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Solid-Earth Sciences and Society 4 Resources of the Solid Earth ESSAY: NATURAL EXPLOITATION All organisms exploit the surrounding environment to sustain their metabolism, and in the process they produce waste. Prokaryotes, single-celled bacteria, have colonized every niche on the Earth's surface, absorbing local chemical compounds and excreting unused or altered compounds. Cities with vast human populations do the same thing—they use natural resources and produce waste. Whether a single-celled organism or a complex society, the efficient location and exploitation of resources and the production and appropriate disposal of neutral or recyclable wastes determine success or failure, life or death. The resources required for a complex civilization are more diverse than those needed by simpler organisms. Besides the obvious needs for primary materials—chemical and energy sources—shared by all living beings, humans depend on physical and biological systems that process primary resources. The ability to invade potentially hostile environments depends on the use of many of the Earth's subsystems. We require large amounts of water and landscapes that provide the means to feed and shelter us. Water may well be the Earth's most vital resource. While regions subject to drought are usually concerned with the quantity of available water, all communities must now care for the quality of water. In the United States, irrigation methods and personal habits deplete ancient aquifers and drain mountain runoff. At the same time, toxic chemicals and dangerous pathogens can seep into water supplies. Only with conservation and careful planning will water become a renewable resource again; education programs are needed to deter both sophisticated cultures and simple communities from fouling their own supplies. All organisms run on energy. In plants and most animals energy is supplied by proteins and sugars. Human societies require fuel to operate the mechanisms that supply food, warmth, and services. Less complex communities depend on wood for energy, but since the Industrial
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Solid-Earth Sciences and Society Revolution energy sources have expanded to include gas, coal, oil, steam, and fissionable materials. Mineral resources produce the tools that enable society to supply water, food, fuel, and manufactured goods to growing populations. Exploration and extraction respond quickly to market values of minerals, and market values vary according to technological innovation. Certain minerals will always be needed, but there is a point at which the price of supplying a product to market is more than the price of developing techniques that may render that product obsolete. Because technological developments cannot be predicted in the long run, the need for some minerals cannot be predicted. Curiously enough, research into the formation of all these resources involves an understanding of fluid movement within solid materials. Separate investigations of the solid, fluid, and gaseous envelopes of the Earth are no longer possible. Researchers now are reorienting their goals to address an earth system that integrates geology, hydrology, and atmospheric sciences with biochemical elements. The breadth of the earth system allows for full appreciation of the consequences of concentration and redistribution of material by natural causes and human intervention. Often the search for resources is frustrated, and even when it is successful their extraction can be difficult and dangerous. To warrant the effort there must be a degree of profit. As market values change, managers must decide whether a particular resource is economic. If it is economic, it is worth the effort to discover and extract deposits. There are unlimited amounts of all the compounds and elements that humankind needs, but they are not usually concentrated into deposits that are economically worthwhile. If a deposit is worth the effort, or if it can be reasonably assumed that it will become worthwhile, it is classified as a reserve. New discoveries and new extraction techniques contribute to the increasing quantity of what can be considered reserves. But the rising population continually puts more demand on available resources. As accumulations of waste material grow and concentrations become more hazardous, a new factor affects assessments of a resource's economic value: the cost of landscape reclamation and by-product neutralization. Communities have come to understand that they can no longer dump sewage into streams and let solid wastes accumulate indefinitely. Mining enterprises have come to understand that they can no longer leave mountainsides gouged and stripped, with piles of tailings leaching toxic compounds into the watershed. As understanding of the earth system grows, resource scientists can moderate the effects of society on nature. One exciting research area is the ability of wetlands to clean contaminated fluids. Wetlands and marshes were once considered useless wasted tracts. If not left to hunters and trappers, these regions were often drained. Researchers have now concluded that the chemical and biological processes that prevail in marshy environments can remove toxic compounds from contaminated water. Constructed wetlands are now being introduced as systems that cleanse wastewater and return acid levels to natural levels. Specific bacteria can clean up specific compounds through bioleaching, biosorption, and bioreduction.
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Solid-Earth Sciences and Society Researchers have developed ways to reclaim mining sites by conservation methods and recycling. Techniques used for extraction of minerals from low-grade ore can be adapted to detoxify contaminated soils as well as water. And mining practices in use now, such as surface landscaping and sealing mine walls to reduce seepage through the mine into the water table, have successfully minimized environmental modification. Incorporating the traditional practice of backfilling spent caverns with tailings to prevent subsidence, modern reclamation efforts strive to recreate the original scene as closely as possible. Recovery of petroleum resources also can threaten the environment. Oil spills come to mind—the Exxon Valdez spill and the oil spill released into the Persian Gulf during the fighting to reinstate the status quo of the Kuwaiti Emirate. But petroleum geologists are proud of their efforts to reduce the dangers of spillage during the production phase. Today, oil lost to the environment during production is much less than the amount released naturally through seepage. The greatest dangers from oil spillage are found in the transportation phase—and tanker transportation is the most dangerous of all. The burning of coal produces emissions that accelerate global warming trends. Nuclear energy creates radioactive by-products that can threaten the environment in a variety of ways—as emission into the atmosphere or invasion into the groundwater. Even burning wood causes smog. But nature does have the ability to absorb some of this abuse—it has a carrying capacity. The carrying capacity is the upper limit of a system's ability to support all components within the bounds of available resources. When the carrying capacity is exceeded, a threshold is crossed, and new equilibria establish themselves. Often a new equilibrium spells disaster for the components supported by the former system. For living beings crossing such a threshold can mean extinction. The carrying capacity of a natural system may be threatened by various means. Natural climatic changes can devastate landscapes and destroy soils just as efficiently as humans can in their roles of gatherer, farmer, or skyscraper builder. Thresholds of stress are crossed whenever a natural disaster hits—earthquakes, volcanoes, and floods all result from natural systems thrown into a different order. Seismologists, volcanologists, and hydrologists experiment and observe, in search of greater understanding of the natural systems, their carrying capacities, and their dangerous thresholds. That understanding should result in the ability to predict the potential for problems, and such predictions might permit mitigation of the intensity of an event—or at least provide time to warn populations to evacuate endangered regions and thus save lives. The humans who occupy this planet are profoundly dependent on the ordered operation of its natural systems. Human populations exploit the minerals, fuels, soils, and waters, straining against capacities and adapting to limits. That straining and adapting is what characterize life: it's completely natural—as extinction will be, if the human species strains too hard or adapts too slowly.
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Solid-Earth Sciences and Society ROCK-FLUID INTERACTIONS Traditionally, the science of geology concerned rocks and minerals—the solid part of the natural environment. But over the past two centuries, geologists have become increasingly aware that divisions between solid, liquid, and gaseous environments can be unnecessarily restrictive. The phases are interactive and interdependent; they are not distinct. The nature of the crust cannot be understood separately from the atmospheric and oceanic systems. Most recently, earth scientists have been surprised to detect evidence of organic forms thriving in the depths of the crust and in the heights of the atmosphere. Rock, water, air, and biota interchange molecules throughout a layer of skin covering the planet. The list of interdependent processes lengthens every day as new discoveries are made, and it reflects much geological research—as it is currently defined. Understanding of rock-fluid interactions began with the study of groundwater flow. Empirical laws were developed in the 1800s to define the rate and intensity of the underground flow feeding springs and wells. Further studies have revealed characteristics of fluid systems that are determined by permeability of the rock, composition and volume of the fluid, and pressure and temperature gradients within the system. These characteristics can be determined close to the surface through wells, but rock-fluid interaction occurring at great depth must be deduced from examination of outcropping rocks that formerly lay far below the surface. Outcrops generally provide evidence of the effects left by deeply circulating fluids, only rarely offering samples of the fluid itself. Indications from wells and outcrops suggest that fluids may be present in significant amounts at most crustal levels, although they are locally sporadic, and that the surrounding rocks undergo chemical modification as a result of contact with migrating fluids. These conclusions are consistent with observations of the pivotal role played by fluids in the genesis of both mineral and fossil fuel concentrations. Recent geophysical studies have added to the insights about fluids within the crust. Electrical conductivity inferred for great depths suggests a persistent aqueous fluid phase, while seismic reflections from possible low-velocity zones imply abnormally high fluid pressures. This information supports the opinion that extensive fractures and large volumes of aqueous fluids permeate the deep crust. FIGURE 4.1 Vein/joint abundance map of the Sierrita system, Arizona. The total number of fractures per centimeter increase as the pluton (patterned area) is approached. Figure from S. R. Titley, NRC, 1990, The Role of Fluids in Crustal Processes. Researchers testing the behavior of crustal rock have concluded that fluid proportion decreases with depth, but they do not understand the transition between the extremes of saturation and scant traces. At every level water acts to redistribute heat in hydrothermal systems. Because an increase in temperature raises fluid pressure, any substantial introduction of magma into the crust will initiate a convecting system of groundwater around the magma body (Figure 4.1). The convecting water transports heat from the magma, controlling its cooling rate, which affects the crystallization rate of the rock and thus some of its subsequent identifying characteristics as a solid. The convecting water also redistributes chemical components from the intrusive body, and from the surrounding host rock, to more remote locations. Even if the surrounding rocks are initially impermeable, the heat generates enough pore-fluid pressure to open hydraulic fractures, creating permeability. Subsequent episodes repeat the whole process until the fractures fill with minerals, permeability decreases, and fluid flow abates. At the same time, the magma must release its influence along a different front to shut down the intricately integrated feedback system. Horizontal and vertical movement—convection and advection—of fluid through rock disperses chemical components and supports chemical reactions between the minerals and fluids. Dissolution, precipitation, ion exchange, and sorption continue as the fluids migrate through the matrix. Material that does not dissolve may be forced into migration
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Solid-Earth Sciences and Society along the front of the fluid plume; this is what happens to oil and gas. The pressure of the aqueous fluid drives hydrocarbons into reservoir rocks where they collect and remain, if a seal successfully traps them. Otherwise, the pressure of groundwater and their own buoyancy will force them to the surface. Understanding the role of fluids in the crust necessitates analysis of the interacting thermal, chemical, mechanical, and hydrological processes. Researchers believe that role may extend to influencing, perhaps even initiating, tectonic events. Extremely high pore-fluid pressures, which are characteristic of actively tectonic regions, may facilitate major crustal movements. Frictional resistance to slippage and faulting becomes negligible in certain cases of high pore-fluid pressure. While seismologists analyze the influence of fluids on fault susceptibility, research continues to reveal how aqueous fluids move in subduction zones and return to the surface through volcanic eruptions. Aqueous fluids also cycle through crustal material at ocean spreading centers, spewing from vents loaded with particulate matter as "black smokers." On continents such fluids bubble to the surface as geothermal springs and geysers. Ores, those materials that contain valuable metals or other materials, can form by many concentration processes involving chemical reaction with water. Water can seep through soil horizons, leaching solutes away and leaving residual materials such as the bauxite deposits that form aluminum ore. When it reaches solid bedrock, water sustains weathering of minerals and carries away the residue. Deep within the crust, water percolates through the metamorphic zones where igneous intrusions shoulder into the native rocks and contributes to the process of change. And where hot igneous rock and cool saline water make contact along the 40,000-km length of the oceans' spreading centers, researchers can watch minerals precipitate. These observations support analogies that help describe processes characterizing other areas of igneous activity, such as volcanic arcs and continental rifts. Eventually, even the oldest water returns to the surface through uplift, exposure, and erosion; then it quickens again and churns through a shorter episode along the surface. But once the fluids reach the surface, they do not cease their interaction with the rocks. Oceans continue to pound against the shores, as waves and rocks break each other. Rivers erode the mountains and carry them away. Rain pelts against outcrops, dislodging a grain at a time. Rainwater seeps into fractures and pores, expands on freezing, and thus weathers the rocks mechanically. Water flowing along the surface also dissolves rocks through chemical weathering, forming sinkholes, caverns, caves. Geologists have always had an appreciation of the links between the solid-earth and its fluid envelopes, but they are now realizing that those envelopes permeate the patches of soil that clothe the continents and the ooze that shrouds the ocean floor. Hydrogen, oxygen, and carbon compose a major proportion of the elements that circulate through the air, ocean, and crust in a variety of fluid forms—coupling into compounds, migrating through pores, dissolving, and precipitating. That circulation of hydrous fluids, in different phases and forms, through the few kilometers between the mantle and space makes this planet what it is. WATER RESOURCES The Earth is the water planet. This claim is not based on a mere fluid veneer. The distinctive features that set the Earth apart from other solid planets—the deep, wide oceans; the abundance of living beings; even the buoyant, mutable, silica-rich continents—can be attributed to circulation, and concentration, of water. In the narrow view, water is the most critical resource required for human survival. In the wider view, it is a necessary component of many earth subsystems (Figure 4.2). Most water exists, rich with salt, in the oceans, and many theorists agree that this has been the rule for nearly all of earth history. Theories proposing a hydrous mantle that slowly generated the ocean waters by gradual degassing do not resolve problems associated with retention of large amounts of water-bearing minerals within the host mantle. Water is continuously cycling through the shallow mantle (Figure 4.3). Lithospheric slabs plunge down into the mantle at subduction zones, notably along the deep oceanic trenches. These slabs, detected by instruments that sense density anomalies, contain water in the form of hydrous minerals—inorganic chemical compounds that incorporate the components of water. The volatile water returns to the surface in complex processes associated with subduction zones, resulting in volcanic arcs that arise where one ocean plate subducts beneath another ocean plate or in volcanic spines that run along the edge of a continent where an oceanic plate subducts beneath it. Certain ancient volcanoes, such as those found in the South African interior, generated material containing hydrous minerals that came from
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Solid-Earth Sciences and Society FIGURE 4.2 The hydrologic cycle as a global geophysical process. Enclosed areas represent storage reservoirs for the Earth's water, and the arrows designate the transfer fluxes between them. Figure from NRC, 1991, Opportunities in the Hydrological Sciences. depths exceeding 150 km. These data suggest that some surface water has been recycled to great depths. Hydrous minerals have even been found imbedded in diamonds that form only at temperatures and pressures found at depths greater than 100 km. All but a fraction of the water remains at or near the surface in six interacting reservoirs that can be listed according to decreasing volume (Figure 4.4). The largest volume of water—1.35 billion km3—circulates freely throughout the oceans. There is a substantial amount of water frozen in glacial ice sheets and ice caps, but it is still less than 2 percent of the oceans' volume. Permeating the pores and cracks of the crust, groundwater forms a reservoir with 0.7 percent of the oceanic volume. For all the vast reaches of fresh water we swim in and sail on, only 130,000 km3—not even 0.01 percent of all the oceans—fills the lakes and rivers. And only trace amounts, relative to the oceans' vast capacity, cycle through the atmosphere as vapor and through the crust as aqueous fluids. Water circulates among these reservoirs in a system known as the hydrologic cycle, and it abides in the disparate reservoirs for varying times. In an average year about 60,000 km3 of water is carried over the United States in the atmosphere. This represents an amount sufficient to cover all the land areas to a depth of 30 cm. Of this amount, one-tenth falls as meteoric water—rain or snow. About two-thirds of that precipitation returns immediately as evaporation or moves up through plant roots, carrying nutrients from the soil, and enters the atmosphere as transpiration through leaves. The remaining one-third runs along the surface, accumulating in arroyos, brooks, and creeks. They flow together, gathering as streams and rivers, and pause to form lakes. Eventually, after carving or molding the land and sustaining or sapping the groundwater, rivers run down to sea level, building deltas and mixing with the salty ocean. Ocean, runoff, rain, and vapor in the atmosphere constitute the overwhelming bulk in the hydrologic cycle. The other stores of water involve much slower cycling, although the volumes they contain are substantial. Of particular significance—economically, scientifically, and socially—are the residual products resulting from reactions between subsurface water and the
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Solid-Earth Sciences and Society FIGURE 4.3 Circulation of water in a variety of reservoirs. Water and other volatiles return to the surface in complex processes associated with expulsion in subduction zones and related volcanism. minerals it encounters. The small proportion of rainfall that enters the groundwater reservoir may return to the surface through natural springs or feed dwindling stream flows. Or it may move through rocks of various composition, dissolving minerals and carrying them away. Or it may displace lighter fluids, forcing them into other rocks. Water Quality Water circulates through the hydrologic cycle, dissolving elements, sometimes carrying them over great distances, and eventually depositing them into sinks. Earth systems depend on that circulation to constantly supply their moisture requirements. Wa FIGURE 4.4 The volumes of water in the near-surface reservoirs of the Earth (in thousands of cubic kilometers). The total volume is about 1.5 billion km3; a comparable volume may be dispersed within the Earth's interior.
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Solid-Earth Sciences and Society FIGURE 4.5 Schematic representation of contaminant plumes (arrows indicate flow direction) possibly associated with various types of waste disposal. From NRC, 1984, Groundwater Contamination. ter dissolves salts from soil, carries them to the ocean, and then evaporates, leaving the collected residue to accumulate. Moving through the atmosphere, water arrives again over the land surface to replenish the puddles, rivulets, lakes with fresh water. But within the past few decades Americans have realized that increased concentrations of toxic residues are contaminating fresh water prematurely—long before it can naturally process the material—largely because of the actions of humans. Traditionally, waste products have been allowed to flow into the nearest body of water. As a consequence, streams, estuaries, and large parts of the coastal environment have become contaminated. Coastal zones, including estuaries, are areas of active sedimentation, and deposited materials often contain toxic wastes. These wastes may seep to the surface or landward into aquifers. They may be exhumed—either naturally or through channel dredging and widening—and redistributed by erosion. Solid wastes placed in landfill sites and other terrestrial depositories are gradually dissolved by moving groundwater; in many cases they contaminate the groundwater supply (Figure 4.5). Because streamflow is often nourished by groundwater, dissolved contaminants can eventually make their way into streams and other water courses. Groundwater contamination studies have produced many surprises. Volatile organic compounds are mobilized through the atmosphere and may become components of the soil, where they remain for long periods of time. Transport through the soil and groundwater is generally slow, and long periods are required to move contaminants significant distances. Hydrologists agree that once contaminated, groundwater will remain contaminated unless remedial action is taken. Much of the water contamination identified today is the result of waste disposal practices 20, 30, 40, or more years ago. There is a significant difference between pollution by toxic compounds and pollution by toxic elements. Compounds may spontaneously decompose, through inherent instability, or may be decomposed by heat, biological action, or catalytic properties of earth materials. Either course may result in the loss of toxic character. Heavy metals are elements and remain toxic unless they are immobilized into an insoluble state or detoxified by chelation. Chelation constrains metal atoms within an innocuous but stable chemical species; the heavy metals are tamed or caged by an organic compound that establishes bonds with the metallic ions and eliminates the potential for the metal to react with any other compound. It is possible that ill-conceived detoxification tactics might accidentally exacerbate the predicament. For example, the native element mercury is toxic but only very slightly soluble. Conversion by industry produces the compound methyl mercury (Hg(CH3)2), which is both soluble and toxic.
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Solid-Earth Sciences and Society Methyl mercury accumulates in short-lived species throughout the food chain with no effect, but when contaminated fish provide the major source food for a human population, mercury concentrations reach malevolent levels. Mercury poisoning results in disorders of the nervous system, mental impairment, and irrational behavior; the mercury compounds used in the production of felt hats during the nineteenth century also produced the stereotypical Mad Hatter. Plants acquire necessary nutrients by absorbing enriched water from the soil. They return almost pure water to the atmosphere through transpiration and leave unwanted minerals, such as residual salts, concentrated in the soil. Salt buildup is an agricultural problem as ancient as the practice of irrigation. On one hand, it is desirable to apply only the amount of water that the plants actually require. On the other hand, sufficient water must be applied to transport residual salts and minerals beyond the root zone. An effective conservation program in irrigated agriculture requires carefully calculated amounts of water to address both plant requirements and residue removal. Further complications arise when the residual salts or minerals collect in sinks before they reach the ocean. For example, in the Central Valley of California, selenium occurs as a trace element in soils and is mobilized by irrigation water. It moves into the drainage canals and to holding reservoirs where it is concentrated. Eventually, aquatic birds high in the food chain receive large doses of this selenium. Currently, there is no obvious solution to the problem other than to retire a substantial area from irrigation or to flush the reservoir continually into the ocean. Either alternative is costly and temporary. One major deficiency in our hydrologic understanding and management has been a lack of systematic measurements of water quality. The National Water Quality Assessment (NAWQA) programs are beginning to address this problem. But for all the millions of cubic kilometers of flowing water, the U.S. Geological Survey (USGS) maintains only a small long-term network of approximately 500 gauging stations where water quality is routinely measured. Water samples from these stations are chemically analyzed for the major anions and cations, while some are tested irregularly for traces of metals and organic materials. To assess the state of the nation's water quality, the Environmental Protection Agency (EPA) relies largely on reports from water quality agencies in the 50 states. The EPA has questioned the adequacy of this information because the states do not share a standardized data base. The agency has begun nationwide sampling to assess the concentrations of particular constituents in surface water, but the appraisal of groundwater is even more limited than that of surface water. Contaminated groundwater has been located at many sites, but there is uncertainty as to the extent of the problem. The contamination is detected in areas devoted to specific land-use patterns, leading to conclusions that are then extended nationwide. This line of reasoning estimates that 0.5 to 2.0 percent of the usable groundwater in the United States is contaminated. Even the higher percentage may be an underestimate: pollutants are generally produced in highly populated areas, while investigations providing the data base tend to concentrate in areas where groundwater use is important, and the two kinds of areas do not necessarily coincide. For instance, there is little information on groundwater contamination in the northeastern urban corridor of the United States, a region dependent on surface water supplies, but common sense suggests that groundwater in that area would be contaminated. Systematic collection of water quality information is difficult and expensive. The problem is one of complexity. There are several hundred, perhaps thousands, of potentially toxic chemicals for which every water sample could be analyzed. Lakes, rivers, and groundwater all occupy three spatial dimensions that make representative samples expensive to obtain. Water quality also varies through time, so that recurrent sampling is required. And, finally, sampling in an extensive geographic area will probably reveal unsuspected links between various reservoirs. Three priorities have been established by the USGS: detecting major contaminated reaches of rivers; determining baselines in uncontaminated areas as benchmarks; and detecting groundwater contamination for those parts of the country where rivers or aquifers, or both, provide major water supplies. The cost for this minimal assessment phase is on the order of $100 million annually. This impressive sum is only 1 percent of the approximate $10 billion spent building new sewage treatment facilities each and every year. Water Supply and Use Every human being requires about 2 liters of fresh water every day to maintain the minimal physiological functions. But many people use more than that amount; the added quantity varies according to an individual's personal habits and standard of living. In North America every individual consumes or
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Solid-Earth Sciences and Society uses material that requires an average of 1,500 liters of water per day. This total includes the water that cools the turbines of power plants and the water that irrigates cotton fields, as well as the moisture that plumps the artichokes and provides the bulk of milk or muscatel. It is the fluid that showers bodies and washes cars. It drips from faucets and drowns the roots of suburban lawns. When it rains, this fluid runs in silken sheets along the slopes of parking lots and collects in open foundations at construction sites. It gets pumped into the sewer system and mixed with organic waste and then runs out—to someplace downstream. As the population expands, and as material expectations rise, the need for water increases at an exponential rate. Over the past 300 years, the amount of water removed from freshwater reservoirs by humans has increased more than 35-fold. Most of the water used in North America does return to the hydrologic cycle after only a short interruption. The problem is that it frequently returns in a very different state and often to a very different reservoir. If pure water is taken from a river and returns to the river contaminated by fecal matter or toxic materials, it may take long reaches of that river out of the supply side. And if vast quantities of water are mined from a 100,000-year-old aquifer and run through an irrigation system, resulting in extensive evapotranspiration, the aquifer may not be replenished for another few hundred thousand years. Because the hydrologic cycle transfers water from one reservoir to another at various rates and because it does not always transfer to the location most convenient for the schemes of civilized minds, humans must use available water resources very carefully. Water cannot be manufactured economically from its component elements and ocean water cannot be desalinated without incurring large, usually unacceptable, expenses. So humans must adapt to the natural limitations on available fresh water imposed by the hydrologic cycle. In the United States the opportunity exists to deliberately formulate water distribution and wastewater treatment policies according to principles of conservation, wisdom, and justice. The United States uses 770 km3 of fresh water every year. About 340 km3 is consumed—exposed for evapotranspiration or consigned to uses sequestered from the hydrologic cycle. The rest is recycled into the system as wastewater. Irrigation uses 330 km3—41 percent of the total—and accounts for 215 km3 of the consumption. Domestic uses amount to 66 km3, consuming 20 km3; and industry uses 294 km3, but consumes only 29 km3. Most of the river and lake water becomes available in the spring and early summer when the snow melts, ice breaks up, and rain falls to flush out—perhaps to flood—systems that run low in late summer. Mitigation of droughts and prevention of floods traditionally require water control projects. Management of water supplies—circulating 740 km3 through U.S. cities, suburbs, forests, and fields—necessitates planning that modifies seasonal supply to match independently fluctuating demands. In the half of the United States west of the 100th meridian—which slices through Texas, Oklahoma, Kansas, Nebraska, South and North Dakota—stream runoff is less than 1 inch in an average year. Throughout that region runoff comes in early spring, largely as snowmelt from mountains hundreds of kilometers away. The water flows through the region months before the optimal time for watering crops. Storage of water—either in artificial surface reservoirs, lakes, or aquifers—dampens the lag in timing between supply and demand. But no reservoirs create water; they only allow a delay of the transfer within the hydrologic cycle. Artificial reservoirs and lakes can be refilled when the runoff returns. Underground aquifers—the groundwater—serve as vast and wonderful reservoirs; but they often cannot be refilled in the next season. Several western states now depend on mining underground aquifers—taking water out faster than the rate of recharge. In the past, official policy toward groundwater use endorsed the idea of safe yield. Safe yield was a concept accepted by hydrologists as a maxim—an aquifer should not be pumped faster than it is naturally recharged. In the early 1960s this idea was replaced by one that treated underground water as a nonrenewable resource: depletion of groundwater is justifiable if it creates an economy that can afford to buy more expensive water when the well runs dry. Adoption of this maxim reflects the development of irrigated agriculture in the High Plains as well as population migration to the Sunbelt. Now, urban and energy developments are coveting the water available to agriculture—especially in the Southwest. This competition will undoubtedly intensify, posing two major issues for society: how local, state, and regional communities can manage increased competition for water and to what extent the country can wean itself from irrigated agriculture in the West. The present domestic and industrial water requirements can be effectively met without serious impact on agriculture. Diverting 10 percent of current agricultural water consumption
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Solid-Earth Sciences and Society FIGURE 4.6 Amount of irrigated acreage (in millions of acres) in the 17 western states. would permit a doubling of water use by others. But even without the competitive pressure from population centers, irrigated agriculture is in trouble. In the western states, irrigation accounts for more than 90 percent of consumptive use, and the surge in groundwater withdrawal over the past 25 years—since the philosophy of safe yield was rejected—has been due almost exclusively to irrigation. In the conterminous United States, the 17 western states consume 84 percent of the country's fresh water, mostly for agriculture. The acreage irrigated in the 17 western states is shown in Figure 4.6. In Texas and California, which account for 42 percent of the total, almost one-half of this water is pumped from the ground. Irrigation is also being increased in the more humid areas of the country to raise crop yield Hydrologists calculate the volume of freshwater supply in terms of relative depletion. Relative depletion is calculated from total consumption plus the total water exported from each drainage basin, divided by the total input of rain and snow. The ratio is expressed as a percentage. Groundwater is not considered part of the total supply because it is not replaced by precipitation. The exclusion of groundwater from the calculation results in relative depletion that can exceed 100 percent in some areas. Several regions in the United States are considered to be critically depleted; in most of the lower Colorado River basin, in Southern California, and in Nevada, depletion exceeds 100 percent. In south-central California, which includes the San Joaquin and Owens valleys, in the High Plains of Colorado and West Texas, and in most of New Mexico, depletion exceeds 75 percent. These relative depletion figures are incomplete and probably low, because instream flow requirements are not included. The instream flow requirement represents the minimum streamflow necessary to preserve aquatic and associated ecosystems.
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Solid-Earth Sciences and Society over large areas, conventional methods can be used to ascertain the thickness and character of beds. Samples, cores, and geophysical logs are analyzed to determine basic characteristics. Where coal beds have complex geometries, other evaluation techniques may be necessary, such as seismic mapping, closely spaced drilling, and exploratory pits. During exploration, the environmental data required to obtain permits for mining are established, including the trace element content of the coal and surrounding formations, groundwater parameters, mineralogy, flora and fauna content, and soil properties. More than one-half of the coal mined in the United States is produced from surface mines. Contour, area, or open-pit mining methods are used where coal seams of sufficient thickness and quality are near the surface, which is generally within 50 to 70 m. Surface mining of steeply inclined seams requires special planning that is specific to the conditions at the site. Where coal seams are deeper, shafts must be constructed to reach the coal and allow room-and-pillar or longwall mining methods. The latter method usually results in eventual subsidence of the land surface. An important research problem involves the correlation of geological parameters with the extraction method to allow optimal coal recovery while still mitigating the effects of subsidence on the hydrology and productivity of overlying soils. Coal can be converted to liquids and gases by a number of different chemical, thermal, combination, or other treatment processes. Liquefaction produces feedstocks for chemicals such as benzene, ammonia, methanol, and acetic acid, as well as sulfur-free petroleum. Some of these processes are available commercially, while others are in various stages of laboratory or pilot plant testing. Some coal beds contain large quantities of methane gas, which can be produced directly. There is current research into using bioengineered microbes and other methods to produce methane gas from the coal. This form of energy exploitation may be applicable to coal beds that have exceptionally large quantities of contained gas or that are too deep or too thin to be mined economically by conventional methods. Limitations of Coal Direct combustion of coal to produce electricity or steam heat requires further research toward the development of higher efficiency standards and cleanup techniques for hot and cold gas combustion and conversion facilities. Research in clean coal technology involves scientists and engineers specializing in combustion chemistry and mechanical engineering, but geologists have a critical role in characterizing what coals will burn most efficiently. Advanced combustion technologies to minimize sulfur dioxide and nitrogen oxides, as well as particulate emissions, have been under active development. These technologies include fluidized-bed combustion, staged slagging combustors, and limestone injection multistage burners. Combustion technology research must be pursued to gain a better understanding of capture mechanisms and to obtain reaction rates. Geoscientists continue studies to select sorbents with optimum reactivity, such as lime, limestone, dolomite, and other natural and man-made carbonates. In addition, desulfurized fuels produced by coal conversion processes require combustion testing to develop acceptable burning properties. In the past 10 years considerable advances have been achieved in hot gas desulfuration using mixed metal oxides, which absorb sulfur and can be regenerated in a multicycle operation. Efforts should continue to develop reliable and cost-effective processes for cleanup of gas-borne constituents such as chlorine, sulfur, nitrogen, alkali compounds, and fine particulates, especially from fluidized-bed combustors, high-pressure gasifiers, and other technologies that promise higher efficiencies in electricity generation. Complementary studies are needed for development of an integrated approach to solving problems of coal use such as the control of disposal and the use of waste materials from coal cleaning, fluidized-bed, and other advanced combustion processes. Problems in user equipment that are attributed to the corrosive effects of noxious elements such as chlorine need to be minimized; methods for fine grinding and dewatering of coal need to be improved; and methods for particle-size enlargement or pelletization of fine coal need to be refined. Preparation of coal for the consumer market includes removal of contaminants such as mineral matter, sulfur, or other undesirable elements without substantially changing the general organic structure of the coal. Physical cleaning, such as washing, gravity separation, or flotation, remains the most economical and widely used technique. Geoscientists study the form, size, and distribution of the mineral matter contained in coals to guide the efforts of mineral preparation engineers in evaluating the efficiency of different processes, including oil agglomeration and column flotation, and of different reagents. Research continues on innovative
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Solid-Earth Sciences and Society wet and dry methods, such as magnetic or electrostatic removal, to maximize removal of iron sulfides. Considerably more research is needed to improve the removal of organic sulfur. Chemical, thermal, and microbial cleaning that breaks carbon-to-sulfur bonds and that can be combined in a two-step process with physical cleaning is being sought. Other approaches being investigated include genetic engineering to design efficient, organic, sulfur-consuming microbes and the use of microbes to alter the surface of iron sulfides to allow for its removal by physical cleaning processes, such as flotation. Termination of the government-supported Synthetic Fuels Corporation in the early 1980s and recognition of the high cost associated with upgrading of single fuels from coal has led to the research concept of the coal refinery. In a coal refinery a combination of solid and multiphase products and fuels would be produced from coal by chemical, thermal, or other treatments. To date, research into production of a clean solid fuel, with simultaneous coproduction of gases and/or liquids, has not produced an economically viable and technically acceptable product for combustion in conventional utility equipment. Issues such as agglomeration of some coals during heating also must be addressed. Future coal refinery efforts may well depend on a better understanding of organic composition and the role of mineral matter; these will help identify the most selective and mildest forms of treatment necessary to produce an appropriate mix of marketable solid and multiphase products. Every stage of coal development, from exploration to consumption, affects the environment. For example, acid mine waters can be neutralized, but predicting the movement of near-surface groundwater in surface or underground mining is more difficult. The effects of such elements from fluidized-bed combustion wastes on groundwater quality is not known. Other research should focus on the technical viability of disposing of scrubber sludge wastes in abandoned or existing underground mines, considering the potential effects on groundwater and surface subsidence. Sources of Energy from the Internal Engine All of the previously discussed energy sources are driven primarily by the external engine influencing earth systems. But the Earth's internal engine also produces vast amounts of energy that invite exploitation. Early humans were well aware of the heat coming from below the surface—volcanoes were the chimneys ventilating the forge of the god Vulcan, and thermal springs and geysers were considered sure signs of a sacred presence. Many societies attribute healing powers to naturally heated springs; popular spas have grown around such locations as the retreat established by the ancient Romans at Bath, England, and the early-twentieth-century hot-spot, Saratoga Springs, New York. Attempts to use the warm waters for heating homes and workplaces have traditionally been small in scale. Since the discovery of radioactive energy resulting from the decay of radioactive elements within the Earth, scientists have hoped to use internal heat generated by this process and offer a new, cheap, unlimited energy source to society. Research continues to perfect, and expand, both methods of harnessing energy from within the Earth. Nuclear Energy A theoretically promising method of harnessing the internal heat generated by the natural radioactivity of the Earth is to mine uranium minerals, extract uranium from such concentrations, and assemble a critical mass in a reactor. Heat generated by the fission process (the spontaneous or induced splitting of atomic nuclei with consequent release of energy) can, when controlled within a reactor, be used to generate electricity. This method of generation is widely used in the world today. In France nearly three-quarters of all electricity is nuclear generated. In the United States the proportion is much smaller and is currently declining. Uranium-powered reactors remain important to the United States, and a few other countries, for powering nuclear submarines and other vessels. One reason for its limited use in the United States is that nuclear power may not be economically competitive. This lack of competitiveness stems from a variety of causes, some of which are relevant to earth science research. Uranium ores were mined on a substantial scale in the United States for about 30 years but are not marketable today due to the availability of higher-grade, lower-cost ores from abroad. Worldwide uranium exploration over the past 50 years has profited from government interest in access to fissionable material and from the fact that the natural radioactivity of the element makes concentrations unusually easy to detect. Uranium occurs in both oxidized and reduced states and is highly mobile in aqueous solutions in its oxidized state. Most uranium mined in the United States has come from ancient stream channels on the Colorado Plateau, in Wyoming, and on the Texas coastal
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Solid-Earth Sciences and Society FIGURE 4.16 Schematic cross section of uranium-ore roll and surrounding rocks in Wyoming. Because uranium-ore rolls are of variable width, no scale is given. plain. In these areas deposition of uranium minerals was localized where oxidized groundwater, carrying uranium in solution, came in contact with organic reducing materials, such as plant matter in the form of logs or leaves. Anaerobic sulfate-reducing bacteria may have been important in precipitating uranium minerals at the reduced surface (Figure 4.16). The transport and deposition of uranium present yet another example of the importance of fluid flow through porous media in geologically significant environments. Research related to uranium deposits is, in many ways, similar to the basin analysis that dominates research in the petroleum industry. The nuclear power industry faces a continual challenge in seeking options to dispose of waste materials. This costly need is another reason for the decline in the use of uranium as a means of electric power generation in this country. Geoscientists are active in research related to this problem, since the currently preferred disposal option is to deposit radioactive waste materials beneath the surface. The possible interaction of fluids with buried radioactive waste and the subsequent migration of those fluids through porous rocks to the biosphere must be projected over the long intervals during which hazardous material can remain radioactive. Related research opportunities occur where radioactive wastes have already been emplaced. Both of these areas of research involve fluid flow and chemical interaction in porous media. While some policy makers strive for complete isolation of nuclear wastes over very long durations, some researchers feel that such materials must be regarded as byproducts that will be used as resources in the future. This opinion demands accessibility to radioactive wastes; many environmentalists agree that accessibility is desirable but for the purpose of monitoring—not with an eye toward exploitation. Nuclear power plants add no carbon dioxide to the atmosphere, in contrast to all fossil fuel plants. As our understanding of the possible effects of carbon dioxide emissions emerges over the next decade, it is possible that nuclear power plants may become more acceptable. There is a need to be ready for this eventuality, and additional research on uranium mineralization and waste isolation should be undertaken now. Geothermal Energy Another method of harnessing the energy generated within the Earth by radioactive decay is the direct extraction of heat from hot rocks that remain buried (Figure 4.17). Energy generated from this source is called geothermal energy, and research on its extraction is an active field in the geosciences. Most of the geothermal energy used in the world today comes from volcanic areas and areas of active extensional faulting where hot, or partly molten, rock approaches the surface closely enough to be accessible by drilling. Natural steam or hot water, confined by an impermeable seal and heated by the magma or hot rock, is extracted from holes drilled into the geothermal system and is converted at the surface to electricity. The combination of crustal features required for a geothermal energy supply occurs rarely: hot rock near the surface with a reservoir of confined water that is large, permeable, shallow, adequately recharged for a life of decades, and low in dissolved solids. Proximity to an energy market is also an advantage. Geothermal energy has been used successfully for generating electricity in California, Mexico, Japan, Italy, New Zealand, Iceland, and Tibet, but large-scale economic geothermal production is not widespread. Problems arise because of depletion of reservoirs and undesirable environ-
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Solid-Earth Sciences and Society FIGURE 4.17 Development of an active geothermal field. mental effects. An exciting challenge for the geoscientist is to locate exploitable geothermal resources lacking obvious surface manifestations. Remote sensing (especially by infrared techniques that reveal heat), geochemical, and geophysical methods are being developed and tested for this purpose. Other uses of geothermal energy have been developed. Hot waters are used for space heating, agriculture, and mariculture in Iceland. Apartments in the suburbs of Paris and elsewhere in Europe are warmed by groundwaters. Boron from geothermal waters has been marketed in Italy. Possible developments in the future extend to extracting heat from hot dry rocks by injecting cold water and recovering heated water or steam. RESOURCE DEPENDENCY Geothermal energy use is an obvious example of how developing better comprehension of rock-fluid interactions can lead to efficient resource exploitation. Throughout this chapter more subtle interactions have been discussed. The concentration of traditional minerals, the accumulation of fossil fuels, and the deposition of uranium minerals all result from rocks and fluids interacting chemically, thermally, and mechanically. As scientists study this crucial and fundamental field, the problems associated with each of these resources will be solved one by one, and society will become better equipped to live on the Earth's surface without permanently harming it. The need for resources has always been a major stimulus for scientific advance, providing both economic reward and intellectual challenge. The discoveries made and the problems presented by the resource industry have kept scientists busy explaining the hows and whys. Once an explanation becomes established, further discoveries and data accumulation by industry either ratify or reject prevailing opinions about how crust has evolved from the matter and energy of the core and mantle. An explanation that holds provides a model from which the resource industry can speculate confidently on the locations and forms of future discoveries. Historically, advances in knowledge gained through collaborations between scientific theory and social necessity have led to greater understanding of natural systems. More recently, scientists have considered the reciprocal relationships between natural systems and human activity within
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Solid-Earth Sciences and Society those systems. Consideration of these relationships may result in predictions of natural disaster potential and in responsible planning that can avoid suffering and loss of life. But scientific consideration of the relationship between natural systems and human endeavors can also provide assessments of those activities that threaten the environment—disasters caused by humankind. RESEARCH OPPORTUNITIES The Research Framework (Table 4.1) summarizes the research opportunities identified in this chapter and in other disciplinary reports and references. These topics, representing significant selection and thus prioritization from a large array of research projects, are described briefly in the following section. Resource recovery is restricted to the top 10 km of the crust, and most of it is from much shallower depths. Understanding of the structure of the shallow crust and of the processes operating to form and modify that crust, especially those involving the flow of water through rock, provides a certain unity to resource research. It is convenient to define three arbitrary depth zones (with gradational boundaries) from the surface downward. The most widespread and generally used resources are land and water; the most dominantly used water is at or near the surface (0 to 10 m). At intermediate depths (10 to 100 m) groundwater development and surface mining are major activities, and remote sensing of properties becomes increasingly important. The shallow crust, at depths of 100 m to 10 km is the domain of deep mining, deep groundwater, and the petroleum industry. It is here that remote (geophysical) sensing from the surface by a wide range of techniques and advanced logging of boreholes become critical in understanding the crust. Making the best use of mineral and energy resources calls for understanding the earth systems of which they form a part and for appreciating the need for waste isolation and the environmental consequences of mineral development. For these reasons, the research opportunities identified for earth systems outlined at the ends of Chapters 2 and 3, and those related to environmental considerations at the end of Chapter 5, are relevant to much research on depletable resources. The focus for this chapter is deliberately restricted to topics identifiable as important under Objective B: ''Sustain Sufficient Resources." Many research topics relate to more than one Research Theme. The comprehensive topic of "Sedimentary Basin Analysis," for example, involves all the research themes. Similarly, the subject of "Water-Rock Interaction" relates to at least themes I-IV and has particular importance in basin analysis and in modeling of ore formation. Sedimentary Basin Analysis The material carried out of drainage basins is deposited in the sedimentary basins of the world. It is from these sedimentary basins—both active basins currently being filled and ancient basins that were filled long ago—that the world's oil, gas, coal, and groundwater, together with many of its mineral deposits, including its uranium deposits, are produced. Research in resources should continue to stress a multidisciplinary basin analysis approach, emphasizing detailed studies of specific depositional environments in outcrops and cores in conjunction with physical measurements of rock properties. Organic Geochemistry and the Origin of Petroleum The processes of maturation of organic material and diagenesis merit continued study by observation, experiment, and modeling. Such phenomena as natural cracking and migration require emphasis. The whole forms an important activity in relation to the broad field of sedimentary basin analysis. Kinetics of Water-Rock Interaction Understanding the kinetics of water-rock interaction is a research frontier critical to sustaining both water and mineral resources. Mineral surface catalysis, poisoning effects, and complex mineralogy make this understanding hard to achieve in systems at temperatures from 100° to 500°C; at less than 100°C, organisms, organic material, and materials added to groundwater by humans play corresponding roles. Water Resources Analysis of Drainage Basins Surface waters are best understood in terms of drainage basins that allow such processes as erosion, deposition, and water and sediment transport to be addressed in an appropriately integrated way. An immediate resource challenge is presented by the
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Solid-Earth Sciences and Society TABLE 4.1 Research Opportunities Objectives Research Areas A B. Sustain Sufficient Resources Water, Minerals, Fuels C D I. Global Paleoenvironments and Biological Evolution ■ Evolution of mineral deposits through time ■ Coal petrology and quality II. Global Geochemical and Biogeochemical Cycles ■ Most of the opportunities listed under III below relate to integral parts of biogeochemical cycles ■ Organic chemistry and the origin of petroleum III. Fluids in and on the Earth ■ Kinetics of water-rock interaction ■ Analysis of drainage basins ■ Water quality and groundwater contamination ■ Modeling water flow and hydrocarbon migration ■ Source-transport-accumulation models ■ Numerical modeling of depositional environments ■ In situ mineral resource extraction ■ Crustal fluids IV. Crustal Dynamics: Ocean and Continent ■ Sedimentary basin analysis ■ Surface and soil isotopic ages ■ Prediction of mineral resource occurrences ■ Concealed ore bodies ■ Intermediate scale search for ore bodies ■ Exploration for new petroleum reserves ■ Advanced production and enhanced recovery methods ■ Coal availability and accessibility ■ Concealed geothermal fields V. Core and Mantle Dynamics Facilities - Equipment - Data Bases ■ Deep seismic studies, three-dimensional data, complementary advanced well logging ■ Advanced supercomputing facilities ■ Continental scientific drilling ■ Oceal drilling ■ Space-borne measurements, LANDSAT, SPOT, HIRIS, magnetometer, gravity survey ■ Geophysical techniques, side-looking radar from aircraft ■ Laboratory equipment with high spatial resolution and high-precision analytical capability ■ Geographic information systems ■ Data bases on topography, geology, geochemistry, and geophysics drainage basins of the western United States. Policy decisions on the allocation of surface waters are driven by jurisdictional considerations. Recognition of the drainage basin as the fundamental scientific unit, provides a basis for effective communication with decision makers in providing information useful for the allocation of scarce surface waters. Surface and Soil Isotopic Ages The development and application of new techniques will allow ages to be assigned to surfaces and shallow rock materials, which should improve understanding of both the processes and the rates of landscape modification. Improvement in the ability
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Solid-Earth Sciences and Society to quantify these ages in years will revolutionize understanding, which is becoming more urgent as appreciation of the possibility of anthropogenically modified climatic change spreads. Water Quality and Groundwater Contamination To reach a realistic baseline on water quality nationally, chemical and physical measurements must be made at a vast network of stations. To assess change, frequent repeat measurements will be needed. Part of the national water quality problem relates to the relatively small volumes of rock where toxic and radioactive waste materials have entered the groundwater. Challenges in this frontier area range from asking whether there may be some places where the wisest course may be to do nothing to assessing possible roles for novel techniques, such as remediating organic wastes using microorganisms, including special genetically engineered microbes. Modeling Water Flow Thermal, chemical, and fluid transport models for water need to be integrated into four-dimensional models—that is, models that involve variation with time. Mineral Resources Source-Transport-Accumulation Models for Mineral Resources Mineral resource studies are poised for dramatic advances through broad application of the models that guide modern petroleum research and exploration. Integrated studies, involving all the essential superposed geological processes, offer great opportunities, particularly as they can now draw on a wealth of new global tectonic and geochemical concepts and predict new types of mineral deposits. Quantitative geological mapping offers one of the greatest opportunities for significantly advancing our understanding of mineral resources and their relations to the geological features and processes. New quantitative mine-scale and regional-scale maps are both needed. Prediction of Mineral Resource Occurrences Mineral deposit models must be built that contain and identify the most important information for resource prediction, and practical methods must be pioneered for making resource predictions for which the confidence and accuracy can be estimated. Incorporation of organic geochemistry is required. These models are the fundamental building blocks for the advancement of mineral resource sciences. The challenge of preparing sufficiently reliable models is immense. Numerical Modeling of the Depositional Environment of Ore Bodies Modern computers have recently made possible numerical modeling of the complex hydrologic, geological, and geochemical systems related to ore formation. For the first time, drawing on reasonably comprehensive thermodynamic/kinetic data bases for water-rock interactions and fluid flow models, it is possible to develop integrated models that reasonably reflect natural systems for flow through media with irregular fractures, accommodating conditions under which liquids boil and allowing fluid compositions to change with time. Progression toward comprehensive computational systems could provide screening of the maze of geological variables to help indicate which are most important to ore formation. In Situ Mineral Resource Extraction The extraction of metals from mineral deposits by the circulation of fluids offers the potential for economic mining with potentially lower costs and less environmental disruption. The great potential and challenge of in situ mining are the integration and application of decades of advances in the diverse fields of mineral deposit geology, hydrogeology, geophysics, rock mechanics, geochemistry, structural geology, geoengineering, and chemical engineering. Determination of the effects of organisms and organic geochemistry is important. Crustal Fluids A major research objective is to identify and characterize each type of fluid, its distribution, and how it came to be. It would be best to start with fluids in modern environments, including modern ore-forming environments (such as the black smokers and the Red Sea) and shallow crustal settings (i.e., Smackover and Salton Sea brines). Opportunities abound for experimental research into alternate reaction paths, which reactions occur, why those paths are followed, how fast they occur, and what governs their rates. One critically important
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Solid-Earth Sciences and Society objective is the description of metal complexing and mineral solubilities under a variety of geologically realistic conditions. Development of thermodynamic models for appropriate trace elements and volatile components will permit numerical modeling of magma differentiation and possible identification of critical variables affecting ore-bearing fluids. Evolution of Mineral Deposits Through Time The evolution of deposits presumably signals changes in the types and/or intensities of processes as well as in the atmosphere, oceans, thermal regimes, climate, and tectonics. Study of the evolution of resource types through time and their relations to other features should therefore guide our understanding of earth processes. In turn, this understanding should sharpen our knowledge of ore genesis and our ability to predict known and unknown deposit types that are associated with particular periods of earth history and particular geological features. Concealed Ore Bodies Even the largest of ore bodies occupies a tiny area of the land surface, so production of mineral wealth has been concentrated in those places where surface indications of ore bodies are strongest. A challenging research frontier is to find ways of locating buried ore bodies in the many areas where surface signs are lacking. This is rather like looking for a needle in a haystack, and part of the challenge is to develop coherent exploration strategies that are not prohibitively costly. Intermediate-Scale Search for Ore Bodies Mineral explorationists identify this level of search as a research frontier. The characterization of environments likely to be hosts to particular classes of ore body on the basis of recognition of ancient and modern plate tectonic environments has proved to be powerful in distinguishing blocks of land that are promising for exploration on the scale of thousands of square kilometers. On a very local scale new deposits can often be found in close proximity to existing mines. The challenge is to establish criteria permitting recognition of potential ore-bearing areas at scales intermediate between these extremes. Energy Resources Exploration for New Petroleum Reserves In much of the world where the petroleum industry is less mature than in the United States, the challenge lies in exploration for new reserves in new oil fields, calling for an integrated approach to basin analysis that ranges from establishment of the tectonic environments in which basins have developed; through interpretation of depositional, structural, and thermal evolution; to an understanding of oil and gas generation within the basin, of fluid migration, and of related diagenetic change; and finally to definition of the types of traps in which oil and gas are held. Advanced Production and Enhanced Recovery Methods Because of the maturity of the petroleum industry in the United States, the challenge is to produce more oil from existing fields in well-known basins. Drilling, well testing, sampling, logging, advanced seismic methods, sedimentology and organic geochemistry, as well as modeling, need to be developed toward an integrated understanding of reservoir structure and dynamics. Advanced production methods such as those involving in situ bacterial modification will call for close interaction between solid-earth scientists and reservoir engineers. If bacterial techniques are to prove useful, they will depend greatly on current frontier research into the organic chemistry of petroleum. Coal Availability and Accessibility Total coal resources in the United States are large, but knowing only their size is not sufficient information. Some coals are not minable because their combustion produces unacceptable amounts of toxic material; others are less accessible to mining than appears from simply mapping the distribution of coal beds. The amount of coal that is available for mining and the accessibility of those "available coal resources" are much less than the overall deposit size. This is because of land-use restrictions, mining methods, and the thickness of individual beds. Such studies are being conducted in the Appalachian and Illinois coal basins. For a more realistic assessment of potentially available coal resources, they should be expanded to include all major coal-producing regions of this country.
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Solid-Earth Sciences and Society Coal Petrology and Quality The increased use of coal in power generation and in other more sophisticated uses requires knowledge of the quality of coal to be used. Microscopic study of the different materials that make up coal is proving important. Different materials characterize different environments of origin and different combustion responses. Information about chemical elements, mineral macerals (organic components), and their interrelationships will allow for more environmentally acceptable and economically efficient use of coal. Concealed Geothermal Fields Hot rock, abundant water in a sealed reservoir, and access to a market for the electricity produced must all coexist for a geothermal field to be exploitable. We may have failed to discover geothermal reservoirs with little surface manifestation. The development of remote sensing methods of detection, especially infrared survey from the air, geochemical methods, and geophysics, together make up a challenging field. Facilities, Equipment, and Data Bases Facilities Activities that are too large to be operated by a single agency, university, or national laboratory can be considered facilities, and there are several examples of these in resource research. Access to advanced supercomputing capabilities is needed for testing models of processes in the shallow crust. Deep seismic studies using the consortia approaches that have been so successful in the past decade have a continuing role, and, where continental scientific drilling is perceived as an essential part of research, there is an established mechanism for bringing it into play under the existing interagency agreement. Ships of the University-National Oceanographic Laboratory Systems's (UNOLS) fleet and the Ocean Drilling Program are involved in experiments relevant to resource research, for example, under the RIDGE program. Satellite data from SPOT and Landsat are important in mineral research, and it is important that these be available to researchers on a continuing basis and at reasonable cost. Instruments with the capabilities of the High-Resolution Imaging Spectrometer (HIRIS) and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), proposed for as instruments for National Aeronatics Space Administration's (NASA) Earth Observing System, would be marvelous for resource research, as would a low-orbit magnetometer mission, such as ARISTOTELES. Gravity and magnetometry data obtained from aircraft for poorly known continental areas could also be important, but plans for development are at a very early stage. Equipment Most of the laboratory equipment that is needed for research in resources is similar to that used in the kinds of laboratory investigation identified in Chapters 2, 3, and 5. Advanced chemical analytical equipment and facilities for isotopic analysis, including mass spectroscopy of organic materials, has become a general need. New methods with high spatial resolution and high-precision analytical capability such as laser-ablated inductively coupled plasma-source mass spectrometry seem likely to be capable of yielding large amounts of useful information. Bacterial research may find a focus in resource and environmental research at this time. The largest field for advanced equipment development is in exploration for petroleum and minerals. Expenditures on mineral and petroleum exploration in the United States annually run at more than $1 billion, much of which is spent on the acquisition and processing of reflection seismic data. Three-dimensional seismic surveys are expected to become much more widely used in the coming decade, and processing and archiving the large quantities of data generated by this practice will present a challenge. The availability of three-dimensional seismic data will contribute greatly to our understanding of the shallow crust and will call for complementary advanced well logging and well-to-well measurements. Mineral explorationists use advanced geophysical research techniques, including audiomagnetotelluric methods, and remote sensing from space and aircraft by methods such as side-looking radar and high-wavelength-resolution infrared spectroscopy are beginning to be used. Geochemical prospecting is emphasizing the use of pathfinder elements as complementary to direct search for metals, and soil gas exploration is developing. All these instrumental developments have a part to play in the integrated effort to understand the properties and processes of the shallow crust, which is the concept unifying resource research at this time.
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Solid-Earth Sciences and Society Data Bases In many ways the preparation and skilled use of data bases provide the greatest frontier challenge in resource research. This comes about because most resource issues involve handling a diverse variety of spatial data together. For example, hydrologists commonly need good digital topographic data. They also need geological maps of both surficial and bedrock distribution and may need data on water quality and quantity for both surface water and groundwater over an area of interest. The ability to access this kind of information at will and to use it as separate "layers" is the essence of the geographic information systems approach. Once the data are accessible, the challenge is to interpret them by constructing and testing models of the systems under study. In the United States access to important data bases is improving all the time, but there are opportunities for improvements that could revolutionize both the way resource research is done and the likelihood of attaining useful results. For example, mineral explorationists are compiling data bases that enable them to use pattern recognition with advanced computational techniques, including expert systems. Some high-priority data bases for resource research follow. Topographic Data Base. The digital topographic data for the United States available from the U.S. Geological Survey (USGS) is as good as any in the world, but there is a continuing need to update the data base for change and to review its quality, which, simply because of its vast size, is not uniform. On a worldwide scale, digital topographic data are only very locally as good as those of the United States; we draw attention to the recommendations of other Academy committees, which, for rather different reasons, have recommended obtaining better data in various ways, culminating in a dedicated space mission to acquire a coherent high-resolution topographic data set for the land surface of the Earth. Geological Map Data Base. Geological maps of the United States are of varied resolution and uneven quality, and relatively few of them are accessible in digital form. The Association of American Geologists, working with the USGS, has defined an approach to obtaining the kind of geological map coverage that is needed. The need to move more rapidly to improve geological maps of bedrock and surficial deposits in the United States and overseas is regarded Geophysical Data. Data bases for geophysical data are varied and needs are diverse. A major distinction can be made between data acquired for commercial purposes such as petroleum exploration, which is not normally within the public domain, and data acquired by state and federal agencies, which is commonly freely available. Commercially acquired data are to a considerable extent traded within industry, and some publicly held information is useful for commercial activity. In the long run some commercially acquired data may enter the public domain. A serious question is whether nationally useful information may be lost through these current practices, especially for data sets where the cost of archiving in usable form is substantial. To give a single example of a publicly acquired data set that is likely to be important in exploration, airborne magnetic data at high spatial resolution will be important in the search for hidden ore bodies. BIBLIOGRAPHY National Research Council Reports NRC (1981). Studies in Geophysics: Mineral Resources: Genetic Understanding for Practical Applications, Geophysics Study Committee, Geophysics Research Board, National Research Council, National Academy Press, Washington, D.C., 119 pp. NRC (1982). Studies in Geophysics: Climate in Earth History, Geophysics Study Committee, Geophysics Research Board, National Research Council, National Academy Press, Washington, D.C., 198 pp. NRC (1983). Opportunities for Research in the Geological Sciences, Committee on Opportunities for Research in the Geological Sciences, Board on Earth Sciences, National Research Council, National Academy Press, Washington, D.C., 95 pp. NRC (1983). Fundamental Research on Estuaries: The Importance of an Interdisciplinary Approach, Geophysics Study Committee, Geophysics Research Board, National Research Council, National Academy Press, Washington, D.C., 79 pp. NRC (1984). Studies in Geophysics: Groundwater Contamination, Geophysics Study Committee, Geophysics Research Board, National Research Council, National Academy Press, Washington, D.C., 179 pp. NRC (1987). Geologic Mapping in the U.S. Geological Survey, Committee Advisory to the U.S. Geological Survey, Board on Earth Sciences, National Research Council, National Academy Press, Washington, D.C., 22 pp. NRC (1988). Scientific Drilling and Hydrocarbon Resources, Committee on Hydrocarbon Research Drilling, Board on Mineral and Energy Resources, National Research Council, National Academy Press, Washington, D.C., 89 pp. NRC (1989). Technology and Environment, Advisory Committee on Technology and Society, National Academy of Engineering, National Academy Press, Washington, D.C., 221 PP. NRC (1989). Margins: A Research Initiative for Interdisciplinary Studies of Processes Attending Lithospheric Extension and Convergence , Ocean Studies Board, National Research Council, National Academy Press, Washington, D.C., 285 pp.
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Solid-Earth Sciences and Society NRC (1989). Prospects and Concerns for Satellite Remote Sensing of Snow and Ice, Committee on Glaciology, Polar Research Board, National Research Council, National Academy Press, Washington, D.C., 44 pp. NRC (1990). Rethinking High-Level Redioactive Waste Disposal: A Position Statement of the Board on Radioactive Waste Management, Board on Radioactive Waste Management, National Research Council, National Academy Press, Washington, D.C., 38 pp. NRC (1990). Studies in Geophysics: Sea Level Change, Geophysics Study Committee, Board on Earth Sciences and Resources, National Research Council, National Academy Press, Washington, D.C., 234 pp. NRC (1990). Studies in Geophysics: The Role of Fluids in Crustal Processes, Geophysics Study Committee, Board on Earth Sciences and Resources, National Research Council, National Academy Press, Washington, D.C., 170 pp. NRC (1990). Competitiveness of the U.S. Minerals and Metals Industry , Committee on Competitiveness of the Minerals and Metals Industry, National Materials Advisory Board, National Research Council, National Academy Press, Washington, D.C., 140 pp. NRC (1990). Ground Water Models: Scientific and Regulatory Applications , Water Science and Technology Board, National Research Council, National Academy Press, Washington, D.C., 302 pp. NRC (1990). A Review of the USGS National Water Quality Assessment Pilot Program, Water Science and Technology Board, National Research Council, National Academy Press, Washington, D.C., 153 pp. NRC (1990). Ground Water and Soil Contamination Remediation: Toward Compatible Science, Policy, and Public Perception: Report on a Colloquium , Water Science and Technology Board, National Research Council, National Academy Press, Washington, D.C., 261 pp. NRC (1990). Surface Coal Mining Effects on Ground Water Recharge, Water Science and Technology Board, National Research Council, National Academy Press, Washington, D.C., 159 pp. NRC (1991). Toward Sustainability: Soil and Water Research Priorities for Developing Countries, Committee on International Soil and Water Research and Development, Water Science and Technology Board, National Research Council, National Academy Press, Washington, D.C., 65 pp. NRC (1991). Opportunities in the Hydrologic Sciences, Committee on Opportunities in the Hydrologic Sciences, Water Science and Technology Board, National Research Council, National Academy Press, Washington, D.C., 348 pp. NRC (1991). Undiscovered Oil and Gas Resources: An Evaluation of the Department of the Interior's 1989 Assessment Procedures, Board on Earth Sciences and Resources, National Research Council, National Academy Press, Washington, D.C., 108 pp. plus appendices. NRC (1991). Managing Water Resources in the West Under Conditions of Climate Uncertainty, Water Science and Technology Board, National Research Council, National Academy Press, Washington, D.C., 344 pp. NRC (1992). Water Transfers in the West: Efficiency, Equity, and the Environment, Water Science and Technology Board, National Research Council, National Academy Press, Washington, D.C., 359 pp. Other Reports Department of Energy (1991). National Energy Strategy, U.S. Government Printing Office, Washington, D.C., 217 pp. plus appendices. U.S. Congress, Office of Technology Assessment (1991). U.S. Oil Import Vulnerability: The Technical Replacement Capability, OTA-E- 503, U.S. Government Printing Office, Washington, D.C. USGS (1987). Geologic Applications of Modern Aeromagnetic Surveys, U.S. Geological Survey Bulletin 1924, 106 pp.
Representative terms from entire chapter: