Download Tectonics, Earthquakes and Volcanoes

EARTH’S INTERIOR
TECTONICS, EARTHQUAKES & VOLCANOES
INTERIOR STRUCTURE
• The Earth is divided into several layers based on
similar temperatures, materials, pressure, and depth
INTERIOR STRUCTURE
The materials that make up
the Earth separated as the
Earth cooled. The lighter
materials rose to the surface
and the heavier materials
sunk to the center.
Movement of heavy metals in
the liquid outer core is
responsible for the Earth’s
magnetic field.
INTERIOR STRUCTURE
The mantle of the Earth is made
of a mixture of hard, rigid rocks
in the lower mantle and plastic,
more flexible rocks in the upper
mantle.
HOT MATERIAL RISES,
COOL MATERIAL SINKS
The differences in temperature
between the upper and lower
portions of the mantle plus the
flexibility of the upper mantle
cause currents of material that
move the crust above the
mantle.
INTERIOR STRUCTURE
The crust of
the Earth is
broken up
into sections
called
tectonic
plates
made up of
the
lithosphere.
INTERIOR STRUCTURE
Oceanic crust is heavier and more dense so it sinks
and stays below the water. Continental crust is
lighter and less dense so it rises above the water.
PLATE TECTONICS
• Geologist have known that
the Earth’s landmasses have
not remained in the same
place throughout time
• Early mapmakers first
considered the idea that
the continents have moved
because of the similarity of
coastlines between certain
continents.
PLATE TECTONICS
• History of plate movement based on current
evidence.
PLATE TECTONICS
History of Discoveries
• 1500’s Abraham Ortelius(Dutch) noticed the fit of
the continents surrounding the Atlantic Ocean and
proposed (incorrectly) that the continents became
separated by a series of earthquakes and floods
• 1800’s Eduard Suess(Austrian) proposed that the
Southern continents had once been joined in a
single landmass
PLATE TECTONICS
• 1900’s Alfred Wegener(German) hypothesized that
all the landmasses fit together in a supercontinent
called Pangea in his 1912 publication
• He reasoned that as the supercontinent broke
apart the geologic structures fractured leaving
small gaps along what would otherwise be
matching coastlines
• He found evidence on the modern continents to
support his theory of an ancient supercontinent
PLATE TECTONICS
Continental Drift Hypothesis: states that the
continents had once been joined to form a single
supercontinent (Pangaea) and began to break
apart 200 million years ago to form the present
landmasses
Evidence to support the hypothesis:
- Continent shapes
- Fossils
- Geologic Patterns
- Climate Patterns
PLATE TECTONICS
Continent Shapes:
- Scientists have studied
the shorelines of
continents to see how
they may have fit
together
- The most obvious
connection lies
between Africa and
South America
PLATE TECTONICS
Fossils:
- The same fossil
groups have been
found on separate
continents with
distances too great
for organisms to
travel if the
continents were in
the same places.
PLATE TECTONICS
Geologic Patterns:
- Similarities in mountain ranges show that the
mountains on separate continents may have been
formed when they were joined together
NOW
THEN
PLATE TECTONICS
Climate Patterns:
- Glacier evidence on
all of the modern
day continents
suggest that the
continents all fit
together and were
located around the
area of modern day
Antartica
PLATE TECTONICS
Wegener’s Missing Pieces
• Explanation of WHAT caused
the continents to move
• Explanation of HOW the continents
continued to move
He was never able to answer these two questions in his
lifetime. He froze to death on an expedition to Greenland
still investigating evidence to support his hypothesis.
PLATE TECTONICS
• After Wegener’s death in 1930
scientists continued to search for
the mechanisms behind his
continental drift hypothesis
• Shortly after his death Arthur
Holmes proposed that mantle
convection was the driving force
behind the movements of the
continental landmasses. His theory
was proven correct but not until
years after his initial proposal.
Arthur Holmes
1890 - 1965
PLATE TECTONICS
• Until the 1900’s the belief was that the ocean floor
was completely flat and unchanging
• During WWII submarine warfare and the use of
SONAR began to prove this belief to be false when
underwater mountains and valleys were mapped
to help guide the submarines across the Atlantic
Ocean
PLATE TECTONICS
• The maps of the ocean surface, sediment cores
and magnetic readings after WWII confirmed that
the ocean floor is constantly changing and shows
evidence of the tectonic activity proposed by
Arthur Holmes.
PLATE TECTONICS
Theory of Plate Tectonics: theory that helps explain
the formation and movement of the tectonics plates
which make up the Earth’s crust
This led to the
formation of the
modern day
landmasses and
their current
locations.
PLATE TECTONICS
Modern day plate sizes and locations:
PLATE MOVEMENT
• Plates meet at locations called plate boundaries.
• Where these plates meet movement causes
activities like earthquakes, volcanoes, and
mountain building
PLATE MOVEMENT
Divergent Boundaries: places where the tectonic
plates are moving apart
Examples: mid-ocean ridges, rift valleys
PLATE MOVEMENT
Divergent Boundaries
Seafloor spreading: as oceanic plates move apart
new ocean floor is built by cooling lava
PLATE MOVEMENT
Divergent Boundaries
Continental Rift Valleys:
places in the middle of a
continental plate where
spreading is occurring
PLATE MOVEMENT
Convergent Boundaries: plate
boundaries where two plates are
moving together
- Types of convergent boundaries rely
on the type of crust that is being
moved together
PLATE MOVEMENT
Convergent Boundaries
Oceanic vs. Continental
-forms where a piece of
oceanic crust is subducted
(pulled under)beneath a
section of continental crust
Subduction zone: Ocean plate
slides under continental plate
and forms a deep-ocean
trench and continental
volcanic arc
PLATE MOVEMENT
Convergent Boundaries
Oceanic vs. Oceanic
- Forms when one oceanic
plate is subducted under
another oceanic plate.
- Creates a deep ocean
trench and a volcanic
island arc
PLATE MOVEMENT
Convergent Boundaries
Continental vs. Continental
- Forms when two
continental plates collide
and form mountain ridges
PLATE MOVEMENT
India and Eurasia Collision
PLATE MOVEMENT
Transform Fault Boundary:
plate boundary where two
plates move past each other
along a fault (break in the
crust)
- High numbers of earthquakes
occur in these areas
Example: San Andreas Fault
PLATE MOVEMENT
What causes this movement?
Isostasy: the idea that the
upper mantle of the Earth is
elastic and will adjust to the
weight of the plates above it
ISOSTASY ANIMATION
PLATE MOVEMENT
What causes this movement?
Convection currents: circulation of molten rock within
the mantle. As hot magma rises and cool rock sinks
plates begin to move
EVIDENCE OF PLATE TECTONICS
The Earth supplies evidence for plate tectonics on a
daily basis because it is constantly changing.
Map of worldwide earthquake and
volcano activity.
- Tectonic activity
like seafloor
spreading,
earthquakes and
volcanoes are the
best source of
evidence to prove
the plate tectonics
theory
EVIDENCE OF PLATE TECTONICS
Earthquake: shaking and trembling that results from
sudden movement of part of the Earth’s crust
Reasons Why Earthquakes
Occur:
- Volcanic eruption
-collapse of a cavern
-impact of meteor
-major cause: stress that
builds up and causes
faulting
TECTONIC CHANGES
Tension
Stress: a force acting on a
material
Compression
Tension: stress that pulls apart
Shear
Compression: stress that
pushes together
Shear: stress that twists
TECTONIC CHANGES
Stress: the force
that acts on a
material
CAUSES
Strain: a
weakening or
change in a
material
TECTONIC CHANGES
2 types of Strain
• Elastic – material deforms and then
goes back to its original shape after
the stress is removed
• Like a rubber band
• Ductile – material deforms and stays
deformed after the stress is removed
• Like play-doh
TECTONIC CHANGES
Fault – a fracture or break in rock that
happens when stress is applied too
quickly or strain is too great
• Faults are often
concentrated around
plate boundaries
•When stress is relieved
around a fault it causes
an earthquake
TECTONIC CHANGES
Normal Fault: tensional stress pulls
plates apart and stretches the Earth’s
crust
TECTONIC CHANGES
Reverse fault: compression stress pushes
the plates together and squeezes the
crust
TECTONIC CHANGES
Strike-Slip fault: shear stress forces plates
to move past each other
EARTHQUAKES
When the stress becomes too much the
plates experience a sudden shift and
release of energy.
Elastic Rebound Theory:
theory that explains how
rocks that are strained
past a certain point will
fracture and spring back
to their original shape
EARTHQUAKES
• Earthquake Anatomy
Epicenter: point
on Earth’s surface
directly above
the focus
Focus: point
beneath the
Earth’s surface
where the rocks
break or move
apart
EARTHQUAKES
Earthquake Wave Motion
P Waves:
-move fastest
-move through solid, liquid or gas
-push-pull waves
EARTHQUAKES
Earthquake Wave Motion
S Waves:
-travel slower
-move side to side
-travel through solids
EARTHQUAKES
Earthquake Wave Motion
L Waves:
-move slowest
-move like ripples on a pond
-move only through the crust
EARTHQUAKES
Earthquake Wave Motion
Earthquake information is picked up by seismic
recording stations around the world.
Seismograph: instrument that detects and measures
seismic waves
EARTHQUAKES
P waves travel faster
so they arrive first
followed later by S
waves. The further the
distance from the
epicenter the longer
the time between
earthquake waves.
Blue lines = primary waves
Red lines = secondary waves
EARTHQUAKES
Seismogram: seismograph’s record of waves; shows
vibration lines from the shaking motion of the
earthquake waves
The amount of
time between the
P and S waves
indicate how far
from the epicenter
the recording
station is.
EARTHQUAKES
• The distance from the epicenter can be
calculated using the arrival times for the
P and S waves and then pinpointed
using information from 3 or more
recording stations.
EARTHQUAKES
Where 3 circles from 3
separate recording stations
overlap, a smaller
approximate epicenter can
be located.
EARTHQUAKES
Common Earthquake Locations
• Most earthquakes occur along plate boundaries
Pacific ring of fire: an area surrounding the pacific
ocean with a high concentration of earthquakes and
volcanoes.
EARTHQUAKES
Richter scale: scale that measures how much energy
an earthquake releases (magnitude)by assigning a
number from 1 to 10
TECTONIC PLATE MOVEMENT
Tsunami: series of large
waves caused by the
displacement of a
large volume of water
- Often triggered by
earthquakes, volcanic
eruptions, landslides, or
glaciers breaking
EVIDENCE OF PLATE TECTONICS
Volcanism: any activity that includes the movement
of magma toward the surface of the Earth
Volcano: a place where magma comes to the
surface
VOLCANOES
Volcanic Zones
SUBDUCTION ZONE
- Most common volcanic
area
- Usually explosive and
with lava eruptions
MID-OCEAN RIDGE
- Slow, fluid eruptions
VOLCANOES
Volcanic Zones
Hot spots: areas of
volcanic activity in
the middle of a
lithospheric plate
VOLCANOES
Anatomy of a Volcano
Vent: any opening that
brings magma to the
surface
Crater: funnel-shaped pit
or depression at top of a
volcano
Caldera: collapsed crater
after a volcanic eruption
VOLCANOES
Famous Calderas
Yellowstone Volcano,
United States
Santorini Caldera,
Greece
VOLCANOES
Volcanic Eruptions
STAGE 1: sudden shallow
earthquakes and rapid uplift
of the ground surface
Yellowstone uplift
STAGE 2: cracking of the
ground surface, and possible
evaporation of the overlying
groundwater
VOLCANOES
Volcanic Eruptions
STAGE 3: eruption of lava and volcanic ash cloud
VOLCANOES
Volcanic Material
pyroclastic material: solid fragments ejected from a
volcano
VOLCANOES
VOLCANOES
VOLCANOES
Volcanic Material
lava: magma that reaches
the surface
Magma: molten rock deep
underground
* Main difference: temperature, viscosity and the
amount of gas
VOLCANOES
Lava Types
Some lava cools with a
smooth, solid surface
Hawaii: Pahoehoe
Some lava cools with
sharp, jagged edges
Hawaii: Aa
VOLCANOES
Types of Volcanoes
• Shield Volcanoes
-composed of quiet lava
flows
-form gently sloping,
dome- shaped mountain
-basaltic (mafic) magma
VOLCANOES
Types of Volcanoes
• Cinder Cone Volcano
- Made mostly of tephra
and other rock particle
- Formed from explosive
eruptions
- Not very high, narrow
base, steep sides
- Grantic (felsic) magma
VOLCANOES
Types of Volcanoes
• Stratovolcano (Composite volcano)
- built up of alternating layers of rock
and lava
- explosive eruptions at first with
tephra, then quiet with lava
- forms large, cone-shaped mountains
- made of grantic and basaltic
magma