This Document Contains Chapters 11 to 14 Chapter 11 Mass Wasting Chapter Outline 11.1 Introduction 11.2 Factors That Influence Mass Wasting 11.3 Types of Mass Wasting GEO-FOCUS 11.1: Southern California Landslides 11.4 Recognizing and Minimizing the Effects of Mass Wasting Key Concepts Review Learning Objectives Upon completion of this material, the student should understand the following. • It is important to understand the different types of mass wasting because mass wasting affects us all and causes significant destruction. • Factors such as slope angle, weathering and climate, water content, vegetation, and overloading are interrelated, and all contribute to mass wasting. • Mass movements can be triggered by such factors as overloading, soil saturation, and ground shaking. • Mass wasting is categorized as either rapid mass movements or slow mass movements, • The different types of rapid mass movements are rockfalls, slumps, rock slides, mudflows, debris flows, and quick clays; each type has recognizable characteristics. • The different types of slow mass movements are earth-flows, solifluction, and creep; each type has recognizable characteristics. • People can minimize the effects of mass wasting by conducting geologic investigations of an area and stabilizing slopes to prevent and ameliorate movement. Chapter Summary • Mass wasting is the downslope movement of material under the direct influence of gravity. It may result in loss of life, as well as millions of dollars in damage annually. • Mass wasting occurs when the gravitational force acting on a slope exceeds the slope's shear strength (the resisting forces that help maintain slope stability). • The major factors causing mass wasting include slope angle, weathering and climate, water content, overloading, and removal of vegetation. It is usually several of these factors in combination that results in slope failure. • Mass movements are generally on the basis of their rate of movement (rapid versus slow), type of movement (falling, sliding, or flowing), and type of material (rock, soil, or debris). • Rockfalls are a common mass movement in which rocks free-fall. They are common along steep canyons, cliffs, and road cuts. • The two types of slides are slumps and rockslides. Slumps, or rotational slides, involve movement along a curved surface and are most common in poorly consolidated or unconsolidated material. Rock slides, also known as block slides, occur when movement takes place along a more or less planar surface, and they usually involve solid pieces of rock. • Rate of movement (rapid versus slow), type of material (rock, sediment, or soil), and amount of water are the criteria used to recognize the several types of flows. • Mudflows consist of mostly clay- and silt-sized particles and contain up to 30 percent water. They are most common in semiarid and arid environments and generally follow preexisting channels. • Debris flows are composed of larger particles and contain less water than mudflows. • Earthflows move more slowly than either debris flows or mudflows, and move downslope as thick, viscous, tongue-shaped masses of wet regolith. • Quick clays are clays that spontaneously liquefy and flow like water when they are disturbed. • Solifluction is the slow downslope movement of water-saturated surface material and is most common in areas of permafrost. • Creep, the slowest type of flow, is the imperceptible downslope movement of soil or rock. It is the most widespread of all types of mass wasting. • Complex movements are combinations of different types of mass movements in which no single type is dominant. Most complex movements involve sliding and flowing. • The most important factor in reducing or eliminating the damaging effects of mass wasting is a thorough geologic investigation to outline areas susceptible to mass movements. • Although mass movement cannot be eliminated, its effects can be minimized by building retaining walls, draining excess water, regrading slopes, and planting vegetation. Enrichment Topics Topic 1. Beauty versus Death. In January 2005, a mudslide roared down a slope in La Conchita, California, fatally burying 10 people. Two slides had struck in March 1995, fortunately killing no one. Geologists warn that further slides are inevitable and may even be larger. The reason is that the ground underneath that part of California rises at a rate of 15 feet every 1,000 years and the slopes are already unstable. When there is excess rain, a slide can result. The slides are so fast that no warning system could be designed to avert tragedy. While some residents of the 160 homes in the town have packed up, citing the excess danger, others say the town’s natural beauty is worth the risk. Indeed, many other locations in California are prone to landslides, floods, and wildfires. Why should this one be abandoned? But even if a way can be found to protect the town, who should pay? And what if the cost of saving the town is worth more than the town itself? As it is, the new landslide made short work of a $400,000 retaining wall built after the 1995 slide. Topic 2. Better than Water. While water is always cited as the best erosional agent, human activities cause 10 times more erosion than all natural processes put together. Syracuse University geologist Bruce Wilkinson has a number of papers out on the topic. http://bulletin.geoscienceworld.org/cgi/content/abstract/119/1-2/140 Topic 3. Fires and Mass Wasting. The devastating fires that strike southern California every few years increase risk of soil erosion, earthflows, debris flows, and mud flows. Mass wasting becomes more probable in such circumstances because these brushfires leave a waxy residue from the grasses as a covering on the ground surface. Thus, when heavy rainfall occurs, water cannot readily percolate into the soil. Sheet and rill runoff soaks into these soils along natural fissures in the soil and openings created by creep. When groundwater is concentrated in this manner, the slope’s stability is significantly reduced, allowing for the potential for mass wasting. http://landslides.usgs.gov/research/wildfire/ Common Misconceptions Misconception 1: Most damage caused by mass wasting results from large, rapid, dramatic landslides. Fact: The greatest amount of property damage from mass wasting is caused by the slow, often imperceptible types, such as creep. Misconception 2: Mudflows are most common in humid areas with lots of rainfall. Fact: Mudflows are most common in arid and semi-arid regions where occasional heavy rainstorms saturate the regolith and turn it into a mudflow. Lecture Suggestions 1. When mass wasting is discussed, many students can relate to their own experiences building sand castles at the beach. Ask them whether they could build a steeper pile (or attain a greater angle of repose) with wet or dry sand. What happens to the sand castle structure as it loses moisture and the surface tension between the particles diminishes? Finally, note how the addition of too much water makes the sand into a slurry which cannot be piled up but will flow instead. 2. Compare the stability of a variety of materials by pouring samples of soil, fine sand, coarse gravel, etc. into piles. Discuss the factors that affect the angle of repose. Encourage students to look at piles of gravel, sand, etc. that they might see near cement factories or at construction sites. What can they tell about the material from the shape of the piles? 3. Students are fascinated by disasters, and so it’s always good to pepper your lecture with a few examples. The La Conchita California Landside of 2005 and the Armero, Columbia tragedy of 1985 are two to start with. They have different causes and different outcomes. 4. Explore how human activities have exacerbated the hazards of mass wasting. How have fire, deforestation, construction all played a role in the increase in landslides and other downslope processes? How has human development raised the stakes on the consequences of mass wasting? 5. Find a map of your area and see if you can identify possible locations of mass wasting. If you can take the students on a field trip, look for signs of mass wasting in the field. Consider This 1. If you purchased property and planned to build your home on a slope, describe the ideal set of geologic conditions that you would look for. Answer: Ideal Geologic Conditions: Look for a stable slope with well-drained, consolidated rock or compacted soil. Ensure the slope has a gentle gradient, minimal history of landslides, and good drainage to prevent water accumulation. 2. On your purchased property from above, describe the precautions you would take if a study revealed the possibility of one of the following: i. slumps ii. rock glides iii. mudflows iv. debris flows v. earthflows vi. creep Answer: Precautions: • Slumps: Stabilize the slope with retaining walls or terracing and ensure proper drainage. • Rock Glides: Reinforce the slope with anchors or netting to prevent rock movement. • Mudflows: Implement effective drainage systems and create barriers to redirect flow. • Debris Flows: Build diversion channels and maintain vegetation to reduce runoff. • Earthflows: Stabilize with retaining structures and improve drainage. • Creep: Regularly monitor and maintain slope stability with appropriate landscaping and drainage. 3. How do volcanic processes and mass wasting processes intersect? When is the most damage from a volcanic eruption due to mass wasting? Answer: Intersection of Volcanic and Mass Wasting Processes: Volcanic eruptions can trigger mass wasting through the rapid deposition of volcanic materials like ash and lava, which can destabilize slopes. Most damage occurs when heavy volcanic deposits, such as pyroclastic flows or lahars, lead to landslides or debris flows, exacerbating the effects of the eruption. Internet Sites, Videos, Software, and Demonstration Aids Internet Sites 1. U.S.G.S. Geologic Hazards Team http://geohazards.cr.usgs.gov/ The team works in earthquake hazards, landslide hazards and the geomagnetism program. The site contains slides of landslides. 2. USGS Landslides, http://www.usgs.gov/themes/landslid.html The risks posed by landslides to various regions around the United States. 3. National Landslide Information Center, http://landslides.usgs.gov/nlic/ The U.S. Geological Survey databases on landslides and landslide research. Videos 1. Earth Revealed. Annenberg Media http://www.learner.org/resources/series78.html (1992, 30 mins., free video): • #16: Mass wasting. Mass wasting is a result of many factors and can cause many problems for people who build on slopes • #26: Living With Earth, Part II, Humans’ Impact on Earth. Fuels, how they are converted in to usable energy and the effects of their use. 2. Erosion: Landslide! Insight Media (2000, 54 mins.) The causes of landslides and how they can be prevented and their damage mitigated. Slides 1. National Geophysical Data Center, slide sets Landslides, set 1 Landslides, set 2 2. Geophoto Publishing. 35 mm transparencies or digital images, http://geophotopublishing.com/ Mass Wasting 3. Geologic Hazards Slide Set: Landslides. National Geophysical Data Center. 4. Mass Wasting, digital images. GeoPhoto Publishing. Answers to Figure-Related Critical Thinking Questions ❯❯ Critical Thinking Question Figure 11.11 Explain how the geologic planes of weakness in this slope plus water from rainfall influenced development of the depicted slide. Answer: Bedding planes between formations can act as “planes” of weakness if they are no longer horizontal, especially if the plane is inclined parallel to a sloped surface. Additionally, water can increase instability: add to the weight of a weakened mass – especially if the lower formation has significantly lower permeability with clay minerals that can help “grease the skids”. Water’s greatest influence, however, comes from increased pore pressure that may be the triggering mechanism. The geologic planes of weakness, such as bedding planes or faults, facilitated the development of the slide by providing weak zones where failure is more likely. Rainfall introduces water that reduces friction along these planes and increases the slope’s weight, making it more prone to sliding. This combination of pre-existing weaknesses and added water destabilizes the slope, leading to the slide. ❯❯ Critical Thinking Question Figure 11.12 Is there anything that could have been done after the first rock slide that might have prevented the second one 27 years later? If not, should people be allowed to build on known active slide areas? Answer: Since mass wasting is mostly a result of water, one of the main ways that rock slides could be prevented is to divert the water away from the slope. This could be accomplished by drainage ditches. Another method is to reduce the slope. One technique for that is the cut-and-fill method. Benching could be used and this method creates flat areas on the hillside that decelerates the movement of material downward. Whether or not the area needs to be declared unsuitable for building is a serious question and one that deserves consideration. After the first rock slide, measures such as installing stabilization structures (e.g., retaining walls, rock bolts) and improving drainage could have reduced the risk of a subsequent slide. Even with these measures, building on known active slide areas remains risky. Ideally, development should be avoided in such zones to prevent future hazards and ensure safety. ❯❯ Critical Thinking Question Figure 11.15 Why are debris flows typically composed of larger particles than mudflows? Answer: Since debris flows typically move at speeds of 25 miles per hour or more, they acquire the energy to pick up large particles (debris) within their path. Debris flows are typically composed of larger particles than mudflows because they carry a mix of coarse materials like rock fragments and soil, which results from the breakdown of slopes during intense rainfall or rapid snowmelt. Mudflows, on the other hand, consist mainly of finer, more cohesive materials like silt and clay that are more easily mobilized by water. ❯❯ Critical Thinking Question Figure 11.24 Locate the line that shows horizontal contact between rocks of different stability. What is the potential for mass wasting along this line, and why? Answer: Mass wasting has already occurred along this contact because of “oversteepening.” The line showing horizontal contact between rocks of different stability typically indicates a boundary where more stable rock meets less stable rock. The potential for mass wasting along this line is high because the contrast in stability can create a weak zone where failure is more likely, especially if the less stable rock is prone to sliding or erosion under stress or water infiltration. ❯❯ Critical Thinking Question Figure 11.25 What two features in this photo can you identify that indicate mass wasting at this location is both a current and potential problem? Answer: The porosity of the ground is indicated by the amount of vegetation growing on the hill. This porosity would allow rainfall to infiltrate the soil providing an impetus toward earth slides. Additionally, the extremely steep slope lends itself to mass wasting. In the photo, features indicating that mass wasting is both a current and potential problem include: 1. Active Landslide Scars: Recent or ongoing slides showing exposed, disturbed soil or rock. 2. Evidence of Ongoing Movement: Cracks, bulges, or tension features in the slope indicating continued instability and future potential for further mass wasting. ❯❯ Critical Thinking Question Figure 11.27 Given the height of this road cut, how effective do you think benching will be in helping to stabilize this slope? What other measures can be taken to minimize the damage from potential mass wasting? Answer: Failures will continue above each bench with such steep bedding: benches should be wider and layback slope angles gentler. Problem? Probably not enough real estate! Too steep for plantings – slope fences across these surfaces have been used, but it cannot prevent the erosion. Benching, while helpful, might be limited in effectiveness for very high road cuts as it primarily reduces slope steepness and provides small platforms to catch debris. For greater stability, additional measures such as installing retaining walls, improving drainage, and using slope stabilization techniques like rock bolts or netting can be crucial in minimizing potential mass wasting damage. Suggested Answer to Selected Short Answer Question (Answers to question 7 and question 8 provided in the appendix to the text) 10. What features of slope stabilization do you see in this photograph (❚ Figure 1) of a housing development in Concord, California? You should be able to recognize at least three features. Suggested Answer: Slope stabilization can occur in a variety of way and three are clearly visible in Figure 1. 1. Drainage – a series of ditches have been built into the hillside to collect and divert water to appropriate channels 2. Benching – involves cutting a series of benches or steps into a hillside. This process reduces the overall average slope. As is shown in Figure 1, benching is often used on steep hillsides in conjunction with a system of surface drains to divert runoff. 3. Planting vegetation – helps stabilize slopes by holding the soil together and reducing the amount of water in the soil. In the photograph of the housing development in Concord, California, features of slope stabilization include: 1. Retaining Walls: Structures built to hold back soil and prevent erosion. 2. Terracing: Series of step-like levels cut into the slope to reduce gradient and manage runoff. 3. Drainage Systems: Pipes or channels designed to direct water away from the slope to prevent saturation and instability. Chapter 12 Running Water – Streams and Rivers Chapter Outline 12.1 Introduction 12.2 Water on Earth 12.3 Running Water 12.4 Running Water, Erosion, and Sediment Transport 12.5 Deposition by Running Water GEO-FOCUS 12.1: The Mississippi River Delta—Past and Present 12.6 Can Floods Be Predicted and Controlled? GEO-INSIGHT 12.1: Floods and Flooding 12.7 Drainage Systems 12.8 The Evolution of Valleys 12.9 Water as a Natural Resource Key Concepts Review Learning Objectives Upon completion of this material, the student should understand the following. • Running water, one part of the hydrologic cycle, does considerable geologic work. • Water is continuously cycled from the oceans to land and back to the oceans. • Running water transports large quantities of sediment and deposits sediment in or adjacent to braided and meandering rivers and streams. • Alluvial fans (on land) and deltas (in a standing body of water) are deposited when a stream's capacity to transport sediment decreases. • Flooding is a natural part of stream activity that takes place when a channel receives more water than it can handle. • The several types of structures to control floods are only partly effective. • Rivers and streams continuously adjust to changes. • The concept of a graded stream is an ideal, although many rivers and streams approach the graded condition. • Most valleys form and change in response to erosion by running water coupled with other geologic processes such as mass wasting. Chapter Summary • Water continuously evaporates from the oceans, rises as water vapor, condenses, and falls as precipitation. About 20 percent of this precipitation falls on land and eventually returns to the oceans, mostly by surface runoff. • Runoff takes place by sheet flow, a thin, more or less continuous sheet of water, and by channel flow, confined to long, trough-like stream and river channels. • The vertical drop in a given distance, or the gradient, for a channel varies from steep in its upper reaches to more gentle in its lower reaches. • Flow velocity and discharge are related, so that if either changes, the other changes as well. • Erosion by running water takes place by hydraulic action, abrasion, and solution. • The bed load in channels is made up of sand and gravel, whereas suspended load consists of silt- and clay-sized particles. Running water also transports a dissolved load. • Braided streams have a complex of dividing and rejoining channels, and their deposits are mostly sheets of sand and gravel. • A single sinuous channel is typical of meandering streams that deposit mostly mud, with subordinate point-bar deposits of sand or more rarely, gravel. • Broad, flat floodplains adjacent to channels are the sites of oxbow lakes, which are simply abandoned meanders. • An alluvial deposit at a river's mouth is a delta. Some deltas conform to the three-part division of bottomset, foreset, and topset beds, but large marine deltas are much more complex and are characterized as stream, wave, or tide dominated. • Alluvial fans are fan-shaped deposits of sand and gravel on land that form best in semiarid regions. They form mostly by deposition from running water, but debris flows are also important. • Rivers and streams carry runoff from their drainage basins, which are separated from one another by divides. • Sea level is ultimate base level, the lowest level to which streams or rivers can erode. Local base levels may be lakes or where streams or rivers flow across resistant rocks. • Water is an important natural resource, most of which is saline water in the oceans. Only a small percentage of all water is on land in lakes, swamps, groundwater, and streams and rivers. • Graded streams tend to eliminate irregularities in their channels, so they develop a smooth, concave profile of equilibrium. • A combination of processes, including downcutting, lateral erosion, sheetwash, mass wasting, and head-ward erosion, are responsible for the origin and evolution of valleys. • Stream terraces and incised meanders usually form when a stream or river that was formerly in equilibrium, begins a new episode of downcutting. Enrichment Topics Topic 1. Big River in the Dry Western U.S. The Colorado River originates high in the Rocky Mountains of Colorado, fed year-round by snowmelt, rain, and groundwater. As the river travels across the parched lands of Utah, Arizona, and into Mexico, evaporation far exceeds precipitation. The Colorado River provides water to rapidly growing desert cities in California (Los Angeles), Nevada (Las Vegas), and Arizona (Phoenix and Tucson), primarily from the dams at Lake Mead and Lake Powell. Scientists have recognized that, as the desert southwest suffers through a continuing drought, dry times may be more typical of the weather pattern of the region than were the wet years when the river water was initially allocated. In response to the drier climate and to the likelihood that climate change will likely cause further rainfall reductions in the region, states have come together to agree to new water allocations. In April 2007, seven western states and the federal government agreed that if water allocations were cut, the reductions would be shared equally among the states. Just as this was about to take effect, the years became wetter and there is a temporary reprieve. Water allocations in the southwestern U.S. are a fascinating and ever changing topic. Topic 2. Power at a Price. The Three Gorges Dam, the world’s largest dam, on China’s Yangtze River is scheduled to become fully operational in 2012. At more than 600 feet high (183 m) and 1.5 miles (2.4 km) wide, the dam will create a reservoir hundreds of feet deep and nearly 400 miles long. The turbines will create as much electricity as 18 nuclear power plants or 15 coal burning plants. Part of the reason for the project is to end the Yangtze’s massive floods, which have killed more than one million people in the past century. The dam’s cost, though, is great. The rising waters will flood 395 square mile (632 square km) of land, displacing 1.2 million people from nearly 500 cities, towns, and villages along the river. Magnificent scenery and irreplaceable architectural and archeological sites will be lost including ancestral burial sites, temples dating back hundreds of years, and even fossil locales. China relocated 1.24 million residents, some to other provinces. Relocated farmers struggle since the Yangtze’s floodplains are among the most fertile land in China and the replacement land is unlikely to be as productive. Alterations of river conditions will further endanger baiji dolphins (Lipotes vexillifer) and finless porpoises (Neophocaena phocaenoides), among other creatures. The price tag for the dam may be as high as $50 billion. Topic 3. History of the Clean Water Act. During the 1950s and 1960s, water quality declined, since not all cities had sewage treatment plants, not all pollutants were treated in them, and many new chemicals were being put into the water. Intensive agriculture increased the runoff of nutrients, herbicides, and insecticides. Industrialization and urbanization intensified. The precipitous decline in water quality came to a head in 1969 when the Cuyahoga River, a tributary of Lake Erie, caught fire as it flowed through downtown Cleveland, Ohio. This spurred Congress to pass the Clean Water Act of 1972, which established air quality standards, set emissions limits, empowered state and federal government with enforcement, and increased funding for air pollution research. The law, amended in 1990, now regulates 189 toxic air pollutants, oversees alternative fuels, and also restricts the pollutants that contribute to acid rain and stratospheric ozone depletion. The amended law introduced a market-based system for controlling the emissions that cause acid rain, known as cap-and-trade. The goal is to restore and maintain the cleanliness of the nation’s waters for recreation, fishing, and wildlife. The Clean Water Act, like the Clean Air Act and the Endangered Species Act, comes under political attack periodically when people forget the pollution levels that once existed. Common Misconceptions Misconception 1: With the knowledge that we have today, and with the science, engineering, and technology at our disposal, we can largely do what we want to with such a simple, inanimate thing as running water. Fact: Running water has to conform to definite “laws” which are as immutable as other physical laws in physics or chemistry. We may be able to constrain running water to perform some actions that we desire, but there may be required reactions which we do not necessarily want. It is essential that we understand all the likely consequences of our actions before we make a decision to “control” a stream or stream system, so that we know the full price we may have to pay. Misconception 2: Due to the Clean Water Act and other measures, water in the United States is now clean. Fact: There are many pollutants that are not regulated. Many have not been studied or have not been studied in combination with other pollutants that are released into the environment. Some of these are endocrine disruptors, which mess with the endocrine system that regulates an animal’s growth, development, and maturation, by sending out hormones as chemical messengers. Lecture Suggestions 1. When discussing graded streams, diagram the factors that act to increase rates of erosion and deposition in terms of a sine-cosine curve balanced about an axis of equilibrium, with deposition represented by positive values and erosion represented by negative values. Point out that a stable equilibrium is never reached, but instead, all streams are in a constant flux about such an equilibrium state. 2. Drainage basin types are readily recognized if geologic maps are used to illustrate their configurations. If the essentials of geologic maps can be briefly explained, the relationships among geologic structures, drainage basin patterns, and landforms can be easily understood. The same can be demonstrated for incised and superposed streams. 3. It’s fun to let students play with sediment and water for a while to see how they interact. What is the effect of water on sand if only a small amount of water is added? A larger amount? How much water must be added for the sand to flow? 4. Some of Earth’s most amazing features are the result of water erosion. Show slides of the Grand Canyon and discuss how the Colorado River did its amazing work. 5. Students have very little sense of how much humans have impacted the natural world. Be sure that they understand how dams impact habitats, how pollution affects the natural world, and the way that people can use water as a resource. Consider This 1. If some submarine canyons extend seaward from stream mouths, is sea level really an ultimate base level? Answer: Sea Level as Base Level: Sea level is not always the ultimate base level, as submarine canyons extending from stream mouths suggest that local base levels can be influenced by factors such as tectonic activity or sediment supply, which can affect erosion and deposition patterns beyond just sea level. 2. All physical systems tend toward a state of homeostasis or dynamic equilibrium. Is the dynamic equilibrium of a graded stream ever actually reached? Answer: Dynamic Equilibrium in Graded Streams: The dynamic equilibrium of a graded stream is rarely fully achieved due to ongoing changes in sediment supply, base level, and climatic conditions, which continually adjust the stream’s gradient and sediment load. 3. If deposition is inhibited during times of glacial advance (less meltwater and sediment load) and enhanced during time of glacial retreat (more meltwater carrying greater sediment loads), how might a study of the number of and stratigraphy of stream terraces in the lower Mississippi Valley be a gauge of the number of glacial advances and retreats? Answer: Stream Terraces and Glacial Cycles: The number and stratigraphy of stream terraces in the lower Mississippi Valley reflect glacial advances and retreats, as each terrace corresponds to a period of sediment deposition during glacial retreats and erosion during advances, providing a record of glacial activity. 4. Explain why many streams in the Rocky Mountains cut directly across mountain ranges. Answer: Streams Cutting Across Ranges: Streams in the Rocky Mountains cut directly across mountain ranges due to their ability to maintain their course through active uplift and erosion, often exploiting pre-existing weaknesses or faults in the rock. 5. The Army Corps of Engineers commonly straightens and otherwise modifies the course and dimensions of streams. What are some of the effects that the straightening of a stream channel could have? Answer: Effects of Stream Channel Straightening: Straightening a stream channel can increase flow velocity, reduce sediment deposition, lead to increased erosion downstream, disrupt ecosystems, and alter flood patterns, potentially causing ecological and structural issues. 6. If you were a city planner in a community through which a stream flowed, what information would you need in order to determine where, or if, a development project should be located in the vicinity of a stream? Consider a variety of stream and drainage basin types. Answer: Information for Development Projects: As a city planner, you would need data on floodplain boundaries, sediment load, streamflow patterns, erosion rates, and historical flood records, as well as understanding the type of stream and drainage basin to assess risks and make informed decisions about development. Internet Sites, Videos, and Demonstration Aids Internet Sites 1. Water Resources of the United States, USGS, http://water.usgs.gov/ Water sources, water quality, natural disasters caused by water, and scientific methods used to understand water, from the United States Geological Survey. 2. Water use in the United States, USGS, http://water.usgs.gov/watuse/ The water use site is updated every five years, includes fact sheets, estimated withdrawals from various sources, from the United States Geological Survey. Videos 1. Wild River: The Colorado. PBS Home Video, DVD (2006, 60 mins.) The Colorado River from its headwaters in the Rocky Mountains through Utah and into Mexico 2. When the Water Tap Runs Dry, PBS Home Video, DVD (2009, 40 mins.) Water shortages are another consequence of climate change. How will society respond to less water coming through our taps? 3. Flood! NOVA Online, PBS. http://www.pbs.org/wgbh/nova/flood/ The Great Flood of 1993 taught us that containing rivers is not as easy as it looks. 4. Stream Systems and the Fluvial Processes. Insight Media (1994, 30 mins.) Running water and how it shapes Earth’s surface features. 5. Geomorphology: Study of the Shape of the Earth. Insight Media (2005, 20 mins.). The forces that shape the Earth and the landforms they create. 6. River Landforms. Insight Media (1996, 26 mins.) Landscapes and features found along rivers and the processes that created them. 7. Rivers: Shapers of Earth Landscapes. Insight Media (2001, 26 mins.) Types of streams and river processes. 8. Running Water: How It Erodes and Deposits. Insight Media (2003, 41 mins.) How running water changes the surface of the Earth. 9. Water Erosion and Landforms. Insight Media (1999, 15 mins.) How rivers and glaciers create landforms. 10. Weathering. Insight Media (1999, 16 mins.) Physical and chemical weathering of minerals and rocks. 11. Weathering and Erosion. Insight Media (2000, 24 mins.) How wind, water and gravity cause weathering and erosion and create landforms. 12. The Water Cycle. Insight Media (1980, 15 mins.) Basic principles of the water cycle. 13. Water Planet. Insight Media (2003, 27 mins.) The origins of water on Earth. 14. Badlands: A Battle of Erosion. Instructional Video USA, DVD (30 mins.) The work of running water and wind on sedimentary rock as seen in Badlands National Park. 15. Rivers of Stone: A Visit to Colorado National Monument. Instructional Video, USA, DVD (30 mins.) Rock formations and erosion in western Colorado. 16. The Geology and Natural History of Arches National Park. Instructional Video, USA, DVD (30 mins.) The formation of the arches, the rock they’re made out of and the plants and animals of the park. 17. The Formation of Natural Arches and Bridges. Instructional Video, USA, DVD (11 mins.) Weathering and erosion and how they create these features. 18. Earth Revealed. Annenberg Media http://www.learner.org/resources/series78.html (1992, 30 mins., free video): • #19: Running Water I: Rivers, Erosion and Deposition. Features of rivers, types, parts and characteristics of rivers, including flooding • #20: Running Water II: Landform Evolution. The Colorado River and how it has carved the Grand Canyon, includes the processes of erosion and deposition. Slides and Demonstration Aids 1. Educational Images, Ltd. slide sets, http://www.educationalimages.com/cg120001.htm a. Erosion Slides and Surface Features 2. Major Landforms. Insight Media (2009, CD-ROM) 72 images of landforms with aerial and ground views and erosional stages of some types. 3. Ward’s stream table landform simulation system. Ward’s Natural Science. Features two separate stream flows. Answers to Figure-Related Critical Thinking Questions ❯❯ Critical Thinking Question Figure 12.18 What are some of the functions of a dam and its reservoir? Answer: Some of the functions of dams and reservoirs are to maintain an area’s water supply, to provide hydroelectric power, stabilization of water flow to prevent flooding, irrigation, and recreation. Suggested Answer to Selected Short Answer Question (Answers to question 6 and question 9 provided in the appendix to the text) 7. The discharge of most streams and rivers increases downstream, but in a few cases, it actually decreases and they eventually disappear. Explain why. Suggested Answer: In most rivers and streams, discharge increases downstream as more and more water enters a channel, but there are a few exceptions. Because of high evaporation rates and infiltration, the flow in some desert waterways actually decreases downstream until the water disappears. And even in perennial rivers and streams, discharge is obviously highest during times of heavy rainfall and at a minimum during the dry season. The discharge of streams and rivers typically increases downstream due to the accumulation of tributary flow. However, in some cases, discharge decreases and streams may disappear due to high evaporation rates, infiltration into porous ground, or diversion for irrigation or other uses, which reduces the flow before it reaches its mouth. Chapter 13 Groundwater Chapter Outline 13.1 Introduction 13.2 Groundwater and the Hydrologic Cycle 13.3 Porosity and Permeability 13.4 The Water Table 13.5 Groundwater Movement 13.6 Springs, Water Wells, and Artesian Systems 13.7 Groundwater Erosion and Deposition 13.8 Modification of the Groundwater System and Its Effects GEO-FOCUS 13.1: Hydraulic Fracturing: Pros and Cons GEO-INSIGHT 13.1: Arsenic and Old Lace 13.9 Hydrothermal Activity Key Concept Review Learning Objectives Upon completion of this material, the student should understand the following. • Groundwater is one reservoir of the hydrologic cycle and accounts for approximately 22 percent of the world's supply of freshwater. • Porosity and permeability are largely responsible for the amount, availability, and movement of groundwater. • The water table separates the zone of aeration from the underlying zone of saturation and is a subdued replica of the overlying land surface. • Groundwater moves downward because of the force of gravity. • In an artesian system, groundwater is confined and builds up high hydrostatic pressure. • Groundwater is an important agent of both erosion and deposition and is responsible for karst topography and a variety of cave features. • Modifications of the groundwater system may result in a lowering of the water table, saltwater incursion, subsidence, and contamination. Chapter Summary • Groundwater is part of the hydrologic cycle and an important natural resource. It consists of all subsurface water trapped in the pores and other open spaces in rocks, sediment, and soil. • Porosity is the percentage of a material’s total volume that is pore space. Permeability is the capacity to transmit fluids, and is dependent on porosity, but also on the size of the pores or fractures and their interconnections. • The water table is the surface separating the zone of aeration (in which the pores are illed with air and water) from the underlying zone of saturation (in which the pores are filled with water). The water table is a subdued replica of the overlying land surface in most places. • Groundwater moves slowly downward under the influence of gravity through the one of aeration to the zone of saturation. Some of it then moves along the surface of the water table, and the rest moves from areas of high pressure to areas of low pressure. • Groundwater velocity varies greatly and depends on a number of factors. Generally, the average velocity of groundwater is a few centimeters per day. Springs are found wherever the water table intersects the ground surface. Some springs are the result of a perched water table—that is, a localized aquiclude within an aquifer and above the regional water table. • Water wells are openings made by digging or drilling down into the zone of saturation. When water is pumped from a well, the water table in the area around the well is lowered, forming a cone of depression. • In an artesian system, confined groundwater builds up high hydrostatic pressure. For an artesian system to develop, an aquifer must be confined above and below by aquicludes; the aquifer is usually tilted so that it can build up hydrostatic pressure; and the aquifer must be exposed at the surface so that it can be recharged. • Karst topography develops by groundwater erosion in many areas underlain by soluble rocks. It is typically characterized by sinkholes, caves, solution valleys, and disappearing streams. • Caves form when groundwater in the zone of saturation weathers and erodes soluble rock such as limestone. Common cave deposits include stalactites, stalagmites, columns, drip curtains, and travertine terraces. • Modification of the groundwater system can cause serious problems such as lowering of the water table, saltwater incursion, subsidence, and contamination. • Groundwater quality is mostly a function of the kinds of materials that make up an aquifer, the residence time of water in an aquifer, and the solubility of rocks and minerals. • Contamination by humans is becoming a serious problem and can result from landfills, septic systems, toxic waste sites, and industrial effluents, all of which affect the quality of the groundwater. • Hydrothermal refers to hot water, typically heated by magma, but also resulting from Earth’s geothermal gradient as it circulates deeply beneath the surface. Manifestations of hydrothermal activity include fumaroles, hot springs, and geysers. • Geothermal energy is energy produced from Earth’s internal heat and comes from the steam and hot water trapped within Earth’s crust. It is a relatively nonpolluting form of energy that is used as a source of heat and to generate electricity. Enrichment Topics Topic 1. Life in a Groundwater Reservoir. It may seem impossible, but organisms have been found in some porous groundwater aquifers and karst features despite that there is no light, little oxygen, and scant nutrients. Called stygobionts, the creatures occupy the dark spaces between sand grains. Stygobionts are colorless, eyeless, and have worm-shaped bodies for easier movement. They move and metabolize more slowly and have longer life spans than typical aquatic organisms. Without light for photosynthesis, food energy comes into the ecosystem as organic matter from the surface. The food web is simple—microbes, such as bacteria and fungi, consume the organic matter and serve as food for somewhat larger invertebrate predators. Because food is scarce, most stygobionts will eat whatever they can find, a good adaptation to have in an extreme environment. Topic 2. Bangladesh and Arsenic. Well-meaning aid organizations wanted to save rural Bangladeshis from the sewage-contaminated surface water they once drank that annually killed about 250,000 children. To gain access to the underlying groundwater, they drilled more than 14 million tube wells, although the local people called the groundwater “devil’s water.” It turned out that the aquifers lying beneath Bangladesh contain high arsenic concentrations, and now about 29 percent of all wells in Bangladesh contain water with arsenic levels higher than the guidelines established by the World Health Organization. The result is that as many as 20,000 Bangladeshis die of arsenic poisoning each year. Arsenic in low levels poisons slowly, and the seriousness of the situation was not immediately realized. In the mid-1990s, large numbers of people began appearing with signs of arsenic poisoning—tumors and blisters on the bottoms of their feet and on the palms of their hands. Internally, arsenic attacks the kidneys and lungs. Prolonged exposure is linked to several types of cancer, diabetes, skin thickening, numbness, partial paralysis, liver disease, and digestive system problems. Over time, the damage done by arsenic poisoning can be undone with clean water and nutritious foods, but most of the victims are too poor to have access to these commodities. Arsenic can be filtered out of the water, but many rural communities cannot afford the treatment technology. Research is being done on less expensive systems that exploit the affinity of arsenic for the magnetic mineral magnetite. When added to a bucket of well water, this mineral attracts the arsenic, which is then collected with a magnet and discarded. In the meantime, alternative water supplies are being constructed in the most affected areas. Topic 3. Bacterial Bioremediation. MTBE was used as a gasoline additive between 1992 and 1998, when the EPA classified it as a potential human carcinogen. Ready-to-pump gasoline, including additives, is stored in underground tanks at service stations. Tens of thousands of these tanks have leaked, leading to MTBE contamination in approximately 300 water systems in 36 states. Cleaning up groundwater is extremely difficult since the water and the host rock must be treated. One method of cleaning groundwater is bacterial bioremediation. Microorganisms that consume the contaminant are found or are specially bioengineered to breakdown the contaminant. Once the organism is in hand, it is bred in large numbers and released into the contaminated aquifer. The organism consumes all of the contaminant; when it has nothing left to eat, it die outs. Since 2003, bioremediation has been taking place on a massive MTBE plume in the San Fernando Valley of California. The San Fernando Valley groundwater supplies 10 percent of the city’s drinking water. Contaminated water is pumped into a system containing MTBE-loving microbes, called PM1, for bioremediation. After several trips, the MTBE levels drop below the detection limit and the clean water is reinjected back into the aquifer. This process saves 10 million gallons (38 billion liters) of water a year that might otherwise be lost from drinking water supplies. Common Misconceptions Misconception 1: Water underground flows in streams or is located in caves or pools. Fact: Except for special cases, such as in areas of karst topography or where well-developed lava tubes are present, groundwater is present in the pore spaces of rocks in a blanket-like body, an aquifer, with a water table. Misconception 2: There is something unique or special about the properties of artesian water. Fact: Artesian water is that which is under pressure because it is in a confined aquifer, and therefore it may rise toward the surface if the aquifer is breached, as by a well or spring. There is no difference in the chemical composition or other properties of the artesian water—for medicinal value, brewing, or any other purpose. Lecture Suggestions 1. You can demonstrate Darcy’s Law (Velocity of groundwater movement = Permeability Gradient) using a large glass cylinder with openings at each end and packed with glass marbles. Allowing water to flow through, you can show how the velocity with which the water moves through this material, which has a fixed permeability, varies with the gradient—by tilting the cylinder to different angles. 2. Point out how an artesian system is one where water is able to flow uphill because it has been confined and is under pressure. This is not unlike the water distribution system that may be in the classroom, where water flows up and out the faucet because it has been confined in the pipes and is under pressure, which is maintained usually by storing the water at a higher elevation in a tank. 3. A sample of sand from a swimming pool filter can lead to a discussion of porosity and the ability of an aquifer to remove particulate matter from groundwater. Ask students why sand is used and whether just any sand will do. What are the qualities of the grains that would make them suitable for use in a filter? Another natural filter that has applications for its ability to remove particles as small as 1 micron from water is diatomaceous earth. Ask the students to suggest other natural materials that might be useful in this manner. 4. Use the Ogallala Aquifer as an example of overuse of a groundwater resource. On average, water is being pumped from the aquifer at eight times the rate that it is being recharged. The water table is dropping as much as 3 to 5 feet per year. Have the students discuss what the effects of this will be since this aquifer is the main water source for the rich farmland of the Midwestern United States. 5. Compare and contrast hydrothermal vents at mid-ocean ridges with geysers on land. Both are fascinating! Consider This 1. Can groundwater exist in igneous and metamorphic rocks? Answer: Groundwater in Igneous and Metamorphic Rocks: Yes, groundwater can exist in igneous and metamorphic rocks if these rocks have sufficient fractures, faults, or weathered zones that allow water to accumulate and flow. 2. How might the existence of hot springs in Georgia, Arkansas, and the Black Hills be explained? Answer: Hot Springs Explanation: The existence of hot springs in areas like Georgia, Arkansas, and the Black Hills can be explained by geothermal activity, where heat from deeper magma chambers or hot rock formations heats groundwater, causing it to rise to the surface. 3. If you were a hydrologist employed by a construction company planning a large development project in an arid region, along an ocean coast, and downstream from a large city and a landfill, what factors would you need to consider and what data would you need in order to plan a sufficient water supply for the new development? Answer: Factors and Data for Water Supply Planning: Consider factors such as local groundwater recharge rates, water quality, existing water rights, and potential contamination sources. Data needed includes hydrological studies, historical water usage records, and water quality assessments to ensure a sustainable and clean water supply. Internet Sites, Videos, Software, and Demonstration Aids Internet Sites 1. Groundwater and Drinking Water, EPA, http://www.epa.gov/safewater/ Protecting public health by protecting groundwater and drinking water. 2. The Groundwater Foundation, http://www.groundwater.org/ News about groundwater. 3. Virtual Cave, http://www.goodearthgraphics.com/virtcave/ The wonders of different types of caves including solution caves. 4. USGS: Geology of Caves, http://www.nature.nps.gov/GEOLOGY/usgsnps/cave/cave.html The geology of caves including how to explore them. Videos 1. Yellowstone: Land to Life. Nature, PBS (2009, 30 mins.) A lyrical interpretation of the geology of Yellowstone. 2. How Chemicals Move Through Soil. Insight Media (1996, 27 mins.) Chemical interactions with soil and their affect on water quality in groundwater. 3. Ground Water. Insight Media (1999, 14 mins.) The distribution and importance of groundwater. 4. Underground Water. Insight Media (1000, 20 mins.) How groundwater forms and the basics of groundwater hydrology. 5. Earth Revealed. Annenberg Media http://www.learner.org/resources/series78.html (1992, 30 mins., free video): • #21: Groundwater. Basics of groundwater and the importance of this water source to humankind. 6. Underground Water. Instructional Video, DVD (21 mins.) Groundwater and how people tap into it are investigated. 7. Let’s Explore a Cave. Instructional Video, DVD (21 mins.) An introduction to caves and caverns including visits to a few caves. 8. Timpanogos Cave. Instructional Video, DVD (30 mins.) 9. Geysers and Hot Springs of Yellowstone. Instructional Video USA, DVD (19 mins.) The geothermal basins at Yellowstone National Park. Answers to Figure-Related Critical Thinking Questions ❯❯ Critical Thinking Question Figure 13.1 How can some Earth materials be porous, yet not permeable? Give an example. Answer: The Weathering chapter explained it best: as particle size decreases, the collective surface areas increase AND the spaces surround those particles increase. Porosity increases as particle size decreases. However, as particle sizes decrease, so does the pore sizes; reducing pore throats, eventually “choking” off the flow communication “pore to pore.” ❯❯ Critical Thinking Question Figure 13.3 If you were drilling a water well on your property and struck water at a considerably shallower depth than your neighbors, should you consider drilling deeper, or just celebrate your good fortune at not having to pay for a deeper well? Answer: It may be wise to extend the well screen at least as deep as the neighbor’s to insure against the inevitable drawdown that both of you will cause – your well will experience it first if you don’t. ❯❯ Critical Thinking Question Figure 13.6 If the elevation of the wellhead is at or above that of the artesian-pressure surface, why then will the well be nonflowing? Answer: By “nonflowing”, you mean that the well’s confined water pressure will not flow out of the well & on to the surface: confined or unconfined ground water flows. Confined pressure water bearing zones (a better term than aquifer) will not rise above their potentiometric surfaces, a surface that is not horizontal as it declines due to friction. Potentiometric head declines over distance. ❯❯ Critical Thinking Question Figure 13.7 Why is karst topography typically restricted to humid and temperate climates? Answer: Karst processes function best where precipitation is abundant and growing season is fairly long: the solution caves of Kentucky and the sinkhole region of Florida are good examples, but sinkholes exist in the Michigan Basin, a well known limestone region, with the sinkholes common in the northeast part of the Lower Peninsula with thin glacial cover. ❯❯Critical Thinking Question Figure 13.8 Why are sink holes becoming more prevalent in Florida, especially in areas experiencing population growth? Answer: Sink holes are a naturally occurring feature in the Florida landscape because it is underlain by thick carbonate deposits that are susceptible to dissolution by circulating ground water. Sinkholes tend to represent a connection between ground water and surface water. Aggressive pumping, as a result of growing population, industry, and agriculture, can induce sinkholes by abruptly changing ground-water levels and disturbing the equilibrium between a buried cavity and the overlying earth materials. ❯❯ Critical Thinking Question Figure 13.26 Although geothermal energy is a relatively nonpolluting form of energy used as a source of heat and to generate electricity, why is it typically a more expensive form of energy? (Hint: Which contains more dissolved minerals, hot or cold water?) Answer: Geothermal gradient is a function of depth within the Earth’s crust: with depth ground water becomes warmer. Warmer water dissolves & holds more minerals than cooler water. Use of this warm water for energy if brought to the surface involves engineering technologies to deal with fairly caustic water that requires high pressures and constant monitoring and replacement parts. The water quality of deeper reservoirs cannot be left on the surface, if that is where the energy exchange takes place: it is usually sent back underground. Suggested Answer to Selected Short Answer Question (Answers to question 8 and question 9 provided in the appendix to the text) 7. Why should we be concerned about how fast the groundwater supply is being depleted in some areas? Suggested Answer: Groundwater is the largest source of usable, fresh water in the world. In many parts of the world, especially where surface water supplies are not available, domestic, agricultural, and industrial water needs can only be met by using the water beneath the ground. A myriad of problems ensue when groundwater is pumped at a faster rate than it is being discharged, such as lowering of the water table and wells not being able to reach the water, land subsidence, and increased cost to pump the water. We should be concerned about the rapid depletion of groundwater supplies because it can lead to reduced water availability for drinking, agriculture, and industry. Over-extraction can cause problems such as land subsidence, reduced water quality, and the drying up of wells and natural springs, ultimately impacting ecosystems and human communities. Chapter 14 Glaciers and Glaciation Chapter Outline 14.1 Introduction 14.2 The Kinds of Glaciers GEO-INSIGHT 14.1: The Little Ice Age 14.3 Glaciers—Moving Bodies of Ice on Land 14.4 The Glacial Budget GEO-FOCUS 14.1: Glaciers and Global Warming 14.5 Erosion and Transport by Glaciers 14.6 Glacial Deposits 14.7 What Causes Ice Ages? Key Concepts Review Learning Objectives Upon completion of this material, the student should understand the following. • Moving bodies of ice on land known as glaciers cover about 10 percent of Earth's land surface. • During the Pleistocene Epoch (Ice Age), glaciers were much more widespread than they are now. • Water frozen in glaciers constitutes one reservoir in the hydrologic cycle. • In any area with a yearly net accumulation of snow, the snow is first converted to granular ice known as firn and eventually into glacial ice. • The concept of the glacial budget is important to understanding the dynamics of any glacier. • Glaciers move by a combination of basal slip and plastic flow, but several factors determine their rates of movement and under some conditions, they may move rapidly. • Glaciers effectively erode, transport, and deposit sediment, thus accounting for the origin of several distinctive landforms. Chapter Summary • Glaciers currently cover about 10% of the land surface and contain about 2.15% of all water on Earth. • A glacier forms when winter snowfall exceeds summer melt and accumulates year after year. Snow is compacted and converted to glacial ice, and when the ice is about 40 m thick, pressure causes it to flow. • Glaciers move by plastic flow and basal slip. • Valley glaciers are confined to mountain valleys and flow from higher to lower elevations, whereas continental glaciers cover vast areas and flow outward in all directions from a zone of accumulation. • The behavior of a glacier depends on its budget, which is the relationship between accumulation and wastage. If a glacier has a balanced budget, its terminus remains stationary; a positive or negative budget results in the advance or retreat of the terminus, respectively. • Glaciers move at varying rates depending on slope, discharge, and season. Valley glaciers tend to flow more rapidly than continental glaciers. • Glaciers effectively erode and transport because they are solids in motion. They are particularly effective at eroding soil and unconsolidated sediment, and they can transport any size sediment supplied to them. • Continental glaciers transport most of their sediment in the lower part of the ice, whereas valley glaciers may carry sediment in all parts of the ice. • Erosion of mountains by valley glaciers yields several sharp, angular landforms including cirques, arêtes, and horns. U-shaped glacial troughs, fiords, and hanging valleys are also products of valley glaciation. • Continental glaciers abrade and bevel high areas, producing a smooth, rounded landscape known as an ice-scoured plain. • Depositional landforms include moraines, which are ridge-like accumulations of till. The several types of moraines are terminal, recessional, lateral, and medial. • Drumlins are composed of till that was apparently reshaped into streamlined hills by continental glaciers or floods. • Stratified drift in outwash plains and valley trains consists of sand and gravel deposited by meltwater streams issuing from glaciers. Ridges, known as eskers, and conical hills called kames are also composed of stratified drift. • Major glacial intervals separated by tens or hundreds of millions of years probably occur as a result of the changing positions of tectonic plates, which in turn cause changes in oceanic and atmospheric circulation patterns. • Currently, the Milankovitch theory is widely accepted as the explanation for glacial-interglacial intervals. • The reasons for short-term climatic changes, such as the Little Ice Age, are not understood. Two proposed causes are changes in the amount of solar energy received by Earth and volcanism. Enrichment Topics Topic 1. Snowball Earth. A controversial hypothesis suggests that during 10 million years of the Precambrian, Earth was covered with ice up to 1 km thick during which time nearly all life was wiped out. Computer models show that if the polar ice caps grow beyond a certain point, runaway freezing occurs. Evidence for the snowball hypothesis includes signs of past glaciation in places that should have been too hot. But if snowball Earth existed, how did it escape the ice? One possibility is that volcanoes with tops above the ice pumped greenhouse gases into the atmosphere. With the water cycle at a standstill because the water was all in ice, there was no rain and the greenhouse gases remained in the atmosphere. Eventually there was intense global warming and a big thaw about 600 million years ago. With the planet freed from ice, complex organisms could then evolve. Topic 2. Ice Cores and the Paleoenvironment. The most powerful window into past climate is the ice contained in glaciers and ice caps. To collect an ice core, scientists drill a hollow pipe into an ice sheet or glacier. The cores taken from the Greenland and Antarctic ice caps supply data that span long periods of time. Two Greenland cores go back 100,000 years, while one Antarctic core goes back 420,000 years through four glacial cycles. The European Project for Ice Coring in Antarctica, (EPICA) about two miles (3,190 m) long, has cut through eight glacial cycles covering 740,000 years and is still being drilled. Gases and particles trapped in snowfall can be analyzed by examining ice layers. These substances represent atmospheric conditions at the time the snow fell. Scientists can analyze CO2 in the gases to determine the concentration of that greenhouse gas at the time and to ascertain its source, whether from volcanic eruptions or burning fossil fuels, for example. The presence of Beryllium-10 in the ice core is evidence of the strength of solar radiation. Ash indicates a volcanic eruption; dust, an expansion of deserts; and pollen, the types of plants that were on the planet at the time. The amount of pollen found in the ice layer may be an indicator of the amount of precipitation that fell. Paleoclimatologists can discern air temperature at the time the snow fell by measuring the ratios of different isotopes of oxygen and hydrogen. These isotope ratios also reveal global sea level. Topic 3. Global Warming and a European Ice Age? Global ocean circulation is driven by the frigid, saline waters of the North Atlantic. In this region, sea ice forms and the water left behind is saline and cold. Salty, cold water is dense, so it sinks. The “hole” in the surface ocean is filled with relatively warm water that is pulled north from the equatorial region. This current is known as the Gulf Stream and it travels from the equator, up the eastern United States, then across the North Atlantic to Europe, where it splits. Some warm water moves south along Europe and some moves north through the English Channel. This warm water keeps Europe, particularly the British Isles, warmer than they would be for their latitude. However, global warming could stop this circulation. If waters in the North Atlantic become too warm to form sea ice, they will be less dense than the water beneath and will not sink. This will stop the pull of the Gulf Stream; Europe will no longer get the benefit of the warm water and could plunge into a new ice age. Common Misconceptions Misconception 1: There was one great Ice Age in the recent past. Fact: In North America, at least four major episodes of glaciation separated by interglacials can be recognized during the Pleistocene. In Europe, at least six or seven advances and retreats are recognized, and deep-sea cores record at least 20 warm-cold cycles. Misconception 2: We do not need to worry about global warming because a new ice age is coming. Fact: Indeed, scientists think that we are currently in an interglacial period and that we will enter a new glacial time in the future. However, we can’t count on this happening for hundreds or thousands of years, and human systems depend on climate being much as it has been for the past century or two. Therefore, global warming must be a concern. Lecture Suggestions 1. The general topic of climatology could be introduced prior to lectures on glaciation. 2. The deposition of till in ground moraines and terminal/recessional moraines can be likened to a lawn fertilized by a spreader. When moving, the fertilizer is evenly spread across the ground. However, when stationary and with the chute open, the fertilizer will accumulate in a ridge-like pile. 3. Basal slip may be explained by analogy with the phenomenon that permits ice-skaters to glide over ice. The weight of the skater is concentrated on the skate blade, and this pressure is great enough to melt the ice beneath. It is this thin layer of water that permits basal slip of the skate and thus the skater. Similarly the weight of 40 m or more of ice will cause some basal melting and thus basal slip. 4. A model planetarium would be useful for demonstrating the variations in orbital parameters on which the Milankovitch theory is based. 5. There is a lot of evidence that the effects of global warming are already being felt. This is particularly true in the polar regions. In the Arctic, loss of sea ice is destroying the habitat needed by polar bears as the ice they hunt from the population of ringed seals, their main food, declines. It is worth finding the latest information on the effects of warming temperatures on the Arctic to share with the class. Consider This 1. Both valley and continental glaciers produce depositional landforms. However, valley glaciers carry sediment within all levels as well as on their surface, while continental glaciers carry sediment only in the lower levels and at their base. How then do continental glaciers produce such stratified drift deposits as eskers and kames, while valley glaciers do not? Answer: Continental glaciers produce stratified drift deposits like eskers and kames because they melt and deposit sediment in complex patterns, including under the ice and in meltwater channels. Valley glaciers, in contrast, generally carry sediment in a more confined manner within the glacier, leading to less stratification in their deposits. 2. Suggest a plausible relationship between the Milankovitch cycles and the production/removal of atmospheric carbon dioxide. Answer: Milankovitch cycles, which influence Earth's climate through changes in its orbit and axial tilt, affect the amount of solar radiation reaching Earth. These climate variations can alter atmospheric carbon dioxide levels by influencing temperatures and carbon cycle processes, which in turn can either release or sequester CO₂. 3. Predictions of global warming project 0.9 to 3.6oF (0.5 to 2oC) increase in the global average annual temperature by the middle of the 21st century if nothing is done to reduce greenhouse gas emissions. Such an increase in temperature would result in some melting of glaciers and an increase in sea level of between 7 and 32 inches (18 and 81 cm) by the end of the century (IPCC report, 2007). a. What regions of the world would be most severely affected by such a rise in sea level? b. What effects would such a sea level rise have on the ground water supplies of coastal cities? c. What effects would such a sea level rise have on sediment deposition at the mouths of large rivers or depositional environments such as the Mississippi Delta? d. What effects would such a sea level rise have on coastal erosion? Answer: a. Low-lying coastal areas like Bangladesh, the Netherlands, and Florida would be most severely affected by sea level rise. b. Coastal cities may face saltwater intrusion into groundwater supplies, reducing the availability of fresh water. c. Increased sea level could lead to altered sediment deposition patterns, potentially causing sediment to be redistributed further offshore or altering delta formations. d. Higher sea levels would likely accelerate coastal erosion, as waves and storm surges reach further inland and impact more of the coastline. Internet Sites, Videos, and Demonstration Aids Internet Sites 1. Deglaciation of North America, U.C. Santa Barbara, animation http://emvc.geol.ucsb.edu/1_DownloadPage/Download_Page.html#IceAge Watch ice recede (and sometimes advance) over North America. 2. Flooding of SF Bay, U.C. Santa Barbara, animation http://emvc.geol.ucsb.edu/1_DownloadPage/Download_Page.html#IceAge Watch water levels in the San Francisco Bay from the ice ages to the present. 3. Global Change Research Program, U.S. GeologicalSurvey http://www.usgs.gov/climate_landuse/ Climate change science with explorations of ongoing research. 4. Intergovernmental Panel on Climate Change, http://www.ipcc.ch/ The latest climate change report from the IPCC. 5. Pew Center on Global Climate Change, http://www.pewclimate.org. Basics of climate change science plus recent climate change news. DVDs 1. Warnings from the Ice. NOVA, PBS, DVD (2008, 54 mins.) The collapse of ice sheets in Antarctica could trigger a catastrophic rise in sea level around the world. 2. Extreme Ice. NOVA, PBS, DVD. A unique photo archive of melting glaciers in remote locations in the Arctic, Alaska and the Alps created through time-lapse photography. 3. Mystery of the Megaflood. NOVA, PBS, DVD (2005, 60 mins,) A glacial dam breaks, causing a gigantic flood that wipes out the animals in its vicinity. 4. Gulfstream and the Next Ice Age, PBS, DVD (2007, 142 mins.) Explores the dire prediction that warmer temperatures will disrupt ocean currents in the Gulf Stream 5. Global Warming: What’s Up with the Weather? NOVA, PBS DVD (2000, 112 mins.) Weather is different now, more extreme. Why? 6. Glaciers. Insight Media (2008, 30 mins.) Where glaciers are found, their role as geologic forces and the formations they create. 7. Glaciers that Shape Our Earth. Insight Media (2004, 51 mins.) Glaciers and their effects on the surface of the Earth. 8. Hot Planet: Cold Comfort. Scientific American Frontiers, PBS DVD (2005, 30 mins.) The predicted effects of global warming. 9. Hot Times in Alaska. Scientific American Frontiers XIV. PBS DVD (2004, 60 mins.) The results of warming temperatures already been seen in Alaska and what’s in store in the future. 10. Earth Revealed. Annenberg Media http://www.learner.org/resources/series78.html (1992, 30 mins., free video): • #23: Glaciers. Glacial landforms, how glaciers move, and the ice ages. 11. Glaciers. Insight Media (DV4, 15 mins.) Glacial erosion and deposition in action. Slides 1. Active Glaciers. Insight Media (2005, Windows CD-ROM). High-resolution photographs that show images of glaciers and glacial features. 2. Continental Glaciation. Insight Media (2005, Windows CD-ROM) Aerial and ground images of the physical features caused by continental glaciation. 3. Educational Images, Ltd. slide sets, http://www.educationalimages.com/cg120001.htm a. Alpine Glaciation b. Glacial Erosion and Deposition Answers to Figure-Related Critical Thinking Questions ❯❯ Critical Thinking Question Figure 14.8 How do you think the debris in the foreground (Fig. 14.8) was deposited? Answer: In the picture of Figure 14.8 b, the deposit in the foreground (at the bottom of the photograph) is most likely till in an end moraine, either terminal or recessional, depending on the previous progress of this glacier. ❯❯ Critical Thinking Question Figure 14.10 Why is the basalt in this image broken into 5- and 6-sided polygons? Answer: The view is the top, erosional surface of cooling or columnar joints in this thick larva flow (see volcanic rocks chapter). The basalt in the image is broken into 5- and 6-sided polygons due to columnar jointing. This occurs as the basalt cools and contracts, creating hexagonal columns and fractures. The cooling process causes the rock to contract and form these characteristic geometric patterns, which are common in large basalt lava flows. ❯❯ Critical Thinking Question Figure 14.13 How does a U-shaped glacial trough differ from a mountain valley eroded by running water? Answer: Streams in mountain settings are typically downcutting through the apex of their V-shaped valley with mass wasting moving material down the steep slopes of the valley walls (flood plains and lateral erosion appear later). Once the ice dominates this same valley, the glacier extends high up those valley walls gouging out slopes like a bulldozer. ❯❯ Critical Thinking Question Figure 14.18 Was running water important in the origin of any of the features in this illustration? Answer: Figure 14.18 a & b show outwash deposits, glacial drift deposited by running melt water in eskers, kames and braided stream deposits. Without seeing Figure 14.18, I can provide a general approach. Running water is crucial in the formation of many geological features, such as river valleys, canyons, and sediment deposits. It shapes landscapes through erosion and sediment transport, creating distinct features like deltas, alluvial fans, and river terraces. If the illustration includes any of these features, running water would indeed be an important factor in their formation. ❯❯ Critical Thinking Question Figure 14.19 How can you determine how far this erratic was transported? Answer: Many erratics are large enough to recognize the original formation source such as the jasper pebbled metaconglomerates common in Michigan, Ohio and Indiana which came from Bruce Mines in Ontario, Canada. ❯❯ Critical Thinking Question Figure 14.21 In addition to moraines, what other features of glacial erosion can you identify? Answer: Truncated spurs with triangular facets, hanging valleys were eroded by glacier ice, but the arêtes at the top of those spurs & horns in the distance formed above glacial ice by freeze-thaw/mass wasting cycles. ❯❯ Critical Thinking Question Figure 14.22 Why do you think that the water in the stream has a milky appearance? Answer: When glaciers move over bedrock, it abrades the rock. Abrasion thoroughly pulverizes rocks, yielding an aggregate of clay- and silt-size particles that have the consistency of flour—hence, the name rock flour. Rock flour is so common in streams discharging from glaciers that the water has a milky appearance. Suggested Answer to Selected Short Answer Question (Answers to question 7 and question 10 provided in the appendix to the text) 9. Explain in terms of the glacial budget how a once-active glacier becomes stagnant. Suggested Answer: A glacial budget comprises “accumulation” and “wastage,” which correspond to yearly fluctuations in the glacier. If more of the glacier is lost to wastage, the glacier shrinks. This would be a negative budget. If the glacier gains by accumulation, the glacier grows and this is a positive glacial budget. If a negative budget persists long enough, the glacier will disappear. A glacier becomes stagnant when its accumulation (input) and ablation (output) are out of balance. Specifically, if the glacier's rate of ice accumulation is less than its rate of melting and sublimation, the glacier can no longer advance and eventually becomes stagnant. This imbalance results in the glacier not moving forward, leading to a period of inactivity where the glacier's size stabilizes or shrinks. Solution Manual for The Changing Earth: Exploring Geology and Evolution James S. Monroe, Reed Wicander 9781285733418
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