Weathering Chemical and Physical & Erosion

All of Earth's energy is produced by the Earth’s core and the sun. Review: All of Earth's energy is produced by the Earth’s core and the sun. All rocks start as magma beneath the Earth's surface. The magma either cools above ground or below ground and turns into an igneous rock.

Build a Statue Someone wants to build a statue of you that needs to last forever! What type of rock should you make the statue out of?

Weathering Once Igneous rocks reach the surface they begin to experience Weathering.

Processes of Weathering: Two Types Mechanical (Physical) and Chemical

Definition of Mechanical Weathering The breaking down of rocks into smaller pieces without changing the rock’s chemical composition

Types of Mechanical Weathering

Types of Mechanical weathering 1. Biological activity- Living organisms. Plant roots & seeds grow into a crack and break it apart as the roots begin to spread and grow.

Weathering by plants

Weathering by sandmartins nesting in cliff

Types of Mechanical Weathering 2. Exfoliation- peeling away of outer layers. Heat from the sun causes the rocks to expand, contract, and then peel.

Example of exfoliation:

Types of Mechanical weathering 3. Frost wedging- is when water fills a crack and freezes, causing the rock to break apart

Frost wedging-

Types of Mechanical weathering 4. Abrasion- collision and grinding of rocks that results in breaking and wearing away of particles.

Water-carries particles that grind away at the rocks

Abrasion takes place in: fast-moving streams beaches subject to storm waves desert environments with high winds beneath glaciers that are loaded with fragments of rock.

Stronger rocks are harder to break down! What’s the point? Stronger rocks are harder to break down! Weaker rocks are easier to break down!

Observe the effects of mechanical weathering.

Chemical Weathering…. Definition: When the Chemical properties of rock are transformed through chemical reactions.

Types of Chemical Weathering 1. Reactions with Carbon Dioxide (Carbonation) Water combines with Carbon Dioxide to form a weak acid that eats away at rocks and minerals

Stalactites caused by carbonation Limestone is eaten away by acid and deposits as it drips from ceiling of cavern

Types of Chemical Weathering 2. Reactions with Water: Some minerals dissolve after reacting with water. The dissolved minerals form new secondary minerals

Feldspar combines with H2O to form a common clay called kaolin

Types of Chemical Weathering 3. Reactions with Oxygen = Oxidation When rocks containing Iron (Fe) interact with oxygen – O2 to form Iron Hydroxides (gaining oxygen, losing electrons)

Oxidation = rust!

Oxidation = rust!

Types of Chemical Weathering 4. Acid Precipitation When Coal and petroleum are burned, chemicals are released into the air and react with water molecules to form acid rain.

Types of Chemical Weathering Acid Rain

Types of Chemical Weathering 5. Plant acids – plants secrete acids that eat away the rock

Lichens and mosses grow on rocks and secrete weak acids that dissolve the surface