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Dune Types in the Issaouane Erg, Eastern Algeria
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Published September 11, 2006
One of the main reasons that rainless regions like the Sahara Desert are interesting from the perspective of landscape science is that the work of flowing water—mainly streams and rivers—becomes less important than the work of wind. Over millennia, if enough sand is available, winds can generate dunes of enormous size, arranged in regular patterns. Long, linear dunes stretch generally north to south across much of northeast Algeria, covering a vast tract (~140,000 square kilometers) of the Sahara Desert known as the Erg Oriental. Erg means “dune sea” in Arabic, and the term has been adopted by modern geologists. Spanning this image from a point on the southwest margin of the erg (image center point: 28.9°N 4.8°W) are a series of 2-kilometer-wide linear dunes, comprised of red sand. The dune chains are more than 100 meters high. The “streets” between the dunes are grayer areas free of sand.
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Golden Gate, San Francisco, California
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Published September 4, 2006
The Golden Gate of San Francisco Bay is one of the most recognizable straits in the world due to the Golden Gate Bridge that spans it. This high-resolution astronaut photograph is a nearly cloud-free view of the northern part of the San Francisco metropolitan area.
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250,000 Earth Photographs from the International Space Station
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Published August 28, 2006
The crew of Expedition 13 recently passed a major milestone: as of late August 2006, more than one quarter of a million images of Earth had been taken from the International Space Station. The 250,000th image is an oblique view (a photograph taken from a side angle) of the city of Christchurch, New Zealand. This view provides a sense of perspective and accents topography, in contrast to nadir (directly downwards) views. Snow highlights the peaks of the Banks Peninsula to the southeast of the city. The peninsula has a radically different landscape compared to the adjoining, flat Canterbury Plains, where Christchurch (gray patch to the north) is located. The Banks Peninsula is formed from the overlapping cones of the extinct Lyttelton and Akaroa volcanoes. Subsequent erosion of the cones formed the heavily dissected terrain visible in the image, and sea level rise led to the creation of several harbors around the Peninsula. Erosion continues unabated today, as evidenced by the apron of greenish blue, sediment-laden waters surrounding the Banks Peninsula.
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Mount Etna, Sicily
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Published August 14, 2006
One of the most consistently active volcanoes in the world, Sicily’s Mount Etna has a historical record of eruptions dating back to 1500 BC. This astronaut photograph captures plumes of steam and possibly ash originating from summit craters on the mountain: the Northeast Crater and Central Crater, which includes two secondary craters (Voragine and Bocca Nuova).
Calcite Quarry, Michigan
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Published August 7, 2006
While the Great Lakes region of North America is well known for its importance to shipping between the United States, Canada, and the Atlantic Ocean, it is also the location of an impressive structure in the continent’s bedrock: the Michigan Basin. Formed during the Paleozoic Era (approximately 540–250 million years ago) the Basin looks much like a large bullseye defined by the arrangement of exposed rock layers that all tilt inwards, forming a huge bowl-shaped structure. The outer layers of the Basin include thick deposits of carbonates—rocks containing carbon and oxygen, such as limestone—deposited over millions of years when a shallow sea covered the region. These carbonate rocks are mined throughout the Great Lakes region using large open-pit mines. The largest carbonate mine in the world, Calcite Quarry, appears in this astronaut photograph.
Ship Traffic on the Suez Canal, Egypt
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Published July 31, 2006
This astronaut photograph captures a northbound convoy of cargo ships entering the Mediterranean Sea from the Suez Canal in Egypt.
Yates Oilfield, West Texas
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Published July 24, 2006
The Permian Basin of west Texas and southeastern New Mexico is one of the most productive petroleum provinces of North America. The area holds one of the thickest deposits of rock from the Permian Period, which lasted from approximately 290 to 251 million years ago. The Basin is a large depression in the bedrock surface along the southern edge of the North American craton, an ancient core of continental crust. The Basin filled with thick layers of sediment during the Paleozoic Era (about 545 to 251 million years ago) as the region was alternately covered by shallow oceans, or exposed as coastal salt flats. The sediments hardened into primarily organic-rich carbonate and minerals such as common table salt. Later activity in the Earth’s crust caused folding of the sedimentary layers, creating ideal conditions for the formation, trapping, and storage of petroleum. In this astronaut photograph, numerous white well locations and petroleum drilling structures mark the Yates Oil Field in the layered sedimentary rocks of the Permian Basin.
Tenerife Island, Spain
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Published July 17, 2006
Tenerife is the largest of the Canary Islands, a Spanish possession located off the northwestern coast of Africa. The central feature of this astronaut photograph is the elliptical depression of the Las Cañadas Caldera that measures 170 square kilometers (about 65 square miles).
Nukuoro Atoll, Federated States of Micronesia
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Published July 10, 2006
Located just north of the equator, this classically shaped atoll is part of the Caroline Islands, which stretch northeast of Papua New Guinea in the western Pacific. Nukuoro Atoll is one of 607 islands that make up the Federated States of Micronesia.
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Dallas-Fort Worth International Airport, TX
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Published July 3, 2006
The largest airport in Texas, Dallas-Fort Worth International (DFW) is also the fourth largest in the world, and it occupies more surface area than the entire island of Manhattan in New York. This astronaut photograph captures the entire airport and portions of the surrounding Dallas-Fort Worth metropolitan area.
Site of Carthage, Tunisia
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Published June 26, 2006
The city-state of Carthage in North Africa was founded by Phoenician settlers in 814 BC, and it subsequently became the seat of a trade empire that controlled much of the western Mediterranean region (including most of the former Phoenician lands). Carthage was completely destroyed by the Roman Republic during the Third (and final) Punic War (149-146 BC). The end of Carthage has been made notorious by the story that the Romans allegedly sowed the city with salt to ensure that no further rivals to their power would arise there. However, given the great value of salt at the time and the strategic importance of the city’s location, scholars dispute whether the event actually occurred. Following the destruction of Carthage, Roman dominance of the Mediterranean continued until the fall of the Western Empire in 476 AD.
Aves Island
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Published June 19, 2006
Named Isla de Aves in Spanish, (meaning “Island of the Birds”) Aves Island lies west of the Lesser Antilles in the Caribbean. It provides a nesting site to green sea turtles (Chelonia mydas) and, of course, birds. Because the abundant bird droppings, known as guano, could be used in fertilizer and gunpowder, guano miners worked on the island until they depleted the supply. Since its discovery by Europeans, likely in the late 16th century, Aves Island was subsequently claimed by several European nations. The island is currently claimed by Venezuela, although disputes about ownership of the island, and the surrounding exclusive economic zone in the Caribbean, continue today.
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