This Document Contains Chapters 3 to 6 Chapter 3 Minerals—The Building Blocks of Rocks Chapter Outline 3.1 Introduction 3.2 Matter–What Is It? 3.3 Explore the World of Minerals 3.4 Mineral Groups Recognized by Geologists 3.5 Mineral Identification GEO-INSIGHT 3.1: The Precious Metals 3.6 Rock-Forming Minerals GEO-FOCUS 3.1: The Industrial Minerals 3.7 How Do Minerals Form? 3.8 Economic Geology Key Concepts Review Learning Objectives Upon completion of this material, the student should understand the following. • All matter, including minerals, is made up of atoms that bond to form elements and compounds. • Geologists have a specific definition for the term mineral. • You can distinguish minerals from other naturally occurring and manufactured substances. • Minerals are incredibly varied, yet only a few are particularly common. • Geologists use physical properties such as color, hardness, and density to identify minerals. • Minerals originate in various ways and under varied conditions. • Some minerals, designated rock-forming minerals, are particularly common in rocks, whereas others are found in small amounts. • Some minerals and rocks are important natural resources that are essential to industrialized societies. Chapter Summary • Matter is composed of chemical elements, each of which consists of atoms. Protons and neutrons are present in an atom’s nucleus, and electrons orbit around the nucleus in electron shells. • The number of protons in an atom’s nucleus determines its atomic number. The atomic mass number is the number of protons plus neutrons in the nucleus. Bonding results when atoms join with other atoms; different elements bond to form compounds. With few exceptions, minerals are compounds. • Ionic and covalent bonds are most common in minerals, but metallic and van der Waals bonds are found in some. • Minerals are crystalline solids, which means that they possess an ordered internal arrangement of atoms. • Mineral composition is indicated by a chemical formula, such as SiO2 for quartz. • Some minerals have a range of compositions because some elements substitute for one another if their atoms are about the same size and have the same electrical charge. • About 3,800 minerals are known, and most of them are silicates. The two types of silicates are ferromagnesian and nonferromagnesian. • In addition to silicates, geologists recognize carbonates, native elements, hydroxides, oxides, phosphates, halides, sulfates, and sulfides. • Structure and composition control the physical properties of minerals, such as luster, crystal form, hardness, color, cleavage, fracture, and specific gravity. • Several processes account for the origin of minerals, including cooling magma and lava, weathering, evaporation of seawater, metamorphism, and organisms using dissolved substances in seawater to build their shells. • A few minerals, designated rock-forming minerals, are common enough in rocks to be essential in their identification and classification. Most rock-forming minerals are silicates, but some carbonates are also common. • Many resources are concentrations of minerals or rocks of economic importance. They are further characterized as metallic resources, nonmetallic resources (industrial minerals), and energy resources. • Reserves are that part of the resource base that can be extracted profitably. Distinguishing a resource from a reserve depends on market price, labor costs, geographic location, and developments in science and technology. • The United States must import many resources to maintain its industrial capacity. Canada is more self-reliant, but it too must import some commodities. Enrichment Topics Topic 1. Mega Crystals. In “the Sistine Chapel of Crystals,” gypsum crystals up to 50 feet long are found. They are the largest natural crystals on Earth! How did these crystals form? Unlike most caves, these caves are hot! Why are they hot? There is a plan to open the cave for tourists. How can this be done without destroying this beautiful natural resource? http://www.crystalinks.com/mexicocrystals.html Topic 2. Theory of the Atom. Although the theory of matter as a composite of extremely small, independent particulate units known as atoms originated with Greek philosophers, it is only recently that scientists have been able to observe and photograph, and even manipulate single atoms and their movement using the scanning electron microscope. Thus, until the invention of the electron microscope, the theory of the atom and all theory based on it were deduced from observation and experiment, the subject never having been observed. This is an example of how evidence can be used to create hypotheses and theories. Topic 3. A Gold Rush in Greek Mythology. Strabo, an ancient Greek historian and geographer, wrote that the inhabitants of Colchis, a country on the eastern shore of the Black Sea, used to separate gold carried down from the mountains in streams. They did this by running the stream sediments, in water, through troughs lined with fleeces. The gold stuck to the fleeces while the accompanying sediment was carried away. These fleeces were then hung to dry, after which the gold could be knocked off, like beating a carpet. According to Greek mythology, tales of the “Golden Fleece” inspired Jason and his crew on the Argo, and these Argonauts (the Greek, nautikos means sailor) sailed in search of it. Common Misconceptions Misconception 1: Geologists are all rock hounds. Fact: While all practicing geologists need to know something about rocks and minerals, only a relatively small proportion actually collects, seeks, or studies rocks for a profession. Many geologists are employed by the fossil fuel industry, searching for deposits of petroleum, natural gas, and coal. Many others are engaged in the environmental and hydrologic fields, helping discover, define, and remedy problems such as pollution, water supply, and waste disposal. Still others apply their skills to engineering geology problems, helping locate sites for dams, bridges, and other structures. Some participate in fields of study in which rocks and minerals play little part. Misconception 2: If a stone scratches glass, it must be a diamond. Fact: Since glass has a hardness (measured on the Mohs scale) of about 5½, then any mineral with a greater hardness can scratch it. This includes most of the rock-forming silicates. Lecture Suggestions 1. Cleavage planes are probably the most difficult mineral property for students to recognize. Point out that they can be recognized by naturally fractured and flat surfaces which all reflect or “wink” light at the same time when turned in the light. Also point out that although surfaces that are parallel to one another have the same cleavage plane, a sample need not show evidence of more than one cleavage surface in order to qualify it as a cleavage plane. 2. To demonstrate that cleavage within a crystal continues down to a very small scale (theoretically all the way to an atomic scale), examine a piece of mica or a crystal of halite and point out that the fracture lines that can be seen indicate the presence of additional planes of weakness within the crystal. Furthermore, one could hammer a halite crystal until the fragments are microscopic, and the three cleavage planes would still give each fragment a cubic shape. 3. Use a broken sample of crystalline quartz to illustrate the difference between crystal faces and cleavage planes. The quartz crystal faces are flat, but when broken, the crystal fractures like glass; it does not possess a cleavage. Compare this to a halite or calcite crystal, both of which do break along flat cleavage planes. Point out that crystal faces are naturally flat, reflective surfaces but differ from cleavage planes in that the former result from a crystal having grown into an open space, while the latter, which is a result of inter-atomic bonding, is seen after fracturing. 4. While the students are examining the quartz crystals, point out the fine, parallel striations that are on the crystal faces. These striations, which are perpendicular to the long axis of the original crystal, are always present on natural quartz crystals and develop during growth. Note that many “quartz crystals” sold as jewelry, art objects, or trinkets do not exhibit these striations. These commercially available crystals, evidently, have either been ground and polished, removing the lines and possibly reshaping the faces, or they might not be real quartz at all. If these “crystals” are actually glass, how could the student tell? 5. Note that streak is a more constant property for a mineral than the overall color, which can vary. Compare the streaks of different forms of the mineral hematite (Fe2O3). If you can, obtain samples which are earthy, sub-metallic, and metallic (specular hematite or specularite). They should all exhibit the same “dried blood” red streak, though their overall colors, as well as lusters, are different. The name hematite, incidentally, is from the Greek haema, meaning blood (the same root is found in hemoglobin, hemophiliac, hematology) in allusion to the color of the streak. Consider This 1. Can a rock be composed of only one mineral? Why or why not? If so, give an example. Answer: Yes, a rock can be composed of only one mineral. For example, limestone is primarily composed of calcite, making it a rock consisting of a single mineral. 2. Can a native element be a mineral? Can a native element be a rock? Why or why not? If yes, give examples of each case. Answer: Yes, a native element can be a mineral and a rock. For instance, gold and copper are native elements that qualify as minerals. Native gold can also be found in its natural, metallic form as a rock, often called native gold ore. 3. Why don't some minerals, such as quartz, break along cleavage planes, while other minerals, such as halite, always do? Answer: Minerals like quartz break in irregular patterns because they lack distinct cleavage planes, whereas halite breaks along cleavage planes due to its regular crystal structure, which facilitates predictable breakage along specific planes. 4. What properties of a mineral might give it special powers, such as the ability to heal? Since there are none, what is the reason that so many people think that minerals do possess powers? Answer: Minerals do not have inherent healing powers, but many people believe in such properties due to cultural traditions and placebo effects. The perceived benefits are often linked to the minerals' appearance or associated symbolism rather than scientific evidence. 5. Why are physical properties more important than chemical composition in determining whether or not a mineral is valued as a gemstone? Answer: Physical properties like color, clarity, and brilliance are crucial for gemstones because they affect their aesthetic appeal and durability, which directly influences their value, whereas chemical composition plays a secondary role. 6. List at least 20 common items that have been derived or fabricated from mineral resources. Answer: Common items derived from minerals include: • Glass (silica) • Ceramics (clay minerals) • Steel (iron ore) • Aluminum cans (bauxite) • Salt (halite) • Plastics (various mineral-based catalysts) • Talcum powder (talc) • Concrete (limestone and clay) • Jewelry (gold, diamonds) • Pencils (graphite) • Cosmetics (mica, talc) • Paints (titanium dioxide) • Batteries (lithium, cobalt) • Fertilizers (potash, phosphate) • Medical equipment (various minerals in ceramics and alloys) • Deodorants (aluminum compounds) • Toothpaste (calcium carbonate) • Cement (limestone, gypsum) • Roofing shingles (asphalt and mineral granules) • Soap (sodium carbonate) 7. Give some examples of how searching for and controlling (or trying to control) mineral resources have played a major role in human history. Answer: Historically, the pursuit of gold and silver drove exploration and colonization. The search for oil and coal has fueled industrial revolutions and conflicts. Control over diamonds has influenced geopolitical and economic dynamics, while mineral resource access has shaped global trade and power balances. Internet Sites, Videos, Software, and Demonstration Aids Internet Sites 1. Diamond Factory. NOVA scienceNOW, PBS (2009, 14:35) http://www.pbs.org/wgbh/nova/sciencenow/0401/01.html Synthetic diamonds and how they can now be created to rival the real thing. 2. The Mineral and Gemstone Kingdom http://www.minerals.net/ A complete guide to rocks, minerals and gemstones. 3. Mineral Galleries http://mineral.galleries.com/ Interesting features of minerals by name, class, and properties. Also includes information on rocks “The Home of Minerals.” 4. Smithsonian Gem & Mineral Collection http://www.gimizu.de/sgmcol/ Some of the spectacular mineral and gem samples housed at the Smithsonian National Museum of Natural History. 5. Ask-A-Geologist http://walrus.wr.usgs.gov/ask-a-geologist/ Get answers to any Earth Science questions from the United States Geological Survey. 6. Mindat.org http://www.mindat.org/index.php A mineral and locality database in which you can search for minerals by properties, chemistry, name and association. Videos 1. Secrets in Salt. NOVA scienceNOW, PBS free video (2009, 11:50) http://www.pbs.org/wgbh/nova/sciencenow/0405/02.html Traces of early life are found in 250 million year old salt deposits. 7. Elements of Earth Science: Rocks, Minerals and Soils. Insight Media (2005, 30 mins.) The rock cycle, minerals, soil and fossil fuels are discussed in this DVD. 8. Introduction to Rocks and Minerals. Insight Media (2004, 25 mins.) The characteristics of common minerals and rocks, and how they are identified. 9. Core Geology, Ambrose Video (2007, 30 mins.) Natural resources and their importance to civilizations throughout human history. 10. Diamonds. Nature, PBS (56 mins.) Discover the processes that create diamonds and the uses of these beautiful minerals to humankind. 11. Earth Revealed. Annenberg Media http://www.learner.org/resources/series78.html (1992, 30 mins., free video): • #12: Minerals: The Materials of Earth A primer on minerals, how they are studied and their importance to human civilization. 12. Planet Earth. Annenberg Media http://www.learner.org/resources/series49.html, (1986, 1 hour, free video) • #5: Gifts from the Earth. Earth’s Natural Resources. Plate tectonics and how it has revolutionized the way geologists search for natural resources. Slides and Demonstration Aids 1. Earth Resources. Insight Media (CD-ROM, 2008) Images of 74 features of natural resources including ore deposits and how they are obtained. 2. Minerals. Insight Media (CD-ROM, 2005) High-quality, high-resolution images of minerals, especially rock forming and metallic and non-metallic specimens. 3. Mineral Identification. Insight Media (2005, CD-ROM) High-resolution images that show the ways to identify minerals. 4. Science Stuff, http://www.sciencestuff.com/, has an assortment of rock and mineral collections, including • Introductory Earth Science Rocks and Minerals • Natural Crystal Collection • Gem Minerals • Scale of Hardness Collection • Advanced Rock and Minerals Collection • Answers to Figure-Related Critical Thinking Questions ❯❯ Critical Thinking Question Figure 3.1 You must explain to an interested audience the distinction between minerals and rocks. How would you do so, and can you think of any analogies that might clarify the points you make? Answer: Rocks are composed of Minerals (one or more…) by definition – Rock = Mineral, Mineral = Rock….But – although rock defined = Mineral(s), the definition for Minerals requires more: “inorganic, naturally occurring, crystalline solid, & composed of a definite chemical composition”…a more elaborate subset type of thing… Examples hit home! Natural diamond vs. synthetic diamond – only one tells us about earth history. Crystalline Solid? This is not true for glass products. (Why?) ❯❯ Critical Thinking Question Figure 3.15 Which of these minerals has a metallic luster and nonmetallic luster? Answer: “All that glistens is not GOLD!” As humans in a high-tech society, we “culturally” understand metals and the “shine” their polished surfaces can take on: like recognizing that the high shine that comes from polished parts of a newly built hot rod engine is from a metal. Not all metals retain that polish forever. We can recognize rust originating from a metal. Yes, the galena has a metallic luster and is considered a metallic as opposed to a non-metallic mineral. The non-metallic minerals calcite, gypsum, and halite, shown on the page with this question, do “shine” but more vitreous, or resinous, or even greasy. Metallic minerals are common to those that can take a polish, but like metals are opaque. ❯❯ Critical Thinking Question Figure 3.16 Refer to the rock cycle in Figure 1.15 and explain at what points in the cycle you would expect minerals to form. Answer: Minerals form in the Igneous process when molten matter solidifies, but minerals come out of the melt at different temperatures according to Bowen’s Reaction Series. The rock formed from these minerals will form in stages. In the Sedimentary process, minerals form when they come out of solution either to form Chemical Sedimentary Rocks or to cement clastic particles together to form Clastic Sedimentary Rocks. Minerals form during Metamorphic processes at grade increases during Progressive (Regional) Metamorphism in response to increases in heat and pressure. As these forces can drive off ions, forming new minerals, Contact Metamorphism can accomplish the same effect. A separate and distinctive type of Metamorphism, Hydrothermal Metamorphism is the mobilization of ions in hot fluids that recombine these ions to create solid minerals. ❯❯ Critical Thinking Question Figure 3.20 Why do you think that the United States and Canada import bauxite (the ore of aluminum) given that both countries have vast exposures of igneous rocks and clay-rich rock from which we can extract aluminum? What factors(s) may change the status of these rocks so that we do extract aluminum from them? Answer: Aluminum is too tightly chemically bound in the alumino-silicates of Igneous rocks or the sheet silicate clay minerals. Weathering best breaks these bonds so that the aluminum is more economically processed from bauxite, an intense weathered soil (“extreme” pedalfer!) typical of more tropical climates than usually found in the US and not found in Canada. If politics change in countries where U.S. and Canada depend on bauxite for aluminum, engineering technology could be developed to find a way to get aluminum from alternative sources, but right now we need to recycle more or conserve present sources. Suggested Answer to Selected Short Answer Question (Answers to question 6 and question 9 provided in the appendix to the text) 8. What factors determine whether a mineral or rock commodity is a resources or a reserve? Suggested Answer: Mineral resources are defined as natural concentrations of minerals or, bodies of rock that are, or may become, of potential economic interest due to their inherent properties. That part of a mineral resource, which has been fully evaluated and is deemed commercially viable to work and has a valid planning permission for extraction is called a mineral reserve. A mineral or rock commodity is classified as a resource based on its general presence and potential for future extraction, whereas it becomes a reserve when it is economically viable to extract and has been quantified with specific data. Factors determining this include market value, extraction technology, economic feasibility, and regulatory approval. Chapter 4 Igneous Rocks and Plutons Chapter Outline 4.1 Introduction 4.2 The Properties and Behavior of Magma and Lava 4.3 How Does Magma Originate and Change? 4.4 Igneous Rocks—Their Characteristics and Classification 4.5 Intrusive Igneous Bodies—Plutons GEO-FOCUS 4.1: Granite—Common, Attractive, and Useful 4.6 The Origin of Batholiths Key Concepts Review Learning Objectives Upon completion of this material, the student should understand the following. • With few exceptions magma is composed of silicon and oxygen with lesser amounts of several other chemical elements. • Temperature and composition are the most important controls on the mobility of magma and lava. • Most magma originates within Earth’s upper mantle or lower crust at or near divergent or convergent plate boundaries. • Several processes bring about chemical changes in magma, so magma may evolve from one kind into another. • All igneous rocks form when magma or lava cools and crystallizes, or by the consolidation of pyroclastic materials ejected during explosive eruptions. • Geologists use texture and composition to classify igneous rocks. • Intrusive igneous bodies called plutons form when magma cools below Earth’s surface. The origin of the largest plutons is not fully understood. Chapter Summary • Magma is the term for a molten rock below Earth's surface, whereas the same material at the surface is called lava. • Silica content distinguishes among ultramafic (65 % silica) magmas. • Magma and lava viscosity depend mostly on temperature and composition: The higher the temperature, the lower the viscosity; the more silica, the greater the viscosity • Minerals crystallize from magma and lava when small crystal nuclei form and grow. • Rapid cooling accounts for the aphanitic textures of volcanic rocks, whereas comparatively slow cooling yields the phaneritic textures of plutonic rocks. Igneous rocks with markedly different-sized minerals are porphyritic. • Igneous rock composition is determined mostly by the composition of the parent magma, but magma composition can change so that the same magma may yield more than one type of igneous rock. • According to Bowen's Reaction Series, cooling maffic magma yields a sequence of minerals, each of which is stable within specific temperature ranges. Only ferromagnesian silicates are found in the discontinuous branch of Bowen's Reaction Series. The continuous branch yields only plagioclase feldspars that become increasingly enriched with sodium as cooling occurs. • A chemical change in magma may take place as early ferromagnesian silicates form and, because of their density, settle in the magma. • Compositional changes also take place in magma when it assimilates country rock or one magma mixes with another. • Geologists recognize two broad categories of igneous rocks: volcanic or extrusive and plutonic or intrusive. • Texture and composition are the criteria used to classify igneous rocks, although a few are defined mostly by texture. • Crystallization from water-rich magma results in very large minerals that form rocks known as pegmatite. Most pegmatite has an overall composition similar to granite. • Intrusive igneous bodies known as plutons vary in their geometry and their relationship to country rock: Some are concordant, whereas others are discordant. • The largest plutons, known as batholiths, consist of multiple intrusions of magma during long periods of time. • Most plutons, including batholiths, are found at or near divergent or convergent plate boundaries. Enrichment Topics Topic 1. Igneous Rock Classification. There are lots of ways to classify igneous rocks. Grab a handful of igneous rocks, preferably with their chemical analyses, and explore some of those ways—color-texture, modal, normative. http://csmres.jmu.edu/geollab/Fichter/IgnRx/IgHome.html Topic 2. Devil's Tower. Geologists do not agree on whether Devil’s Tower is the neck of a long-dead volcano or an igneous intrusion. How could geologists tell the difference? http://www.scienceviews.com/parks/devilstowergeology.html Topic 3. Peridotite and Global Warming. Although little peridotite is found at Earth’s surface, there are some large exposures in Oman, Papua New Guinea, and in a few locations in Greece, Yugoslavia and the western U.S. Geologists have found that peridotite reacts with carbon dioxide to form a solid carbonate. They have proposed to inject heated water containing pressurized CO2 into peridotite. The pressure would crack large amounts of rock, which would allow the solution to penetrate further into the rock. The Earth’s heat at depth would speed up the reaction. The reaction would take little energy once it started. The Oman ophiolites could absorb more than 10% of the CO2 released by human activities into the atmosphere. http://www.sciencedaily.com/releases/2008/11/081105180813.htm Common Misconceptions Misconception 1: Once they accept the fact that magmas can exist within Earth's crust, many students believe that these bodies of liquid are squeezed into surrounding rocks, or squirted out at the surface by some unknown forces acting in a manner like the squeezing of toothpaste from a tube. Fact: Magma bodies rise and intrude in response to the simple pull of gravity. Liquid rock—magma—has a lower specific gravity than solid rock. This causes the magma to rise and perhaps, over time, even to deform other rocks. As the magma approaches the surface and the pressure decreases, there is the additional “push” provided by the expansion of the dissolved gases coming out of solution. Misconception 2: Rock needs a heat source to melt. Fact: Decompression melting is common in Earth, especially at mid-ocean ridges. When rock at a high temperature rises in the mantle so that pressure is lowered, its melting temperature lowers as well. The rock can then melt. Lecture Suggestions 1. Bowen's reaction series can be compared to changing two brick walls into two new walls. In one case—the discontinuous series—the bricks are individually removed, and a new wall is simultaneously built from the bricks but in a new pattern. The constituents of olivine, for example, are thus recreated into the new structure of pyroxene. In the second case—the continuous series—bricks are individually removed from the wall and replaced by different bricks having a different color but retaining the original pattern. For plagioclase, an original constituent (calcium) is replaced by a new constituent (sodium) but the structure is never torn down. 2. Bowen's reaction series is a very powerful tool for explaining more than one facet of rock formation. The series helps us understand why some minerals are typically found together in igneous rocks (e.g., olivine and pyroxene with calcium plagioclase; or quartz, biotite, and orthoclase with sodium plagioclase), but others are not (e.g., olivine and pyroxene with sodium plagioclase and orthoclase). Bowen's series also explains temperature relations (why mafic magmas are hotter than felsic ones). It can also be seen why a mafic magma, by giving up heat, can partially melt material to form felsic magma, but the reverse isn't possible. Later, when weathering is discussed, Bowen's series will help understand the greater stability at Earth's surface of the lower temperature minerals (e.g., quartz) and lesser stability of the higher temperature ones (e.g., olivine). 3. Crystal settling may be explained by an analogy of a series of salts that precipitate as saltwater evaporates while the remaining water becomes increasingly saturated in the remaining salts. Precipitation from a solution and crystallization of a magma are not the same thing. 4. Dust off the lava lamp you relegated to the attic and bring it to class. You can use it to illustrate points about how densities vary with temperature, how gravity is the driving force in a rising magma, and what shapes are assumed by the rising bodies as they deform and shoulder aside the other material. You may want to note that unlike the lava lamp example, plutons, once they ascend, do not later descend back into the same rocks through which they rose. 5. Granite batholiths create some of the most amazing mountains in the world. Show some slides of the Sierra Nevada in California and especially the domes of Yosemite to interest students in this amazing rock type and its manifestations. Consider This 1. If small bodies such as dikes (e.g., basalt dikes) and sills cool rapidly and are therefore usually fine grained, how is it possible for pegmatites, having crystals several feet in length, to form in these small bodies? Answer: Pegmatites form from highly differentiated magmas with a high water content, which allows for the growth of very large crystals even in small bodies. These magmas tend to cool slowly, facilitating the development of large crystals despite the small size of the intrusion. 2. Batholiths are believed to have been emplaced and solidified several kilometers underground, yet we can see them exposed in mountain ranges today. What has happened to all of the rocks that must have been above the batholiths? Answer: The rocks above batholiths have been removed by erosion over millions of years, exposing the once-buried batholiths at the Earth's surface. This process reveals the deep-seated igneous rocks that were previously covered by other rock layers. 3. How can a single volcano erupt distinctly felsic composition lavas in one event, and distinctly mafic lavas in another? Answer: A single volcano can erupt felsic lavas in one event and mafic lavas in another due to changes in the magma composition, which can occur from varying sources of magma, fractional crystallization, or the mixing of different magma batches in the magma chamber over time. Internet Sites, Videos, Software, and Demonstration Aids Internet Sites 1. Atlas of Igneous Rocks, Minerals, and Textures http://www.geolab.unc.edu/Petunia/IgMetAtlas/mainmenu.html This University of North Carolina website was developed to help undergraduate students understand igneous and metamorphic rocks. 2. Rob's Granite Page http://uts.cc.utexas.edu/~rmr/ An introduction to granitic rocks from the University of Texas. Videos 1. Journeys from the Center of the Earth: Architecture. Insight Media (2004, 50 mins.) Rocks and how they determined the structures that could be built by ancient civilizations. 2. Intrusive Igneous Rocks. Insight Media (1999, 19 mins.) The formation of intrusive igneous rocks. 3. Rock Cycle. Insight Media (2003, 30 mins.) How minerals form rocks and rocks change into other types of rocks. 4. Elements of Earth Science: Rocks, Minerals, and Soils (2005, 30 mins.) The rock cycle including the three main types of rocks. 5. Earth Revealed. Annenberg Media http://www.learner.org/resources/series78.html (1992, 30 mins., free video): • #14: Intrusive Igneous Rocks. The processes that create intrusive rocks and the types of intrusive rocks that are found on Earth. Slides and Demonstration Aids 1. Geology EOA: Rocks, Minerals and Resources (Mac/Windows CD-ROM) Mineral and rock types and resources discussed and identified. 2. Rock and Topography, 100 slides. Educational Images, Ltd. Slide set including many topics important to introductory geology courses. 3. Intrusive Rocks, digital images. GeoPhoto Publishing. Digital images of intrusive and metamorphic rocks from the continental core. 4. Science Stuff, http://www.sciencestuff.com/, has an assortment of rock and mineral collections, including Introductory Earth Science Rocks and Minerals • Igneous Rock Collection • Metamorphic Rock Collection • Sedimentary rock Collection • Advanced Rock and Minerals Collection • Answers to Figure-Related Critical Thinking Questions ❯❯ Critical Thinking Question Figure 4.3 Which one of these volcanoes would you expect to erupt explosively? Explain. Answer: Mauna Loa Volcano has more mafic lava flow. The Novarupta lava dome in Katmai National Park in Alaska is more viscous.In general, mafic magma/lava tends to be hotter and contain less silicon dioxide than felsic and intermediate magma/lava, so mafic eruptions tend to result in lava flows, but felsic and intermediate eruptions tend to be explosive and quite dangerous. Therefore the Novarupta lava dome in Katmai National Park in Alaska is more likely to erupt explosively. ❯❯ Critical Thinking Question Figure 4.11 Of the magmas that crystallized to form rhyolite, andesite, and basalt, which one would have been the most viscous? How do you know? Answer: Rapid cooling in lava flows results in many small minerals and an aphanitic (fine-grained) texture. Slower cooling yields a phaneritic (coarse-grained) texture. The magmas that produced basalt would have been the most viscous since basalt shows a uniform aphanitic texture while rhyolite and andesite show a more phaneritic texture. . ❯❯ Critical Thinking Question Figure 4.13 How can you tell from these images which specimens are volcanic and which are plutonic? Answer: Volcanic rocks have a more uniform (aphanitic) texture because cooling occurs very rapidly. The specimens with a coarser (phaneritic) texture are plutonic. The cooling in these rocks occurred beneath the earth’s surface and thus at a slower rate, allowing the crystallization of minerals. ❯❯ Critical Thinking Question Figure 4.16 Why do pumice and scoria have so many vesicles but obsidian has none? Answer: Obsidian, pumice and scoria all lack crystals because they cooled too quickly for crystal to form. Scoria and pumice have vesicles of rapid cooling of gas entrained (frothy) felsic lava. ❯❯ Critical Thinking Question Figure 4.20 How can you account for the fact that the dike in the foreground stands above the surface like a wall? Answer: While Ship Rock itself is a result of a highly explosive volcano (volcanic neck), the dikes radiating outward from Ship Rock are believed to have been formed by the extrusion of magma along transform fault boundaries. Suggested Answer to Selected Short Answer Question (Answers to question 7 and question 8 provided in the appendix to the text) 9. How do aphanitic and phaneritic textures form, and what do they tell you about rocks with these textures? Suggested Answer: The terms aphanitic and phaneritic refer to igneous rock textures that are a result of their relative cooling rates. Aphantic textures result when cooling takes place rapidly as in lava flows. The rate at which mineral nuclei form exceeds the rate of growth and an aggregate of many small mineral grains forms. The result is a fine-grained or aphanitic texture, in which individual minerals are too small to be seen without magnification. Phaneritic texture results from slower cooling in which large mineral grains form, thus yielding a coarse-grained or phaneritic texture, in which minerals are clearly visible. Aphanitic textures form from rapid cooling of magma, resulting in crystals that are too small to see with the naked eye, indicating extrusive volcanic rocks. Phaneritic textures result from slow cooling, allowing large, visible crystals to develop, indicating intrusive plutonic rocks. These textures reveal the cooling history and formation environment of the rocks. Chapter 5 Volcanoes and Volcanism Chapter Outline 5.1 Introduction 5.2 Volcanism and Volcanoes 5.3 What are the Types of Volcanoes? GEO-INSIGHT 5.1: Do Volcanic Gases Cause Ozone Depletion? 5.4 Other Volcanic Landforms 5.5 Volcano Belts 5.6 North America’s Active Volcanoes 5.7 Plate Tectonics, Volcanoes, and Plutons 5.8 Volcanic Hazards, Volcano Monitoring and Forecasting Volcanic Eruptions Key Concepts Review Learning Objectives Upon completion of this material, the student should understand the following. • In addition to lava flows, erupting volcanoes eject pyroclastic materials, especially ash and gases. • Geologists identify the basic types of volcanoes by their eruptive style, composition, and shape. • Although all volcanoes are unique, most are identified as shield volcanoes, cinder cones, or composite volcanoes. • Volcanoes characterized as lava domes tend to erupt explosively and are therefore dangerous. • Active volcanoes in the United States are found in Hawaii, Alaska, and the Cascade Range of the Pacific Northwest. • Eruptions in Hawaii and Alaska are commonplace, but only two eruptions have occurred in the continental United States during the 1900s and one in 2004. Canada has had no eruptions during historic times. • Some eruptions yield vast sheets of lava or pyroclastic materials rather than forming volcanoes. • Geologists have devised the volcanic explosivity index as a measure of an eruption’s size. • Most volcanoes are located in belts at or near divergent and convergent plate boundaries. • Some volcanoes are carefully monitored to help geologists anticipate eruptions. • Chapter Summary • Volcanism encompasses those processes by which magma rises to the surface as lava flows and pyroclastic materials, and gases are released into the atmosphere. • Gases make up only a few percent by weight of magma. Most is water vapor, but sulfur-gases may have far-reaching climatic effects, and carbon dioxide is dangerous. • Aa lava flows have surfaces of jagged, angular blocks, whereas the surfaces of pahoehoe flows are smoothly wrinkled. • Other features of lava flows are lava tubes and columnar joints. Lava erupted under water typically forms bulbous masses known as pillow lava. • Volcanoes are found in various shapes and sizes, but all form where lava and pyroclastic materials erupt from a vent. • The summits of volcanoes have either a crater or a much larger caldera. Calderas form following voluminous eruptions, and the volcano peak collapses into a partially drained magma chamber. • Shield volcanoes have low, rounded profiles and are composed mostly of mafic flows that cool and form basalt. Small, steep-sided cinder cones form around a vent where pyroclastic materials erupt and accumulate. Composite volcanoes are made of lava flows and pyroclastic materials of intermediate composition and volcanic mudflows. • Viscous, bulbous masses of lava, generally of felsic composition, form lava domes which are dangerous because they erupt explosively. • Fluid mafic lava from fissure eruptions spreads over large areas to form a basalt plateau. • Pyroclastic sheet deposits result from huge eruptions of ash and other pyroclastic materials, particularly when calderas form. • Geologists have devised a volcanic explosivity index (VEI) to give semiquantitative measure of the size of an eruption. Volume of material erupted and the height of the eruption plume are criteria used to determine the VEI; fatalities and property damage are not considered. • Approximately 80 percent of all volcanic eruptions take place in the circum-Pacific and the Mediterranean belts, mostly at convergent plate boundaries. Most of the rest of the eruptions occur along mid-oceanic ridges or their extensions onto land. • The two active volcanoes on the island of Hawaii and the one just to the south lie above a hot spot over which the Pacific Plate moves. • To effectively monitor volcanoes, geologists evaluate several physical and chemical aspects of volcanic regions. Of particular importance in monitoring volcanoes and forecasting eruptions is detecting volcanic tremor and determining the eruptive history of a volcano. Enrichment Topics Topic 1. Undersea Eruption. Fantastic footage of an undersea eruption in the North Pacific was captured by NOAA. The footage is from 1800 feet below sea level at the Brimstone Pit erupting through the Philippines Plate. http://news.discovery.com/videos/earth-undersea-eruption-now-in-stereo.html Topic 2. Flood Basalts and Mass Extinctions. The Deccan Traps, a region of plateau basalts that erupted about 65 million years ago, may be the cause of the extinction of the dinosaurs and other contemporaneous Late Cretaceous fauna rather than the favored asteroid impact hypothesis. The argument is that the climatic effects of such large scale eruptions would be sufficient to cause extinctions. Professor Andy Saunders has linked the Siberian Traps with the end of Permian extinctions, plus many other extinctions with flood basalt events. http://www.geosociety.org/news/pr/07-59.htm; http://geoweb.princeton.edu/people/keller/deccan/deccan.html http://www.le.ac.uk/gl/ads/SiberianTraps/FBandME.html Topic 3. Volcanism and Antarctic Ice Loss. Climate change may cause the West Antarctic ice sheet to melt, which will raise global sea level. The recent discovery of evidence of a volcanic eruption taking place beneath the ice is a big concern since a volcanic eruption beneath the ice will cause melting from the bottom, as well as melting from warmer temperatures at the top. Add to that the possibility that melting beneath the ice sheet can cause water to lubricate the location where the ice meets the underlying rock and cause the ice sheet to slip into the sea faster. http://news.sciencemag.org/earth/2013/11/magma-boils-beneath-antarctic-ice Common Misconceptions Misconception 1: Below the surface, the inside of Earth is entirely molten. Volcanoes are places where this material “squirts out.” Fact: Below the surface, Earth is solid—although the asthenosphere does behave like a plastic—to a depth of about 1,800 miles. For now, it may be enough to note the distribution of active and recently active volcanoes. These are in belts, or occasional isolated spots, but are by no means randomly distributed, as one might expect if there were molten material everywhere beneath the surface. See also Lecture Suggestion 3, below. Misconception 2: Volcanic eruptions are responsible for global warming. Fact: Some people do not accept that human activities are causing the rise in greenhouse gases that is causing global warming. This suggests the alternative that volcanoes emit more greenhouse gases during eruptions and therefore are responsible for the bulk of the warming. In truth, the amount emitted by volcanoes is relatively tiny. The annual contribution of CO2 to the atmosphere by volcanoes is 200 million tons, less than one percent of the nearly 30 billion tons emitted by human activities. This human enhanced greenhouse effect may cause an average annual global warming of 3 to 5oC over the next 50 years. Lecture Suggestions 1. To demonstrate the concept of viscosity, it is helpful to show students the rates at which different fluids flow down an inclined surface. You can do this by pouring a small amount of each of several types of fluid onto a piece of plywood or similar flat surface. Incline the plywood toward the class so that the fluids flow downward toward them. Vegetable oil, honey, molasses, and oatmeal provide a good range of flow rates. 2. Differential viscosity can also be illustrated in this manner. Place three small samples of honey or molasses in separate beakers. Put one sample in a bath of ice water and another in a bath of hot water before class and let them sit until they warm or cool significantly. By pouring the three samples simultaneously, you can show the students how temperature has a significant effect on the viscosity of a given substance. They may remember this better if you remind them of the old phrase, “as slow as molasses in January.” 3. Is the inside of Earth entirely molten? Aside from an argument based on the distribution of active volcanoes (see Common Misconceptions, above), try this simple demonstration. Bring two identical looking eggs to class, one of them hard boiled, the other uncooked. During the discussion of magma sources, spin the hard cooked egg on its long axis. Then, you may invite (or select) two students to come forward, give each of them one of the eggs, and ask each to spin his/her egg (not too close to the table edge). One student (with the cooked egg) should be able to do this, without much trouble. The other student will find it impossible. Some of the students by now may have guessed at the difference between the eggs, or you can elicit the answer. You can then point out the analogy with Earth, which spins very well (with a little wobble) on its axis. 4. Don't forget the comparison of dissolved gases in a magma coming out of solution as the magma rises to the surface (and pressure is released) to what happens when a bottle of club soda is opened. You can even bring a bottle to class, shake it up, and while pointing it at the class, ask what will happen if you open the top. Even when you don't go through with it, they will get the point. It’s more fun when you “erupt” the bottle, though. 5. Studying volcanoes sounds like a lot of fun but it can be very dangerous. David Johnston died in the May 18, 1980 eruption of Mount St. Helens. His last words were “Vancouver! Vancouver! This is it…” Harry Glicken, who was supposed to be on St. Helens that morning, was killed with two French volcanologists by a pyroclastic flow on Mount Unzen in 1991. In 1993 six volcanologists were killed on Galeras in Columbia while attending a conference on predicting volcanic eruptions. Students may be interested in learning more about these fascinating people and why they are so compelled to study volcanoes that they would put their lives in danger. Consider This 1. Why are felsic magmas more viscous than mafic magmas? Answer: Felsic magmas are more viscous than mafic magmas because they have higher silica content, which increases the magma's viscosity by promoting polymerization of silica tetrahedra, leading to thicker, more resistant flows. 2. Where are the most hotspots found? Are they found everywhere on oceanic plates? Are they found on continental plates? How does a mantle plume penetrate the thickness of the continental lithosphere to create an eruption? Answer: Hotspots are commonly found in the middle of tectonic plates, both oceanic and continental, though not everywhere on oceanic plates. They are found on continental plates, such as the Yellowstone hotspot. A mantle plume can penetrate continental lithosphere by melting through it due to its high temperature and pressure, creating volcanic eruptions. 3. Do volcanic eruptions vary in frequency on a human timescale? Are there certain years or decades in which eruptions are more common? Answer: Volcanic eruptions do vary in frequency on a human timescale, with certain years or decades experiencing higher eruption rates due to changes in volcanic activity patterns, tectonic shifts, and other geological factors. 4. What different kinds of hazards can people living near volcanoes expect? Why do people live on and near known or potentially active volcanoes? What are some benefits which volcanoes may provide? Answer: People living near volcanoes can face hazards like lava flows, pyroclastic flows, ashfall, and lahars. Despite these risks, people often live in these areas due to fertile soils for agriculture, geothermal energy resources, and cultural or economic reasons. Volcanoes also provide benefits such as mineral resources and scenic landscapes that attract tourism. Internet Sites, Videos, Software, and Demonstration Aids Internet Sites 1. Mt. St. Helens: Back From the Dead. NOVA Online, PBS (2010) http://www.pbs.org/wgbh/nova/earth/mt-st-helens.html Life returns to Mt. St. Helens. Could another eruption be in the volcano’s future? 2. Kilauea: Mountain of Fire. Nature Online, PBS (2010) http://www.pbs.org/wnet/nature/episodes/kilauea-mountain-of-fire/introduction/4718/ The world’s most active volcano has been eruption continuously since 1983; it’s Kilauea, on Hawaii’s Big Island. 3. Space Age Volcano Monitoring Network, JPL http://www.jpl.nasa.gov/video/index.cfm?id=858 Monitoring Mount Saint Helens from space using NASA technology. 4. Global Volcanism Program. Smithsonian Institution http://www.volcano.si.edu/ This website looks at Holocene volcanoes and eruptions. You can also use this as a gateway to Google Earth’s volcano map. 5. Deadly Shadow of Vesuvius. NOVA online, PBS (1998) http://www.pbs.org/wgbh/nova/vesuvius/ The story of the ancient Roman city of Pompeii, which was destroyed by the eruption of Mount Vesuvius, and the risk the people of Naples face today. 6. Hawaii Born of Fire. NOVA Online, PBS. http://www.pbs.org/wgbh/nova/hawaii/ A look at the Hawaiian Islands, from molten rock to verdant landscape. 7. Violent Hawaii. Nature, PBS Video. http://www.pbs.org/wnet/nature/episodes/violent-hawaii/video-full-episode/1422/ The Hawaiian Islands create a chain that stretches 1,500 miles across the Pacific Ocean, where volcanoes and living creatures thrive. 8. Volcanoes, United States Geological Survey http://www.usgs.gov/themes/volcano.html The USGS looks at volcanoes has natural hazards, which can bring risks to life, property and infrastructure. 9. Volcano World, Oregon State http://volcano.oregonstate.edu/ Hot topics in volcanology with an archive that covers many topics. 10. Cascades Volcano Observatory http://vulcan.wr.usgs.gov/home.html Mt. St. Helens and other volcanoes of the Pacific Northwest including current activity. 11. Volcano Video Productions http://www.volcanovideo.com/ Video clips and DVDs for sale of volcanic features and eruptions focusing on Kilauea in Hawaii. Includes eruption updates; Kilauea: Close-up of an Active Volcano; Lava Flows and Lava Tubes: What they are and How they Form; Eruption at Sea and others. Videos 1. Volcanoes of the Deep Sea, IMAX (2003, 40 mins.) Volcanoes at spreading centers 12,000 feet below the ocean’s surface with dramatic landscapes and strange creatures. 2. Volcano! Nature’s Inferno. National Geographic DVD (1990, 60 mins.) Learn about volcanoes as you travel around the world and join volcanologists in their efforts to forecast eruptions. 3. Volcano under the City. NOVA, PBS DVD (2006, 60 mins.) An active volcano in central Africa is the study site for a team of scientists. 4. In the Path of a Killer Volcano. NOVA, PBS DVD (1993, 60 mins.) The massive evacuation that was prompted by the imminent eruption of Mount Pinatubo in the Philippines. 5. Mystery of the Megavolcano. NOVA, PBS (2006, 56 mins.) Evidence of the greatest volcanic eruption of the last 100,000 years is found in a remote lake in Southeast Asia. 6. Supervolcano: It’s Under Yellowstone and its Overdue, Discovery Communications (105 mins.) Yellowstone National Park with its amazing geysers and wildlife is above an enormous mantle plume that could erupt at any time. 7. The Earth Revealed. Annenberg/CPB Collection. • # 13: Volcanism. What volcanoes tell scientists about the Earth’s interior, the processes that create them and the various types of volcanic features and phenomena are explored. • # 25: Living With Earth, Part I, Destructive Natural Phenomena. 8. Everything You Need to Know: Volcanoes. Insight Media (2007, 56 mins.). An introduction to volcanoes and the parts of an eruption. 9. Forces that Shape the Earth. Insight Media (2000, 29 mins) Forces that form and reform rocks and landforms on Earth. 10. Volcanism. Insight Media (1999, 15 mins.) The formation of volcanoes and the importance of volcanic activity to the Earth. 11. Volcanoes. Insight Media (2004, 15 mins.) Introduction to basaltic and andesitic volcanism. 12. Volcanoes of the United States. Insight Media (2004, 24 mins.) Ancient and current volcanoes of the U.S. explored. Slide sets 1. Geologic Hazards Slide Sets; Volcanoes, 8 sets available. National Geophysical Data Center. http://www.ngdc.noaa.gov/mgg/image/hazardsimages.html 2. Geothermal Activity and Energy. Educational Images, Ltd. 3. Volcanism, digital images. GeoPhoto Publishing. Answers to Figure-Related Critical Thinking Questions Critical Thinking Question Figure 5.3 Are volcanic gases dangerous to humans? Answer: Yes; H2S repels at first, then deadens the olfactory nerves, then kills. CO and CO2 can kill by denying O2. ❯❯ Critical Thinking Question Figure 5.5 What controls whether a lava flow is aa or pahoehoe? Answer: Both types, aa and pahoehoe, originate from the same sources and are of the same composition. Time and temperature makes the difference: initial flows are hotter and produce more fluid pahoehoe. In time the same flow that produced the pahoehoe may change to the aa characteristic. Later flows from the same volcanic event may be cooler and flow as aa types. Gas content may also have an effect, but the gases are released more rapidly with higher temperatures. ❯❯ Critical Thinking Question Figure 5.6 What inferences can you make about where this pillow lava formed? Answer: The Kenai Fjords park pillow lava appears to be similar to that found in the Mona Schist on US-41 in the UP of Michigan. Flows like this into ocean basins are common at divergent plate boundaries as the top of the ophiolite suite of ocean crust. ❯❯ Critical Thinking Question Figure 5.14 Why do you think lava domes are so dangerous? Answer: Lava domes, just like the one that formed in Mt. St. Helens in July 1980, are indications of fluid pressure building up beneath a thin rock crust. The condition is an indication that an explosion is possible, maybe like that in May. (OK – it did blow, but not as bad.) Domes are messengers, and although not all of them blow dangerously, the message should be acted on. ❯❯ Critical Thinking Question Figure 5.17 Why is magma at divergent plate boundaries mafic, whereas magma at convergent plate boundaries is intermediate or felsic? Answer: In general, these concepts are true, but when you examine volcanoes around the world, there are exceptions to this “rule”. At divergent boundaries source magma comes right from the mantle – mafic concentration! At the convergent boundary where mafic magma may originate as the subducted plate makes contact with the heat of the asthenosphere. But as that mafic diaper moves up through the overlying lithosphere and crust, other processes such as magma mixing, assimilation, and underplating favor the production of granitic and andesitic magma. ❯❯ Critical Thinking Question Figure 5.21 Why are numbers of fatalities and property damage not used in assigning a VEI value to an eruption? Answer: The extent of volcanic impacts can be mitigated by proper warning to populations in harm’s way. Some volcanoes exist in areas without human population pressures. The human toll has nothing to do with the explosivity. Suggested Answer to Selected Short Answer Question (Answers to question 6 and question 10 provided in the appendix to the text) 8. What criteria do geologists use to assign a volcanic explosivity index (VEI) value to an eruption? Suggested Answer: The VEI (Volcanic Explosivity Index) is based on the volume of material explosively ejected and the height of the eruption plume. Geologists assign a Volcanic Explosivity Index (VEI) value based on eruption magnitude, including factors like eruption column height, volume of erupted materials, and duration of the eruption. Additional considerations include the extent of pyroclastic flows and impact on the environment and human settlements. Chapter 6 Weathering, Erosion, and Soil Chapter Outline 6.1 Introduction 6.2 Alteration of Minerals and Rocks 6.3 Mechanical Weathering—Disaggregation of Earth Materials 6.4 Chemical Weathering—Decomposition of Earth Materials 6.5 Soil and its Origin GEO-FOCUS 6.1: Industrialization and Acid Rain GEO-INSIGHT 6.1: Arches National Park, Utah 6.6 Expansive Soils and Soil Degradation 6.7 Weathering and Resources Key Concepts Review Learning Objectives Upon completion of this material, the student should understand the following. • Weathering yields the raw materials for both soils and sedimentary rocks. • Some weathering processes bring about physical changes in Earth materials with no change in composition. • Some weathering processes cause a change in the chemical composition of the parent material. • A variety of factors are important in the origin and evolution of soils. These include climate, the parent material being weathered, the amount of organic material, and slope among others. • Soil degradation involves any loss of soil productivity that results from erosion, chemical pollution, or compaction. Chapter Summary • Mechanical and chemical weathering disintegrate and decompose parent material so that it is more nearly in equilibrium with new physical and chemical conditions. • The products of weathering include rock fragments and minerals liberated from parent material as well as soluble compounds and ions in solution. • Weathering yields materials that may become soil or sedimentary rock. • Mechanical weathering processes include frost action, pressure release, thermal expansion and contraction, salt crystal growth, and the activities of organisms. The particles yielded retain the composition of the parent material. • Chemical weathering by solution, hydrolysis, and oxidation results in a chemical change in parent material and proceeds most rapidly in hot, wet environments. • Mechanical weathering contributes to chemical weathering by breaking parent material into smaller pieces, thereby exposing more surface area. • Soils possess horizons designated, in descending order, as O, A, E, B, and C, which differ from one another in texture, composition, structure and color. • The important factors controlling soil formation are climate, parent material, organic activity, relief and slope, and time. • Soils in humid regions are darker and more fertile than those of semiarid regions. Laterite is soil that forms in the tropics where chemical weathering is intense. • Soil degradation results from erosion as well as from physical and chemical deterioration. Human activities such as construction, agriculture, deforestation, waste disposal, and chemical spills, contribute to soil degradation. • Chemical weathering is responsible for the origin of some mineral deposits such as residual concentrations of iron, lead, manganese, and clay. Enrichment Topics Topic 1. Soils and a Positive Feedback Mechanism for Global Warming. Soils are rich with carbon, which microbes eat. Warmer temperatures are causing microbes to decompose soil carbon faster and release it into the atmosphere. This increases atmospheric CO2, which increases global temperatures and increases the rate at which microbes decompose soil carbon. This is called a positive feedback mechanism for global warming. There are ways to increase the storage of carbon in the soil, but the effect would be small compared to the potential effect of the release of carbon from soil due to warmer temperatures. The only way to reduce the loss of soil carbon is to reduce greenhouse gas emissions into the atmosphere. http://www.csmonitor.com/2006/0421/p09s01-coop.html Topic 2. Soil Erosion and Coral Reefs. Corals cannot exist in muddy water because sediment clogs their feeding apparatus and inhibits oxygen diffusion. Extensive deforestation in tropical areas is resulting in dramatic increases in the rates of soil erosion. This, in turn, is threatening the health and diversity of coral reefs, which exhibit incredible biodiversity and are nurseries for important commercial fish species. In Guam, a soil scientist has planted Vetiver grass on shorelines to keep soil from entering the coastal waters so readily. Different strategies are used in other regions of the world to protect reefs. http://www.sciencedaily.com/releases/2011/04/110408101924.htm Topic 3. Philippine Logging Ban. The Philippine government has taken a drastic step to reducing soil erosion. Over the past decade, the Philippine government has enacted stricter regulations of logging because soil erosion on deforested slopes bring about massive landslides that kill hundreds or thousands of people during storms. In February 2006, for example, a massive landslide killed more than 1,000 people and buried portions of the town of Guinsaugon. In 2011, President Aquino ordered a logging moratorium after 70 people were killed. So many slopes have been deforested that it will be a long while before landslides are reduced in number and severity. http://news.bbc.co.uk/2/hi/asia-pacific/4068477.stm, http://news.bbc.co.uk/2/hi/asia-pacific/4723770.stm Common Misconceptions Misconception 1: Modern agricultural practices, including intensive farming, have been universally good by allowing many more people to live on the planet than would otherwise be possible. Fact: The Green Revolution has kept alive about 1 billion people who would not otherwise have been able to be fed. However, the costs in pollution and topsoil erosion, among many other things, will eventually need to be paid. Allowing 1 billion more people contributes to overpopulation, which causes many more problems. Misconception 2: Granite and marble are for eternity—what do you want on your tombstone? Fact: No rock will retain an inscription and last as a monument forever. All rocks exposed at the surface undergo weathering. The type and rate of weathering depend on several factors, with climate being most important. The acid content of the rainwater is also an important factor. Perusing headstones in old cemeteries is very informative along this line. Lecture Suggestions 1. Point out the importance of soils to everyday activities. For example, if a student has a hamburger for lunch, everything which he/she eats depended on a soil: the lettuce, tomato, and wheat for the bun were grown in soils, and the beef cattle had to eat plants grown in soil. If the hamburger was wrapped in aluminum foil, the aluminum came from bauxite. 2. Stress the distinction between weathering and erosion. 3. Since the Industrial Revolution, acid rain has taken a tremendous toll on some of the great architectural works and outdoor sculptures of the past two millennia. For example, compare the 1853 photo of a gargoyle at Notre Dame Cathedral in Paris (http://en.wikipedia.org/wiki/File:Henri_Le_Secq_near_a_Gargoyle.jpg) with a modern one (http://en.wikipedia.org/wiki/File:Notre_dame-paris-view.jpg). ; . The modern gargoyle is pitted and sharp edges are rounded. 4. Discuss the economic causes of soil erosion. In the article “High Prices Sow Seeds of Erosion” from the New York Times, farmers are afraid that erosion will increase now that marginal lands are being farmed due to high prices for corn and soy beans. http://www.nytimes.com/2011/04/13/business/13erosion.html?scp=1&sq=soil%20erosion&st=cse 5. Many techniques are used to prevent soil erosion. Conservation of cropland is aided by crop rotation, and planting cover crops and windbreaks. Contour farming and terracing and contour tillage are also used on farmland. Logs may be placed perpendicular to a steep slope. Soil conservation requires measures that reduce salination of soils. Consider This 1. The ecosystem encompasses the interactions among the lithosphere, hydrosphere, atmosphere, and biosphere. Soils are very different in different ecosystems. What role do they play in deserts, forests, tundra, and other ecosystems? Answer: Soils in ecosystems vary significantly: desert soils are often sandy and low in organic matter, forest soils are rich in nutrients and organic content, and tundra soils are typically acidic and poorly drained. Each soil type supports the unique plant and animal life of its ecosystem. 2. How did the rates of weathering and erosion change after the evolution of land plants? Answer: After land plants evolved, weathering and erosion rates increased due to plant roots breaking up rocks and vegetation preventing soil erosion, leading to more rapid soil formation and increased sediment transport. 3. What are some of the ways in which the rate of soil erosion can be reduced? Answer: Soil erosion can be reduced through methods such as planting cover crops, terracing, contour plowing, and implementing erosion control structures like silt fences and check dams. 4. Should gossans and other mineral resource-rich laterite soils in tropical regions be mined? Why or why not? Answer: Mining gossans and laterite soils in tropical regions can be problematic due to environmental degradation and loss of biodiversity. However, responsible mining practices and stringent regulations can help mitigate negative impacts while tapping into valuable mineral resources. 5. Is soil a renewable or nonrenewable resource? Answer: Soil is considered a renewable resource but on a very slow time scale. Its renewal depends on natural processes of soil formation, which can take hundreds to thousands of years, making it vulnerable to rapid degradation and loss. 6. What effect might increased soil erosion have on global warming? Answer: Increased soil erosion can accelerate global warming by reducing the soil's ability to store carbon, leading to more carbon dioxide being released into the atmosphere and contributing to the greenhouse effect. Internet Sites, Videos, Software, and Demonstration Aids Internet Sites 1. Natural Resources Conservation Data, U.S. Department of Agriculture http://soils.usda.gov/ 2. U.S.G.S. – Sedimentary Rocks http://geomaps.wr.usgs.gov/parks/rxmin/rock2.html 3. U.S. National Geophysical Data Center, Sediment Thickness of the World’s Oceans http://www.ngdc.noaa.gov/mgg/sedthick/sedthick.html Videos 1. Elements of Earth Science: Rocks, Minerals and Soils. Insight Media DVD (2005, 30 mins.) The rock cycle, the main types of rocks and how fossil fuels are used. 2. From Rock to Sand to Muck: All the Dirt on Soils. Insight Media DVD (1996, 63 mins.) The breakdown of rock into sediments and their decomposition into soils; soil types. 3. The Once Good Earth: Understanding Soil. Insight Media DVD (2005, 46 mins.) The chemical and ecological features of soil. 4. Earth Revealed. Annenberg Media http://www.learner.org/resources/series78.html (1992, 30 mins., free video): • #15: Weathering and Soils. A comparison of weathering in a city versus a remote desert. Slides and Demonstration Aids 1. Educational Images, Ltd. slide sets, http://www.educationalimages.com/cg120001.htm Erosion, Slides and Surface Features 2. National Geographic – images of erosion and weathering http://science.nationalgeographic.com/science/photos/weathering-erosion-gallery/ Answers to Figure-Related Critical Thinking Questions ❯❯ Critical Thinking Question Figure 6.4 Barely visible in the left foreground is a highway. Why do you think these sheet joints might be a problem for highway maintenance crews? Answer: One form of exfoliation, removal of loose surface rock, in rock bodies influenced by pressure release, is mass wasting. The joints are inclined toward the road. When the sheets break off they will slide toward the road. ❯❯ Critical Thinking Question Figure 6.6 Does vegetation, especially trees, have a detrimental effect on rocklike substances such as foundations and sidewalks? Answer: “Darn maple tree keeps popping up the sidewalk slabs. City says to replace it at $300 a slab! Still, taking down the maple tree would be much more expensive.” ❯❯ Critical Thinking Question Figure 6.7 Which do you think would dissolve fastest, rock salt or table salt? Explain. Answer: Rock salt, table salt, halite, NaCl…all the same? OK: Table salt is closest to “pure” NaCl as it is formed from solution extraction and evaporation. Rock salt is usually the physically mined product (Detroit Salt Company) from the original marine precipitate while ocean basins still contained ocean water! This strata of salt also contains other “impurities” from shale to CaSO4; “impurities” that would slow down the dissolving process. ❯❯ Critical Thinking Question Figure 6.9 If you placed some rectangular ice cubes in the sun, how do you think their shape would change as they melted? Answer: Those ice cubes would look like the shape progression documented in Figure 6.9 in this new Chapter 6: check those cubes out in your drink glass! ❯❯ Critical Thinking Question Figure 6.11 Why does soil extend to much greater depths in the tropics compared to deserts? Answer: Weathering and the depth of soil formation are both increased by climate factors of longer seasonal warmth and greater precipitation. Even if temperatures are comparable, then water is the difference. In the tropics, it rains, a lot more than in any desert community (no desert crosses the Equator!). ❯❯ Critical Thinking Question Figure 6.14 Laterite supports lush vegetation but is not very good for agriculture. Why? Answer: In the tropics where laterite soil forms, nutrients are immediately recycled into the vegetation. Because of this process, very little of these nutrients are stored in the soil. Any of the important ions that would contribute to good agricultural soil is intensely weathered into the deep B horizon and the ground water (I prefer 2 words, as a professional hydrogeologist). Suggested Answer to Selected Short Answer Question (Answers to question 8 and question 9 provided in the appendix to the text) 9. How do parent material, particle size, and climate control the rate of chemical weathering? Suggested Answer: Chemical weathering is the decomposition of rocks and minerals through chemical processes such as oxidation, hydrolysis and dissolution. The rate of chemical weathering is affected by various criteria. The effect of parent material on a soil include such feature as soil texture, pH and mineral constituents. Small particle size of rocks accelerate chemical weathering by providing more surface area for chemical reactions. Climatic factors, especially temperature and moisture, have a strong effect on the rate of weathering. Generally, the warmer the temperature and the higher the humidity, promote chemical weathering. Parent material affects chemical weathering based on its mineral composition and hardness; particle size influences the surface area available for reactions, with finer particles weathering faster; and climate impacts weathering rates through temperature and moisture, with warmer and wetter conditions generally accelerating chemical weathering. Solution Manual for The Changing Earth: Exploring Geology and Evolution James S. Monroe, Reed Wicander 9781285733418
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