G2-1

Rocks and Weathering

EQ: What is chemical and mechanical weathering?

G2-1

Weathering

• Weathering – process that breaks up rocks on the Earth’s surface– 2 Types: mechanical (physical) and chemical– Causes: heat, cold, water, ice, oxygen, carbon

dioxide

• Erosion – movement of rock particles by wind, water, ice or gravity

EQ: What is chemical and mechanical

weathering?

G2-1

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.

EQ: What is chemical and mechanical weathering?

G2-1

Mechanical Weathering

• Ice wedging – Water seeps into a crack in the rock, freezes

(expands) and thaws (contracts) repeatedly – Pieces begin to crack

EQ: What is chemical and mechanical weathering?

G2-1

Chemical Weathering

• Chemical Weathering – breakdown of rock through chemical changes.– 5 agents: water, oxygen, carbon dioxide, living

organisms, and acid rain– Produces a different mineral makeup from the

rock they came fromi.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

EQ: What is chemical and mechanical weathering?

G2-1

Chemical Weathering

• Creates holes or soft spots in the rock.• Chemical and mechanical weathering often

work together.– Mechanical breaks apart rock,– More surface area for chemicals to work!

EQ: What is chemical and mechanical

weathering?

G2-1

5 Agents of Chemical Weathering

• Water – most important! Dissolves rock.• Oxygen – combines with iron in the presence

of water (OXIDATION). Causes rust. Makes the rock crumbly, gives it a red/brown color.

• Carbon dioxide-found in air. Mixes water and forms carbonic acid. Weathers marble and limestone.

EQ: What is chemical and mechanical weathering?

G2-1

5 Agents of Chemical Weathering

• Living organisms – plant roots produce a weak acid that slowly dissolves rock.

• Acid Rain – fossil fuels pollute air with sulfur, carbon, and nitrogen compounds. The compounds mix with cloud vapor to form acid.

EQ: What is chemical and mechanical weathering?

G2-1

Rate of Weathering

• Two factors that determine the rate– Type of Rock –• What is it made of?• Is the rock permeable?- full of tiny, connected air

spaces that allow chemicals to seep through it

– Climate• weather conditions• Hot and wet climates weather rock more quickly

EQ: What is chemical and mechanical weathering?

G2-1

Class Work and Homework

Fill InWhat did I learnConfusedSay

Rock Shake Page G46

Read pages G 40 – G 45, #’S 1-5

EQ: What is chemical and mechanical

weathering?