Internal Forces of the Earth

Inner Structure of the Earth

Inner Structure of the Earth Inner Core—dense and solid 4000 miles below surface Outer Core—Molten or liquid Both are mostly hot and made of hot metal (iron) Appro 1,400 miles thick 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 2 miles thick. Below the continents it averages 75 miles in thickness.

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

Divergent Plate Boundary Features Faults Earthquakes Intrusions Volcanoes Crust 6 Tasa Graphic Arts Inc.

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

The Big Burp

The Plate Tectonic Theory The lithosphere—the earth’s crust and upper layer of the mantle—are broken into a number of large, moving plates. The plates slide very slowly over a hot, pliable layer of mantle. 3. The earth’s oceans and continents ride atop of the plates.

Plate Boundary Features To view this animation, click “View” and then “Slide Show” on the top navigation bar. 10

The Ring of Fire A circle of volcanic mountains that are surrounding the Pacific Plate

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?

Collision/Spreading Zones To view this animation, click “View” and then “Slide Show” on the top navigation bar. 14

Convergent Plate Boundaries They collide and push slowly against each other and form a collision or converging zone. Ocean - Continent Ocean - Ocean CC Continent-Continent Tasa Graphic Arts Inc. 15

Converging (Collision) Zone If 2 continental plates collide, mountains are formed. Example: Himalayas

Continental Crush (Collide)

If 2 oceanic plates collide, 1 slides under the other If 2 oceanic plates collide, 1 slides under the other. Islands often form this way. Example: Japan

Ocean – Ocean Convergent Plate Boundary

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.

Ocean-Continent Convergent Plate Boundary

South American Subduction 22

SPREADING ZONE 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).

Red Sea Spreading Center

East African Rift Valley National Geographic Society.

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

Motion at Transform Boundaries To view this animation, click “View” and then “Slide Show” on the top navigation bar. 27

San Andreas 28 http://www.aerialarchives.com/stock/img/AHLB2130.htm

External Forces of the Earth

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

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). H2O + CO2 + CaCO3  --> Ca+2 + 2HCO3-

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

With the snow-draped Sierra Nevada as a backdrop, unique erosion formations called sand tufa stand like giant cauliflower stalks in a dry Arizona lake bed. Before this alkaline lake went dry, tufa formed when a freshwater spring percolated from below and formed calcium carbonate deposits. When the lake's level dropped, these fragile formations surfaced, and wind went to work removing the sand beneath the deposits.

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

A stand of withered red spruce and Fraser fir trees blights a green vista in North Carolina's Mount Mitchell State Park.

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

Desert winds sculpted these gentle swirls out of the limestone hills in Black Gap Wildlife Management Area, Texas. This remote, 100,000-acre (40,470-hectare) area in West Texas contains some of the lowest, driest, and hottest areas in the Chihuahuan Desert.

Erosion—Water Moving water carries sediment Grinds away rock like sandpaper Forms canyons and valleys

Erosion—Glaciers Huge, slow moving sheets of ice When melted, leave behind piles of rock/debris called moraines Great Lakes formed by glaciers

The Bernard Glacier in Alaska's Saint Elias Mountains looks like a huge alpine highway. Glaciers are slow but highly effective shapers of the land, essentially carrying away anything in their path—from soil and rocks to hills and even the sides of mountains.