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Tasa Graphic Arts, Inc. 1210B Salazar Road - Taos, NM USA 87571 Phone: (800) 293-2725 or (575) 758-5535 - Fax: (575) 758-5536 E-mail: info@tasagraphicarts.com |
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Tasa Portfolio Volume 2 Captions |
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Tasa Graphic Arts, Inc. 1210B Salazar Road - Taos, NM USA 87571 Phone: (800) 293-2725 or (575) 758-5535 - Fax: (575) 758-5536 E-mail: info@tasagraphicarts.com |
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Tasa Portfolio Volume 2 Captions |
The images on Tasa Portfolio Volume 2 are related to these subjects:
Running Water Groundwater Glaciers and Glaciation Deserts and Winds Shorelines TGA101.jpg Distribution of Earth's water. TGA102.jpg Earth's water balance. Each year, solar energy evaporates about 320,000 cubic kilometers of water from the oceans, while evaporation from the land (including lakes and streams) contributes 60,000 cubic kilometers of water. Of this total of 380,000 cubic kilometers of water, about 284,000 cubic kilometers fall back to the ocean, and the remaining 96,000 cubic kilometers fall on the land surface. Of that 96,000 cubic kilometers, only 60,000 cubic kilometers of water evaporate from the land, leaving 36,000 cubic kilometers of water to erode the land during the journey back to the oceans. TGA103.jpg Influence of channel shape on velocity. A. The stream in this wide, shallow channel moves more slowly than does water in the semicircular channel because of greater frictional drag. B. The cross-sectional area of this semicircular channel is the same as the one in part A, but it has less water in contact with its channel and therefore less frictional drag. Thus, water will flow more rapidly in channel B, all other factors being equal. TGA104.jpg Relationship of width, depth, and velocity to discharge of the Powder River at Locate, Montana. As discharge increases, width, depth, and velocity all increase in an orderly fashion. (From L. B. Leopold and Thomas Maddock, Jr., U.S. Geological Survey Professional Paper 252, 1953) TGA105.jpg A longitudinal profile is a cross-section along the length of a stream. Note the concave-upward curve of the profile, with a steeper gradient upstream and a gentler gradient downstream. TGA106.jpg A resistant layer of rock can act as a local (temporary) base level. Because the durable layer is eroded more slowly, it limits the amount of downcutting upstream. TGA107.jpg When a dam is built and a reservoir forms, the stream's base level is raised. This reduces the stream's velocity and leads to deposition and a reduction of the gradient upstream from the reservoir. TGA108.jpg When a stream meanders, its zone of maximum speed shifts toward the outer bank. A point bar is deposited when the water on the inside of a meander slows. By eroding its outer bank and depositing material on the inside of the bend, a stream is able to shift its channel. TGA109.jpg Natural levees are gently sloping structures that are created by repeated floods. Because the ground next to the stream channel is higher than the adjacent floodplain, back swamps and yazoo tributaries may develop. TGA110.jpg A. Structure of a simple delta that forms in the relatively quiet waters of a lake. B. Growth of a simple delta. As a stream extends its channel, the gradient is reduced. Frequently, during flood stage the river is diverted to a higher-gradient route, forming a new distributary. Old abandoned distributaries are gradually invaded by aquatic vegetation and fill with sediment. (After Ward's Natural Science Establishment, Inc., Rochester, N.Y.) TGA111.jpg The shapes of deltas vary and depend on such factors as a river's sediment load and the strength and nature of shoreline processes. The triangular shape of the Nile delta was the basis for naming this feature. The present Mississippi delta is called a bird-foot delta. TGA112.jpg During the past 5000 to 6000 years, the Mississippi River has built a series of seven coalescing subdeltas. The numbers indicate the order in which the subdeltas were deposited. The present bird-foot delta (number 7) represents the activity of the past 500 years. Without ongoing human efforts, the present course will shift and follow the path of the Atchafalaya River. The inset on left shows the point where the Mississippi may someday break through (arrow) and the shorter path it would take to the Gulf of Mexico. (After C. R. Kolb and J. R. Van Lopik) TGA113.jpg Relationship between suspended load and discharge on the Powder river at Arvada, Wyoming. (From L. B. Leopold and Thomas Maddock, Jr., U.S. Geological Survey Professional Paper 252, 1953) TGA114.jpg Stream eroding its floodplain. TGA115.jpg Formation of a cutoff and oxbow lake. TGA116.jpg Terraces can form when a stream downcuts through previously deposited alluvium. This may occur in response to a lowering of base level or as a result of regional uplift. TGA117.jpg A drainage basin is the land area drained by a stream and its tributaries. Divides are the boundaries separating drainage basins. TGA118.jpg The drainage basin of the Mississippi River, North America's largest river, covers about 3 million square kilometers. Divides are the boundaries that separate drainage basins from each other. Drainage basins and divides exist for all streams. TGA119.jpg Drainage patterns. A. Dendritic. B. Radial. C. Rectangular. D. Trellis. TGA120.jpg A. Dendritic. TGA121.jpg B. Radial. TGA122.jpg C. Rectangular. TGA123.jpg D. Trellis. TGA124.jpg Stream piracy and the formation of wind gaps. A tributary of stream B erodes headward until it eventually captures and diverts stream A. A water gap through which stream A flowed is abandoned because of the piracy. As a result, this feature is now a wind gap. In this valley and ridge-type setting, the softer rocks in the valleys are eroded more easily than the resistant ridges. Consequently, as the valleys are lowered, the ridges and wind gaps become elevated relative to the valleys. TGA125.jpg Development of a superposed stream. A. The river establishes its course on relatively uniform strata. B. It then encounters and cuts through the underlying structure. TGA126.jpg Distribution of underground water. The shape of the water table is usually a subdued replica of the surface topography. During periods of drought, the water table falls, reducing streamflow and drying up some wells. TGA127.jpg Preparing a map of the water table. The water level in wells coincides with the water table. A. First the locations of wells and the elevation of the water table above sea level are plotted on a map. B. These data points are used to guide the drawing of water table contour lines at regular intervals. On this sample map the interval is 10 feet. Groundwater flow lines can be added to show water movement in the upper portion of the zone of saturation. Groundwater tends to move approximately perpendicular to the contours and down the slope of the water table. (After U.S. Geological Survey) TGA128.jpg Interaction between the groundwater system and streams. A. Gaining streams receive water from the groundwater system. B. Losing streams lose water to the groundwater system. C. When losing streams are separated from the groundwater system by the zone of aeration, a bulge may form in the water table. (After U.S. Geological Survey) TGA129.jpg Arrows indicate groundwater movement through uniformly permeable material. The looping curves may be thought of as a compromise between the downward pull of gravity and the tendency of water to move toward areas of reduced pressure. TGA130.jpg When an aquitard is situated above the main water table, a localized zone of saturation may result. Where the perched water table intersects the side of the valley, a spring flows. The perched water table also caused the well on the right to be successful, whereas the well on the left will be unsuccessful unless it is drilled to a greater depth. TGA131.jpg Distribution of hot springs and geysers in the United States. Note the concentration in the West, where igneous activity has been most recent. (After G.A. Waring, U.S. Geological Survey Professional Paper 492, 1965) TGA132.jpg Idealized diagrams of a geyser. A geyser can form if the heat is not distributed by convection. A. In this figure, the water near the bottom is heated to near its boiling point. The boiling point is higher there than at the surface because the weight of the water above increases the pressure. B. The water higher in the geyser system is also heated; therefore, it expands and flows out at the top, reducing the pressure on the water at the bottom. C. At the reduced pressure on the bottom, boiling occurs. Some of the bottom water flashes into steam, and the expanding steam causes an eruption. TGA133.jpg A. In this figure, the water near the bottom is heated to near its boiling point. The boiling point is higher there than at the surface because the weight of the water above increases the pressure. TGA134.jpg B. The water higher in the geyser system is also heated; therefore, it expands and flows out at the top, reducing the pressure on the water at the bottom. TGA135.jpg C. At the reduced pressure on the bottom, boiling occurs. Some of the bottom water flashes into steam, and the expanding steam causes an eruption. TGA136.jpg A cone of depression in the water table often forms around a pumping well. If heavy pumping lowers the water table, the shallow wells may be left dry. TGA137.jpg Artesian systems occur when an inclined aquifer is surrounded by impermeable beds. TGA138.jpg City water systems can be considered to be artificial artesian systems. TGA139.jpg A. Because fresh water is less dense than salt water, it floats on the salt water and forms a lens-shaped body that may extend to considerable depths below sea level. B. When excessive pumping lowers the water table, the base of the freshwater zone will rise by 40 times that amount. The result may be saltwater contamination of wells. TGA140.jpg A. Although the contaminated water has traveled more than 100 meters before reaching well 1, the water moves too rapidly through the cavernous limestone to be purified. B. As the discharge from the septic tank percolates through the permeable sandstone, it is purified in a relatively short distance. TGA141.jpg A. Originally the outflow from the septic tank moved away from the small well. B. The heavily pumped well changed the slope of the water table, causing contaminated groundwater to flow toward the small well. TGA142.jpg Development of a karst landscape. A. During early stages, groundwater percolates through limestone along joints and bedding planes. Solution activity creates and enlarges caverns at and below the water table. B. In this view, sinkholes are well developed and surface streams are funneled below ground. C. With the passage of time, caverns grow larger and the number and size of sinkholes increase. Collapse of caverns and coalescence of sinkholes form larger, flat-floored depressions. Eventually, solution activity may remove most of the limestone from the area, leaving only isolated remnants. TGA143.jpg A. During early stages, groundwater percolates through limestone along joints and bedding planes. Solution activity creates and enlarges caverns at and below the water table. TGA144.jpg B. In this view, sinkholes are well developed and surface streams are funneled below ground. TGA145.jpg C. With the passage of time, caverns grow larger and the number and size of sinkholes increase. Collapse of caverns and coalescence of sinkholes form larger, flat-floored depressions. Eventually, solution activity may remove most of the limestone from the area, leaving only isolated remnants. TGA146.jpg The only present-day continental ice sheets are those covering Greenland and Antarctica. Their combined areas represent almost 10 percent of Earth's land area. Greenland's ice sheet occupies 1.7 million square kilometers, or about 80 percent of the island. The area of the Antarctic Ice Sheet is almost 14 million square kilometers. Ice shelves occupy an additional 1.4 million square kilometers adjacent to the Antarctic Ice Sheet. TGA147.jpg This map of the portion of North America shows the present-day coastline compared to the coastline that existed during the last ice age (18,000 years ago) and the coastline that would exist if present ice sheets on Greenland and Antarctica melted. (After R. H. Dott, Jr., and R. L. Battan, Evolution of the Earth, New York: McGraw Hill, 1971.) TGA148.jpg The conversion of freshly fallen snow into dense, crystalline glacial ice. TGA149.jpg Vertical cross-section through a glacier to illustrate ice movement. Glacial movement is divided into two components. Below about 50 meters, ice behaves plastically and flows. In addition, the entire mass of ice may slide along the ground. The ice in the zone of fracture is carried along "piggyback" style. Notice that the rate of movement is slowest at the base of the glacier where frictional drag is greatest. TGA150.jpg Ice movement and changes in the terminus at Rhone Glacier, Switzerland. In this classic study of a valley glacier, the movement of stakes clearly showed that ice along the sides of the glacier moves slowest. Also notice that at the same time that the ice within the glacier was advancing, the ice front was retreating. TGA151.jpg The snowline separates the zone of accumulation and the zone of wastage. Above the snowline, more snow falls each winter than melts each summer. Below the snowline, the snow from the previous winter completely melts as does some of the underlying ice. Whether the margin of a glacier advances, retreats, or remains stationary depends on the balance between accumulation and wastage (ablation). When a glacier moves across irregular terrain, crevasses form in the brittle portion. TGA152.jpg Erosional landforms created by alpine glaciers. The unglaciated landscape in part A is modified by valley glaciers in part B. After the ice recedes, in part C, the terrain looks very different than before glaciation. TGA153.jpg A. The unglaciated landscape. TGA154.jpg B. The unglaciated landscape modified by valley glaciers. TGA155.jpg C. After the ice recedes the terrain looks very different than before glaciation. TGA156.jpg Roche moutonnee (French for sheep rock) are formed when glacial abrasion smoothes the gentle slope facing the oncoming ice sheet and plucking steepens the opposite side as the ice rides over the knob. TGA157.jpg End moraines of the Great Lakes region. Those deposited during the most recent (Wisconsinan) stage are most prominent. TGA158.jpg End moraines make up substantial parts of Long Island, Cape Cod, Martha's Vineyard, and Nantucket. Although portions are submerged, the Ronkonkoma moraine (a terminal moraine) extends through central Long Island, Martha's Vineyard, and Nantucket. It was deposited about 20,000 years ago. The recessional Harbor Hill moraine, which formed about 14,000 years ago, extends along the north shore of Long Island, through southern Rhode Island and Cape Cod. TGA159.jpg This hypothetical area illustrates many common depositional landforms. TGA160.jpg Portion of a drumlin field shown on the Palmyra, New York, 7.5-minute topographic map. North is at the top. The drumlins are steepest on the north side, indicating that the ice advanced from this direction. TGA161.jpg Maximum extent of ice sheets in the Northern Hemisphere during the Ice Age. TGA162.jpg Simplified illustration showing crustal subsidence and rebound resulting from the addition and removal of continental ice sheets. A. In northern Canada and Scandinavia, where the greatest accumulation of glacial ice occurred, the added weight caused downwarping of the crust. B. Ever since the ice melted, there has been gradual uplift or rebound of the crust. TGA163.jpg The top map shows the Great Lakes and the familiar present-day pattern of rivers in the central United States. Pleistocene ice sheets played a major role in creating this pattern. The bottom map shows the reconstruction of drainage systems in the central United States prior to the Ice Age. The pattern was very different from today, and there were no Great Lakes. TGA164.jpg Changing sea level during the past 20,000 years. The lowest level shown on the graph represents the time about 18,000 years ago when the most recent ice advance was at a maximum. TGA165.jpg Pluvial lakes of the Western United States. (After R. F. Flint, Glacial and Quaternary Geology, New York: John Wiley & Sons) TGA166.jpg A. The supercontinent Pangaea showing the area covered by glacial ice 300 million years ago. B. The continents as they are today. The white areas indicate where evidence of the old ice sheets exists. TGA167.jpg The shape of Earth's orbit changes during a cycle that spans about 100,000 years. It gradually changes from nearly circular to one that is more elliptical and then back again. This diagram greatly exaggerates the amount of change. TGA168.jpg Today the axis of rotation is tilted about 23.5 degrees to the plane of Earth's orbit. During a cycle of 41,000 years, this angle varies from 21.5 degrees to 24.5 degrees. TGA169.jpg Precession. Earth's axis wobbles like that of a spinning top. Consequently, the axis points to different spots in the sky during a cycle of about 26,000 years. TGA170.jpg Arid and semiarid climates cover about 30 percent of Earth's land surface. No other climate group covers so large an area. TGA171.jpg Idealized diagram of Earth's general circulation. The deserts and steppes that are centered in the latitude belt between 20 degrees and 30 degrees north and south coincide with the subtropical high-pressure belts. Here dry, subsiding air inhibits cloud formation and precipitation. By contrast, the pressure belt known as the equatorial low is associated with areas that are among the rainiest on Earth. TGA172.jpg Many deserts in the middle latitudes are rainshadow deserts. As moving air meets a mountain barrier, it is forced to rise. Clouds and precipitation on the windward side often result. Air descending the leeward side is much drier. The mountains effectively cut the leeward side off from the sources of moisture, producing a rainshadow desert. The Great Basin desert is a rainshadow desert that covers nearly all of Nevada and portions of adjacent states. TGA173.jpg The Aral Sea lies east of the Caspian Sea in the Turkestan desert. Two rivers, the Amu Darya and Syr Darya bring water from the mountains to the south. The shrinking Aral Sea. By the year 2010, all that will remain are three small remnants. TGA174.jpg Stages of landscape evolution in a mountainous desert such as the Basin and Range region of the West. As erosion of the mountains and deposition in the basins continue, relief diminishes. A. Early stage. B. Middle stage. C. Late stage. TGA175.jpg Formation of a blowout. A. Area prior to deflation. B. Area after deflation has created a shallow depression. TGA176.jpg Formation of desert pavement. As these cross-sections illustrate, coarse particles gradually become concentrated into a tightly packed layer as deflation lowers the surface by removing sand and silt. TGA177.jpg As parts A and B illustrate, dunes commonly have an asymmetrical shape. The steeper leeward side is called the slip face. Sand grains deposited on the slip face at the angle of repose create the cross-bedding of the dunes. C. A complex pattern develops in response to changes in wind direction. Also notice that when dunes are buried and become part of the sedimentary record, the cross-bedded structure is preserved. TGA178.jpg Sand dune types: Barchan dunes. TGA179.jpg Sand dune types: Transverse dunes. TGA180.jpg Sand dune types: Barchanoid dunes. TGA181.jpg Sand dune types: Longitudinal dunes. TGA182.jpg Sand dune types: Parabolic dunes. TGA183.jpg Sand dune types: Star dunes. TGA184.jpg This diagram illustrates the basic parts of a wave as well as the movement of water particles with the passage of the wave. Negligible water movement occurs below a depth equal to one-half the wavelength (the level of the dashed line). TGA185.jpg The movements of the toy boat show that the wave energy advances, but the water itself advances only slightly from its original position. In this sequence, the wave moves from left to right as the boat (and the water in which it is floating) rotates in a circular motion. The boat moves slightly to the left up the front of the approaching wave, then after reaching the crest, slides to the right down the back of the wave. TGA186.jpg Changes that occur when a wave moves onto shore. TGA187.jpg Because of wave refraction, the greatest erosional power is concentrated on the headlands. In the bay's the force of the waves is much weaker. TGA188.jpg Beach drift and longshore currents are created by obliquely breaking waves. Beach drift occurs as incoming waves carry sand obliquely up the beach, while the water from spent waves carries it directly down the slope of the beach. Similar movements occur offshore in the surf zone to create the longshore current. These processes transport large quantities of material along the beach and in the surf zone. TGA189.jpg The islands along the south Texas coast are excellent examples of the nearly 300 barrier islands that rim the Atlantic and Gulf coasts. TGA190.jpg Sea stack. TGA191.jpg Tombolo. TGA192.jpg Spit. TGA193.jpg Baymouth bar. TGA194.jpg Jetties are built at the entrances to rivers and harbors and are intended to prevent deposition in the navigation channel. Jetties interrupt the movement of sand by beach drift and longshore currents. Beach erosion often results down current from the site of the structure. TGA195.jpg A. High, middle, and low projections of global sea-level rise, 1990-2100. B. Projected individual contributions to global sea-level change, 1990-2100 for the middle projection in part A. Thermal expansion is responsible for 28 centimeters of the sea-level rise. Melting alpine glaciers and ice caps contribute another 16 centimeters. The impact shown for Antarctica indicates that this massive ice sheet is projected to grow larger during this period. TGA196.jpg The slope of a shoreline is critical to determining the degree to which sea-level changes will affect it. A. When the slope is gentle, small changes in sea level cause a substantial shift. B. The same sea-level rise along a steep coast results in only a small shoreline shift. TGA197.jpg Estuaries along the East Coast of the United States. The lower portions of many river valleys were submerged by the rise in sea level that followed the end of the Ice Age. Chesapeake Bay and Delaware Bay are especially prominent examples. TGA198.jpg Tides on an Earth that is covered to a uniform depth with water. Depending on the Moon's position, tidal bulges may be inclined to the equator. In this situation, an observer will experience two unequal high tides. TGA199.jpg Relationship of the Moon to Earth during A. spring tides and B. neap tides. TGA200.jpg Because this tidal delta is forming in the relatively quiet waters on the landward side of a barrier island, it is termed a flood delta. As a rapidly moving tidal current emerges from the inlet, it slows and deposits sediment. The shapes of tidal deltas are variable.