Name:

Weathering and Soil Formation

Rocks and Weathering

            1. The Effects of Weathering

·         Weathering is the process that breaks down rocks at Earth’s surface.

·         Heat, cold, water, ice, oxygen and carbon dioxide in the atmosphere all contribute to weathering.

·         Erosion is the movement of rock particles by wind, water, ice or gravity.

·         Weathering and erosion work together.

·         Two kinds of weathering: Mechanical & Chemical

            2. Mechanical Weathering

·         Weathering in which rock is physically broken into smaller pieces

·         Rock is broken by freezing and thawing, release of pressure, growth of plants, and actions of animals

·         Abrasion: the grinding away of rock by particles carried by water, ice, wind or gravity.

·         Ice wedging – ice acts like a wedge to break rocks apart

            3. Chemical Weathering

·         Breaks down rocks through chemical change

·         Agents of Chemical Weathering: Water, oxygen, carbon dioxide, living organisms and acid rain

·         Chemical weathering creates holes or soft spots in rock, so the rock breaks apart more easily

A.    Water

·         Most important agent

·         Water dissolves rock

                        B.  Oxygen

·         Rock that contains iron oxidizes or rusts

                        C.  Carbon Dioxide

·         Carbon Dioxide is dissolved in rainwater and in water that sinks through air pockets in the soil.      

·         Carbonic acid weathers limestone and marble easily

                        D.  Living Organisms

·         Seeds grow on rocks

·         Lichens also produce weak acids that weather rocks

                        E.  Acid Rain

·         Burning fuels can pollute the air

·         The result is acid rain that contributes to chemical weathering

            4. Rate of Weathering

·         The most important factors that determine the rate of weathering are type of rock and climate.

                        A.  Type of Rock

·         The minerals that make up a rock determine the rate of weathering

·         Some rock weathers easily because it is permeable or has tiny air spaces

B.     Climate

·         The average weather conditions in an area

·         Chemical and Mechanical weathering occurs faster in wet and hot weather