http://www.brainpop.com/science/weather/weathering/ Lechuguilla Cave, New Mexico Types of Weathering Weathering describes the breaking of rocks into smaller fragments over a long period of time.

Weathering Close up of Cleopatra's Needle Effects man made structures and naturally occurring rocks like mountains wearing down into hills (over millions of years). Since being moved from Egypt to Central Park, NY-has eroded dramatically in 75 years. The markings can barely be read today even though it existed for 3500 years in Egypt.

FYI A trio of obelisks in London, Paris, and New York City. Each is made of red granite, stands about 21 meters (68 feet) high, weighs about 180 tons and is inscribed with Egyptian hieroglyphs.

TWO main types of weathering Mechanical (physical) weathering breaks apart rocks with temperature changes or pressure WITHOUT changing their chemical composition. Mt Mitchell, NC

Ice or Frost Wedging is an example of temperature change. Water freezes in cracks/spaces and expands, forcing the rocks apart. *The main cause of potholes in roads

Mountaintops are weathered quickly this way due to this b/c they are exposed to warm temperatures during the day and freezing at night.

Pressure This is the 2nd example of mechanical weathering. *Occurs when bedrock that is buried deep is pushed upward and then exposed at the surface. This is the 2nd example of mechanical weathering. Pieces peel away

It is then able to expand It is then able to expand. The outer layers are then stripped away called-exfoliation and can cause dome shaped formations. Liberty Cap in Yosemite National Park Half Dome in Yosemite National Park

It is then able to expand It is then able to expand. The outer layers are then stripped away called-exfoliation and can cause dome shaped formations.

*Plants can cause pressure too by wedging their roots down into the cracks of rocks. As the roots grow and expand, they can put pressure on the rocks to split.

Ex. When great amounts of pressure build up, the resulting mechanical effect can be that very large joints, or faults, are created.

Erosion of sedimentary rocks has created natural arches.

Salt weathering of building stone on the island of Gozo, Malta

Chemical weathering Occurs when rocks and minerals undergo changes in their composition as the result of chemical reactions. Caused by Water, Oxygen, CO2, and Acids Water is the main agent of chemical weathering b/c it dissolves some minerals and carries them away. This is called hydrolysis.

More chemical weathering types Oxidation can occur when rocks containing iron come into contact with oxygen and water. RUST will form. Rusted chains on the Golden Gate bridge Chemical Reactions between the rocks and water make new minerals. Ex: Rust on a metal chain Magnetite  Hematite (Contains iron)

A freshly broken rock shows differential chemical weathering (probably mostly oxidation) progressing inward. This piece of sandstone was found in glacial drift near Angelica, New York

When naturally occurring Plant ACIDS come into contact with rock, minerals will be dissolved. The rock is weaker without these and can break into smaller pieces more easily. Lichens secrete acids

Weathering both chemical and mechanical have made it difficult to read these tombstones.

Hoodoos of Bryce Canyon Park. Hoodoos formed over thousands of years by water, ice and gravity. Bryce Canyon gets between 10-19 inches of rain and 100 inches of snow a year and about 200 days of freezing/thawing a year. Also, due to the 4 different rock types-erosion occurs at different rates.

A row of hoodoos at Bryce Canyon National Park.

Effects of climate on weathering Chemical weathering Mechanical weathering Most rapid in areas with lots of moisture and warm temperatures Will occur rapidly in places where there is frequent freezing and thawing. Tropical areas Temperate, colder; mts The climate of a particular region determines how fast weathering occurs.

Why is weathering so important? Leads to soil formation.