Weathering The “W” in W.E.D.L.

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

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.

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

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.

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.

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.

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.

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.

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.

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.

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.

Human impact on Weathering