Weathering and Erosion What is Weathering? • Weathering is the chemical and physical processes that break down rock on Earth’s surface. What does weathering do? • The forces of weathering breaks rocks into smaller and smaller pieces All of these contribute to weathering • • • • • Heat Cold Water Ice Oxygen and carbon dioxide in the atmosphere Mechanical Weathering • Mechanical weathering breaks rock into pieces by freezing and thawing, release of pressure, growth of plants, actions of animals, and abrasion. Ice Wedging • When ice melts, the water seeps deep into the rocks and refreezes. • The rock expands and contracts, breaking the rock down. Release of pressure • When a large piece of rock reaches the surface, the pressure on it is reduced. This causes the rock to flake off. Growth of plants • Plant roots can grow in cracks in rocks, as the roots grow it cracks the rocks more. Actions of animals • Animals can dig, burrow, or break down rocks. Abrasion • The grinding away of rock by rock particles carried by water, ice, wind, or gravity. Chemical Weathering • • • • • • The agents are: Water Oxygen Carbon dioxide Living things Acid rain Water • Water is the most important agent of chemical weathering. • Over time rocks will dissolve in water. How Does Oxygen Change Rocks? • Oxygen mixes with rocks and rusts. • It makes them soft and crumbly. • It makes the rock appear red. Carbon Dioxide • This type of chemical weathering causes acid rain. Living Things • Plants can grow in cracks. • The plant’s roots can dissolve rocks. Acid Rain • For over 150 years, people have been burning coal, oil, and gas. • Burning these fossil fuels can pollute the air with acid. • These acids mix with rain and fall as acid rain. Rate of Weathering • Two things affect rate: -Type of rock -Climate Types of Rock • Rocks with lots of pores weather easiest. • These rocks are said to be permeable. Climate • Climate is the average weather conditions in an area. • Chemical reactions occur faster in areas that are hot and wet. What is Erosion? • Erosion is the movement of rock particles by wind, water, ice or gravity. Wind Erosion • Fast moving wind can carry sand and dust that scour and weather the surfaces they strike. Water Erosion • Sediments being moved by running water. (river, stream, flash flood, etc.) Ice Erosion • Glaciers move over land moving a depositing sediments. Gravity Erosion • This is the underlying force of erosion and deposition. Cause glaciers to move, and sediments to leave wind or water, or causes landslides and mudflows. What is Deposition? • When moving water, ice, wind, or gravity drops a load of Earth materials in a new place. Review • 1. What factors cause mechanical weathering? • 2. Name 3 things that cause chemical weathering. • 3. What factors affect the rate of weathering.