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.