Weathering

Anticipation Guide #4 Ice wedging is a form of chemical

weathering

Erosion is the process where rocks are broken down

The most active erosion agent on the planet is running water

Gravity plays a role in all erosion except wind

Rivers have 3 stages of development

VA SOL

SOL 7 The student will investigate and understand geologic processes…... Key concepts include

b. processes (…weathering, erosion, deposition, and sedimentation) and their resulting features.

Objective

1 Summarize weathering as the process by which rocks are broken down by the action of water, air, and organisms.

2 Distinguish between physical (mechanical) and chemical weathering.

3 Recognize factors that affect the rate of weathering.

Enduring Understandings

Weathering, erosion, and deposition are interrelated processes that form a cycle of forces that wear down and build up the Earth’s surface.

Weathering

Immediately after the first rocks on earth crystallized billions of years ago the process of weathering began to take effect to break them down again.

http://www.uky.edu/AS/Geology/howell/goodies/elearning/module07swf.swf

Weathering

Weathering is the process by which rocks on or near the Earths surface break down and change

Weathering

Erosion is the removal and transportof weathered material from one location to another.

– Materials are transported by moving water, ice or wind

Mechanical Weathering

Before the agents of erosion can pick up and transport Earth materials, these materials must undergo some form of weathering.

Mechanical Weathering

Mechanical weathering (also called physical weathering) is the process by which rocks and minerals break down into smaller pieces

Mechanical Weathering

Mechanical weathering does not change the composition, only the size and shape of the rock

Mechanical Weathering

Temperature plays a significant role in mechanical weathering.

Mechanical Weathering

As water freezes it expands and will crack rocks

Mechanical Weathering

Pressure is another factor in mechanical weathering as overlying layers of rock are removed the pressure is reduced and the exposed surface will expand and crack

Mechanical Weathering

Exfoliation is the process by which the outer layers of rocks are stripped off

Chemical Weathering

Exposed rocks can undergo changes in their chemical composition as well and result in the formation of new minerals and the release of dissolvedsubstances.

Chemical Weathering

Chemical weathering is the process by which rocks and minerals undergo changes in their composition due to chemical reactions

Chemical Weathering

Water, carbon dioxide and acids are common agents

Chemical Weathering

Hydrolysis is the reaction of chemical water with other substances

Chemical Weathering

Oxidation is the chemical reaction of oxygen with other substances

Chemical Weathering

Carbon Dioxide combines with water in the atmosphere to form carbonic acid that falls to the surface as precipitation

Chemical Weathering

Carbonic acid reacts with minerals such as calcite in limestone and marble to dissolve rocks

Chemical Weathering

Acid precipitation (acid rain) is another agent of chemical weathering caused by the oxidation of sulfur dioxide and nitrogen oxides released into the atmosphere by human activities

Chemical Weathering

These gasses combine with water and oxygen in the atmosphere to form sulfuric and nitric acids.

http://www.epa.gov/AIRMARKET/acidrain/education/site_students/acid_anim.html

Factors Affecting the rate of

Weathering

Natural weathering is a very slow process. Certain conditions and interactions can accelerate or slow the process significantly

Factors Affecting the rate of

Weathering

Climate is a major influence. The interaction between temperature and precipitation has the greatest effect on a region’s rate of weathering

Factors Affecting the rate of

Weathering

Physical weathering rates are highest in cool, areas where water undergoes repeated freezing and thawing

Factors Affecting the rate of

Weathering

Chemical weathering rates are highest in areas with warm temperatures and abundant rainfall, and heavy vegetation

Factors Affecting the rate of

Weathering

Rock type and composition also affects the weathering rate. Some are quite resilient (Quartz) while some are easily broken down (Talc)

Factors Affecting the rate of

Weathering

Surface Area interacts with both mechanical and physical weathering as pieces break up through mechanical weathering more surface area is exposed for chemical weathering

http://courses.soil.ncsu.edu/resources/physics/texture/soilgeo.swf

Factors Affecting the rate of

Weathering

Topography is the shape and slope of the Earth’s surface. Materials that lie on steep slopes are more likely to move and expose even more surface area