Published on November 9, 2009
Processes of Change : Processes of Change chemical weathering mechanical weathering deposition moving water glaciers waves wind gravity erosion Acids ice Weathering abrasion EQ: : EQ: How does weathering occur? EQ: Weathering : Weathering Describe three ways abrasion occurs in nature. List three things that cause chemical weathering of rocks. Describe the similarity in the ways tree roots and ice mechanically weather rock. Describe five (5) sources of chemical weathering. Weathering : Weathering Weathering is the process by which rock materials are broken down by the action of physical or chemical processes. Mechanical weathering is the breakdown of rock into smaller pieces by physical means. (ice, wind, water, gravity, plants, animals) Chemical weathering is the process by which rocks break down as a result of chemical reactions. Water, weak acids, and air can cause chemical weathering. 6 Agents of Mechanical Weathering : 6 Agents of Mechanical Weathering 1. Ice – water seeps into cracks during warm weather. When the temperature drops, the water freezes and expands, causing the ice to push against the sides of the crack. This causes the crack in the rock to widen. Abrasion – the grinding and wearing away of rock surfaces through mechanical action of other rock or sand pebbles. The three ways that can cause abrasion are wind, water, and gravity. Three Causes of Abrasion : Three Causes of Abrasion 2. Water – as rocks and pebbles roll along the bottom of flowing water, they bump and scrape against each other, causing these rocks to become rounded and smooth. 3. Wind – wind blows sand and silt against exposed rock eventually wearing away the rock’s surface. 4. Gravity – rocks grind against each other during a rock slide, creating smaller and smaller rock fragments. Anytime one rock hits another rock, abrasion takes place. Plants and Animals : Plants and Animals Some plants (#6) can easily break rocks. The roots grow through existing cracks in rocks. The growth causes the root to expand, forcing the crack to widen. The force can eventually split the rock apart. 7. Animals that live in the soil (moles, prairie dogs, insects, worms, gophers), cause a lot of weathering. By burrowing in the ground, these living creatures brake up soil and loosen rocks to be exposed to further weathering. 5 Agents of Chemical Weathering : 5 Agents of Chemical Weathering Common agents of chemical weathering are water, acids, and air. These agents weaken the bonds between minerals grains of the rock. 1. Water – can cause rock to be broken down and dissolve. Can take thousands of years to take place. 2. Air – the process of oxidation is a chemical reaction in which an element (iron) combines with oxygen, causing rust. (Weak Acids) - acid precipitation, acids in groundwater, acids in living things. Three Sources of Weak Acids : Three Sources of Weak Acids 3. Acid Precipitation – rain, sleet, or snow that contains a high concentration of acid. Normal precipitation is acidic, acid precipitation contains more acid than normal. 4. Acids in Groundwater – carbonic acid or sulfuric acid reacts with rocks in the ground, causing a chemical reaction, eating away at the rock. 5. Acids in Living Things – Lichens produce acids that slowly break down rock. Summary : Summary Ice wedging is a form of mechanical weathering in which water seeps into rock cracks and then freezes and expands. Wind, water, and gravity cause mechanical weathering by abrasion. Animals and plants cause mechanical weathering by turning the soil and breaking apart rocks. Water, acids, and air chemically weather rock by weakening the bonds between mineral grains of the rock. Rates of Weathering : Rates of Weathering What is differential weathering? How does surface area affect the rate of weathering? How does climate affect the rate of weathering? Why do mountaintops weather faster than rocks at sea level? Differential Weathering : Differential Weathering Differential weathering is a process by which softer, less weather resistant rocks wear away and leave harder, more weather resistant rocks behind. Hard rocks weather more slowly than softer rocks. The Shape of Rocks : The Shape of Rocks Weathering takes place on the outer surface of rocks. The more surface area exposed to weathering, the faster the rock will be worn down. As the surface area increases, the rate of weathering also increases. If a large rock is broken into smaller pieces, weathering of the rock happens much faster. The rate of weathering increases because a smaller rock has more surface area to volume than a larger rock. More of the smaller rock is exposed to the weathering process. Weathering and Climate : Weathering and Climate The rate of chemical weathering is faster in warm, humid climates than cold, dry climates because of oxidation. Oxidation happens when the temperature is higher and when water is present. Water increases the rate of mechanical (physical) weathering (ice wedging). Repeated changes in temperature (freeze, thaw, freeze, thaw) is a major factor in mechanical weathering. Weathering and Elevation : Weathering and Elevation Mountaintops weather faster than rocks at sea level because they are exposed to more wind, rain, and ice than rocks at sea level or lower elevations. The increase in wind, rain, and ice increases the effects of mechanical and chemical weathering. This increase in elevation causes peaks of mountains to weather faster. Gravity affects the rate of weathering: Steepness Rainwater Removal of sediment exposes new rock to weathering Abrasion Increased surface area of mountain Summary : Summary Hard rocks weather more slowly than softer rocks. The more surface area of a rock that is exposed to weathering, the faster the rock will be worn down. Chemical weathering occurs faster in warm, humid climates. Weathering occurs faster at high elevations because of an increase in ice, rain, and wind. From Bedrock to Soil : From Bedrock to Soil What is soil (loam) formed from? What is bedrock? What is soil structure? What is humus? What are soil horizons? The Source of Soil : The Source of Soil Soil is a loose mixture of small mineral fragments, organic matter, water, and air that can support the growth of vegetation. Bedrock is the layer of rock beneath soil. Parent rock is the rock formation that is the source of soil. Wind, water, and movements of glaciers can transport or move soil from one place to another. Soil Properties : Soil Properties Soil is made from different-sized materials. Soil texture is the soil quality is based on the proportions of soil particles. Soil texture can influence the ability of water move through the soil. Soil structure is the arrangement of soil particles. Soil Properties : Soil Properties Some soils are rich in nutrients, some are poor in nutrients. A soil’s ability to hold nutrients and to supply nutrients to a plant is describe as soil fertility. Humus is the dark, organic material formed in soil from the decayed remains of plants and animals. Soil Horizons : Soil Horizons Soil horizons are the horizontal layers of soil. The top layer of soil is called topsoil, containing more humus than the other layers of soil, rich in nutrients plants need to be healthy. Good topsoil is necessary for farming. Summary : Summary Soil (loam) is formed from the weathering of bedrock. Soil texture affects how soil can be worked for farming and how well water passes through it. The ability of soil to provide nutrients so that plants can survive and grow is called soil fertility. Soil Conservation : Soil Conservation Why is soil important? How can human activity affect soil erosion? What are three important benefits that soil provides? List five methods of soil conservation. Soil Conservation : Soil Conservation Soil can be endangered, just like plants and animals. It takes thousands of years for soil to form, it is not easy to replace. Soil conservation is a method to maintain the fertility of the soil by protecting the soil from erosion and nutrient loss. The Importance of Soil : The Importance of Soil Soil provides minerals and other nutrients for plant life. All animals get their energy from plants. Soil also provides a place for animals to live. The region a plant or animal lives is called a habitat. Soil holds water for plants to get the moisture or nutrients they need. The Processes of Change : The Processes of Change Lesson 18 Processes of Change (5) : Processes of Change (5) Weathering and erosion wear down, deposition fills in Earth’s surface. Weathering is the slow wearing away or breaking down of objects exposed to Earth’s atmosphere Two kinds of weathering act on Earth’s surface Mechanical weathering Chemical weathering Mechanical Weathering (4) : Mechanical Weathering (4) When objects are broken down into small pieces but their chemical makeup doesn’t change Wind and moving water are two main causes of mechanical weathering Repeated changes in temperature (freeze, melt, freeze, melt again) Chemical Weathering (5) : Chemical Weathering (5) Material of an object is changed Produces underground caverns Statue of Liberty needed repairs because of chemical weathering Examples: Rust Acid rain Erosion (5) : Erosion (5) The natural moving of material from one place to another Erosion transports weathered rock material Causes of Erosion: Moving water Gravity Wind Glaciers (moving rivers of ice) Waves Deposition (5) : Deposition (5) Land torn down in one place is “deposited” in another place Gravity can cause a landslide moving mud, rock and soil down a hill Wind erosion can move sand and deposit it in another area Glaciers (rivers of ice) scrape rocks off the land and moves them downhill Deposition (5) : Deposition (5) Glaciers will stop moving and even retreat and cut a steep U-shaped valley in the land Erosion caused by mountain rivers form V-shaped valleys Hurricanes create waves that erode beaches and cliffs Breaking of waves on a beach can wear it away. The larger the waves, the faster is the rate of erosion.