EARTH SCIENCE geology, the environment, and the universe 2008 (9)

Mass Movements, Wind, and Glaciers BIG Idea Movements due to gravity, winds, and glaciers shape and change Earth’s surface 8.1 Mass Movements MAIN Idea Mass movements alter Earth’s surface over time due to gravity moving sediment and rocks downslope 8.2 Wind Glacial till MAIN Idea Wind modifies landscapes in all areas of the world by transporting sediment 8.3 Glaciers MAIN Idea Glaciers modify landscapes by eroding and depositing rocks GeoFacts • More than 100,000 glaciers exist in Alaska, but ice covers only percent of the state • Glaciers form when more snow falls in an area than melts in the same area • Layers of snow on the glacier create pressure that changes the snow underneath to ice Calving glacier 192 (t)Steve McCutcheon/Visuals Unlimited, (b)Bernhard Edmaier/Science Photo Library, (bkgd)Gregory Dimijian/Photo Researchers Start-Up Activities External Processes that Shape Earth Make this Foldable to explain different processes that shape Earth’s surface LAUNCH Lab How does water affect sediments on slopes? Water has a significant effect on sediments on slopes In this activity, you will demonstrate how the addition of water affects how sediments are held together Procedure Read and complete the lab safety form Place 225 mL of sand in each of three separate containers, such as aluminum pie plates Add 20 mL of water to the first container of sand, and mix well Add 100 mL of water to the second container of sand, and mix well Add 200 mL of water to the third container of sand, and mix well Empty the three mixtures of sand and water onto a tray or piece of cardboard Keep each mixture separate Test each mixture for its ability to be molded and retain its shape Compare your results for the three samples Analysis Describe how the addition of water affected the sand’s ability to be molded in the three samples Explain why one mixture was better able to maintain its shape than the others Infer how water affects sediment on slopes STEP Fold the bottom of a horizontal sheet of paper up about cm STEP Fold in thirds STEP Unfold and dot with glue or staple to make three pockets Label as shown Mmasesnts Move Wind Gla ciers FOLDABLES Use this Foldable with Sections 8.1, 8.2, and 8.3 As you read, use index cards to summarize information in your own words and place them in the appropriate pockets Visit glencoe.com to study entire chapters online; explore • Interactive Time Lines • Interactive Figures • Interactive Tables animations: access Web Links for more information, projects, and activities; review content with the Interactive Tutor and take Self-Check Quizzes Chapter •Section Mass Movements, • XXXXXXXXXXXXXXXXXX Wind, and Glaciers 193 Section Objectives ◗ Analyze the relationship between gravity and mass movements ◗ Identify factors that affect mass movements ◗ Distinguish between types of mass movements ◗ Relate how mass movements affect people Mass Movements MAIN Idea Mass movements alter Earth’s surface over time due to gravity moving sediment and rocks downslope Real-World Reading Link How fast can you travel on a waterslide? A num- ber of factors might come into play, including the angle of the slide, the amount of water on the slide, the material of the slide, friction, and your own mass These factors also affect mass movements on Earth’s surface Review Vocabulary gravity: the force every object exerts on every other object due to their masses New Vocabulary mass movement creep mudflow landslide slump avalanche Mass Movements How landforms, such as mountains, hills, and plateaus, wear down and change? Landforms can change through processes involving wind, ice, and water, and sometimes through the force of gravity alone The downslope movement of soil and weathered rock resulting from the force of gravity is called mass movement Recall from Chapter that weathering processes weaken and break rock into smaller pieces Mass movements often carry the weathered debris downslope Because climate has a major effect on the weathering activities that occur in a particular area, climatic conditions determine the extent of mass movement All mass movements, such as the one shown in Figure 8.1, occur on slopes Because few places on Earth are completely flat, almost all of Earth’s surface undergoes mass movement Mass movements range from motions that are barely detectable to sudden slides, falls, and flows The Earth materials that are moved range in size from fine-grained mud to large boulders Reading Check Describe how gravity causes a mass movement ■ Figure 8.1 Mass movements can cause tree trunks to curve in order to continue growing opposite the pull of gravity, which is toward the center of Earth 194 Chapter • Mass Movements, Wind, and Glaciers Dr Marli Miller/Visuals Unlimited Factors that Influence Mass Movements Several factors influence the mass movements of Earth’s material One factor is the material’s weight, which works to pull the material downslope A second factor is the material’s resistance to sliding or flowing, which depends on the amount of friction, how cohesive the material is, and whether it is anchored to the bedrock A third factor is a trigger, such as an earthquake, that shakes material loose Mass movement occurs when the forces pulling material downslope are stronger than the material’s resistance to sliding, flowing, or falling Water is a fourth variable that influences mass movements The landslide shown in Figure 8.2 occurred after days of heavy rains Saturation by water greatly increases the weight of soils and sediments In addition, as the water fills the tiny open spaces between grains, it acts as a lubricant between the grains, reducing the friction between them Types of Mass Movements Mass movements are classified as creep, flows, slides, and rockfalls Mass movements move different types of materials in various ways Figure 8.2 Mass movements like the one shown here can significantly alter landscapes Summarize the factors that might have been involved in the mass movement ■ Creep The slow, steady, downhill flow of loose, weathered Earth materials, especially soils, is called creep Because movement might be as little as a few centimeters per year, the effects of creep are usually noticeable only over long periods of time One way to tell whether creep has occurred is to observe the positions of structures and objects As illustrated in Figure 8.3, creep can cause once-vertical utility poles and fences to tilt, and trees and walls to break Loose materials on almost all slopes undergo creep One type of creep that usually occurs in regions of permafrost, or permanently frozen soil, is called solifluction (SOH luh fluk shun) The material moved in solifluction is a mudlike liquid that is produced when water is released from melting permafrost during the warm season The water saturates the surface layer of soil and is unable to move downward As a result, the surface layer can slide slowly downslope ■ Figure 8.3 All slopes undergo creep of some kind Tilted fence posts, trees, and poles Section • Mass Movements 195 (t)David McNew/Getty Images, (b)Ralph Lee Hopkins/Photo Researchers Figure 8.4 The city of Armero, in Colombia, was covered in mud and debris by a lahar that contained snowmelt and volcanic material Describe the effect of the lahar on the city shown above ■ ■ Figure 8.5 Mudflows can be extremely destructive and can result in severe property damage, road closures, and power outages Flows In some mass movements, Earth materials flow as if they were a thick liquid The materials might move as slowly as a few centimeters per year or as rapidly as hundreds of kilometers per hour Earth flows are moderately slow movements of soils, whereas mudflows are swiftly moving mixtures of mud and water Mudflows can be triggered by earthquakes or similar vibrations and are common in volcanic regions where the heat from a volcano melts snow on nearby slopes that have fine sediment and little vegetation The meltwater fills the spaces between the small particles of sediment and allows them to slide readily over one another and move downslope A lahar (LAH har) is a type of mudflow that occurs after a volcanic eruption Often a lahar results when a snow-topped volcanic mountain erupts and melts the snow on top of a mountain The melted snow mixes with ash and flows downslope Figure 8.4 shows how a lahar that originated from Nevado del Ruiz, one of the volcanic mountains in the Andes, devastated a town The Nevado del Ruiz is 5389 m high and covered with 25 km2 of snow and ice, which melted when it erupted Four hours after Nevado del Ruiz erupted, lahars had traveled more than 100 km downslope As a result of these lahars, which occurred in 1985, approximately 23,000 people were killed, 5000 were injured, and 5000 homes were destroyed Reading Check Determine what triggers a lahar Mudflows are also common in sloped, semiarid regions that experience intense, short-lived rainstorms The Los Angeles Basin in Southern California is an example of an area where mudflows are common In such areas, periods of drought and forest fires leave the slopes with little protective vegetation When heavy rains eventually fall in these areas, they can cause massive, destructive mudflows because there is little vegetation to anchor the soil Mudflows are especially destructive in areas where urban development has spread to the bases of mountainous areas These mudflows can burry homes, as shown in Figure 8.5 196 Chapter • Mass Movements, Wind, and Glaciers (t)Steve Raymer/National Geographic Image Collection, (b)Gene Blevins/LA Daily News/CORBIS Figure 8.6 Landslides in the Philippines devastated the town of San Ricardo in December 2003 ■ Slides A rapid, downslope movement of Earth materials that occurs when a relatively thin block of soil, rock, and debris separates from the underlying bedrock is called a landslide, shown in Figure 8.6 The material rapidly slides downslope as one block, with little internal mixing A landslide mass eventually stops and becomes a pile of debris at the bottom of a slope, sometimes damming rivers and causing flooding Landslides are common on steep slopes, especially when soils and weathered bedrock are fully saturated by water This destructive form of mass movement causes damage costing almost billion dollars and 25 to 50 associated deaths per year in the United States alone You will explore the movement of a landslide in the GeoLab at the end of this chapter A rockslide is a type of landslide that occurs when a sheet of rock moves downhill on a sliding surface During a rockslide, some blocks of rock are broken into smaller blocks as they move downslope, as shown in Figure 8.7 Often triggered by earthquakes, rockslides can move large amounts of material Figure 8.7 During this rockslide, blocks of rock were broken into smaller blocks as they moved downslope ■ Interactive Figure To see an animation of a rockslide, visit glencoe.com Section • Mass Movements 197 (t)Handout/Malacanang/Reuters/CORBIS, (b)Lloyd Cluff/CORBIS Slumps When the mass of material in a landslide moves along a curved surface, a slump results Material at the top of the slump moves downhill, and slightly inward, while the material at the bottom of the slump moves outward Slumps can occur in areas that have thick soils on moderate-to-steep slopes Sometimes, slumps occur along highways where the slopes of soils are extremely steep Slumps are common after rains, when water reduces the frictional contact between grains of soil and acts as a lubricant between surface materials and underlying layers The weight of the additional water pulls material downhill As with other types of mass movement, slumps can be triggered by earthquakes Slumps leave crescent-shaped scars on slopes, as shown in Figure 8.8 Reading Check Describe what conditions can cause a slump Avalanches Landslides that occur in mountainous areas with ■ Figure 8.8 Slumps leave distinct crescent-shaped scars on hillsides as the soil rotates downward thick accumulations of snow are called avalanches About 10,000 avalanches occur each year in the mountains of the western United States Radiation from the Sun can melt surface snow, which then refreezes at night into an icy crust Snow that falls on top of this crust can eventually build up, become heavy, slip off, and slide downslope as an avalanche Avalanches can happen in early winter when snow accumulates on the warm ground The snow in contact with the warm ground melts, then refreezes into a layer of jagged, slippery snow crystals Avalanches of dangerous size, like the one shown in Figure 8.9, occur on slope angles between 30° and 45° When the angle of a slope is greater than 45°, enough snow cannot accumulate to create a large avalanche At angles less than 30°, the slope is not steep enough for snow to begin sliding A vibrating trigger, even from a single skier, can send this unstable layer sliding down a mountainside Avalanches pose significant risks in places such as Switzerland, where more than 50 percent of the population lives in avalanche terrain ■ Figure 8.9 Vibrations from a single skier can trigger an avalanche Identify the conditions that make a landscape more vulnerable to avalanches 198 Chapter • Mass Movements, Wind, and Glaciers (t)Dr Marli Miller/Visuals Unlimited, (b)Mauritius/SuperStock ■ Figure 8.10 This rockfall in Topanga Canyon, California, was unusual in that it involved mainly one large rock Rockfalls On high cliffs, rocks are loosened by physical weathering processes, such as freezing and thawing, and by plant growth As rocks break up and fall directly downward, they can bounce and roll, ultimately producing a cone-shaped pile of coarse debris, called talus, at the base of the slope Rockfalls, such as the one shown in Figure 8.10, commonly occur at high elevations, in steep road cuts, and on rocky shorelines Rockfalls are less likely to occur in humid regions where the rock is typically covered by a thick layer of soil, vegetation, and loose materials On human-made rock walls, such as road cuts, rockfalls are particularly common Mass Movements Affect People While mass movements are natural processes, human activities often contribute to the factors that cause mass movements Activities such as the construction of buildings, roads, and other structures can make slopes unstable In addition, poor maintenance of septic systems, which often leak, can trigger slides In the Philippines, mudslides, shown in Figure 8.11, were triggered after ten days of torrential rains delivered 200 cm of precipitation A village estimated to have 3000 residents was totally destroyed Figure 8.11 The mudflow on the island of Luzon occurred after days of rain ■ Section • Mass Movements 199 (t)Ted Soqui/CORBIS, (b)Yann Arthus-Bertrand/CORBIS ■ Figure 8.12 Covering hillsides with steel nets can reduce risks of mass movements and harm to humans Identify the type of mass movement that these steel nets help prevent Section Assessment Section Summary Understand Main Ideas ◗ Mass movements are classified in part by how rapidly they occur ◗ Factors involved in the mass movement of Earth materials include the material’s weight, its resistance to sliding, the trigger, and the presence of water Identify the underlying force behind all forms of mass movement ◗ Mass movements are natural processes that can affect human life and activities Think Critically ◗ Human activities can increase the potential for the occurrence of mass movements MAIN Idea Organize the following types of mass movements in order of increasing speed: slides, creep, flows, and rockfalls Analyze how water affects mass movements by using two examples of mass movement Appraise the effects of one type of mass movement on humans Generalize in which regions of the world mudflows are more common Evaluate how one particular human activity can increase the risk of mass movement and suggest a solution to the problem Earth Science Make a poster that compares and contrasts solifluction and a slump Consider the way soil moves and the role of water 200 Chapter • Mass Movements, Wind, and Glaciers Self-Check Quiz glencoe.com Michael Habicht/Animals Animals Reducing the risks Catastrophic mass movements are most common on slopes greater than 25° that experience annual rainfall of over 90 cm Risk increases if that rainfall tends to occur in a short period of time Humans can minimize the destruction caused by mass movements by not building structures on or near the base of steep and unstable slopes Although preventing mass-movement disasters is not easy, some actions can help reduce the risks For example, a series of trenches can be dug to divert running water around a slope and control its drainage Landslides can be controlled by covering steep slopes with materials such as steel nets, shown in Figure 8.12, and constructing fences along highways in areas where rockslides are common Other approaches involve the installation of retaining walls to support the bases of weakened slopes and prevent them from falling Most of these efforts at slope stabilization and mass-movement prevention are only temporarily successful The best way to reduce the number of disasters related to mass movements is to educate people about the problems of building on steep slopes For example, The United States Geological Survey (USGS) collects data about landslides in an effort to learn more about where and when landslides will occur This information helps people decide where they can safely build homes or businesses Section 8.2 Objectives ◗ Describe conditions that contribute to the likelihood that an area will experience wind erosion ◗ Identify wind-formed landscape features ◗ Describe how dunes form and migrate Wind MAIN Idea Wind modifies landscapes in all areas of the world by transporting sediment Real-World Reading Link If you have ever been on a beach on a windy day, you might have felt the stinging of sand on your face Sand travels in the wind if the wind is fast enough Review Vocabulary velocity: the speed of an object and its direction of motion New Vocabulary deflation abrasion ventifact dune loess ■ Figure 8.13 Wind erosion does not affect all areas of the United States equally Observe which areas are subject to wind erosion Wind Erosion and Transport A current of rapidly moving air can pick up and carry sediment in the same way that water does However, except for the extreme winds of hurricanes, tornadoes, and other strong storms, winds cannot generally carry particles as large as those transported by moving water Regardless, wind is a powerful agent of erosion Winds transport materials by causing their particles to move in different ways For example, wind can move sand on the ground in a rolling motion A method of transport by which strong winds cause small particles to stay airborne for long distances is called suspension Another method of wind transport, called saltation, causes a bouncing motion of larger particles Saltation accounts for most sand transport by wind Limited precipitation leads to an increase in the amount of wind erosion because precipitation holds down sediments and allows plants to grow Thus, wind transport and erosion primarily occur in areas with little vegetative cover, such as deserts, semiarid areas, seashores, and some lakeshores Wind erosion is a problem in many parts of the United States, as shown in Figure 8.13 Wind Erosion in the United States Areas of wind erosion Section • Wind 201 Section Objectives Glaciers ◗ Explain how glaciers form ◗ Compare and contrast the conditions that produce valley glaciers with those that produce continental glaciers ◗ Describe how glaciers modify landscapes ◗ Recognize glacial features MAIN Idea Glaciers modify landscapes by eroding and depositing rocks Real-World Reading Link Have you ever wondered what formed the land- scape around you? Glaciers might have left deposits of sediment as well as carved features in rock that you see every day Review Vocabulary Moving Masses of Ice latitude: distance in degrees north and south of the equator A large, moving mass of ice is called a glacier Glaciers form near Earth’s poles and in mountainous areas at high elevations They currently cover about 10 percent of Earth’s surface, as shown in Figure 8.20 In the past, glaciers were more widespread than they are today During the last ice age, which began about 1.6 mya and ended more than 10,000 years ago, ice covered about 30 percent of Earth Areas at extreme northern and southern latitude, such as Greenland and Antarctica, and areas of high elevations, such as the Alps, have temperatures near 0°C year-round Cold temperatures keep fallen snow from completely melting, and each year the snow that has not melted accumulates in an area called a snowfield Thus, the total thickness of the snow layer increases as the years pass The accumulated snow develops into a glacier The weight of the top layers of snow eventually exerts enough downward pressure to force the accumulated snow below to recrystallize into ice A glacier can develop in any location that provides the necessary conditions Glaciers can be classified as one of two types—valley glaciers or continental glaciers New Vocabulary glacier valley glacier continental glacier cirque moraine outwash plain drumlin esker kame kettle ■ Figure 8.20 Greenland Glaciers around the world have changed in distribution throughout geologic time Infer what changes have occurred in the distribution of glaciers around the world North America Europe Asia Africa South America Interactive Figure To see an animation of glacier formation, visit glencoe.com Glaciers (present) Australia Glaciers (18,000 years ago) Antarctica Section • Glaciers 207 FOLDABLES Incorporate information from this section into your Foldable Valley glaciers Glaciers that form in valleys in high, mountainous areas are called valley glaciers The movement of a valley glacier occurs when the growing ice mass becomes so heavy that the ice maintains its rigid shape and begins to flow, much like toothpaste For most valley glaciers, flow begins when the accumulation of snow and ice exceeds 20 m in thickness As a valley glacier moves, deep cracks in the surface of the ice, called crevasses, can form The speed of a valley glacier’s movement is affected by the slope of the valley floor, the temperature and thickness of the ice, and the shape of the valley walls The sides and bottom of a valley glacier move more slowly than the middle because friction slows down the sides and bottom where the glacier comes in contact with the ground Movement downslope is usually slow—less than a few millimeters per day Over time, as valley glaciers flow downslope, their powerful carving action transitions V-shaped stream valleys into U-shaped glacial valleys Reading Check Describe how V-shaped valleys become U-shaped Continental glaciers Glaciers that cover broad, continentsized areas are called continental glaciers These glaciers form in cold climates where snow accumulates over many years A continental glacier is thickest at its center The weight of the center forces the rest of the glacier to flatten in all directions In the past, when Earth experienced colder average temperatures than it does today, continental glaciers covered huge portions of Earth’s surface Today, they are confined to Greenland and Antarctica Data Analysis lab Based on Real Data* Interpret the Data How much radioactivity is in ice cores? Glaciologists have found that ice cores taken from the arctic region contain preserved radioactive fallout Data collected from the study of these ice cores have been plotted on the graph Data and Observations Amount of radioactivity Radioactivity in Ice Cores Pre-test ban (1964–65) High Start of atomicbomb testing (mid-1950s) Chernobyl (1987–88) Think Critically Determine the depth in the ice cores where the highest and lowest amounts of radioactivity were found Describe what happened to the amount of radioactivity in the ice cores between the pretest ban and Chernobyl Infer what happened to the amount of radioactivity in the ice cores after Chernobyl Explain what information or material other than radioactive fallout you think ice cores might preserve within them Low 100 200 300 400 500 Depth (cm) 208 Chapter • Mass Movements, Wind, and Glaciers 600 *Data obtained from: Mayewski, et al 1990 Beta radiation from snow Nature 345:25 (l)Dr Marli Miller/Visuals Unlimited, (c)Karl Weatherly/CORBIS, (r)Adam Jones/Visuals Unlimited Cirque Horn Glacial movement Both valley glaciers and continental glaciers move outward when snow gathers at the zone of accumulation, a location in which more snow falls than melts, evaporates, or sublimates For valley glaciers, the zone of accumulation is at the top of mountains, while for continental glaciers, the zone of accumulation is the center of the ice sheet Both types of glaciers recede when the ends melt faster than the zone of accumulation builds up snow and ice Glacial Erosion Of all the erosional agents, glaciers are the most powerful because of their great size, weight, and density When a valley glacier moves, it breaks off pieces of rock through a process called plucking When glaciers with embedded rocks move over bedrock, they act like the grains on a piece of sandpaper, grinding parallel scratches into the bedrock Small scratches are called striations, and larger ones are called grooves Scratches and grooves provide evidence of a glacier’s history and indicate its direction of movement Glacial erosion by valley glaciers can create features like those shown in Figure 8.21 At the high elevations where snow accumulates, valley glaciers also scoop out deep depressions, called cirques Where two cirques on opposite sides of a valley meet, they form a sharp, steep ridge called an arête When there are glaciers on three or more sides of a mountaintop, the carving action creates a steep, pyramid-shaped peak This is known as a horn The most famous example of this feature is Switzerland’s Matterhorn Valley glaciers can also leave hanging valleys in the glaciated landscape Hanging valleys are formed when tributary glaciers converge with the primary glaciers and later retreat The primary glacier is so thick that it meets the height of the smaller tributary glacier When the glaciers melt, the valley is left hanging high above what is now a river in the primary valley floor Hanging valleys today are often characterized by waterfalls where the tributary glacier used to be Hanging valley ■ Figure 8.21 Glacial erosion by valley glaciers creates features such as cirques, horns, and hanging valleys Careers In Earth Science Glaciologist Glaciologists study snow and ice in the environment They often conduct field research in remote locations on glaciers, ice sheets, and frozen tundra To learn more about Earth science careers, visit glencoe.com Section • Glaciers 209 Glacial till is the unsorted rock, gravel, sand, and clay that glaciers carry embedded in their ice and on their tops, sides, and front edges Glacial till is formed from the grinding action of the glacier on underlying rock Glaciers deposit unsorted ridges of till called moraines when the glacier melts Moraines can be terminal or lateral Terminal moraines are found where the glacier melts, and lateral moraines are located along the direction of glacier flow Figure 8.22 Elongated landforms called drumlins can be grouped together as a drumlin field in areas once covered by continental glaciers Describe how you could identify a drumlin on a topographic map ■ Outwash When the farthest ends of a glacier melt and the glacier begins to recede, meltwater floods the valley below Meltwater contains gravel, sand, and fine silt When this sediment is deposited by meltwater carried away from the glacier, it is called outwash Because of the way water transports sediment, outwash is always sorted by particle size The area at the leading edge of the glacier where the meltwater flows and deposits outwash is called an outwash plain Drumlins, eskers, and kames Continental glaciers that move over older moraines form the material into elongated landforms called drumlins, shown in Figure 8.22 A drumlin’s steeper slope faces the direction from which the glacier came Streams flowing under melting glaciers leave long, winding ridges of layered sediments called eskers, shown in Figure 8.23 A kame is a mound of layered sediment deposited at the retreating glacier face and is conical in shape Kames are also shown in Figure 8.23 Model Glacial Deposition How glaciers deposit different types of rocks and sediments? Glaciers are powerful forces of erosion As they move across the land, they pick up rocks and sediments, and carry them to new locations When a glacier melts, these materials are left behind and deposits form in different shapes Procedure Read and complete the lab safety form Work with a group of to other students One student should obtain four glaciers from your teacher Place the glaciers on a baking pan In front of each glacier, place a popsicle stick (to prevent the glacier from sliding down the pan) Place a textbook under one end of the baking pan (your glaciers should be toward the elevated end of the pan) Observe what happens as the glaciers melt Record your observations in your science journal Dispose of your materials as your teacher instructs Analysis Discuss Did the materials differ in the way they were deposited by the melting ice cubes? Were your results similar to those of your classmates? Explain Explain how this activity modeled the formation of meltwater Apply Which materials in this activity modeled glacial till? Apply How did this activity model glacial deposition and the formation of a moraine? 210 Chapter • Mass Movements, Wind, and Glaciers E R Degginger/Photo Researchers Glacial Deposition Visualizing Continental Glacial Features Figure 8.23 Continental glaciers carve out vast regions of landscape, leaving behind distinctive features such as kames, eskers, drumlins, and moraines Retreating glacier Kame Moraine k roc d Be Drumlins Esker uth So Kames are short cone-shaped mounds of sorted deposits They are shaped from outwash left as glaciers recede Eskers are long ridges of sorted deposits They are shaped from outwash left as glaciers recede Drumlins are shaped as the glacier moves over old moraines They are unsorted To explore more about glacial features, visit glencoe.com Section • Glaciers 211 (l)R.B Colton/USGS, (c)Tom Bean/CORBIS, (r)Gustav Verderber/Visuals Unlimited Thomas & Pat Leeson/Photo Researchers ■ Figure 8.24 These kettle lakes in North Dakota are a result of glacial retreat Describe how you might be able to locate kettles on a topographic map VOCABULARY SCIENCE USAGE V COMMON USAGE Kettle Science usage: a steep-sided depression formed by a glacier Common usage: a metallic pot used for cooking Section Glacial lakes Sometimes, a large block of ice breaks off a continental glacier and the surrounding area is covered by sediment When the ice block melts, it leaves behind a depression called a kettle hole After the ice block melts, the kettle hole fills with water from precipitation and runoff to form a kettle lake Kettles or kettle lakes, such as those shown in Figure 8.24, are common in New England, New York, and Wisconsin With valley glaciers, cirques can also fill with water, and they become cirque lakes When a terminal moraine blocks off a valley, the valley fills with water to form a lake Moraine-dammed lakes include the Great Lakes and the Finger Lakes of northern New York, which are long and narrow Mass movements, wind, and glaciers all contribute to the changing of Earth’s surface These processes erode landforms constantly, and in many ways, they also impact human populations and activities Assessment Section Summary Understand Main Ideas ◗ Glaciers are large moving masses of ice that form near Earth’s poles and in mountain areas ◗ Glaciers can be classified as valley glaciers or continental glaciers ◗ Glaciers modify the landscape by erosion and deposition ◗ Features formed by glaciers include U-shaped valleys, hanging valleys, moraines, drumlins, and kettles MAIN Idea Describe two examples of how glaciers modify landscapes Explain how glaciers form Compare and contrast the characteristics of valley glaciers and continental glaciers Differentiate among different glacial depositional features Think Critically Evaluate the evidence of past glaciers that can be found on Earth today Infer whether valley glaciers or continental glaciers have shaped more of the landscape of the United States Earth Science Deduce how you might distinguish a lake formed in a cirque and a lake formed in a kettle 212 Chapter • Mass Movements, Wind, and Glaciers Self-Check Quiz glencoe.com Slipping Away On the morning of January 10, 2005, the residents of La Conchita, California, awoke to find the highway out of town closed in both directions, due to landslides Around 12:30 P.M many residents heard an ominous roar as the bluff above the town unleashed 600,000 metric tons of dirt and mud, covering four blocks in 10 m of debris Scientists went to the scene to discover exactly what had caused this enormous landslide and whether one could happen again The setting La Conchita is built on a narrow swatch of land between the highway and a huge bluff The bluff is held together weakly, so it is susceptible to being loosened by heavy water content, such as a prolonged, heavy rain The slope is further weakened from the effects of regular landslides, as well as being on a fault line In the two weeks prior to the landslide, the area had received a record amount of rain—about 35 cm—the amount it normally receives in a year! The excess water caused the earth to literally slide off the face of the mountain A history of landslides This event was not, however, the first landslide to hit the area In fact, the mountain bluff is scarred with the evidence of many landslides Ten years earlier, in March of 1995, two devastating landslides hit the area in the span of a week These landslides were also caused by a large amount of rain, but the movement of the earth was relatively slow, so residents were able to get away The 2005 landslide was a continuation of the 1995 slide — the soil that was deposited by the earlier slide was loosened by the rainwater and slipped down the slope After the 1995 slide, the state government erected a retaining wall to keep the landslides at bay However, soil, mud, and debris from the 2005 disaster passed right over parts of the wall The mass movement at La Conchita, California, in 2005 killed ten people The debate Could the 2005 landslide have been detected and the people warned in time to prevent loss of life? Most likely, yes In fact, some of the residents of the town are suing the government for failure to protect their citizens, as well as failure to adequately notify them of the impending danger Are governments responsible for providing warnings and protection to citizens who move into areas that are prone to natural disasters? Or, does the responsibility lie with the citizens that might not have understood the dangers of living in the area? These questions and more are sure to be considered by the residents and government of La Conchita, as well as cities and local governments of disaster- prone areas throughout the United States for years to come Earth Science Debate Research information about a natural disaster that has occurred near your location Hold a classroom debate on the topic of why people should, or should not, live in an area where natural disasters have occurred To learn more about natural disasters, visit glencoe.com Earth Science & Society 213 David McNew/Getty Images USGS MAPPING: MAP A LANDSLIDE This image shows the Tully Valley landslide three days after it occurred The Tully Farms Road is covered up to m deep with clay Background: Around midday on April 27, 1993, in a normally quiet, rural area of New York, the landscape dramatically changed Unexpectedly, almost million m3 of earth debris slid 300 m down the lower slope of Bare Mountain and into Tully Valley The debris flowed over the road and buried nearby homes The people who lived there had no knowledge of any prior landslides occurring in the area, yet this landslide was the largest to occur in New York in more than 75 years Question: How can you use a drawing based on a topographic map to infer how the Tully Valley Landslide occurred? Materials metric ruler Measure the length and width of the Tully Valley in kilometers Double-check your results Analyze and Conclude Interpret Data What does the shape of the valley tell you about how it formed? Determine In what direction did the landslide flow? Determine In what direction does the Onondaga Creek flow? Infer from the map which side of Tully Valley has the steepest valley walls Deduce What conditions must have been present for the landslide to occur? Infer At the time of the Tully Valley Landslide, the trees were bare How could this have affected the conditions that caused the landslide? Procedure Imagine that you work for the United States Geological Survey (USGS) specializing in mass movements You have just been asked to evaluate the Tully Valley Landslide Read and complete the lab safety form Check the map’s scale 214 GeoLab Earth Science Explain why the mass movement event you examined in this GeoLab is classified as a landslide Differentiate a landslide from a creep, slump, flow, avalanche, and rockfall Syracuse U.S Ro ute 20 Landslide area reek aga C o nd On Previous landslides New York Onondaga County 0 1.0 1.5 miles kilometers E W r Ba 1993 landslide nt ou Tully Farms Road eM ain Rattle sna ke N R ow ainb ek Cre Gulf Otisco Road KEY W E Line of landslide section Onondaga C Valley floor Valley walls reek Edge of valley floor Stream channel (arrow shows direction of stream flow) New York Route 11-A Onondaga Creek Brine field GeoLab 215 Download quizzes, key terms, and flash cards from glencoe.com BIG Idea Movements due to gravity, winds, and glaciers shape and change Earth’s surface Vocabulary Key Concepts Section 8.1 Mass Movements • avalanche (p 198) • creep (p 195) • landslide (p 197) • mass movement (p 194) • mudflow (p 196) • slump (p 198) Mass movements alter Earth’s surface over time due to gravity moving sediment and rocks downslope Mass movements are classified in part by how rapidly they occur Factors involved in the mass movement of Earth materials include the material’s weight, its resistance to sliding, the trigger, and the presence of water Mass movements are natural processes that can affect human life and activities Human activities can increase the potential for the occurrence of mass movements MAIN Idea • • • • Section 8.2 Wind • abrasion (p 203) • deflation (p 202) • dune (p 204) • loess (p 206) • ventifact (p 203) Wind modifies landscapes in all areas of the world by transporting sediment Wind is a powerful agent of erosion Wind can transport sediment in several ways, including suspension and saltation Dunes form when wind velocity slows down and windblown sand is deposited Dunes migrate as long as winds continue to blow MAIN Idea • • • • Section 8.3 Glaciers • cirque (p 209) • continental glacier (p 208) • drumlin (p 210) • esker (p 210) • glacier (p 207) • kame (p 210) • kettle (p 212) • moraine (p 210) • outwash plain (p 210) • valley glacier (p 208) 216 Chapter X • Study Guide MAIN Idea Glaciers modify landscapes by eroding and depositing rocks • Glaciers are large moving masses of ice that form near Earth’s poles and in mountain areas • Glaciers can be classified as valley glaciers or continental glaciers • Glaciers modify the landscape by erosion and deposition • Features formed by glaciers include U-shaped valleys, hanging valleys, moraines, drumlins, and kettles Vocabulary PuzzleMaker glencoe.com Vocabulary PuzzleMaker biologygmh.com Vocabulary Review Match the correct vocabulary term from the Study Guide to the following definitions rapid downslope movement of a mass of loose sediment rapidly flowing, often destructive mixtures of mud and water slow, steady downhill movement of loose, weathered Earth materials Replace each underlined word with the correct vocabulary term from the Study Guide Barchans are rock structures shaped by windblown sediments Thick, windblown, fertile deposits of silt that contain high levels of nutrients and minerals are known as desert pavement Deflation occurs when particles such as sand rub against the surface of rocks Explain the differences between the vocabulary terms in the following sets 12 Which is the underlying force that causes all forms of mass movement? A friction B gravity C magnetism D the Coriolis Effect 13 The last continental ice age covered approximately what percent of Earth’s surface? A 10 percent B 20 percent C 30 percent D 50 percent 14 Where are large deposits of glacial loess primarily found? A eastern United States B southeastern United States C southwestern United States D midwestern United States 15 Which has the fastest movement? A solifluction B creep C mudflow D avalanche Use the photo below to answer Questions 16 and 17 valley glacier, continental glacier esker, kame moraine, outwash plain Understand Key Concepts 10 What are elongated landforms made of older moraines over which glaciers move? A drumlins B kettle lakes C eskers D outwash plains 11 Which particles can wind move most easily? A sand B pebbles C silt D gravel Chapter Test glencoe.com 16 Which formed the structure in the photo? A ice C wind B water D organisms 17 Which process formed the structure in the photo? A abrasion C deposition B deflation D migration Chapter • Assessment 217 Gabe Palmer/CORBIS 19 Which statement best describes sediments deposited by glaciers and rivers? A Both glacial and river deposits are sorted B Glacial deposits are sorted, and river deposits are unsorted C Glacial deposits are unsorted, and river deposits are sorted D Both glacial and river deposits are unsorted deposits 23 Which affects the speed of a valley glacier’s movement? A slope of the valley floor B shape of the valley wall C temperature and thickness of the ice D internal chemistry of the glacier Constructed Response 24 Compare and contrast suspension and saltation as they relate to transport of materials by wind 25 Infer What happens to sand particles as the sand becomes saturated with water? Use the photo below to answer Question 20 Use the figure below to answer Question 26 20 Which process most likely created the valley? A running water B glacial ice C landslide D strong prevailing winds 21 Which is a way to reduce the risk of mass movements? A Develop hillsides with roads so they become stable B Allow septic systems to run unmaintained so that they provide a source of nutrients for the soil C Build homes in steep terrain in order to stabilize the slope D Avoid construction and structures on vulnerable slopes 22 Which property is used to classify dunes? A size C shape B composition D density 218 Chapter • Assessment 26 Identify the features of the glacial landscape 27 Diagram and label a migrating sand dune Indicate the prevailing wind direction 28 Contrast a slide, flow, and rockfall 29 Describe the relationship between permafrost and solifluction 30 Identify which mass movements are dependent on the addition of water 31 Describe how particles eroded by wind differ from particles eroded by water 32 Infer how human activities could affect the formation and migration of sand dunes in coastal areas 33 Compare and contrast the formation, shape, and size of particles of a sand dune and a drumlin How are these features used to indicate the direction of wind and glacial movement? Chapter Test glencoe.com Bill Kamin/Visuals Unlimited 18 Which range of slopes is associated with producing an avalanche? A 10 to 20 degrees C 30 to 45 degrees B 20 to 35 degrees D 45 to 60 degrees (l)Philip James Corwin/CORBIS, (r)USGS Think Critically Use the figure below to answer Question 34 Additional Assessment 40 Earth Science Write an editorial for a newspaper advocating why laws are needed to prevent developers from building homes on relatively steep and loosely consolidated hillside areas Document–Based Questions Data obtained from: Natural Hazards-Landslides Information Sheet 2006 USGS The photo below shows the potential for landslides across the continental United States 34 Hypothesize what kind of mass movements might occur after the eruption of Mount St Helens 35 Analyze the conditions that contribute to the likelihood that an area will experience wind erosion, and identify at least three areas in the United States that are prone to wind erosion 36 Infer why wind abrasion is such an effective agent of erosion 37 Predict the shape of a lake formed by a valley glacier Concept Mapping 38 Create a concept map to compare the terms drumlin, esker, and kame For more help, refer to the Skillbuilder Handbook Challenge Question = Very high potential = High potential = Moderate potential = Low potential 41 Identify landscapes or possible triggers for two areas that have very high potential for landslides 42 Infer why the potential for landslides occurring in Florida is low 43 What can be done to reduce the number of deaths due to landslide? Cumulative Review 44 How many valence electrons does oxygen (atomic number 8) have? (Chapter 3) 45 Which compositional type of igneous rock has the lowest silica content? (Chapter 5) 46 What are fossils? (Chapter 6) 39 Hypothesize how the Dust Bowl of the 1930s might have been avoided Chapter Test glencoe.com Chapter • Assessment 219 Standardized Test Practice Multiple Choice What is the strongest factor that controls the development of soils? A parent material B topography C climate D time Why are the 24 time zones located approximately 15° apart? A to line up with the equator B to roughly match lines of latitude C to roughly match lines of longitude D to line up with the prime meridian Use the table below to answer Questions and Identify the term used to describe wind transportation materials by a bouncing motion of particles A suspension B deflation C saltation D abrasion Region Characteristics A semiarid; experiences intense but brief rainstorms B permafrost; much loose, waterlogged material C mountainous; thick accumulations of snow D thick soils on semi-steep and steep slopes’ occasional earthquake activity E arid; high cliffs and rocky shorelines Which mass movement is most likely to occur in Region A? A mudflow B avalanche C slump D rockfall Which mass movement is most likely to occur in Region B? A solifluction B mudflow C avalanche D slump Which branch of science studies humans’ interactions with the environment? A planetary science B environmental science C oceanography D geology When minerals form from a solution? A when the solution is saturated B when the solution is supersaturated C when the solution is unsaturated D when the solution is ultrasaturated 220 Chapter • Assessment Use the geologic cross section below to answer Questions and Shale Sandstone Volcanic ash Limestone Fault Assuming the rock layers shown are in the same orientation that they were deposited, which layer is the oldest? A shale B sandstone C volcanic ash D limestone Which layer would be most helpful to you in determining the absolute age of these rocks? A shale B sandstone C volcanic ash D limestone 10 Which is NOT a feature of valley glaciers? A cirque B loess C moraine D arête Standardized Test Practice glencoe.com Reading for Comprehension Short Answer Arctic Ice Levels Use the table below to answer Questions 11 and 12 Liquid The amount of sea ice in the Arctic shrank dramatically this summer and is now smaller than it has been in a century of record-keeping, new research reveals Scientists say rising temperatures brought on by human-made global warming is probably to blame for the melting trend Most scientists attribute this warming to human activities such as burning fossil fuels The shift could lead to increased coastal erosion and shrinking of habitat for animals like polar bears Melting sea ice may lead to greater coastal erosion, because Arctic storms could produce much larger waves on the open ocean As the sea ice continues to melt, polar habitat also continues to shrink If the decline in sea ice continued, summers in the Arctic could become completely ice-free before the end of this century, scientists warn Final Color of Litmus Paper ammonia blue lemon juice red tea red vinegar red 11 What conclusions can you draw from the results of the litmus paper tests on the liquids as shown in the table? 12 If an unknown liquid did not change the color of litmus paper, what could you infer? Article obtained from Lovgren, S Arctic ice levels at record low, may keep melting, study warns National Geographic News October 3, 2005 13 Describe the formation of soil 19 How could melting sea ice possibly lead to greater coastal erosion? A Polar bears would use more of the land B Humans would use the exposed land for fossil fuels C It would increase global temperatures, ruining the land D Arctic storms could produce larger waves to erode the shoreline 14 Evaluate the negative impact of building in coastaldune areas 15 Distinguish between weathering and erosion 16 What is one reason granite is commonly used in construction? 20 What is causing the sea ice to melt? A increased temperatures B arctic storms C polar bears D time 17 What are some benefits of communicating scientific results? 21 What can be inferred from this text? 18 What are isotopes of an element? NEED EXTRA HELP? If You Missed Question Review Section 10 11 12 13 14 15 16 17 18 7.3 8.1 8.1 1.1 4.1 2.1 8.2 6.1 6.1 8.3 3.2 3.2 7.3 8.2 7.1 5.2 1.3 3.1 Standardized Test Practice glencoe.com Chapter • Assessment 221 ... affected by the slope of the valley floor, the temperature and thickness of the ice, and the shape of the valley walls The sides and bottom of a valley glacier move more slowly than the middle... increase the risk of mass movement and suggest a solution to the problem Earth Science Make a poster that compares and contrasts solifluction and a slump Consider the way soil moves and the role... water to the first container of sand, and mix well Add 100 mL of water to the second container of sand, and mix well Add 200 mL of water to the third container of sand, and mix well Empty the three