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Our Dynamic Earth
Earth as a System
• The Earth is an integrated system that
consists of rock, air, water, and living
things that all interact with each other.
• Scientists divided this system into four
parts:
•
•
•
•
The Geosphere (rock)
The Atmosphere (air)
The Hydrosphere (water)
The Biosphere (living things)
Earth as a System
Earth’s Interior
• Scientists use seismic
waves to learn about
Earth’s interior.
• Seismic waves are the
same waves that
travel through Earth’s
interior during and
earthquake.
Seismic Waves
• A seismic wave is altered by the nature of
the material through which it travels.
• Seismologists measure changes in the
speed and direction of seismic waves that
penetrate the interior of the planet.
• With this technique seismologists have
learned that the Earth is made up of
different layers and have inferred what
substances make up each layer.
Layers of the Earth
• Scientists divide the Earth into three
layers:
– The crust
– The mantle
– The core
• These layers are made up of
progressively denser material toward
the center of the Earth.
Layers of the Earth
 The Earth can be divided into five layers
based on the physical properties of each
layer.
 lithosphere - solid, outer layer of the
Earth that consists of the crust upper
part of the mantle; divided into huge
pieces called tectonic plates.
 asthenosphere - solid, plastic layer of the
mantle beneath the lithosphere; made of
mantle rock that flows slowly, which allows
tectonic plates to move on top of it.
What observations can you make
about the shape of the
continents?
What’s interesting? Just 200
million years ago, this is what the
world looked like:
Plate Tectonics
 Tectonic plates - blocks of lithosphere
that consist of the crust and the rigid,
outermost part of the mantle and glide
across the underlying asthenosphere.
 The continents are located on tectonic
plates and move around with them.
 The major tectonic plates include the
Pacific, North America, South America,
Africa, Eurasian, and Antarctic plates
Plate Boundaries
• Much of the
geological activity at
the surface of the
Earth takes place at
the boundaries
between tectonic
plates.
• Tectonic plates may
separate, collide, or
slip past one
another.
Plate Boundaries
Divergent Boundary:
Plate Boundaries
Divergent Boundary:
 Plates are moving away
from each other
 Midocean ridges are
created and new ocean
floor plates are created
Rift Valleys
Leif the Lucky Bridge Bridge between continents in Reykjanes
peninsula, southwest Iceland across the Alfagja rift valley, the
boundary of the Eurasian and North American continental tectonic
plates.
Plate Boundaries
Convergent Boundary:
 plates are moving toward
each other and are
colliding (3 types)
Convergent Boundaries
•
•
•
•
Create
subduction
zones,
trenches
Create near
coast
volcanoes
Island arcs
are created
Mountain
ranges are
created
– (example:
Himalayan
Mountains)
Himalayan Mountains
Plate Boundaries
Transform Fault Boundary
 Plates are neither moving
toward nor away from each
other, they are moving past
one another.
Transform Fault Boundary
 The plates may move in opposite
directions or in the same
directions but at different rates
and frequent earthquakes are
created (example: San Andreas
Fault)
San Andreas Fault
So is the Earth getting bigger?
o No
o Plates are destroyed as fast as they
are created (2 ways)
o Plates may be subducted and melted
or may push be pushed upward to
form mountains
What types of forces are created?
Tensional Force:
 stretching or pulling
 Creates a normal fault
What types of forces are created?
Compressional Force:
 force pushing something together
 Creates a reverse fault
What types of forces are created?
Shear or Transversal Force:
 a system of forces that operates against a
body from different sides
 Creates a strike-slip fault
What causes this?
Convection currents within the mantle

The up-welling leg of the current creates
a divergent boundary which produces
midocean ridges

The down-welling leg of the current
creates one type of convergent boundary
that results in trenches and a subduction
zone
Earthquakes
• A fault is a break in the Earth’s crust along
which blocks of the crust slide relative to one
another.
• When rocks that are under stress suddenly
break along a fault, a series of ground
vibrations, known as earthquakes, is set off.
• Earthquakes are occurring all the time. Many
are so small that we cannot feel them, but
some are enormous movements of the Earth’s
crust that cause widespread damage.
Earthquakes

The actual place
underground where the
earthquake starts and
rocks break producing
vibrations is called the
focus.

The place on the surface
directly above the focus
is called the epicenter
Seismic Waves
Originate at the focus and travel
outward in all directions
•
–
Three Types: P wave, S wave, surface waves
Foreshocks: small earthquakes that
come before a major earthquake
Aftershocks: Are adjustments in the
crust after in earthquake.
•
•
–
Smaller than main earthquake, but can cause
as much or more damage. They can continue
for weeks to months.
How do we Measure
Earthquakes?
Earthquake waves are recorded by a
seismograph and the recording of waves
on paper is called seismogram
Measuring Earthquakes

Locating the epicenter
1.
2.
3.

Lag time between the arrival of the P wave and the S
wave to the seismograph station is converted to a
distance
A circle with a radius that equals the distance is drawn
around the station.
Three stations can narrow down the location to where the
circles intersect
Locating the focus: the lag-time of the
surface wave will determine the depth of the
focus
Measuring Earthquakes
Earthquakes
• The measure of the energy released by an
earthquake is called magnitude.
• The smallest magnitude that can be felt is
2.0, and the largest magnitude ever recorded
is 9.5. Magnitudes greater than 7.0 cause
widespread damage.
• Each increase of magnitude by one whole
number indicates the release of 31.7 times
more energy than the whole number below it.
Where do Earthquakes Occur?
• The majority of earthquakes take place at or
near tectonic plate boundaries because of the
enormous stresses that are generated when
tectonic plates separate, collide or slip past
each other.
• Over the past 15 million to 20 million years,
large numbers of earthquakes have occurred
along the San Andreas fault in California,
where parts of the North America plate and
the Pacific plate are slipping past one another.
Where do Earthquakes Occur?
Earthquake Dangers
o
Most injuries and deaths are caused
by falling objects and most property
damage results from fires that start

Tsunami: seismic sea wave sometimes
generated when an earthquake originates
on the ocean floor
Earthquake Dangers

Landslides
Volcanoes
 A volcano is a mountain built from magma, or
melted rock, that rises from the Earth’s
interior to the surface, and can occur on land
or in the sea.
 Volcanoes are often located near tectonic
plate boundaries where plates are either
colliding or separating from one another.
 The majority of the world’s active volcanoes
on land are located along tectonic plate
boundaries that surround the Pacific Ocean.
Volcanoes: The Ring of Fire
The Birth of a volcano
What comes out of volcanoes?
•Lava
•Tephra
•Gases
Tephra

•
•
Basically, rock fragments
Also known as pyroclastic rock
fragments.
There are many different possible
sizes, from very small (volcanic ash or
dust to much larger rocks (called
volcanic bombs)
GASES
water vapor, carbon dioxide,
nitrogen, sulfur dioxide,
hydrogen sulfide, chlorine
Types of
Volcanic Eruptions
Two factors determine the type of eruption:


Amount of water vapor &
other gases in the magma
The chemical composition of
the magma
Explosive Eruptions

Trapped gases
under high
pressure will
violently explode
when the magma
reaches the
lower pressure of
the surface.
Explosive Eruptions

Has granitic
magma is very
thick and plugs
the vent
causing the
pressure to
build until it
blows violently
out the vent
Mt. St. Helens
Explosive Eruptions

The high
water content
of the magma
produces more
water vapor
which when
mixed in
granitic
magma
produces
explosive
eruptions
Mont serrat
The eruption of Mt. St. Helens in 1980
Quiet Eruptions

Low
pressure
gas
Quiet Eruptions

Has
basaltic
magma (is
more fluid
and will flow
instead of
explode)
Quiet Eruptions


…and has low
water content
Examples: Hawaii
A typical Hawaiian Eruption
Types of volcanoes
Local Effect of Volcanic
Eruptions
 Clouds of host ash, dust, and gases can flow
down the slope of a volcano at speeds of up to
200 km/hr and sear everything in their path.
 During and eruption, volcanic ash can mix with
water and produce mudflow that runs
downhill.
 In addition, ash that falls to the ground can
cause buildings to collapse under its weight,
bury crops, damage the engines of vehicles,
and cause breathing difficulties.
Global Effect of Volcanic
Eruptions
• Major volcanic eruptions can change Earth’s
climate for several years.
• In large eruptions, clouds of volcanic ash and
sulfur rich gases may reach the upper
atmosphere, and spread across the planet
reducing the amount of sunlight that reaches
the Earth’s surface.
• The reduction in sunlight can cause a drop in
the average global surface temperature.