Weathering, Erosion, and Soil Formation

Standard: S6E5 Students will investigate the scientific view of how the earth’s surface is formed. Describe processes that change rocks and the surface of the earth. Explain the effects of physical processes (plate tectonics, erosion, deposition, volcanic eruption, gravity) on geological features including oceans (composition, currents, and tides). Describe soil as consisting of weathered rocks and decomposed organic material. Explain the effects of human activity on the erosion of the earth’s surface. Describe methods of conserving natural resources such as water, soil, and air.

Rocks & Weathering Essential Questions 1. What is weathering? 2. What is erosion? 3. What is the difference between weathering and erosion?

Weathering The process that breaks down rock and other substances at Earth’s surface. Items contributing to weathering: Heat, cold, water, and ice Oxygen and carbon dioxide in the atmosphere

Types of Weathering Mechanical Weathering – rock is physically broken into smaller pieces. The smaller rock pieces have the same composition as the rock they come from. Chemical Weathering – rocks break down through chemical changes. Produces new minerals as it breaks down. Creates holes or soft spots in rock so the rock breaks apart more easily.

Mechanical Weathering: Causes of mechanical weathering include: Freezing and thawing Release of pressure Plant growth Actions of animals abrasion See Page 178-179 in Science Textbook

Mechanical Weathering The causes of mechanical weathering include freezing and thawing, release of pressure, plant growth, actions of animals, and abrasion. Abrasion – the grinding away of rock by rock particles carried by water, ice, wind, or gravity. See text p. 179

Mechanical Weathering Ice wedging- wedges of ice in rocks widen and deepen. When the ice melts, the water seeps deeper into the cracks. With repeated freezing and thawing, the cracks slowly expand until pieces of rock break off.

Chemical Weathering Causes of chemical weathering include: The action of water oxygen carbon dioxide living organisms acid rain. See science textbook p. 180-181

How does water affect weathering? Rainwater can dissolve minerals that bind rock together. Mudpots: Mudpots are similar to hot springs except that the groundwater has dissolved rocks into clay, creating mud. High levels of acid in the water help to dissolve the rocks quickly. The color of the mud often varies depending on the minerals that are in the rocks. http://www.grandeguides.com/images/05716_nps_mud_pot_near_sulfur_cauldron__mud_volcano_area__harlan_kredit__1974.jpg

Weathering and Erosion The forces that wear down mountains also cause bicycles to rust, paint to peel, sidewalks to crack, and potholes to form. These forces break rocks into smaller and smaller pieces.

Two kinds of Weathering: Mechanical weathering- where rock is physically broken into smaller pieces. Chemical weathering- Process that breaks down rock through chemical changes. (causes of chemical weathering include the action of water, oxygen, carbon dioxide, living organisms, and acid rain)

Chemical Weathering Can produce new minerals as it breaks down rock. (EXAMPLE: granite is made of minerals, including feldspar, quartz, and mica.) As a result of chemical weathering granite eventually changes the feldspar minerals to clay minerals. Creates holes or soft spots in rock so the rock breaks apart more easily.

Chemical Weathering & Water Water weathers rock by dissolving it. When the rock dissolves in water, it mixes uniformly throughout the water to make a solution. Over time, many rocks will dissolve in water.

Chemical Weathering & Oxygen Iron combines with oxygen in the presence of water in a process called oxidation. This process is called rust. (Example: you leave your bicycle outside in the rain, oxygen combines with the iron parts and rust takes place.)

How does oxygen and carbon dioxide in the atmosphere affect weathering?

Chemical Weathering & Carbon Dioxide: Carbon dioxide dissolves in rainwater and in water that sinks through air pockets in the soil. The result is a weak acid called carbonic acid. Carbonic Acid- easily weathers rocks such as marble and limestone.

Chemical Weathering & Living Organisms Small seed sometimes fall on rocks and sprout. The roots push into cracks in the rock. As the roots grow, they produce weak acids that slowly dissolve rock around the roots. Lichens – plantlike organisms that grow on rocks– also produce weak acids that chemically weather rock.

Lichens—break down rock and other materials.

Chemical Weathering & Acid Rain Burning of coal, oil, and gas for energy pollutes the air with sulfur, carbon, and nitrogen. These compounds react chemically with the water vapor in clouds---forming acids. These acids mix with raindrops and fall as acid rain. Acid rain causes very rapid chemical weathering.

Rate of Weathering: The most important factors that determine the rate at which weathering occurs are the type of rock and the climate. Type of Rock- minerals making up a rock determines how fast it will weather. Permeable (material full of tiny air spaces that allow water to seep through) rock weathers at a fast rate because water seeps through the spaces and it dissolves. Climate – average weather conditions. Both chemical and mechanical weathering occur faster in wet climates. Rainfall provides water needed for chemical changes as well as for freezing and thawing.

Definition: Two types: 1) Mechanical - rock is physically broken into smaller pieces. 2) Chemical - rock is broken down through chemical changes. Characteristics: The processes that break down rock and other substances at Earth’s surface. Weathering Mechanical: abrasion ice wedging Chemical: water, oxygen (oxidation), carbon dioxide, living organisms, acid rain. Magma lava melting Examples: Non-Examples:

What is Erosion? The removal of rock particles by wind, water, ice, or gravity. Weathering and erosion work together with deposition continuously to wear down and carry away and build up the rocks at Earth’s surface. The weathering & erosion we see today also shaped Earth’s surface millions of years ago.

Definition: Characteristics The removal of rock particles by wind, water, ice, or gravity. Works with weathering to continuously wear down and carry away rocks at Earth’s surface. Works with weathering to continuously wear down and carry away rocks at Earth’s surface. Uniformitarianism - states that the same processes that operate today operated in the past. Erosion Wave action, wind Mass Movement Landslides Mudflows Slump Creep Dump trucks Bulldozers See textbook p 205-207 Examples: Non-Examples: