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Sunglint images can reveal numerous details of water circulation that are otherwise invisible. This image was taken during the Indian Ocean northeast monsoon season. Predominant winds in this area create sinuous surface water patterns on the leeward side of and between the islets (image right). A south-flowing current flows in the deeper water through the Maldives most of the year (image left), with fan-shaped surface currents formed by local tides pulsing in and out of the shallow water near the islands (image top and bottom).
The largest island seen here (image center) is 6 kilometers (4 miles) long, and it is one of the outer ring of larger islands that make up the 70-kilometer- (40-mile-) long, oval-shaped Malé Atoll. Shores facing deeper water have well-defined beaches. Numerous small, elliptical coral reef islets are protected within the ring of shallow water to the northeast (image right). These islets are mostly awash at high tide, with dry ground appearing in tiny patches only. A small boat was navigating between the islets at the time the image was taken, as indicated by its v-shaped wake at image top right. Images like these illustrate why the Republic of Maldives, surrounded by water, is one of the most outspoken countries in stressing the dangers of rising sea levels.
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While the image is not detailed enough to see damage to individual buildings or roadways, some indicators of earthquake damage are visible, especially in the large version of the image. A dark smoke plume is visible at image lower left near an oil refinery in Hualpén. At image lower right, parts of the road bed of a single-lane bridge over the Río Biobío appear to have collapsed. A smaller, white smoke plume is visible at image right near the Universidad de Concepción. Smoke, probably related to the earthquake, was observed over Santiago in images acquired by the Moderate Resolution Imaging Spectroradiometer on NASA’s Terra satellite less than one hour after this astronaut photograph was taken.
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Salt domes start during past periods of alternating wet and dry climate. A common scenario is an enclosed basin that is alternately flooded and then subjected to extreme drying. High rates of evaporation deposit thick layers of salt minerals, such as common table salt and gypsum (a chalky mineral that is a major component of wallboard). These layers are eventually buried by sediments. If the salt layers are buried deeply enough, the pressure can cause them to flow. Salt has lower density than the surrounding rock, so it tends to flow upwards, pushing up the overlying layers of rock to form a dome. While many salt domes retain a cap of the youngest rock layers at the surface, in some cases the underlying salt extrudes all the way to the surface.
This astronaut photograph illustrates the varying character of surfaces on Sir Bani Yas. The central mountains of Jebel Wahid (image center) mark the location of the Sir Bani Yas salt dome. The dome has breached the surface but exposed salt, primarily gypsum, is eroded, leaving a rugged, insoluble cap made of fragments of the overlaying sedimentary and volcanic rocks. Sand and silt derived from the Jebel Wahid and surrounding gravel-covered areas form beaches along the outer edge of the island.
Sir Bani Yas Island was the personal retreat of the late Sheikh Zayed Bin Sultan Al Nahyan who was president of the UAE from 1971-2004. He established a nature preserve on the island for animals native to the Arabian Peninsula (including striped hyena, cheetah, oryx, ostrich, and gazelle) that is now open to the public. The numerous orchard plots that cover much of the island were part of a desert agricultural research program also started by the late Sheikh. Tan graded areas along the western and northeastern coast of the island (image bottom and image left) may be revegetated with additional plots or developed for other land uses.
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The image depicts the roughly 100 kilometer (60 mile) east-west extent of the Houston metropolitan area. Houston proper is at image center, indicated by a “bull’s-eye” of elliptical white to orange-lighted beltways and brightly lit white freeways radiating outwards from the central downtown area. Suburban and primarily residential urban land uses are indicated by both reddish-brown and gray-green lighted regions that reflect a higher proportion of tree cover and lower light density. Petroleum refineries along the Houston Ship Channel are identified by densely lit areas of golden yellow light. Rural and undeveloped land rings the metropolitan area, and Galveston Bay to the southeast (image lower right) provides access to the Gulf of Mexico. Both types of non-urban surface appear dark in the image.
You can see more nighttime imagery of cities, and learn about techniques that astronauts use to photograph them in the Earth Observatory feature Cities at Night.
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This detailed astronaut photograph of Llullaillaco illustrates an interesting volcanic feature known as a coulée (image top right). Coulées are formed from highly viscous, thick lavas that flow onto a steep surface. As they flow slowly downwards, the top of the flow cools and forms a series of parallel ridges oriented at 90 degrees to the direction of flow (somewhat similar in appearance to the pleats of an accordion). The sides of the flow can also cool faster than the center, leading to the formation of wall-like structures known as flow levees (image center). Llullaillaco is also a well-known archaeological site; the mummified remains of three Inca children, ritually sacrificed 500 years ago, were discovered on the summit in 1999.
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This astronaut photograph features a large impoundment area (image center) containing light tan and gray waste materials (“spoil”) from of the Escondida mine complex. The copper-bearing waste, which is a large proportion of the material excavated from open pit excavations to the north (not shown), is poured into the impoundment area as a liquid (green region at image center), and dries to the lighter-toned spoil seen in the image. The spoil is held behind a retaining dam, just more than 1 kilometer (0.6 miles) long, visible as a straight line at image lower left.
Escondida means “hidden” in Spanish, and it refers to the fact that the copper ore body was buried beneath hundreds of meters of barren rock, and the surface geology gave no signs of its presence. Instead it had to be located by a laborious drilling program following a geologic trend—an imaginary line hundreds of kilometers long established by other known copper finds—with which Escondida lined up.
Escondida produces mainly copper concentrates. Assisted by gravity, the concentrates are piped as slurry down to the smaller port of Coloso just south of Antofagasta, where they are dewatered for shipping. The mine began operating in 1990.
