Rocks and Weathering

1. Rocks and Weathering EQ: What is chemical and mechanical weathering?

2. Weathering • Weathering – process that breaks up rocks and other substances at the Earth’s surface • Two types of weathering, mechanical and chemical • Heat, cold, water, ice, oxygen and carbon dioxide contribute to weathering • Erosion – movement of rock particles by wind, water, ice or gravity

3. Mechanical Weathering • Mechanical weathering – rock is physically broken into smaller pieces • Caused by heating and cooling, freezing and thawing, growth of plants, actions of animals, and abrasion • Abrasion- grinding away of rock by rock particles carried by water, ice, wind or gravity • Works slowly , over long periods of time. Eventually wears away whole mountains

4. Mechanical Weathering • Ice wedging • Occurs in cold climates • Water seeps into a crack in the rock, freezes (expands)and thaws (contracts) repeatedly • This process expands the rock slowly and pieces crack off

5. Chemical Weathering • Chemical Weathering – process that breaks down rock through chemical changes. • Agents are water, oxygen, carbon dioxide, living organisms, and acid rain • Produces a different mineral makeup from the rock they came from i.e. – granite begins with minerals of feldspar, quartz and mica. After chemical weathering, granite changes feldspar to clay http://www.classzone.com/books/earth_science/terc/content/visualizations/es1202/es1202page01.cfm

6. Chemical Weathering • Creates holes or soft spots in the rock allowing it to break apart more easily • Chemical and mechanical weathering often work together. • Mechanical weathering breaks apart rock • This process exposes more surface area of the rock to chemical weathering

7. Five agents of Chemical Weathering • Water – most important agent of chemical weathering. Wears away rock by dissolving the rock, mixing it uniformly to make a solution • Oxygen – combines with iron in the presence of water. This is oxidation. Causes rust. This process makes the rock crumbly and gives it a red or brown color

8. Five agents of Chemical Weathering • Carbon Dioxide – found in our air. Dissolves in water and forms a weak acid called carbonic acid. Weathers marble and limestone • Living organisms – as plant roots grow they produce a weak acid that slowly dissolves rock around the roots • Acid Rain – cause is burning fossil fuels that pollute air with sulfur, carbon, and nitrogen compounds. The compounds mix with cloud vapor to form acid.

9. Rate of Weathering • Two factors that determine the rate • Type of Rock – • Depends on the minerals that make up the rock • Is the rock permeable – full of tiny, connected air spaces that allow chemicals to seep through it • Climate • Average weather conditions of an area • Hot and wet climates weather rock more quickly

10. Class Work and Homework Fill In What did I learn Confused Say Rock Shake Page G46 Read pages G 40 – G 45, #’S 1-5