Internal/ExternalForces of theEarth

Inner Structure of the Earth

1.Inner Core—dense and solid

2.Outer Core—Molten or liquid

• Both are mostly hot and made of hot metal (iron)

Inner Structure of the Earth

3. Mantle—thick layer of rock (1800 miles thick); mostly solid, but has pockets of magma (melted rock)

4. Crust—very thin layer; rocky surface

·    Below the oceans, the crust is about 5 miles thick. Below the continents it averages 22-75 miles in thickness.

Inner Structure of the Earth

Internal Forces that Shape Landforms

1.Volcanoes—form when magma inside the earth breaks through the crust. Lava flows and may produce a large, cone-shaped mountain

Internal Forces that Shape Landforms

2. Fault—a break in the earth’s crust. Movement along a fault can send out shock waves, causing an earthquake.

1.The lithosphere—the earth’s crust and upper layer of the mantle—are broken into a number of large, moving plates.

The Plate Tectonic Theory

2. The plates slide very slowly over a hot, pliable layer of mantle.

3. The earth’s oceans and continents ride atop of the plates.

The Plate Tectonic Theory

The Ring of Fire

A circle of volcanic mountains that are surrounding the Pacific Plate

The Ring of Fire

2. Hot Spots: hot regions deep within the mantle that produce magma, which rises to the surface. Volcanic island chains form as oceanic plates drift over the hot spot. Example: Hawaiian Islands.

What Happens When

Plates Meet?

They collide and push slowly against each other and form a collision or converging zone.•If 2 oceanic plates collide, 1 slides under the other. Islands often form this way.

Converging (Collision) Zone

•If 2 continental plates collide, mountains are formed. Example: Himalayas

Converging (Collision) Zone

Continental Crush (Collide)

They meet, or CONVERGE and form a subduction zone. *If an oceanic plate collides with a continental plate, the heavier oceanic plate will slide under the lighter, continental plate. Results: volcanic mountain building and earthquakes.

Subduction

Plates pull away from each other and form a spreading zone. These areas are likely to have earthquakes, volcanoes, and rift valleys (a large split along the crest of a mountain).

SPREADING ZONE

Spreading Zone

At a FAULT, the plates will grind or slide past each other rather than colliding. Example: San Andres Fault.

Fault

External Forces of

the Earth

Weathering

• Changes in the earth’s surface over thousands or millions of years

• Breaks down rock at or near the earth’s surface into smaller pieces

Weathering

• Weathering is either mechanical or chemical, depending on the forces involved.

Mechanical weathering

• rock is actually broken or weakened physically.

Mechanical weathering

Frost Wedging: most common form; water freezes to ice in a crack (water expands 10% when frozen). Ice widens the crack and splits the rock.

Mechanical weathering

• Seeds: Seeds will take root and grow in the cracks of a rock. As the plant grows, the rock will split.

Chemical Weathering

• Alters the rock’s chemical make-up by changing the minerals that form the rock. Most important forces are water (H2O) and carbon dioxide (CO2).

Chemical Weathering

• Carbonic Acid: CO2 from the air or soil combines with H2O to make carbonic acid. When the acidic water seeps into the cracks in certain rocks (limestone) it dissolves the rocks away. Examples: caves

Chemical weathering • Acid Rain: Chemicals in the

polluted water combine with water vapor and then fall back to the earth as acid rain. Acid rain destroys wildlife, pollutes water, destroys forests, and eats the surface of buildings, statues, and natural rock formations.

Chemical Weathering

• Acid Rain is known to be caused by industrial pollution, volcanic activity, and acid producing agents in the oceans.

Erosion• The movement of weathered

materials such as gravel, sand, and soil.

• An agent of mechanical weathering• Three common forms

–Wind–Water–Glaciers

Erosion—Wind

• Most damaging in areas that are dry and with few plants

• Wind-blown sand carves and/or smooths natural and man made formations

Erosion—Water

• Moving water carries sediment

• Grinds away rock like sandpaper

• Forms canyons and valleys

Erosion—Glaciers

• Huge, slow moving sheets of ice• Carry dirt, rocks, boulders• Movement carves out huge

basins• When melted, leave behind piles

of rock/debris called moraines• Great Lakes formed by glaciers