Geology 101. Reading Guides for Chapters 6 and 12

Transcription

1 Geology 101 Name Chapter 6: Weathering and Soils (p. 160): Reading Guides for Chapters 6 and 12 This chapter is about the processes involved in the disintegration of rock. Weathering is often mistaken for erosion which is the removal and transportation of weathered rock materials. These processes are clearly related to each other, but we will attempt to use these terms correctly. The photograph of Arches National Park on page 162 shows an arch that was created by both the weathering of the rock and the subsequent removal of the weathered rock to create the arch. Weathering (page 162): What is the difference between mechanical and chemical weathering? Mechanical Weathering (page 163): What are some ways in which mechanical weathering occurs? Chemical Weathering: (p. 166): For those who have had a chemistry course, you may be able to follow the chemical formulas in this section, but since most of the students in this class have not had a previous chemistry course, I will not expect you to know these formulas or be able to use them. If you have questions or would like to know more about them, see me during an office hour. In this section three types of chemical weathering are discussed, but the authors did not label these processes. The first type of chemical weathering is oxidation. This is formed by the oxidation of iron-rich minerals in rocks. This oxidation often creates a or color in the soils or the weathered products. The second type of chemical weathering is dissolution. In this type of weathering soluble ions are dissolved by acidic water. What two common types of rocks are most susceptible to this weathering? How is the acidic water formed in natural environments? The third type of chemical weathering is hydrolysis. In this type of weathering silica-based rocks, such as granite are converted to other minerals, such as clay. Hydrolysis is also dependent on acidic water to initiate the reaction. An important concept is that hydrolysis happens at a faster rate when the temperature of the water is warmer and when the water is more acidic.

2 Most sandstones (a common sedimentary rock that we will study later in the quarter) are composed of grains of quartz sand. Why is quartz more common in sand than the abundance of quartz in un-weathered rock? Explain how spheroidal weathering happens. In review: List the three primary chemical weathering processes: 1) 2) 3) Rates of Weathering (page168): In general, rocks with more mafic minerals (dark colored) will chemically weather (faster/slower) than more felsic minerals. We can explain this trend because mafic minerals formed at higher temperatures, so they are the (least/most) stable at the earth s surface. (Hint: the minerals olivine and pyroxene are most common in mafic rocks, while quartz is most common in felsic rocks. Use the figure on page 110 and the discussion on page 168 to answer the questions above. If you need help, let me know.) What role does climate have in promoting chemical weathering? What type of climate does chemical weathering occurs at the fastest rate? Slowest rate? 2

3 Dramatic landscapes are formed in places such as Bryce Canyon National Park from differential weathering and erosion. Explain why some rocks may weather faster than others in a place that has the same climate. (2 sections) Soil and Controls of Soil Formation (pages170 and 171) In most places, the Earth s surface is covered by a layer of weathered debris. This layer is called. Soils are a special part of this zone. What is soil? What is humus? What are the primary controls of soil formation? The Soil Profile and Classifying Soils (pages ) will not be covered on the exam. If you are a Natural Resources major or your are considering a major in agriculture, you may want to read these sections. Impact of Human Activities on Soil (page 176): This is an important topic for all of us since our food availability is dependent on healthy soils, but read the part on Erosion: Losing a Vital Resource. What is the primary process that erodes soil? Weathering and Ore Deposits (page 180): You will not be tested over this section, but you might find it interesting to find out how products such as aluminum foil is mined from weathering products. 3

4 Chapter 12: Mass Wasting: The Work of Gravity (page 318) The Importance of Mass Wasting (page 320) Most the concepts in this section are relatively common-sense, but are important in understanding how the Earth works. On page 321 the diagram of the Grand Canyon indicates that mass wasting is responsible for most of the erosion in the canyon and only the narrow section directly above the river is due to the movement of sediment by the Colorado River. Also, one can see the different slopes created by the differential weathering and erosion of various rock types. It is also logical the erosion processes tend to produce a flatter landscape over time. If internal processes that uplift mountains stops, erosion processes reduce the angle of the slopes over time. Controls and Triggers of Mass wasting (page 322): We may read a newspaper account of a landslide and the article may something like: the slide was caused by the heavy downpour of rain during the past 24 hours. In the introduction to this section the authors make a point that the rain was mostly like a and that there could be multiple causes for a landslide. What is the role of water in promoting mass wasting? The angle of repose is defined as: The angle depends on the and of the particles. It is important to note that the angle of repose concept applies to particles not consolidated rock slopes. Besides adding water to slopes and oversteepening, what are two other triggers that may initiate mass wasting events? Explain how each one initiates a movement. Some landslides happen without a discernible trigger. What process that we have studies in this reading guide may be responsible for these mass movements? Classification of Mass-Wasting Processes (page 326): The classification of landslides is based on the type of materials, the type of motion, and to some degree the rate of motion. 4

5 What are the three types of motion of a landslide? The very slow movement of the regolith is termed. Rapid Forms of Mass Wasting and Slow Movements (pages 327 to the end of the chapter) 1. A mass movement that rotates as a block along a concave slip plane. Usually occurs in cohesive materials. 2. Relatively dry mass movements. They ooze downslope with a relatively high viscosity 3. The Gros Ventre mass movement is an example. 4. Described as wet concrete to soupy mixture not much thicker than muddy water. The type most often called a mudslide. 5. A very slow type of mass movement that affects slopes at most latitudes. Freezing and thawing is one way this process occurs. 6. The fastest type of mass movement occurs when loose sediment or rocks breaks free 7. This type of mss movement moves along a defined slip plane. Normally parts of the mass hold together. 8. Common in semi-arid regions. Similar to mudflows but particles are larger. A. creep B. solifluction C. rock slide D. slump E. debris flow F. earthflow G. fall H. slide What are some characteristics of slumps? 5