Notepack 15A Do now: Look at these rock formations. How do you think they were formed?

Weathering

Weathering Weathering is the process of breaking down of the materials of Earth’s crust into smaller pieces.

Two Types Of Weathering: 1) Physical weathering is breaking rock by force. The rock material is the same but smaller. Cracking Pounding Scraping 2) Chemical weathering is where the rock material is changed into another substance by reacting with a chemical.

Physical Weathering Process by which rocks are broken down into smaller pieces by external conditions. Types of Physical weathering Frost heaving and Frost wedging Plant roots Friction and impact Burrowing of animals Temperature changes

Frost Wedging Frost wedging is the process of splitting rock as the results of water expanding inside a crack as it freezes. The stress created by the expanding ice forces the crack to widen. As the crack widens, more water fills the crack, forcing the crack to widen as this new water freezes

Frost Heaving Frost heaving is similar to Ice wedging except ice form under rocks causing the rock to move out of its original position. This could cause erosion under the rock to occur.

Plant Roots Sometimes seeds fall into cracks of rocks. When the seed grows, its roots secret a chemical which breakdown rocks, so that the root have room to grow.

Friction and Repeated Impact Friction and repeated impact can occur in three ways. Moving water Moving Ice Move air (wind)

Friction and Repeated Impact - Water As water moves across rock, the water molecules rub against the rock, slowly grinding the rock down. Sometimes hard materials are mixed in with moving water. These materials may smash against rock, chipping away at it. Since water is heavy, sometimes the pressure of water is enough to push through rock.

Friction and Repeated Impact - Ice In very cold regions of the world, glaciers form as the results of thousands of years of snow pile up onto itself. These thick sheet on ice are very heavy and begin to move down mountain sides. As they move material trapped in the ice begin to move with the glacier- grinding along the bottom against the ground. Scraping at the rock.

Friction and Repeated Impact - Wind As wind moves across rock, the air molecules rub against the rock, slowly grinding the rock down. Sometimes hard materials (like sand) are mixed in with moving air. These materials may smash against rock, chipping away at it.

Burrowing of Animals Many animal will dig holes and tunnels in the ground for shelter and a way to move safely from one place to another. Earthworms secrete a chemical with help breakdown rocks so they can move through the ground.

Chemical Weathering The process that breaks down rock through chemical changes. The agents of chemical weathering Water Oxygen Carbon dioxide Living organisms Acid rain

Water Water weathers rock by dissolving it

Water - Caves Caves are the results of water dissolving limestone resulting from underground streams or seepage from the surface.

Water - Sinkholes Sinkholes are the results of the roof of a cave collapsing.

Oxygen Iron combines with oxygen in the presence of water in a processes called oxidation The product of oxidation is rust

Carbon Dioxide CO2 dissolves in rain water and creates carbonic acid Carbonic acid easily weathers limestone and marble

Living Organisms Lichens that grow on rocks produce weak acids that chemically weather rock

Acid Rain Compounds from burning coal, oil and gas react chemically with water forming acids. Acid rain causes very rapid chemical weathering

Rates of weathering will be influenced by 3 main factors: Surface area exposed The type of mineral the rock is made of Environmental Climate

Rates of weathering will be influenced by: Surface area exposed Surface area exposed - weathering only occurs on the surface of rock. The more surface exposed, the faster the weathering will occur. A full, solid block has the least surface area. The interior is safe from exposure. A smashed piece has greatest surface area exposed. The interior can now be attacked.

Rates of weathering will be influenced by: Mineral composition Mineral composition- some minerals are more resistant than others. Some materials are very hard, so they ware down slowly. Some materials are very soft, so they ware down quickly. ex.:Quartz is resistant to chemical and physical weathering.

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Rates of Weathering will depend on: Climatic Conditions Cold and/or dry climates favor physical weathering. Warm and wet climates favor chemical weathering. Frost action works best in areas where the temperature fluctuates wildly.

Soil - The product of weathering Soil- rocks, minerals (mainly sand and clay), and organic material (regolith and organic matter) Soil forms layers of different characteristics called horizons. Soil formation is important because complex plants can grow.