Lab: What effect does increased surface area on weathering? 11-17-09 Topic: Weathering DN: Water is a major agent of chemical weathering because water cools the surrounding when it evaporates; dissolves many minerals that make up rocks; has a density of 1g/cm3; has the highest specific heat of all common Earth materials.

What causes the Earth to wear down? 1. PHYSICAL/ MECHANICAL WEATHERING – rocks are broken apart increasing the surface area. ROCK BEFORE WEATHERING = ROCK AFTER WEATHERING (just smaller)

What causes the Earth to wear down? 2. CHEMICAL WEATHERING – Chemical reactions CHANGE minerals. ROCK BEFORE WEATHERING ≠ ROCK AFTER WEATHERING

What are agents of Mechanical Weathering? Frost action Wave action Growth of plants abrasion Actions of animals Temperature changes What factors are involved in mechanical weathering? Changes in temperature and pressure.

PHYSICAL WEATHERING FROST ACTION – FROST WEDGING MOST IMPORTANT IN OUR CLIMATE (effect of temperature) FROST ACTION – FROST WEDGING ALTERNATE FREEZE AND THAW Water expands when frozen

ROCKS ARE CRACKED BY WATER FREEZING

EXAMPLES: POT HOLES AND FROST HEAVES

PHYSICAL WEATHERING – ROOT ACTION (effect of pressure) PLANT ROOTS UPLIFT AND FRACTURE ROCK

Wave Action Waves pounding against rocks - sand and rocks in the waves help to break up the shoreline.

PHYSICAL WEATHERING - ABRASION ROCK PARTICLES GRIND AGAINST ONE ANOTHER WATER WIND

Abrasion Both wind and water can cause abrasion as rock fragments bounce off each other.

Abrasion This “moon looking” picture of an Antarctic rock, shows weathering from the wind blown sands.

Stream abrasion ‘cutting tools’ of the stream which ‘downcut’ the stream’s V-shaped channel as they roll along.

Exfoliation: As pressure decreases the outer layers of rock are stripped away.

Actions of animals loosen and break apart rocks in soil

How does the hardness of a rock relate to the rate of weathering? Rate of physical weathering depends on the resistance (hardness) of the rock and on the kind of climate.

Chemical Weathering The process that breaks down rock through chemical changes. 1) Changes kind of material (ex. iron into iron oxide - rust) 2) Surface phenomenon - reactions occur on the surface of rocks, not inside them (usually). 3) Like most chemical reactions, water is required. 4) Hotter = faster 5) Fastest chemical weathering occurs in warm/moist climates

Agents of chemical weathering Water Oxygen Carbon dioxide Living organisms Acid rain

Water hydration - minerals in rocks combine with water.

Chemical Weathering: Rust What items have you seen rust? What can you do to prevent or reduce rusting?

EXAMPLES OF CHEMICAL WEATHERING OXIDATION OCCURS when free oxygen combines chemically with metallic elements (usually iron) AKA RUST

CARBONATION Water containing carbonic acid dissolves minerals (all rain water is slightly acidic) Most strongly affected are calcite minerals: limestone and marble

CARBONATION Stalagmites and stalactites

Living Organisms Plant-like organisms produce weak acids that slowly dissolve rock.

Acid Rain Compounds from burning coal, oil and gas react chemically with water forming acids.

Activity: What effect does increased surface area have on weathering?