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The Process of Weathering Rocks. Weathering. The breaking down of rock into smaller pieces that remain next to each other. Weathering forms sediments . There are two types of weathering. Two Types of Weathering.
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Weathering • The breaking down of rock into smaller pieces that remain next to each other. • Weathering forms sediments. • There are two types of weathering.
Two Types of Weathering • Mechanical weathering is the breaking down of rock without any change in the chemical composition of the rock. • Sometimes called “physical” weathering • Rock is torn apart by physical force, rather than by chemical breakdown • Smaller pieces do not move to a new location, but remain next to one another until erosion carries them away.
Mechanical Weathering: Ice Wedging • Water enters the cracks in rocks and then freezes and expands about 10%. • The ice puts stress on the walls around the cracks and causes cracks to get deeper and wider. • Water can flow deeper into the rock as the ice thaws. As the cycle repeats, rocks grow weaker over time. • Along the cracks, the rock will break into angular pieces over time.
Mechanical Weathering :Exfoliation • Rocks formed deep in the Earth are under a huge amount of pressure. • When the overlying rock is removed by erosion, pressure is released and the once buried rocks are exposed. • Expansion occurs along the outer parts of rocks. This stress will cause fractures to form parallel to the rock surface. • Along the exposed rock fractures, sheets of rock will break away.
MechanicalWeathering: Thermal • Thermal weathering is a result of extreme changes in temperature that causes the expansion or contraction of rock. • Common in deserts, where it is hot in the day and cold at night; different minerals expand and contract at different rates causing the rock to split • The outer layers peel off into thin sheets.
Mechanical Weathering : Biotic (Force) • Biotic weathering is caused by living organisms. • Most often, plant roots are the cause. • They act as a wedge, widening and extending the cracks. • Digging animals can also cause weathering.
Two Types of Weathering 2. Chemical weathering is the breaking down of rock into smaller pieces because of chemical changes within the rock. • Rock reacts with water, gases, and solutions (may be acidic); these reactions will add or remove elements from minerals. • Rocks fall apart because the bonds holding them together are broken down by chemical reactions.
Chemical Weathering: Oxidation • When oxygen combines with other elements in rocks, a chemical reaction known as oxidation occurs and new types of rock are formed. • The new types of rock are easier to break apart because they are much softer than the original substances. • A reddish-brown coloration on the surface is called rusting.
Chemical Weathering: Hydrolysis • Hydrolysis is the weathering reaction that occurs when water and chemical compounds in a rock meet. • This results in the decomposition of the rock surface by forming new compounds. • The most common reaction is the hydrolysis of feldspars producing clay (kaolinite).
Chemical Weathering: Carbonation • When carbon dioxide reacts with water or rain, carbonation occurs and a weak carbonic acid is formed. • This is the same acid found in soda. • The acid is too weak to harm plants and animals, but slowly causes feldspars and limestone to decompose. • New types of softer substances are formed within the rocks.
Chemical Weathering: Biotic (Acid) • Lichens and similar plants live on the surfaces of rocks. • Plants lower the local pH to make it more acidic. • Their roots give off a chemical that dissolves rocks and minerals.
