1. Weathering
The “W” in W.E.D.L.

2. Weathering
Weathering - The process of breaking down rocks into smaller pieces.
Two Types:
Mechanical Weathering - Physically breaking rocks.
Chemical Weathering - Chemically changing rocks.

3. Mechanical Weathering
Ice Wedging/Frost Action - The repeated freezing and melting of water.
Water seeps into a small opening or crack. When it freezes it expands and the crack widens. The constant freezing and melting breaks the rock apart.

4. Mechanical Weathering
Organic Activity/Roots
Roots of plants can hold soil.
Root Pry--As plant roots grow they expand the crack.

5. Mechanical Weathering
Thermal Expansion
The changes in temp. from night to day causes particles of rock to break and flake off.
Exfoliation - When the particles break off in parallel sheets.

6. Mechanical Weathering
Abrasion -Wearing away of rocks by particles carried by wind, water or other forces.
In deserts wind easily moves sand particles and creates unusual shapes.
River water carries particles that wear sharp rocks into smooth round stones.

7. Mechanical Weathering
Mass Wasting - Landslide, Mudslide, Lahars
Gravity - Pulls loosened rock down a cliff. As the rocks fall they collide and break into smaller pieces. Occurs on steep slopes and where roads have been cut thru a mountain. Creates Talus slopes.

8. Chemical Weathering Changes occur in the chemical makeup of the rocks.
Water can dissolve the minerals that hold rocks together.
Minerals in a rock absorb the water like a sponge and break apart.
Water mixed with acids cause minerals to change the rock into a new rock.

9. Chemical Weathering Oxidation
Oxygen chemically combines with another substance.
Iron combines with O2 in the air and makes iron oxide (rust). The rocks turn red, this indicates oxidation is occurring.
Qxygen mixes with Copper it makes rocks green.

10. Chemical Weathering Carbonation Acid Rain/Sulfuric Acid
Carbon dioxide in the air dissolves in rain, a weak carbonic acid is formed.
This weak acid is able to dissolve some kinds of rocks, like feldspar and limestone.
This makes Caves and Karst topography.
Acid Rain/Sulfuric Acid
Forms from the burning of coal.
Strong acid that will wear away and corrode rocks, metal and other material quickly.
Acid Rain also kills forests & lakes/ponds.

11. Chemical Weathering Plant Acids
Lichens and mosses produce a weak acid that may dissolve rocks and minerals.
The rocks break into smaller and smaller pieces.
This process, is important in soil formation.

12. Climate & Rate of Weathering
The rate of weathering depends on: the type of rock and the climate it is in.
The composition of the Rock
Type of minerals in the rock
The climate
Rocks in cool or warm dry climates weathers slowly.
Rocks in warm, humid climates with moisture and weak plant acids will dissolve quickly
Amount of time rock is exposed.
Amount of exposed surface area
As rocks break down more surface area is exposed and it breaks down faster.

13. Human impact on Weathering