Investigation 3: Rocks and Weathering

Key Question How do different types of rocks weather?

Weathering Is the breakdown of rock into smaller and smaller pieces. Undergo weathering either by mechanical or chemical means.

Mechanical Weathering Also called physical weathering. Is simply the breakdown of rock into smaller pieces by physical means. These physical means include ice, wind, water, gravity, plants, and animals.

Types of Mechanical Weathering 1. Ice –Water seeps into a crack in a rock during warm weather and then freezes during cold weather. –The ice expands, pushing against the sides of the crack, forcing it to open wider. –This is called ice wedging.

2. Wind, Water, and Gravity Abrasion –Is the action of rocks and sediments grinding against each other and wearing away exposed surfaces. –Rocks and pebbles abrade by rolling along the bottoms of a stream, river, or the ocean. –Wind could blow small particles of sand against rock surfaces. –Rocks fall from higher altitudes, crash against the floor or each other and break down.

3. Plant Weathering Plant send their roots into existing cracks in rocks. As the roots get bigger the crack gets bigger, eventually breaking the rock in two. This can affect sidewalks and paved driveways.

4. Animal Earthworms- burrow through the soil and move soil particles around. This exposes fresh surfaces to continue weathering. Ants, mice, rabbits etc. contribute to the mixing and digging that aids in weathering.

Pictures of Mechanical Weathering

Chemical Weathering Is the chemical breakdown of rocks and minerals into new substances. Most common agents are: water, weak acid, air, and soil.

Types of Chemical Weathering 1. Water -It will breakdown almost any material over time. -By dropping a piece of chalk in water it will dissolve very quickly. 2. Acid Precipitation - Carbonic acid found in rain and snow can rapidly weather rock - Comes from natural sources such as volcanoes - Comes from the burning of fossil fuels such as coal and oil. It gives off gases that combine with water in the atmosphere.

Cont. Chemical Weathering 3. Acid in Ground Water - Increase carbonic or sulfuric acid in a water supply can cause the formation of huge underground caves. - Usually occurs in areas of large limestone deposits. 4. Acids in living things (Lichens) - Lichens - symbiotic relationship between a fungus and algae. - found growing on rocks and trees - produce organic acids that eat away at the surfaces.

Cont. Chemical Weathering 5. Oxidation - Air reacts with iron causing a chemical reaction. - Rust is the end product - Can occur in rocks with a high iron content.

Pictures of Chemical Weathering

The Earth System and Weathering Karst –Landform formed by chemical weathering. –Animals, humans, fossil fuels add carbon dioxide into the atmosphere creating acid rain. –This acidic water travels through the water supply and breaks down rocks. –In areas of pure limestone the acid breaks down the rock underground causing the karst. –This lead to the formation of underground caverns. –This is also called a sinkhole.