Weathering, Erosion, and Soil

Yosemite Valley, California Mountains Carved by Glaciers

Grand Canyon, Arizona Carved out by the Colorado River

Bryce Canyon, Utah Acidic Rainfall has worn away these rocks. The harder rocks remain standing… but for how long?

Weathering The 2 G’s and the 3 W’s Process by which rocks are broken down due to exposure to processes occurring at the Earth’s surface Caused by Water Waves Wind Gravity Glaciers The 2 G’s and the 3 W’s

2 Types of Weathering A. Mechanical Weathering also called Physical weathering Rock is broken down into smaller pieces of the same material (no change in composition) B. Chemical Weathering The breakdown or decomposition of rock that occurs when minerals are changed into different substances (change in composition)

Mechanical/Physical Weathering Frost (Ice) Wedging Process in which water freezes in the cracks of rock and wedges (pushes) it apart because water expands when it freezes. Occurs where there are frequent freezes and thaws.

Explain what is happening.

Frost/Ice Wedging can cause Potholes to form in pavement

Mechanical/Physical Weathering 2. Abrasion The wearing away of rock material by grinding action Usually caused by sediment in Wind, Water, and Glaciers

Wind abrasion- sandblasting effect on stationary rocks as seen here in Arches National Park

Hydraulic abrasion- water & sediments flowing over boulders as seen here in Ohiopyle State Park, Pennsylvania Notice the rounded river rocks

Mechanical/Physical Weathering 3. Plants and Animals Plant roots can split rock Also known as: “Root pry” or “Root action” Animals dig holes ,breaks up rocks

Tree growing out of rock, Shenandoah National Park Tree roots also break up sidewalks

Mechanical/Physical Weathering Exfoliation- gradual peeling of layers due to uplift and frost action, typical of granite domes like those in Yosemite N.P.

Exfoliation of Igneous rock

O2 Chemical Weathering Chemical Weathering The breakdown or decomposition of rock that occurs when minerals are changed into different substances (change in composition) Involves Water ,water vapor, Acids, and/or Oxygen O2

Chemical Weathering Hydrolysis Carbonic Acid in water dissolves Calcite. This chemical weathering can hollow out underground Caverns Limestone and Dolomite both dissolve because they contain Calcite

Acid rain (carbonic acid) weathering the details of statues and tombstones Ex: Marble and Limestone

Chemical Weathering Oxidation This is why Mars is the red planet Oxidation of minerals with iron (magnetite, pyrite) results in the formation of rust or iron oxide. This is why Mars is the red planet Copper turns rocks green

Rate of Weathering Surface area Rock composition Climate How fast a rock weathers depends on 3 factors: Surface area Rock composition Climate

Rate of Weathering Surface area The greater the surface area, the faster the weathering rate There are more surfaces to be weathered

Rate of Weathering Rock composition Some minerals are more resistant than others For example, quartz is more resistant (harder) than calcite Quartz Calcite

Rate of Weathering Climate (long term pattern of moisture and temperature) Weathering rates are faster in warm, wet climates Desert vs. Rainforest