GEOL 1330 (Lecture 8 - Weathering and Soil)
GEOL 1330 (Lecture 8 - Weathering and Soil) GEOL 1330
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This 3 page Class Notes was uploaded by Julian Quesada on Monday February 22, 2016. The Class Notes belongs to GEOL 1330 at University of Houston taught by Dr. Daniel Hauptvogel in Spring 2016. Since its upload, it has received 34 views. For similar materials see Physical Geology in Geology at University of Houston.
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Date Created: 02/22/16
GEOL 1330 LECTURE 8 WEATHERING AND SOIL Physical Weathering -Weathering: The physical and chemical processes that breakdown rocks -Physical Weathering: processes that physically break apart a rock (river, avalanche, etc.) -Chemical weathering: chemical transformation of a rock into new compounds (rust, melting, etc.) -Physical (mechanical) weathering includes: -Frost wedging: Occurs when water freezes in the cracks of rocks -As water freezes it expands, and can cause the rocks to break -Sheeting/exfoliation: Occurs due to a decrease in pressure -Biological activity can wedge rocks apart as plant roots grow in cracks (root wedging) -Can also create acids to chemically weather rocks -Other physical weathering processes include: -Tectonic stresses -Thermal stresses -Freezing and thawing -Abrasion by wind/water -Powerful wave action at the shoreline -Salt crystallization in cracks -Expansion/contraction of wet/dry clay -Types of chemical weathering include -Dissolution: happens when a solid (rocks and minerals is dissolved into ions -Water is actually a great solvent -So is acid -Oxidation: occurs when an element loses electrons -e.g. rusting -Responsible for red coloring in many rocks -Hydrolysis: occurs when hydrogen ions replace other positive ions (cations) found in the crystal structure -The primary way silicate minerals decompose -Occurs in water or acidic conditions -This replacement creates new minerals -Water with a lot of dissolved ions is referred to as "hard" water -If you have hard water at home, the dissolved ions react with soap, making it seem like you can't get soap off Weathering Rates -The rate at which rocks and minerals weather is primarily controlled by -Top Hat Question -These gravestones were created around the same time, yet look different from one another. What is the best explanation? (The gravestone on the right has an eroded face, whereas the one on the left looks normal) -The rocks used for the gravestone on the left is more resistant to weathering -Rock on left is granite and rock on right is marble. Marble is calcite rich which is very susceptible to weathering -Differential weathering*** is when one material weathers easier and faster than another -Usually due to differences in mineral composition and atomic structure Soil Formation -Weathering is a key process in the formation of soil -Soil: combination of minerals, organic matter, air, and water -Soil formation is controlled by -Parent material: Affects the rate of weathering (and thus soil formation) and fertility -Time: The longer a soil has been forming, the thicker it becomes and the less it resembles the parent material -Climate: the most important factor in soil development -Temperature and precipitation -Hot and wet = heavy chemical weathering -Cold and dry = heavy physical weathering -Plants and Animals: Affect the physical and chemical properties -Mixing of the soil by borrowing organisms -Most organic matter comes from plants -Topography: Soils develop poorly on steep topography -Top Hat Question -Which do you think is the primary factor in soil -Climate -Precipitation and temp control break down of rocks and therefore, production of soil
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