stages of
volcanic
activity?
What
landforms are
created by
volcanoes?
silica, thick and sticky that
plugs up the vent causing
great pressure to build & go
BOOM!
 Pyroclastic flow= hot ash,
poison gases, cinders &
bombs hurtling down the
volcano, killing all in it path
 Active= currently erupting
 Dormant= “sleeping”, will
erupt sometime in the future
 Extinct= will never erupt
again…maybe!
1) shield volcano= sloping mtn
made by quiet eruptions of
thin runny lava over & over
& over; Hawaii
2) cinder cone volcano= layers of
cinders, bombs and ash from
explosive eruptions build a
steep sided hill/mtn; Paricutin
3) Composite Volcano= quiet
eruptions alternate with
explosive eruptions forming
TALL cone shaped mtnslayers of ash & lava; Mt. Fuji
in Japan & Mt. St. Helens in
USA
4) Lava Plateau= many FLAT
layers of thin, runny lava that
erupts through cracks in the
surface; Columbia Plateau in
USA
5) Caldera= a hole that is
collapsed from a volcano;
Crater Lake, Yellowstone
National Park