Encyclopedia of Global Resources part 35 ppsx

other elements, although exact proportions vary. Pu - rified diatomite is essentially silica (SiO 2 ), with an av- erage molecularmass of60.8. Diatomite has a melting point of 1,710° Celsius and a density of 2.3 grams per cubic centimeter. Heating it to high temperatures forms crystalline silica. Diatomite is usually white (if pure), buff, gray, and rarely black. In situ, it is generally found as a soft sedimentary rock or as powder. Raw diatomite is typi- cally processed by a series of crushing, drying, size- reduction, and calcining procedures to produce different grades of diatomite for different specialized applications. Description, Distribution, and Forms Diatomite is a soft, chalklike, fine-grained sedimentary rock composed primarily of the fossilized silica shells of microscopic algae called diatoms. It is finely porous, is low in density, and has low thermal conduc- tivity. Diatom frustules are composed of twosymmetri- cal silica valves, which can be elaborately ornamented with tiny holes and protrusions. These tiny holes are what make diatoms an ideal material for filtration. The word “diatom” comes from Greek diatomos, meaning “cut in half,” because of the two valves. Diatoms live in a wide range of moist environments, although most abundantly in marine (oceanic) and lacustrine (freshwater) environments.Three main types of diatomite deposits are recognized in the United States: marine rocks near continental margins, lacustrine rocks formed in ancient lakes or marshes, and sedimentary rocks in modernlakes,marshes,and bogs. Another commonly used term for diatomite, diatomaceous earth, more properly refers to uncon- solidated or less lithified forms of diatomite. One of the most important marine diatomite deposits is near Lompoc, California, reported to be the world’s largest producing district by volume. Eco- nomically important lacustrine deposits in the United States are found in Nevada, Oregon,Washington, and eastern California. In 2007, the United States produced 33 percent of the world’s diatomite. Other lead- ing producers were China (20 percent), Denmark (11 percent; all moler diatomite, containing 30 weight percent clay),Japan(6 percent), andFrance (4 percent). History Some of the earliest references to diatomite are to the ancient Greeks’ probable use of it to form lightweight bricks for building; they also used diatomite as an abrasive. In 535 c.e., the Roman Emperor Justinian I used diatomite bricks in building the church of St. So- fia in Constantinople (now Istanbul). Diatomite use became industrially important to Western Europe after 1867, when Alfred Nobel in- vented dynamite. Pulverized diatomite was commonly used to absorb and stabilize the nitroglycerine used to make dynamite. By the late 1800’s, the United States had become the primary producer of diatomite. By 1900, diatomite’s uses had expanded to include many of its present-day uses, including beer filtration and building materials. During the 1920’s, techniques for calcining (ther- mally treating) and grading diatomite enabled a wider variety ofusesfor this resource. ByWorld War II, the U.S. Army and Navy made wide use of diatomite to purify drinking water, to remove oil from boiler and engine water, and to create low-light-reflectance paints for ships. Obtaining Diatomite Because of its abundance and usual occurrence near the surface in the United States, most diatomite produced is obtained from open-pit mines. The diatomite is excavated by machine after the overburden is removed. Outside the United States—particularly in China, Chile, and France—underground diatomite mining is fairly common. These mines are usually pit- and-pillar mines excavated by machine, although some small mines are excavated using hand tools. In Iceland, diatomaceous mud is dredged from Lake Myvatn. Diatomite is often dried in the open air near the mine before processing. Diatomite processing is often carried out near the mine from which it is extracted. Raw diatomite may contain up to 65 percent water and is expensive to transport. Primary crushing of ore is usually done with spiked rolls and hammer mills, reducing the ore to 1.25-centimeter pieces while limiting damage to the diatom structure. Passage through heated air, milling fans, and air cy- clones further dries the diatomite and begins to classify for size as well as remove impurities of different density. Processing aims to separate individual diatom valves without destroying their structure, which is key to filtration uses. Calcining, which increases filtration rate, specific gravity, and particle hardness, as well as oxidizing iron, is usually done with rotary kilns. Calcining ispar - ticularly important for filter grades. 310 • Diatomite Global Resources Uses of Diatomite Diatomite is primarily used as a filtration medium but also is used for insulation, as a filler and absorbent, and as a mild abrasive, in addition to some specialized medical uses. The most common use of diatomite is in filtration, because of its finely porous nature. These uses include water purification, beer and wine filter - ing, and the removal of oils from water. As a water filtration element, diatomaceous earth usuallyisused as a layer on a filter element or septum (a permeable cover over interior collection channels), called pre- coat filtration. Diatomite water filtration systems are Global Resources Diatomite • 311 Data from the U.S. Geological Survey, . U.S. Government Printing Office, 2009.Source: Mineral Commodity Summaries, 2009 51,000 27,000 24,000 110,000 60,000 33,000 32,000 653,000 130,000 Metric Tons 700,000600,000500,000400,000300,000200,000100,000 United States Mexico Japan Italy Iceland Germany Peru Spain Other countries 25,000 440,000 76,000 24,000 52,000 220,000 71,000 Czech Republic Costa Rica Commonwealth of Independent States China Chile Denmark (processed) France Diatomite: World Mine Production, 2008 lightweight, cheap, and simple and can remove bacte - ria and protozoans as well as cysts, algae, and asbestos. This usage of diatomite first became important during World War II, when the U.S. Army needed a water filter suitable for mobile military operations. The first municipal diatomaceous-earth water filtration system was set up in 1948, and more than two hundred oper- ate presently in the United States. Diatomite is also used to filter nonpotable water, such as that which is used in swimming pools. Diatomite began to be used after Prohibition to filter beer and wine in the United States, replacing wood pulpinfilters. It isalsoused to filter liquidsweet- eners, oils and fats, petroleum and other chemicals, and pharmaceuticals. Another major use of diatomite is in building, where it is used for lightweight blocks and bricks and for thermal insulation (high clay-content Danish moler in particular). Diatomite is also a frequent cement additive; diatomite for cement requires less processing. As a filler, diatomite has many uses. In addition to providing bulk, diatomite can reduce reflectivity in paints, reduce caking in granular mixtures, and provide a variety of effects in plastics, including prevent- ing film sticking. Diatomite is absorbent and often used for cleaning industrial spills and in cat litter. As an insecticide, diatomite is less toxic than chemical pesticides, as it works by absorbing lipids from insects’ exoskeletons, causing dehydration. However, it harms beneficial insects as well as pests. Diatomite also is used as a growing medium for hydroponics and an additive in various types of potting soil, because it retains water and nutrients while draining quickly, similar to vermiculite. Medical-grade diatomite is some- times used for deworming, as the sharp edges of the frustules are thought to kill parasites, but the efficacy of this is questionable. Diatomite is also used in cosmetics—for example, in facial masks to absorb oil—and as a minor abrasive in jewelry polishes and toothpastes. Some processes for extracting and purifying DNA use diatomite, which will remove DNA but not RNA or proteins. Diatomite and a highly concentrated denaturing agent are used to remove DNA, and then a slightly alkaline, low ionic strength buffer (such as water) can be used to extract DNA from the diatomite. While diatomite can be replaced by other materi - als—such as silica sand, perlite, talc, ground lime, ground mica, and clay—for most of its applications, its abundance, availability, and low cost make it a pop- ular and heavily used resource. Melissa A. Barton Further Reading Fulton, George P. Diatomaceous Earth Filtration for Safe Drinking Water. Reston, Va.: American Society of Civil Engineers, 2000. Stoermer, Eugene F., and John P. Smol, eds. The Dia- toms: Applications for the Environmental and Earth Sci- ences. NewYork: Cambridge University Press,1999. U.S. Geological Survey. Minerals Yearbook. Washing- ton, D.C.: Author, 2008. Web Site U.S. Geological Survey History and Overview of the U.S. Diatomite Mining Industry, with Emphasis on the Western United States http://pubs.usgs.gov/bul/b2209-e/ See also: Clays; Lime; Silicates; Water. 312 • Diatomite Global Resources Source: Mineral Commodity Summaries, 2009 Data from the U.S. Geological Survey, .U.S.GovernmentPrinting Office, 2009. Filter aids 52% Cement additives 26% Absorbents 12% Fillers 9% Biomedical 1% U.S. End Uses of Diatomite Dimension stone Category: Mineral and other nonliving resources Where Found Dimension stone, or natural stone, is mined in quarries around the world. The largest concentrations are found in China, India, Italy,Canada,andSpain.In the United States, a country that produces less than 15 percent of the worldwide supply (although it is the dominant market for the stone), quarries are found in thirty-five states, principally (in order of percent- age) Indiana, Vermont, Georgia, Wisconsin, and Mas- sachusetts. Primary Uses Dimension stone is used primarily for domestic decorating and home improvements in upscale housing. It also provides massive block foundation support for large-scale engineering projects, as well as material for monuments, memorial stones, and walkways. Technical Definition Dimension stone is any natural rock—igneous, metamorphic, or sedimentary—precisely cut from a quarry to a specific size (in blocks or slabs) for a specific function (as opposed to crushed stone, which is fractured rubble blasted from quarries to facilitate its removal). Commercially, granite is the most widely used (about one-third of the dimension stone quar- ried), followed by limestone, marble, sandstone, and, to a much lesser extent, slate and travertine. The deci- sion about which class of dimension stone is to be used is based on color and texture as well as appearance and durability. Description, Distribution, and Forms Because dimension stone requires precise mining, must maintain a usable appearance throughout the excavation process, and has a comparatively high expense in transportation, it accounts for roughly only 2 percent of the total rock mined annually. In the United States, for instance, approximately 1.4 million metric tons of dimension stone are mined annually. Dimension stone can beeitherrough block (for heavy construction and residential foundations) or dressed block (for statuary, paving stones, and domestic deco - ration), with its distinctive luster. In fact, finish also is used to classify types of dimension stone. In addi - tion to being reflective, surfaces can be pitted, nonreflective (both smooth and rough), and pat- terned (often produced by hand). The four principal types of dimension stone— granite, limestone, marble, and sandstone—are graded by color, grain, texture, mineral patterns and swirls, natural surface finish, durability, strength, and mineral makeup. For instance, dimension granite, an igneous rock, is valued for its relative availability; its durability in the face of weathering and environmental pollution, specifically acid rain, because it is most often used for exterior construction projects; its uni- form texture; its hardness; and its variety of colors. Di- mension limestone, a sedimentary rock composed largely of calcite, is easy to cut into massive blocks and, although not impervious to acid rain, is remarkably durable (the Pyramids at Giza are made of dimension limestone). However, because of dimension limestone’s enormous weight, it is used primarily for foundations and smaller buildings. Dimension marble is a metamorphic rock that is both durable and strong. With its exquisitely smooth, polished surface, marble can be cut into large blocks (up to63metric tons) and used to create spectacular public buildings (for instance, the Taj Mahal and the Lincoln Memorial). Di- mension sandstone, a sedimentary rock, is most often light gray or yellowish-brown; however, its tendency to streak because of weathering creates striking, aesthet- ically appealing striation effects. Its surface is coarse and finely grained. It is particularly fragile, susceptible to weathering, and has to be replaced; thus it is limited in its uses. History Using carefully cut, ponderous blocks of durable rock for majorengineeringundertakingsdates to antiquity in both the Far East, predominantly China, and the Mediterraneanbasin, most notably the stunning pyra- mid constructions in Egypt, the marble temples around Athens, andthemosques of Turkey. By the Re- naissance, rich mineral deposits of marble and granite in Italy and Spain were being utilized to construct great cathedrals and a wide variety of public buildings, courthouses, and palaces. Because of the precise method for cutting the stone, as well as the often extraordinary cost of transporting a massive amount of chiseled rock without damaging its integrity, dimension stone was used almost exclusively for public proj - ects financed by monarchies, the Catholic Church, or wealthy aristocrats. Global Resources Dimension stone • 313 Large deposits of granite, limestone, and marble found in New England and in the Middle Atlantic states, most notably Tennessee and Indiana, made dimension stone affordable in the New World. Dimen- sion stone played an enormous role in shaping the look of (and providing the architectural support for) many public edifices and private residences across the United States. By the mid-twentieth century, however, newer building materials—reinforced concrete, alu- minum, and steel—eclipsed dimension stone. That changed dramatically when environmental concerns about the pollution created by the production of those construction materials returned attention to all-natural dimension stone. In addition, the home building boom in the United States during the 1990’s created a market of upscale consumers interested in using natural stone to decorate their custom-built homes. In the same decade, interest in dimension stone was bolstered by large-scale public construction projects, most notably the Denver International Air- port, the Korean War Veterans Memorial, the Na- tional World War II Memorial, and the Franklin Del- ano Roosevelt Memorial (the latter three are located in Washington, D.C.). Obtaining Dimension Stone The process of obtaining dimension stone—drilling, extracting, cutting, shaping, and polishing—is usually tailored to follow a specific mining order; dimension stone is seldom mined without a contract for a particular project. Since the 1960’s, extracting dimension stone has been enhanced, and made comparatively easy, by significant developments in engineering tools. Unlike the excavation of crushed stone, which relies on indiscriminate detonations and heavy machinery, the recovery of usable dimension stone requires care. Each type of dimension stone requires its own methodology depending on the needs of the construction project, the depth of the mineral de- posit, and the mining operation’s financial resources. The methodology is further impacted by the location of the vein—whether cutting into a hill (called a bench quarry) or digging into the flat ground, operations that can go to 90 meters. Obtaining dimension stone begins with limited blasting. Then jet piercers, which use a high-velocity jet flame—a concentrated, highly combustible blast of oxygen and fuel oil shot through a nozzle under enormous pressure—channel into the quarry face. In the case of marble, limestone, and sandstone, safer electrical drilling machines with steel chisels that chop channels into the walls and cut away the desired blocks are frequently used; this method is more time- consuming. In the case of granite and marble, once channels are created, large blocks are pried from the quarry face or extracted from the quarry mine and cut on site into usable shapes (ranging from 0.3 to 18 meters long and 4 meters thick), called mill blocks. Each block is then removed from the quarry area with derricks. In turn, these blocks are processed for their specific project, that is, given the appropriate shape, size, dimension, and finish by certified masons who use a variety of precision saws. Diamond saws are used most often because of their hardness and their ability to cut intricately and carefully. Uses of Dimension Stone Despite the availability of less expensive substitute building materials, the extraordinary expense of such precisely cut stone, and the care needed during its transportation, dimension stone has maintained its position within the engineering and architectural fields for close to three millennia. Slabs of cut stone, most often granite or sandstone, provide a reliable, 314 • Dimension stone Global Resources Source: Mineral Commodity Summaries, 2009 Data from the U.S. Geological Survey, .U.S.GovernmentPrinting Office, 2009. Limestone 35% Granite 32% Miscellaneous 17% Sandstone 12% Marble & slate 4% U.S. End Use of Dimension Stone durable, and attractive foundation for both buildings and residences.However, the useofthe stone for spectacular building projects is the use most often recognized by people. Dimension stone such as granite and marble is most associated with grand public spaces and with important monuments dedicated to histori- cally significant people and events, public buildings (like banks and government facilities), cathedrals, grand private homes, upscale hotels, cemetery head- stone markers, and elegant mausoleums. In addition, thinner cuts of dimension marble are used for clad- ding, the outer skin of stone applied to buildings to protect the foundation stone and to give the building an aesthetic quality. Dimension stone creates an elegant, tasteful, and earthy feel to home interiors. It provides tops for kitchen counters and bathroom vanities as well as material used for staircases and ornamental arches in homes where owners are interested in creating distinctive—and expensive—custom-designed interior effects. Because no two slabs of dimension stone are exactly alike, interior effects can be both striking and individual. Because of the wide variety of textures and colors in natural stone, homeowners can complete virtually whatever decorating motif they conceive by using cut stones for floor tiles, walkways, flagstones, ornamental statuary, and roofing shingles. Joseph Dewey Further Reading Adams, Heather, and Earl G. Adams. Stone: Designing Kitchens, Baths, and Interiors with Natural Stone. New York: Stewart, Tabori & Chang, 2003. Bell, Ron. Early History of Indiana Limestone. Bloom- ington, Ind.: AuthorHouse, 2008. Dupré, Judith. Monuments: America’s History in Art and Memory. New York: Random House, 2007. Greenhalgh, Michael. Marble Past, Monumental Pres- ent: Building with Antiquities in the Mediaeval Mediter- ranean. Boston: Brill, 2008. Isler, Martin. Sticks, Stones, and Shadows: Building the Pyramids. Norman: University of Oklahoma, 2001. Web Site U.S. Geological Survey Minerals Information: Dimension Stone Statistics and Information http://minerals.usgs.gov/minerals/pubs/ commodity/stone_dimension/ See also: Diamond; Granite; Igneous processes, rocks, and mineral deposits; Limestone; Marble; Open-pit mining; Sand and gravel; Sandstone; Sedimentary processes, rocks, and mineral deposits. Dow, Herbert H. Category: People Born: February 26, 1866; Belleville, Ontario, Canada Died: October 15, 1930; Rochester, Minnesota Herbert H. Dow’s main discovery was that underground liquid brine from prehistoric saltwater oceans contained many chemicals. He sought a way to extract these chemicals from the Earth and was initially successful in extracting bromine. He later discovered ways to extract other chemicals from the brine, including magnesium, sodium, calcium, and chlorine. His later research led to more efficient methods of extraction. Biographical Background Although born in Canada, Herbert H. Dow lived in that country for about only six weeks. His American parents returned to Derby, Connecticut, where his fa- ther worked as a mechanical engineer. In 1878, his fa- ther’s company, the Derby Shovel Manufacturing Company, moved to Cleveland, Ohio, and the family moved too. In 1884, Dow entered the Case School of Applied Science in Cleveland (now Case Western Re- serve University), where he studied chemistry. While still a student at Case, Dow realized the importance of subterranean brine as a source of chemicals. His first successful extraction process was for bromine, a chemical used in sleep medicines and by photogra- phers. Upon graduation from Case, Dow became a professor of chemistry at Huron Street Hospital Col- lege in Cleveland and continued to work on his research to develop a cost-effective method of extracting bromine. In 1890, with the assistance of several associates, Dow established the Midland Chemical Company in Midland, Michigan. Midland was selected for the company’s location because of the high-quality bromine in the subterraneanwaters underneath that city. A short time later, because of differences of opinion between Dow and his backers, Dow left Midland and returned to Cleveland, where he founded the Dow Global Resources Dow, Herbert H. • 315 Process Company. After developing methods to ex - tract chemicals such as chlorine and sodium, Dow became wealthy. He moved his company to Midland, where it became Dow Chemical Company in 1896. By 1900, he had taken over the Midland Chemical Com- pany. Impact on Resource Use By 1891, Dow had perfected the electrolysis process of extracting bromine that became known as the “Dow process.” Many of Dow’s patents were for efficient means of extracting chemicals from other substances. Thus, he was able to lower the cost of chemical prod- ucts and produce those chemicals more efficiently and effectively. For example, in the early 1900’s, Ger- many was the center of the chemical industry, but Dow was selling bromine for less than 75 percent of the price charged in Europe. Dow expanded during World War I by producing chemicals used in explo- sives. Following the war, the company became active in supplying chemicals to the automobile industry. Dow also improved the quality of gasoline. By the time of his death at the Mayo Clinic in 1930, Dow had re- ceived more than ninety patents for processes for extracting chemicals. Although Dow’s research dealt with how to mine chemicals from ancient oceans, his ideas and technology have had broader uses. The same methods can be used to mine modern seas. Thus, shortly after Dow’s death, his company opened its first seawater processing plant. Dow was one of the founders of the modern chemical industry. He took halogen science from theory to reality. Dale L. Flesher See also: Bromine; Calcium compounds; Chlorites; Magnesium; Marine mining. Drought Category: Environment, conservation, and resource management Drought is a shortage of precipitation that results in a water deficit for some activity. Droughts occur in both arid and humid regions. Traditional and modern so - cieties have evolved methods of adjusting to the drought hazard. Background In order to analyze and assess the impacts of drought, as well as delimit drought areas, the characteristics of “drought” must be defined. Conditions considered a drought by a farmer whose crops have withered during the summer may not be seen as a drought by a city planner. There are many types of drought: agricultural, hydrological, economic, and meteorological. The Palmer Drought Severity Index is the best known of a number of indexes that attempt to standardize the measurement of drought magnitude. Neverthe- less, there remains much confusion and uncertainty on what defines a drought. Roger Graham Barry and Richard J. Chorley, in At- mosphere, Weather, and Climate (1992), noted that drought conditions tend to be associated with one or more of four factors: increases in extent and persis- tence of subtropical high-pressure cells; changes in the summer monsoonal circulation patterns that can cause a postponement or failure of the incursion of wet maritime tropical air onto the land; lower ocean surface temperatures resulting from changes in ocean currents or increased upwelling of cold waters; and displacement ofmidlatitudestormtracks by drier air. Effects of Drought Drought can have wide-ranging impacts on the environment, communities, and farmers. Most plants and animals in arid regions have adapted to dealing with drought, either behaviorally or through specialized physical adaptations. Humans, however, are often un- prepared or overwhelmed by the consequences of drought. Farmers experience decreased incomes from crop failure. Low rainfall frequently increases acrop’s susceptibility to disease and pests. Drought can particularly hurt small rural communities, especially local business people who are dependent on purchases from farmers and ranchers. Drought is a natural element of climate, and no region is immune to the drought hazard. Farmers in more humid areas grow crops that are less drought re- sistant. In developing countries the effects of drought can include malnutrition and famine. A prolonged drought struck the Sahel zone of Africa from 1968 through 1974. Nearly 5 million cattle died during the drought, and more than 100,000 people died from malnutrition-related diseases during just one year of the drought. Subsistence and traditional societies can be very re - silient in the face of drought.AmericanIndianseither 316 • Drought Global Resources stored food for poor years or migrated to wetter areas. The !Kung Bushmen of southern Africa learned to change their diet, find alternate water sources, and generally adapt to the fluctuation of seasons and climate in the Kalahari Desert. More than any other event, the Dust Bowl years of the 1930’s influenced Americans’ perceptions and knowledge of drought. Stories of dust storms that turned day into night, fences covered by drifting soil, and the migration of destitute farmers from the Great Plains to California captured public and government attention. The enormous topsoil loss to wind erosion, continuous crop failures, and widespread bankrupt- cies suggested that the United States had in some way failed to adapt to the drought hazard. Federal Drought Response in the United States Beginning in the 1930’s, the federal government took an increasing roleindrought management and relief. In 1933, the federal government created the Soil Ero- sion Service, known today as the Natural Resources Conservation Service. No other single federal program or organization has had a greater impact on farmers’ abilities to managethedrought hazard. President Franklin D. Roosevelt’s Prai- rie States Forestry Project (1934-1942) planted more than 93,078 hectares of shelterbelts in the plains states for wind erosion control. The federal government purchased approximately 400,000 hectares of marginal farmland for re- planting into grass. Federal agencies constructed water resource and irrigation projects. Post-Dust Bowl droughts still caused hard- ships, but the brunt of the environmental, economic, and social consequences of drought were considerably lessened. Fewer dust storms rav- aged the plains. New crop varieties and better farming practices decreased crop losses during drought years. Government programs and better knowledge have enabled families and communities to better cope with drought. Coping with Future Droughts Numerous attempts have been made to predict droughts, especially in terms of cycles. However, attempts to predict droughts one or more years into the future have generally been unsuccess - ful. The shorter the prediction interval, the more accurate the prediction. Nevertheless, progress has been made in estimating drought occur - rence and timing. For example, the El Niño/South- ern Oscillation may be aprecursor to droughtin some areas. Possibly with time the physical mechanics of climate and drought will be understood adequately for long-term predictions to have value. Perhaps of greater value is the current capacity to detect and monitor drought in its early stages (usually meaning within one to twelve months). Early recogni- tion of potential drought conditions can give policy makers and resource managers the extra time needed to adjust their management strategies. Information on soil moisture conditions aids farmers with planting and crop selection, seeding, fertilization, irrigation rates, and harvest decisions. Communities that have a few months’ warning of impending drought can in- crease water storage, implement water conservation measures, and obtain outside sources of water. The progress made in the world’s developed countries has not always been available to the developing nations. Overpopulation and overuse of agricultural lands have resulted in regional problems of desertifi- Global Resources Drought • 317 A drought results from a lack of precipitation that causes massive water short - ages, affecting entire populations of people. (©Galyna Andrushko/ Dreamstime.com) cation and have impeded the ability of developing na - tions to respond. Monitoring equipment can be costly. Furthermore, drought adjustments used in the United States may not be applicable to other countries’ drought situations. David M. Diggs Further Reading Allaby, Michael. Droughts. Illustrations by Richard Garratt. Rev. ed. New York: Facts On File, 2003. Barry, Roger G., and Richard J. Chorley. Atmosphere, Weather, and Climate. 6th ed. New York: Methuen, 1992. Brichieri-Colombi, Stephen. The World Water Crisis: The Failures of Resource Management. New York: I. B. Tauris, 2009. Collier, Michael, and Robert H. Webb. Floods, Droughts, and Climate Change. Tucson: University of Arizona Press, 2002. Hewitt, Ken, ed. Interpretationsof Calamity from the View- point of Human Ecology. Boston: Allen & Unwin, 1983. Riebsame, William E., Stanley A. Changnon, Jr., and Thomas R. Karl. Drought and Natural Resources Man- agement in the United States: Impacts and Implications of the 1987-89 Drought. Boulder, Colo.: Westview Press, 1991. Wilhite, Donald A., ed. Drought: A Global Assessment. New York: Routledge, 2000. _______. Drought and Water Crises: Science, Technology, and Management Issues. Boca Raton, Fla.: Taylor & Francis, 2005. _______. Drought Assessment, Management, and Planning: Theory and Case Studies. Boston: Kluwer Academic, 1993. Worster, Donald. Dust Bowl: The Southern Plains in the 1930’s. 25th anniversary ed. New York: Oxford Uni- versity Press, 2004. Web Sites Agriculture and Agri-Food Canada Drought Watch http://www.agr.gc.ca/pfra/drought/mapscc_e.htm National Integrated Drought Information System U.S. Drought Portal http://www.drought.gov/portal/server.pt/ community/drought_gov/202 National Oceanic and Atmospheric Administration Drought Information Center http://www.drought.noaa.gov See also: Atmosphere; Climate and resources; Deser- tification; Dust Bowl; Erosion and erosion control; Ir- rigation; Weather and resources. Dust Bowl Category: Historical events and movements Date: 1930’s The environmental catastrophe called the “Dust Bowl” was centered inthe southernGreatPlains of the United States and was caused by a combination of extended drought and human misuse of the land. Definition The Dust Bowl represents one of the most salient ex- amples of environmental maladaptation in modern history. The region called the “Dust Bowl” included a swath of territory stretching 480 kilometers east-west and 800 kilometers north-south in the Great Plains. The Dust Bowl was centered in the panhandles of Texas and Oklahoma, southeastern Colorado, north- eastern New Mexico, and western Kansas. High rates of soil erosion and recurring dust storms character- ized the Dust Bowl region. The term “Dust Bowl” was used in an article by an Associated Press reporter in 1935; the phrase stuck and quickly came to refer to the entireregion of theGreatPlains during the1930’s. Overview Relatively wet climatic conditions and good grain prices had stimulated extensive settlement of agricul- turally marginal areas of the Great Plains during the 1910’s and 1920’s. Government policies and Great Plains boosters had encouraged thousands of people to settle in areas that often averaged less than40centi- meters of precipitation annually. Compounding the problem, farmers practiced agricultural techniques that made the soil highly susceptible to wind and water erosion. In many parts of the United States and most areas of the GreatPlains,the period between 1930 and 1941 represents some of the driest years on record. Annual 318 • Dust Bowl Global Resources rainfall in the Dust Bowl region dropped to single dig- its. A combination of low rainfall, exposed soil, and high winds resulted in extensive dust storms. The U.S. Soil Conservation Service kept a recordof dust storms of “regional” extent: There were fourteen in 1932, thirty-eight in 1933, twenty-two in 1934, forty in 1935, sixty-eight in 1936, seventy-two in 1937, sixty-one in 1938, thirty in 1939, and seventeen each in both 1940 and 1941. Some of these huge dust storms made their way east, where they deposited dust on ships 480 kilometers out in the Atlantic Ocean. Dust Bowl conditions and the Great Depression of the 1930’s caused widespread farm foreclosures and a mass migration from the region. Penniless, the mi- grants moved to major urbanareas or to other agricultural areas, such as California. The plight of these “Okies” was immortalized in John Steinbeck’s novel The Grapes of Wrath. The Dust Bowl experience forced the region’s resi- dents and the federal government to find ways to better adapt to the area’s marginal climate. New and more effective tillage techniques were used to con- serve moisture and minimize erosion. Summer fallowing became a widespread practice after the Dust Bowl experience. Surface and subsurface water resources were exploited for irrigation use. A direct out- growth of the Dust Bowl years was a plethora of government programs to protect the land and farmers during periods of drought. For example, the Soil Ero- sion Service, a part of Franklin D. Roosevelt’s New Deal program, was established as a temporary agency in 1933 to aid Great Plains farmers. It became perma- nent in 1935, and its name changed to the Soil Con- servation Service (later the Natural Resources Con - servation Service). The effort to adjust to the Great Plains environment paid off when major periods of Global Resources Dust Bowl • 319 A Dust Bowl farmer uses a tractor to clear sand covering his cropland in 1937. (AP/Wide World Photos) . erosion. In many parts of the United States and most areas of the GreatPlains,the period between 1930 and 1941 represents some of the driest years on record. Annual 318 • Dust Bowl Global Resources rainfall. developing nations. Overpopulation and overuse of agricultural lands have resulted in regional problems of desertifi- Global Resources Drought • 317 A drought results from a lack of precipitation that causes massive. southernGreatPlains of the United States and was caused by a combination of extended drought and human misuse of the land. Definition The Dust Bowl represents one of the most salient ex- amples of environmental