3.1 - Weathering Define mechanical and chemical weathering. Identify agents of weathering. Discuss factors that influence weathering.

Footprints on the Moon Footprints left on the Moon from one of the Apollo missions from 1963-1972. Why will these footprints always exist on the moon?

What is Weathering? Process that breaks solid rock into sediments

Himalayan Mtns. Appalachian Mtns

2 Main Types of Weathering Mechanical Weathering Chemical Weathering

Mechanical Weathering Breaks rocks down into smaller pieces without changing the chemical composition of the rock Some Agents of Mechanical Weathering Ice Wedging Abrasion Biological Weathering: Plants and Animals Human Activities

Ice Wedging

Abrasion Caused by rocks bumping into each other Makes rocks with sharp or jagged edges smooth and round Agents of Abrasion: Gravity Moving Water Wind Glaciers

Moving Water causes abrasion as particles in the water collide and bump against one another.

Wind Strong winds carrying pieces of sand can sandblast surfaces. http://education-portal.com/academy/lesson/wind-action-effects-on-the-desert-landscape.html#lesson

Glaciers Ice in glaciers carries many bits and pieces of rock. Rocks embedded at the bottom of the glacier scrape against the rocks below. The Burren County Clare, Ireland

Biological Weathering: Plants A plant’s roots can grow into a crack or fracture in rock and gradually grow larger, wedging open the crack.

Biological Weathering: Animals

Human activities Human activities are responsible for enormous amounts of mechanical weathering, by digging or blasting intorock to build homes, roads, subways, or to quarry stone.

Chemical Weathering works through chemical reactions that cause changes in the minerals of rock. Agents of Chemical Weathering Water (Hydrolysis) Carbon dioxide (Carbonation) Oxygen (oxidation) Acid Rain

Water Hydrolysis = water reacts with compounds in rock causing the compounds to dissolve/break apart Leaching = occurs as water breaks down compounds in rock and carries ions away Check out this animation of how water dissolves salt: http://www.northland.cc.mn.us/biology/Biology1111/animations/dissolve.html

Carbon Dioxide Carbon dioxide (CO2) combines with water as raindrops fall through the atmosphere to form carbonic acid. Carbonic acid dissolves rocks. Many limestone caves have been formed by the action of carbonic acid.

Oxygen Oxidation is a chemical reaction that takes place when oxygen reacts with another element. Minerals that are rich in iron break down as the iron oxidizes and forms new compounds. Iron oxide (rust) produces the red color in soils.

Acid Rain Pollutants, such as sulfur and nitrogen, from fossil fuel burning, create sulfuric acid and nitric acid. These acids react with water in the atmosphere to form acid rain.

Factors that Affect the Rate of Weathering Exposure to the Atmosphere Composition of Rock Climate

Exposure to the Atmosphere Rocks exposed to the atmosphere weather faster than rocks that remain unexposed. Mechanical weathering can speed up the rate of chemical weathering by increasing the surface area of rock.

Composition of Rock Different rock types weather at different rates. Igneous rocks (especially intrusive) weather slowly because it is hard for water to penetrate them. (ex. Granite) Other types of rock, such as limestone, are easily weathered because they dissolve in weak acids. Different minerals weather at different rates. Some minerals dissolve easily in water while others do not.

Which type of climate do you think has a higher rate of weathering? Climate is weather averaged over a long period of time. Chemical weathering increases as: Temperature increases: Chemical reactions proceed more rapidly at higher temperatures. Precipitation increases: Since water participates in both mechanical and chemical weathering, more water strongly increases weathering. Which type of climate do you think has a higher rate of weathering?