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From a geographical perspective, the photograph demonstrates how the Platte River system has determined transportation and settlement patterns for centuries. Modern Highway 80 follows the North Platte, and Highway 76 follows the South Platte. The presence of transport routes and rivers—as sources of water in a semiarid region—in turn determine the location of towns: the city of North Platte stands out as a light gray area on the floodplain at the confluence of the North and South Platte rivers, as do two smaller towns, Gothenburg and Cozad, farther downstream (image top right).
The distribution of cropland visible in this image also reveals interesting geographical information about the characteristics of the land surface. The flattest surfaces are easiest to farm and have the highest density of farmed fields. These flat surfaces lie on the river floodplains, but are also present on the higher surrounding surfaces. Between the heavily cultivated land in the river floodplain and the uplands is a strip of rough country that is difficult to farm. As a result, it stands out as a gray strip running parallel to the green croplands of the floodplains.
The famous Nebraska Sand Hills, recognizable by their characteristic scalloped texture north of Lake McConaughty, are a hummocky sand dune field (now vegetated). According to the U.S. Drought Monitor, westernmost Nebraska was abnormally dry in the last three months—covering the time when this image was taken (September 5, 2007). The impact of the water deficit on grass cover can be seen in the image: dry areas are brown (image lower left), and moister areas farther east are greener (image right).
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The capital city of Stanley lies on the eastern tip of East Falkland. The local inhabitants are mainly English speakers, and interestingly, the islands have become a center of English-language learning for students from South America.
The windy and relatively dry climate, which receives roughly 600 millimeters (24 inches) of precipitation annually, has given rise to natural vegetation comprised of treeless grassland with scattered bogs. The grasslands are ideal for sheep rearing—the dominant occupation until recent decades, when fishing (mainly squid for Spain) and tourism became the mainstays of the economy. These expanses of grassland provide ready fuel for fires, as indicated by the several long smoke plumes visible in this astronaut photograph. This near-nadir image was acquired at the southernmost extent of the International Space Station’s latitudinal orbit range of approximately 52 degrees north to 52 degrees south relative to the surface of the Earth.
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Mining first began in Bingham Canyon in the late nineteenth century, when shafts were sunk to remove gold, silver, and lead deposits that played out by the early 1900s. It would take the advent of open-pit mining in 1899 to turn the Bingham copper deposit into an economically favorable resource. In open-pit mining, the copper-containing rocks are excavated from the surface downward in terraces. By the 1930s, open-pit mining had turned “the Hill” at Bingham Canyon into “the Pit.”
This astronaut photograph of the Bingham Canyon Mine shows parallel benches (stepped terraces) along the western pit face. These benches range from 16 to 25 meters high, and they provide access for equipment to work the rock face and maintaining the stability of the sloping pit walls. A dark, larger roadway is also visible directly below the benches. Brown to gray, flat-topped hills of gangue (waste rock) surround the pit, and are thrown into sharp relief by shadows and the oblique (from the side) viewing angle of the photograph. Reservoirs for leach water (associated with ore processing) are visible to the south of the city of Bingham Canyon.
Today’s copper market is booming thanks to global demands from construction, telecommunications, and electronics sectors of the economy. The Kennecott Utah Copper Company removes about half a million tons of material from the Bingham Canyon Mine every day for processing. In 1906, the rate of removal was 100,000 tons of material per month. Over 17 million tons of copper have been removed to date. Geological and engineering models suggest that the mine can be deepened by an additional 200 meters before extraction costs become greater than the value of the remaining copper.
The geological and chemical processes that produce copper deposits also produce minerals such as iron sulfides, which react with water or oxygen on the surface to produce colorful minerals. Geologists can sometimes use satellite observations to identify places where the topography and the rock types on the surface suggest copper ores might be present below ground. Read the feature story Prospecting from Orbit for more information.
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The velocity of Saskatchewan River slows significantly as the river enters Cedar Lake; as the velocity slows, silt, clay, sand, and gravel are deposited at the river mouth. These deposits (light tan and gray in the image), called alluvium by geologists, border the active channels of the Saskatchewan and Summerberry Rivers.
As the deposits accumulate, they impede the river’s flow. Old channels are abandoned, and new ones form as the river seeks an easier path into the lake. Through this process (known as avulsion), the delta builds and branches out over time. A typical “bird’s foot”-shaped delta is currently forming at the mouth of the Saskatchewan River (image lower right). The bird’s-foot structure is approximately 13 kilometers wide. The Mississippi River’s active delta has the same general form, but it is much larger—approximately 50 kilometers wide.
The bogs in the Saskatchewan delta are saturated enough that peat (dead plant material that accumulates in a water-saturated environment) has formed. Over long periods of time and under the right geological conditions, peat deposits can become coal. The accumulation of plant and animal remains in the water-logged, oxygen-poor environment greatly slows down decay. In addition to setting the stage for coal formation, these conditions also preserve fossils of many kinds. The delta sediments at Cedar Lake are a rich source of fossil-bearing amber that was preserved along with coal deposits during the Late Cretaceous (about 65–99 million years ago). These deposits were not formed locally, however; they have washed into the delta from coal deposits over a thousand kilometers to the west of Cedar Lake.
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Dust storms have occurred over the Aral Sea region for thousands of years, but the half-century of drastic shrinking of the sea brought an important change in dust composition. By the time this photograph was taken, the dust included fertilizer and pesticide washed into the inland sea from the extensive cotton fields of the Amu Dary’a floodplain. Years of liberal application of agricultural chemicals resulted in concentration of these pollutants on the seabed, now exposed to the wind and transported hundreds of kilometers in a generally easterly direction. Research suggests that the remobilized chemicals are the cause of high rates of many diseases in the populations along the north, east, and southern margins of the Aral Sea.
Negative health effects were only one of the unexpected consequences of the shrinking of the sea, whose retreat made international news for many years due to the loss of the fishing industry and other significant ecological problems. Another negative consequence was the loss of the stabilizing influence of a large body of water on the region’s continental climate (cold winters combined with hot, dry summers). Large bodies of water cool down and heat up more gradually than land surfaces, so they moderate both extreme cold and extreme heat. Since the decline of the Aral Sea, summers have become shorter and hotter, and winters are longer; overall, the climate is drier. Frosts occur later in the spring and earlier in the fall, shortening the growing season.
Restoration efforts are underway for the North Aral Sea, which has been cut off from the South Aral Sea by a dam. In spring 2007, scientists announced that the North Aral Sea was refilling more rapidly than they originally expected.
References
Micklin, P.
(1998). Desiccation of the Aral Sea: A water management disaster in
the Soviet Union. Science, 241, 1170-1176.
doi:10.1126/science.241.4870.1170
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This astronaut photograph illustrates the largely pristine nature of these islands. The islands are located in the rain shadow of mountains on the Baja Peninsula to the west, and arid conditions prevail through much of the year. The scarcity of water has limited human presence on the islands, and allowed flora and fauna unique to each island to flourish, particularly reptiles. The islands are also home to colonies of seabirds and seals, both of which take advantage of deep, productive waters adjacent to the eastern Baja coast. Shallow waters and high levels of nutrients can also lead to blooms of green phytoplankton; two such blooms can be seen along the coastline of Isla Las Animas (image center right, in north- and west-facing bays). Winds and currents roughen the surface waters around the islands, and sunlight reflecting off the water makes the patterns visible (silver-gray regions). Regions of dark blue water indicate calm surface conditions, or the presence of oils and surfactants that decrease surface tension.
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The famous Faro Lighthouse occupies the top of a steep island—now connected by a bridge to the mainland—at the mouth of the estuary (image lower left). The Faro Lighthouse is the second tallest in the world, after Gibraltar’s. The wide, straight, almost vertical line of the railroad bisects the city.
This image shows sea features well, primarily ocean swells coming in from the southwest, which appear as a series of parallel lines covering the entire sea surface in this image. The diverse activities that go on in busy urban areas do not always mix easily: an oil slick offshore of the tourist beaches appears as a dark line along the left side of the image.
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The plants and animals of Isla Blanquilla are an interesting mixture of arid (cacti, iguanas) and introduced species (wild donkeys and goats), but it is particularly notable for the presence of black coral. Black coral is something of a misnomer, as it refers to the skeleton of the coral rather than the living organism, which is usually brightly colored. Black corals around the world are harvested for use in jewelry and other craftwork, so much so that the species has been listed for protection under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).
The island is the southernmost above-water exposure of the Aves Ridge, a seafloor topography feature of the southernmost Caribbean Sea. The island’s basement rock (the oldest rocks in an area) is visible in the western (bottom) third of the island. These granite rocks date back to the last part of the Mesozoic Era (the Cretaceous Period, 146-65 million years ago) and the first part of the Cenozoic Era (the Paleocene Epoch, 65-54.8 million years ago). The remainder of the island consists of three limestone terraces deposited on the older basement rock. The terraces get younger from west to east (bottom to top) across the island. The terraces record fluctuating sea levels during the Pleistocene Epoch (the Ice Age, 1.8 to about 10,000 years ago). The changes in sea level on the island may have been due to glacial advances and retreats during the Ice Age, or tectonic uplift of the island, or a combination of both processes.
References
Schubert, C.
(1977). Pleistocene marine terraces of La Blanquilla Island,
Venezuela, and their diagenesis. In D. L. Taylor, Ed., Proceedings of
the Third International Coral Reef Symposium (pp.149–154). Miami:
University of Miami. University of California Museum of
Paleontology. Tour of Geologic Time. Accessed November 21,
2007.
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Sunglint also illuminates water surfaces in the adjacent Gulf of Mexico and West Cote Blanche Bay. The variations in brightness comes from differences in surface roughness, which changes based on wind-driven waves or currents and the presence of surfactants—molecules that reduce the water’s surface tension. Synthetic detergents are surfactants, but natural surfactants are also produced by plants, including seaweed.
Marsh Island is a popular fishing, shrimping, and birding location. The island has lost nearly 3,000 hectares (7,000 acres) of vegetation and land area due to erosion, with a corresponding loss of habitat for local and migratory birds, shrimp, alligators, and deer. While Marsh Island is uninhabited, it has been the focus of intensive development for management of erosion, such as revegetation of deteriorated marsh areas. Leveed canals help drain areas for above-surface revegetation, while sill dams (submerged ridges that separate two water basins) help stabilize water levels and foster regrowth of important sub-surface vegetation such as widgeon grass.
