Weathering is the process that produces change in the surface of rocks exposed to the atmosphere and/or hydrosphere.

Physical Weathering: Frost action- Water seeps into small cracks in rocks. When the water freezes it expands creating great pressure. The crack widens and allows water to seep deeper into the rock. Plant action- Tiny root hairs seek out small cracks and pits in rock. Once the root hairs find a place they grow and expand. The expansion causes great pressure and cracks the rock. Exfoliation (pressure unloading) Rocks formed deep in the Earth are made under high pressure. When these rocks are brought to the surface (via volcanos or the material above is eroded) the pressure is released and the rocks expand. Since the rocks aren't elastic they will crack. May also be caused by alternate heating and cooling of rocks by weather conditions. Abrasion- rubbing by other rocks. Chemical Weathering: Oxidation- Oxygen in the atmosphere chemically reacts with minerals. ex.: rusting of a nail Water (hydrolysis)- Minerals are dissolved in water. ex.: Halite, calcite Acid- Carbonic acid: C02 dissolves in rain water forming a weak acid. Acid Rain: Sulfur Dioxide in the atmosphere dissolves in rain water forming a strong acid (sulfuric acid). Rates of weathering will be influenced by: Surface area exposed- weathering occurs on the surface. More surface exposed, the faster the weathering will occur. A broken piece of material will have more surface area than the piece if it was all together. Mineral composition- some minerals are more resistant than others. ex.:Quartz is resistant to chemical and physical weathering. Climatic Conditions that affect weathering: Cold and/or dry climates favor physical weathering. Warm and wet climates favor chemical weathering. Homework on Weathering Soil: The product of weathering Soil- rocks, minerals (mainly sand and clay), and organic material (regolith and organic matter) The final outcome of weathering is soil solution. Soil solution is where the minerals have been broken down into ions and mix with ground water. Soil forms layers of different characteristics called horizons. Residual soil is located above the rock that it is formed from (parent rock). Transported soil has been moved from an other location. Most soil on the Earth's surface is transported.

Horizon	Layer	Description
A	Top soil	Small sediments and organic material. Dark in color.
B	Sub soil	Lighter in color- no organic material.
C	Partially weathered bedrock	Larger rocks
Bedrock	Bed rock	Solid rock

Human activity uses soil faster than it is replaced naturally. Conservation measures must be taken to ensure that there will be soil in the future. Erosion Erosion is the process of moving sediment from on location to another. Most soils are transported rather than residual. The most important FORCE of erosion is Gravity. The most important AGENT of erosion is Water. The amount of erosion by a stream depends on the velocity and volume of water flow. Velocity is influenced by the slope & volume of a stream. As the velocity increases the size of the particles that can be transported will get bigger. (See chart in Handy Dandy Earth Science Reference Tables) Volume (amount of water flowing) is influenced by rainfall. The shape of a stream will determine where erosion will occur. The fastest water goes to the outside of the curve. The outside curve gets eroded away. In a straight run of water, the fastest water runs above center of the stream. The rate of erosion increases where the velocity increases. (Direct Relationship) Running water can carry sediment in three ways: Suspension- "floating" it along suspended in the water. Rolling and bouncing along the bottom. Solution- dissolved in the water. Deposition: -the process of dropping material out of transportation. The characteristics of particles give information about the erosion and deposition environments. Water sediments get rounded and polished. Sorting occurs. particles can be fairly large. deposition occurs where the water slows down. ex.: where the river widens or where it dumps into a large body of water. As water slows gradually, smaller and smaller particles drop out causing horizontal sorting. Wind sediments are rounded and have a frosty appearance (tiny pits from impacts of flying sand give the frosted appearance) sorting occurs. particles are small Ice (glaciers) Sediments are harp-edged May have scratches or a polished side where they came in contact with the ground. deposits are unsorted and can be very large. Gravity Sharp-edged unsorted no limit in size

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