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The floodplain is generated by sediments delivered by both rivers. The evidence for this is that the entire surface is crisscrossed by the wider traces of former Paraná River channels, as well as numerous narrower traces of the Verde. The floodplains along both rivers are bordered by numerous rectangular agricultural fields. The dominant crops along this part of the Paraná River are coffee, corn, and cotton.
Turbid water, such as that in the Verde River, is common in most rivers that drain plowed agricultural land, as some topsoil is washed into local rivers after rains. A long tendril of brown water extends from the Verde into the main channel of the Paraná, where it hugs the west bank and remains unmixed for many kilometers. This effectively shows the direction of river flow from orbit: right to left for the Paraná, and upper left to image center for the Verde.
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The eye-catching appearance of the city at night displays the urban development pattern. In this image—taken with a long focal-length lens and digital camera optimized for fast response and high light sensitivity—several interesting patterns can be observed. The highways and major streets are sharply defined by yellow-orange lighting, while the commercial and residential areas are resolved into a speckle pattern of individual white, blue, and yellow-orange lights. Several brilliantly lit areas are large hotel and mall complexes, including the Burj Khalifa Tower. At 828 meters (2,717 feet), it is the world’s tallest building.
The brilliant lighting of the city contrasts sharply with both the dark Persian Gulf to the northwest, and largely undeveloped and unlit areas to the southeast. Likewise, the clusters of lighting in the Palm Jumeira complex correspond to the relatively small part of the archipelago that has been developed. Isolated areas of blurred city lights are due to patchy clouds.
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As recently as 1986, there was little to no agricultural activity in the Wadi As-Sirhan Basin. But over the past 26 years, agricultural fields have been steadily developed, largely as a result of the investment of oil industry revenues by the Saudi government. Crops grown in the area include fruits, vegetables, and wheat.
The fields are irrigated by water pumped from underground aquifers. That water is distributed in rotation about a center point within a circular field—a technique known as center-pivot agriculture. The approach affords certain benefits compared to traditional surface irrigation, such as better control of water and fertilizer use. This so-called “precision agriculture” is particularly important in regions subject to high water loss due to evaporation. By better controlling the amount and timing of water application, evaporative losses can be minimized.
For a sense of scale, the agricultural fields in active use (dark green) or fallow (brown to tan), are approximately one kilometer in diameter. While much of the Wadi As-Sirhan Basin shown here is sandy (light tan to brown surfaces) and relatively flat, low hills and rocky outcrops (dark gray) of underlaying sedimentary rocks are visible at image left and right.
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Lake Sakakawea is named—in the Hidatsa language—for the Shoshone woman generally known as Sacagawea, or “Bird Woman.” iIn 1805 –1806, she accompanied the Lewis and Clark Expedition as an interpreter and guide.
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Astronauts on the International Space Station captured this photograph of the area in January 2012. (Note that the image is rotated so north is to the lower left.) Muddy, yellow-brown water marks the center of the basin, with a ring of dark brown muds and burnt vegetation on the exposed lake floor to the north (lower left). The shoreline supports a thin line of reeds and floating grass vegetation, which appears as dark green in the image.
The usually dry Wadi Batha empties into Lake Fitri from the east (image top). Over time, water flow in Wadi Batha has created a large delta, which occupies the entire top left third of the image (for scale, the lake is 23 kilometers long). Lake Fitri and its surroundings have been designated under the Ramsar Convention as a wetland of international importance.
Other features of the image reveal evidence of significant climate change. The dry borders of the lake show that it was many times larger in years past. Numerous sweeping curves of ancient beaches are now situated many kilometers from the modern shoreline; those past shorelines also sit at higher altitudes. Inland lakes are highly sensitive to the equilibrium between the amount of inflow from contributing rivers (like Wadi Batha) and evaporation. Each beach ridge therefore shows a different lake level and thus a different balance in the lake-river-climate system. A smaller river enters from the south (top right) and cuts through the beach reaches on its way to the lake.
The irregular, elongated tan patches to the west (lower right) are linear dunes aligned parallel to the dominant winds, which blow from the northeast. The dunes have all formed on the downwind side (southwest) of the lake; the lake bed and delta provide the sands. The dunes indicate that the lake has been almost or completely dry on repeated occasions during past climatic phases—often enough for these great dunes (many kilometers long and several meters high) to form even in the lowest parts of the lake. The islands visible in the center of the lake are remnants of dunes, though smaller than those on the lake margin presumably because waves from the lake have eroded them. Villages occupy the points of some major dunes and of some islands, where fishermen can gain easy access to the lake.
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This astronaut photograph from the International Space Station highlights the southeastern part of the South at night, including the eastern Gulf of Mexico and lower Atlantic Seaboard states. The view is part of a time-lapse series of images that extends from just southwest of Mexico to northeast of Newfoundland, Canada. New sequences from the Space Station are regularly posted on the Crew Earth Observation videos page.
Following the American Civil War (1861-1865), the southern U.S. continued to be mostly agrarian until the latter half of the 20th century, when increased migration from other areas of the country and immigration from outside the U.S. led to increased urbanization. The brightly lit metropolitan areas of Atlanta, Georgia (image center) and Jacksonville, Florida (image lower right) appear largest in the image, with numerous other urban areas forming an interconnected network of light across the region.
A large dark region to the northwest of Jacksonville is the Okefenokee National Wildlife Refuge. Likewise, the ridges of the Appalachian Mountains form dark swaths to the north of Atlanta and west of Charlotte, North Carolina (image center). The faint gold and green line of airglow—caused by ultraviolet radiation exciting the gas molecules in the upper atmosphere—parallels the horizon (or Earth limb).
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This astronaut photograph from the International Space Station highlights the large island of Majorca (also known as Mallorca in Spanish), on which the provincial capital of Palma is located. Like the other Balearic Islands, Majorca is a popular holiday destination for Europeans, with tourism forming a major part of the island’s economy. The 5,400 square kilometer (2,100 square mile) island offers many recreational opportunities, with mountainous regions along the northwest coastline and eastern third. The central region of Majorca includes agricultural lands (tan, light brown, and green, image center), forested patches and corridors (dark green, image center), and urban centers (gray). Diving is a popular activity for those visiting the coastal beaches.
In addition to Majorca, the other major islands of the archipelago include Ibiza, Formentera, and Minorca. The small island of Cabrera to the southwest (image lower right) hosts the Parc Nacional de l’Arxipélag de Cabrera.
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The summit of Payún Matru is dominated by a roughly 15-kilometer wide caldera (image center), formed by an explosive eruption approximately 168,000 years ago. Several dark lava flows, erupted from smaller vents and fissures, are visible in the northwestern part of the field. One distinct flow, erupted from Volcan Santa María (northwest of Payún Matru), is approximately 15 kilometers long.
A number of small cinder cones—appearing as brown dots due to the short lens used—are built on older lava flows (grey) to the northeast. While there is no recorded observation of the most recent volcanic activity, oral histories suggest that eruptions were witnessed by indigenous peoples.
Most Andean volcanoes and earthquakes follow the trend of the greater Andes mountain chain, and are aligned roughly north-south above the tectonic boundary between the subducting (descending) Nazca Plate and the overriding South American Plate, as predicted by plate tectonic theory. Volcanic centers that are located some distance from the major trend—such as Payún Matru—typically result from more complex geological processes, and can provide additional insight into the subduction process.
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The tapestry pattern is due to the fact that the agricultural fields are closely tied to access roads, with rectangular fields extending outwards perpendicular to the roadways. A similar pattern—embedded within a different social, historical, and economic context—can be seen in the Rondonia region of western Brazil.
Snow cover highlights the rectangular fields interspersed with dark green forested patches. The urban area of Saint Georges (image right) is visible as a light gray region along the Chaudière River. The Parc national de Frontenac borders parts of Lac (lake) St.-Francois at image lower left, providing an area for outdoor recreation within the intensive agricultural landscape.
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At image right, the broad grey-green shield volcano of Emi Koussi is marked by three overlapping calderas that were formed by eruptions. The calderas form a large, oblong depression at the 3,415–meter (11,200 foot) high summit of the volcano. A smaller crater sits within the larger caldera depression. While volcanic activity has never been observed—nor mentioned in historical records—an active thermal area can be found on the southern flank.
The circular Aorounga Impact Crater lies approximately 110 kilometers (68 miles) to the southeast of Emi Koussi and has its origins in forces from above rather than below. (Note that the image is rotated so that north is at the bottom.) The Aorounga structure is thought to record a meteor impact from approximately 345 to 370 million years ago. The crater in the image may be but one of three impact craters formed by the same event; the other two are buried by sand deposits. The linear features (image lower left) that arc around Emi Koussi and overprint Aorounga and the surrounding bedrock are known as yardangs—rock ridges formed by wind erosion.
