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The Baths British Virgin Islands Casey Sullivan. View from Macchu Pichu Peruvian Andes Emma Conroy. Lake George, NY Brian Gilligan. Cinque Terre "Five Lands" of Italy Sarah Bruce . GEOPHYSICAL PROPERTIES OF THE EARTH. ISOSTASY. Lithosphere floats on the underlying denser, heat-

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The Baths

British Virgin Islands

Casey Sullivan


View from

Macchu Pichu

Peruvian Andes

Emma Conroy


Lake George, NY

Brian Gilligan



GEOPHYSICAL PROPERTIES OF THE EARTH

ISOSTASY

Lithosphere floats on the underlying denser, heat-

softened, partially melted aesthenosphere.

Areas with greater mass sink deeper into the

aesthenosphere.

Equilibrium between lithospheric segments (plates)

and aesthenosphere beneath them is called

ISOSTASY.



GEOPHYSICAL PROPERTIES OF THE EARTH

ISOSTASY

Lithosphere, because of its lower density “floats” or

“sinks” to find its own isostatic equilibrium.

Continental lithosphere is less dense so a larger

proportion of it “floats” above the aesthenosphere.

Changes in mass cause it to rise and fall.

Similar to a boat unloading or loading cargo.

Removal of mass causes it to rise.

Addition of mass causes it to sink.

Rise after removal of mass is called ISOSTATIC REBOUND.



GEOPHYSICAL PROPERTIES OF THE EARTH

EARTH’S MAGNETIC FIELD

Penetrates and surrounds the Earth.

Extends into space approximately 60,000 km.


GEOPHYSICAL PROPERTIES OF THE EARTH

EARTH’S MAGNETIC FIELD

Obvious cause would be the Earth’s

iron core.

But, the core is too hot to be a

permanent magnet.

However, magnetic fields such as

those that surround the Earth

can be produced by an electrical current.

So, we think of the Earth now as a giant electromagnet.

The electrical field is produced by the movement of

electrons through the molten iron of the liquid

outer core.


GEOPHYSICAL PROPERTIES OF THE EARTH

EARTH’S MAGNETIC FIELD

The rotation of the Earth sets the

liquid in motion.

Moving currents generate the

magnetic field.

This, then, generates more

electrical currents.

Produces a SELF-EXCITING DYNAMO.


GEOPHYSICAL PROPERTIES OF THE EARTH

MAGNETIC REVERSALS

Magnetic pole moves around all the time, but in general

it is in close proximity to the geographic pole.

Earth’s magnetic field reverses occasionally.

Magnetic north and south poles switch position.

Happens every ~ 500,000 years.

We think it takes ~ 1000 to 5000 years to switch,

but evidences suggest it can be only ~100.

How do we know…..



GEOPHYSICAL PROPERTIES OF THE EARTH

MAGNETIC REVERSALS

Normal is when magnetic pole is in the northern hemisphere.

Reversed is when magnetic pole is in the southern hemisphere.


MASS MOVEMENT

MASS MOVEMENT is the process by which Earth

materials (bedrock, unconsolidated sediments

and soils) are transported down slopes by

gravity.

Every slope is susceptible to mass movement.

Movement can be slow or fast.

Between 1925 and 1975 cost $75 billion.

Loss of life < 1000.



Information provided by

Dylan Harrison-Atlas


MASS MOVEMENT

CAUSES OF MASS MOVEMENT

GRAVITY, FRICTION AND SLOPE ANGLE

Gravity tries to pull particles downward.

Friction tries to stop downward movement.

When friction is overcome, particles move.

Greater slope angle, tendency to move increases.


MASS MOVEMENT

CAUSES OF MASS MOVEMENT

GRAVITY, FRICTION AND SLOPE ANGLE

Bubble Rock,

Acadia Natl. Park

Maine


MASS MOVEMENT

CAUSES OF MASS MOVEMENT

SLOPE COMPOSITION

SOLID BEDROCK

Things to consider in terms of slope composition.

Fractured vs. unfractured

Amount of mechanical weathering

Occurrence of bedding planes

Solubility (limestone)

Foliation orientation

Columnar jointing


MASS MOVEMENT

CAUSES OF MASS MOVEMENT

SLOPE COMPOSITION

UNCONSOLIDATED MATERIAL

Angle of Repose


MASS MOVEMENT

CAUSES OF MASS MOVEMENT

WATER CONTENT

Water is the most significant factor in slope failure.

Small amounts of water actually increase cohesiveness

of unconsolidated sediments.

Holds sand grains together, due to surface tension.


MASS MOVEMENT

CAUSES OF MASS MOVEMENT

WATER CONTENT


MASS MOVEMENT

CAUSES OF MASS MOVEMENT

WATER CONTENT

Water also encourages growth of vegetation.

Helps discourage slope failure.

Water also increases mass of slope.

Too much water reduces friction between grains and

consequently cohesiveness, which leads to slope

failure.


MASS MOVEMENT

CAUSES OF MASS MOVEMENT

WATER CONTENT


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