2 Weathering ProcessesWeathering - the natural process by which atmospheric and environmental agents, such as wind, rain, and temperature changes, disintegrate and decompose rock at or near the surface.There are two main types of weathering processes—mechanical weathering and chemical weathering.Each type of weathering has different effects on rock.
3 Mechanical Weathering Mechanical weathering is strictly a physical process and does not change the composition of the rock.Common agents of mechanical weathering are ice, plants and animals, gravity, running water, and wind.Physical changes within the rock itself affect mechanical weathering.
5 Heat causes expansion; cooling causes contraction. Thermal expansionRepeated daily heating and cooling of rock;Heat causes expansion; cooling causes contraction.Expanding and contracting causes cracks.
6 AbrasionIs the grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particlesAbrasion is caused by gravity, running water, and wind.
7 Organic Wedging Plants and animals Root wedging widens fractures in rock.
8 Organic Activity Digging and burrowing activities. Earthworms and other animals that move soil expose new rock surfaces to both mechanical and chemical weathering.
9 Chemical Weathering Chemical alteration of minerals. Chemical reactions commonly occur between rock, water, carbon dioxide, oxygen, and acids.Most effective in a warm, humid climate.Chemical weathering changes both the composition and physical appearance of the rock.
10 CHEMICAL WEATHERING OXIDATION ROCKS / MINERALS CHEMICALLY REACT WITH THE OXYGEN IN THE ATMOSPHERE, CAUSING A DECOMPOSITION ON THE MATERIALS
11 CHEMICAL WEATHERINGDissolution - mineral completely dissolves, leaving only ions in solution.
12 Section 2 Rates of Weathering Factors influencing Weathering Rates The processes of mechanical and chemical weathering generally work very slowly.Rock Structures – chemical/mineral composition, Physical featuresTopographyClimate
21 O horizon Organic rich, humus Organic mineral matterOrganic rich, humusDecaying organic matter releases nutrients
22 A horizon Organic rich, often dark in color Zone of leaching (lots of chemical weathering)Organic rich, often dark in colorDecaying organic matter releases nutrients
23 B horizon High clay content, reddish color from iron. Zone of accumulation – minerals (clay and iron oxide) are washed down from above.High clay content, reddish color from iron.Able to retain moisture because of clay content
24 C horizon Parent material – grading from weathered to unweathered. Parent material can be:BedrockStream sedimentsVolcanic ash
25 Controls of Soil Formation Parent MaterialTimeClimatePlants and AnimalsSlope
26 Soil and ClimateClimate is one of the most important factors that influences soil formation.Climate determines the weathering processes that occur in a region.These weathering processes, in turn, help determine the composition of soil.
27 Soil and TopographyBecause rainwater runs down slopes, much of the topsoil of the slope washes away.Therefore, the soil at the top and bottom of a slope tends to be thicker than the soil on the slope.Topsoil that remains on a slope is often too thin to support dense plant growth.
28 Section 4 Erosionerosion a process in which the materials of Earth’s surface are loosened, dissolved, or worn away and transported from one place to another by a natural agent, such as wind, water, ice, or gravityWhen rock weathers, the resulting rock particles do not always stay near the parent rock.Various forces may move weathered fragments of rock away from where the weathering occurred.
29 Soil ErosionOrdinarily, new soil forms about as fast as existing soil erodes.Some farming and ranching practices increase soil erosion.Soil erosion is considered by some scientists to be the greatest environmental problem that faces the world today.
30 Soil ConservationCertain farming techniques can increase the rate of erosion.Land clearing accelerates topsoil erosions.Soil erosion can be prevented by soil conservation methods