Weathering and Erosion

Mechanical WeatheringChemical Weathering

Examine the illustration below that shows volcanic mountain formation. Note that the volcanoes bring new

rock to the surface.

Weathering

• Mechanical or chemical weathering is a surface process that breaks rocks into smaller pieces.

• Freezing• Thawing• Oxygen in the air• Plants• Animals• Weather

Mechanical Weathering

• Breaks rocks into smaller pieces without changing them chemically.

• The small pieces are identical in composition to the original rock.

• Ice wedging • Living beings

Ice Wedging

• The freezing and thawing cycle breaks up rocks.

• Ice wedging occurs when water seeps into rock cracks and freezes. Interestingly, water EXPANDS when it freezes. As the water freezes in the rock crack, sections of rock are broken off. Ice wedging is common in areas where the climate includes a cold season.

Ice WedgingNote how the water can freeze and expand in rock

cracks.

Plants and animals

• Plants grow in inconvenient places. Their roots grow into cracks in rocks where water collects.

• Roots become thicker and longer exerting pressure and wedging rock apart.

Note that the roots are creating large cracks in the rock.

Plants and animals

• Gophers and prairie dogs weather rock, burrowing in the ground.

• When they burrow through sediment, they break the rocks.

Prairie dogs burrowing into the soil. Note the small rocks that are now exposed

Interest Scientific Fact:

• Earthworms are a major factor in the weathering of rock. Earthworms tunnel through the soil looking for food. As they tunnel, they bring rock flakes to the surface and expose covered rock to the weathering effects of air and water.

Earthworms

Abrasion

• Abrasion is the grinding of rocks. Abrasion may occur because of the action of wind, running water, waves, and gravity.

• Wind, running water, and waves push smaller particles of rock into other rock eventually causing pieces to chip away. Rocks fall and tumble as gravity pulls them down hill. When this happens, the rocks chip or break apart.

Note how the wind has weathered the rock.

Remember this:

Rocks are weathered when small pieces of rock are pushed across other rock or when a rock falls.

Abrasion

Abrasion

Abrasion occurs when small pieces of rocks are pushed into or across another rock. Over time this results in chipping or wearing down of the rocks. Rocks are weathered when small pieces of rock are pushed across other rock or when a rock falls.

Abrasion

Interesting Scientific Fact:

The Grand Canyon continues to be weathered by the action of the small grains of rock that are carried along by the Colorado River.

Review 1

• Describe how rocks are mechanically weathering.

• Explain how carbonic acid weathers rocks.

• Describe how soil forms. What factors are important.

Agents of Erosion

• Erosion is the wearing away and removal of rock and sediment.

• Agents:• Gravity• Ice• Wind• water

Gravity

• Gravity is a force that pulls every object toward every other object.

• Gravity pulls everything on Earth toward its center.

• Mass movement is when gravity causes rock or sediment to move down a slope.

Mass Movement

• Creep process in which sediments move slowly downhill.

• Common where freezing and thawing occur.

Creep

Mass Movement

• Slump occurs when a mass of rock or sediment moves downhill, leaving a curve scar.

Slump

SLUMPS

• Slumps are: • often clay-rich (cohesive unit) • slow to rapid • have spoon-shaped failure surfaces • show clear scarp face at head (top) • end in earthflows at toe (bottom)

Slump

Slump

Mass Movement

• Rock Slides layers of rock break loose from slopes and slide to the bottom.

• Million of cubic meters of rock roaring down a mountain at speeds greater than 250 Km/h.

Rock Slides

Mass Movement

• Mudflows where heavy rains or melting snow and ice saturate sediments.

• Mudflows is a mass of wet sediment that flows downhill over the ground surface.

Mudflows

Mudflows

Mudflows

Ice

• Continental glaciers.• Valley glaciers.• Mountain glaciers.

• Ice can remove rock from mountaintops.• Ice forms cirques.• Ice can remove rock layers from land’s

surface.

Ice

Wind

• The erosion of the land by wind is called deflation.

• Deflation can lower the land’s surface by several meters.

• Abrasion is a form of erosion that can make pits in rocks and produce smooth, polished surfaces. ( deserts, cold regions with strong winds).

Wind

Water

• Water that flows over Earth’s surface is called runoff.

• Runoff causes erosion, especially if water is moving fast.

• Sheet erosion is a thin sheet of water can carry loose sediment grains with it, causing erosion of the land.

Water

Water