WEATHERING How does the Earth Change?

Weathering — breaking down of rocks into sediments (smaller pieces). 2 methods - Mechanical (physical) Chemical

1) Mechanical Weathering — rocks are broken apart by a physical force. (Chemical formula of rock is not changed) Temperature Change- Heat e-x-p-a-n-d-s; cold contracts therefore the already existing cracks in the rocks become larger over time. This usually helps start the whole process.

Animals/Humans: digging, burrowing, building structures, mining

Ice Wedging Water seeps into a crack in a rock When the water freezes, it expands by 10% The force of the expansion applies pressure on the rock and causes it to crack more. This is called ice wedging

Root Pry Roots of trees and other plants enter into cracks of rocks. As the plants get bigger, so do the roots. The growing roots force the cracks further apart. Photo Source: http://www.uwm.edu/~caberg/mtp5/virft/glacial/pix/lrgD4-05.jpg

Abrasion Abrasion is the grinding away of rock by other rock particles. These rock particles can be carried by water, wind, ice or gravity. These particles scrape away at other rocks like sandpaper on wood as they rub or roll against the surface.

2) Chemical Weathering — chemical reactions break down rock (Chemical formula of rock changes)

Iron + Oxygen = Iron Oxide(rust) Oxidation Oxidation is when oxygen(O2) combines with other elements, especially iron (Fe) and forms rust Chemical reaction: Fe + O2 FeO2 Iron + Oxygen = Iron Oxide(rust)

Acid Rain Sulfur from industrial burning of coal dissolves in rain water forming weak sulfuric acid. This acid corrodes or dissolves rock, etches metal, and slowly destroys many other substances. Photo source: http://edutel.musenet.org:8042/gravenet/images/close_lamb.JPG

Carbonation Water and carbon dioxide combine to form carbonic acids which dissolve limestone to form caves (stalactites and stalagmites)

Plant Acids Mosses and lichens produce acids that dissolve rock. This allows them to live on the rock.

The rate of weathering depends on the type of rock and the climate (hot and wet, cold and dry, etc.).

Rate of Weathering Type of rock – the more permeable the rock the faster it weathers (permeable means it lets water in between the particles-like a sponge) Climate – average weather conditions of an area over time.

Rate of Weathering Chemical weathering - more rapid in warm/wet weather – rocks weather faster in climates that are hot and wet. Mechanical weathering – more rapid in cold climates where freezing and thawing are frequent (ice wedging)