Transcript Weathering
http://www.brainpop.com/science/w eather/weathering/ Chemical weathering is weathering that changes the chemical makeup of the rock. It occurs when chemical reactions dissolve or alter the minerals in rocks and transform them into different minerals. It occurs at or near Earth’s surface. Usually caused by reactions with Oxygen, water, or acids. OXIDATION: occurs when oxygen combines with another substance and new substances called oxides are formed ex: Rust is an iron oxide Many rocks contain iron and weaken or crumble when oxidation occurs. ACIDS: carbon dioxide can dissolve in the rain to form weak carbonic acid. When this acid comes into contact with certain minerals, a chemical change called carbonation occurs. ex: calcite is changed by this process. Acids are also formed from certain green plants, such as moss. Decaying organisms can produce acids, too. As acid seeps into the cracks in a rock, it can break the rock apart. WATER: most chemical weathering is caused by water. Water reacting with a mineral that has little water content is called hydrolysis ex: feldspar undergoes hydrolysis to become clay After they have undergone hydrolysis, the rocks may crumble apart if they are heated or dried even a little! Mechanical weathering involves only physical changes, such as alterations in size and shape. The chemical makeup of the rock does not change! Ex: ripping a piece of paper Also called “physical weathering” Temperature changes: rocks can be broken by changes in temperature. -heat causes expansion -cooling causes the rock to contract Repeated expansion and contracting can cause breakage over time Ice wedging- the repeated freezing and melting of water in the cracks of rocks causes ice wedging. When water freezes, it expands, causing the crack in the rock to widen. ex: potholes are caused by ice wedging Root Action: plant roots search for minerals and nutrients. They often grow into cracks in the rock. The pressure of the growing root causes the rocks to break apart over time. -Change in phase (mineral type) and composition due to the action of chemical agents. -Usually caused by reactions with oxygen, water, or acids. -Effects the structure and integrity of a rock -Breaks down rock into fragments --key stage in forming soil -doesn’t change chemical characteristics -physical decomposition of a rock into smaller fragments, each with the same properties as the original. -examples include frost wedging, pressure and temperature changes, and root damage http://www.brainpop.com/science/weather/weathering/quiz/