Weathering and erosion How did the Grand Canyon form?

Bellringer In your Science notebook write what you think would happen if you: - put water on a penny - put milk on a penny - put soda on a penny Write why you think the different liquids will cause a different change.

Objectives Describe how ice, water, wind, gravity, plants, and animals cause mechanical weathering. Describe how water, acids, and air cause chemical weathering of rocks.

Definitions Weathering – process where rock materials are broken down into smaller pieces by physical or chemical processes. Mechanical Weathering Breakdown of rock by physical means Similar to physical change Chemical Weathering Breakdown of rock by chemical means Similar to chemical change

Mechanical Weathering Ice The alternate freezing and thawing of soil and rock, called frost action, is a form of mechanical weathering. Abrasion Abrasion is the grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles. Wind, Water and Gravity Wind, water, and gravity carry rocks, causing them to abrade against one another Rocks shaped by wind blowing sand are called ventifacts.

Mechanical Weathering (cont.) Plants As a plant grows, the force of the expanding root becomes so strong that it can break a rock apart. Animals Almost any animal that burrows causes mechanical weathering by mixing and digging through soil and rock particles.

Chemical Weathering Water Acid Precipitation Acids in Groundwater Even hard rock, such as granite, can be broken down by water. The next slide shows how this can happen. Acid Precipitation The high level of acidity in acid precipitation can cause very rapid weathering of rock. Acids in Groundwater When acidic groundwater comes into contact with limestone, the limestone is dissolved and forms karst features.

Chemical Weathering (Cont.) Acids in Living Things Some living things, such as lichens, produce acids that can slowly break down rocks. Air Oxygen in the air causes oxidation. Oxidation is the chemical reaction in which an element, such as iron, combines with oxygen to form an oxide.

How is sand formed?

Examples Mechanical weathering Chemical weathering Can you think of an example of mechanical or chemical weathering? Mechanical weathering rocks sand smooth stones Chemical weathering rust (Oxidation) caves sinkholes

Differential Weathering Differential weathering is a process by which softer, less weather resistant rock wear away and leave harder, more weather resistant rock.

Weather and Climate What do you think would change how fast something weathers? Does temperature changes (climate) make a difference? Chemical weathering occurs in warm humid places faster. How high in the air is it? Places at higher elevations will have harsher conditions of precipitation. How steep is the mountain? Gravity will pull things down the mountain faster.

Get into Pairs Answer the following questions in your notebook: How can plants break down rock? If I told you there were tiny microscopic organisms that lived on rocks (called lichens) how do you think they cause the rock to break down? What are the three factors that determine the rate at which rock weathers?