9.1 Weathering

Describe how potholes form. Describe how water flows down into cracks that form of potholes.

Weathering The process by which rock materials are broken down by physical or chemical processes.

Mechanical Weathering The breakdown of rock into smaller pieces by physical means. Ice Wedging One kind of frost action (the alternate freezing and thawing of soil and rock). Water goes between cracks in rock, freezes and pushes rock apart.

Abrasion The grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles. Example: using chalk on a board.

How can sediment transported in a stream cause abrasion? Sediment transported in a stream can cause abrasion when the moving sediment scrapes against other rocks or against the stream bed.

Exfoliation The process by which sheets of rock peel away from a large body of rock because pressure is removed.

Plant Growth The roots of plants grow in the cracks of rock, when the roots grow it expands the crack in the rock.

Animal Actions Animals that burrow cause mechanical weathering by moving the soil around to cause it to break down even farther.

How can animals cause mechanical weathering? Animals cause mechanical weathering by breaking soil into smaller particles through activities like burrowing.

Mechanical Weathering

Chemical Weathering The process by which rocks break down as a result of chemical reactions. Water Water dissolves some of the chemicals that make up rock. Takes thousands of years.

Acid Precipitation Rain, sleet, or snow that contains a higher concentration of acid than normal. Volcanoes, air pollution, coal, and oil combine with water in the atmosphere to form acids.

Acids in Groundwater Water flows through rock underground (groundwater) containing dilute acids and comes in contact with limestone. Can form caverns.

Acids in Living Things Dilute acids are in all living things. These acids come in contact with rock surface and react with chemicals.

Air Oxidation – Oxygen in the air reacts with the iron in the rocks. Example: When bike comes in contact with water for a long time and will rust.

What is oxidation? Oxidation is a type of chemical weathering that happens when an element combines with oxygen. Oxidation happens more quickly when water is present.

Chemical Weathering

Review Questions Describe three ways abrasion occurs in nature. Abrasion can be caused by wind, water, and gravity. 2. Describe the similarity in the ways tree roots and ice mechanically weather rock. Both tree roots and ice can force cracks in rocks to expand.

Compare the weathering processes that affect a rock at Earth’s surface and a rock underground. A rock on Earth’s surface tends to be weathered more because it is exposed to wind, precipitation, and the effects of gravity. A rock buried underground does not experience weathering from wind, precipitation, or gravity. If moss begins growing on a rock, how might the weathering of this rock change? The weathering of the rock might happen faster because the acids that the moss produces will speed up chemical weathering of the rock.

9.1 Review Mechanical weathering Chemical weathering Ice wedging Plant growth Exfoliation Acid precipitation Abrasion Weathering Oxidation