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This geological feature extends more than 550 kilometers (342 miles) northeast to southwest across the center of Zimbabwe, varying from 3 to 12 kilometers (2-8 miles) in width. The southern end of the dyke is captured in this astronaut photograph.
Layered mafic intrusions are usually associated with economically important metals such as chromium, nickel, copper, platinum, titanium, iron, vanadium, and tin. Chromium, in the form of the mineral chromite, and platinum are particularly abundant in the Great Dyke and actively mined. Younger faults have offset sections of the Dyke along its length; two of the most obvious faults in the image are indicated, with arrows showing the relative directions of offset.
While the Great Dyke and its metal ores are products of geologic processes from the deep past, more recent events have also left their mark on the landscape. Two large burn scars from fires are visible at image top center.
An older, more detailed view of the Great Dyke can be found in an astronaut photograph available here.
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The deepest part of Lake Lahontan survives today as Pyramid Lake, and it is well known to geologists because of the spectacular calcium carbonate deposits found there. The lake takes its name from one such pyramid-shaped deposit of tufa, rock formed by the precipitation of calcium carbonate from spring water, lake water, or a combination of the two. Over time, these deposits develop a wide variety of forms—including mounds, towers, sheets, and reefs—while sometimes coating other rocks. The tufa is exposed when water levels drop due to changes in regional climate, the diversion of water for human use, or both (Mono Lake in California for example).
This astronaut photograph also captures sunglint—light reflected off of a water surface back towards the observer—on the northern (lower end in this image) and southeastern (upper) ends of the lake. Two large spiral whorls are visible in sunglint at the northern end, likely the result of wind patterns that disturb the water surface and cause localized variations in the amount of light reflected back to the International Space Station.
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Following Sudan’s independence from Egypt and the United Kingdom in 1956, allocation and control of Nile River water was divided between Egypt and Sudan by the Nile Waters Treaty signed in 1959. Today, other countries within the Nile basin—including Ethiopia, Kenya, Rwanda, Tanzania, and Uganda—are seeking more equitable allocation and utilization of the water and recently (2010) signed a new water use pact challenging the 1959 treaty.
Beyond the issues of water rights, several local tribes will be displaced by the planned 170 kilometer (105 mile) reservoir, and the flooded region contains significant but little-studied archeological sites. The Sudanese government has a resettlement program in place for the tribes, and a variety of international institutions have been conducting “salvage ” or “rescue” archeological surveys since 1999. Such rescue surveys seek to preserve as much information as possible from sites that will be destroyed or otherwise made inaccessible (in this case by flooding).
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The floodplain is shown here as a tangle of twisting meanders and loops (image center). The darkest areas are brushy vegetation along the present course (filled with blue-green water); wisps of vegetation are also visible along flanking swampy depressions, or sloughs. An older floodplain appears as more diffuse dark vegetation (image upper left), where relict bends are overlain by a rectangular pattern of cotton fields. The straight channel of a new diversion canal—one of 16 from this point downstream—can be seen along the east bank of the river. The older floodplain is fed from the Chardara Reservoir, immediately upstream (not shown). Half the river flow is controlled from reservoirs, and half from direct water take-off from canals. In contrast to the intensive agricultural use of water shown here, water control in the mountain valleys upstream is oriented more toward power generation.
The river flows for 2,200 kilometers, from the Tien Shan Mountains west and northwest to the Aral Sea—the dying waterbody at the low point of the basin. Water has been withdrawn from the river for agriculture for many decades. Although the Syr Darya is the second largest river flowing into the Aral Sea, its discharge is not very large and it is easily depleted. Control of the river is vested in the Syr Darya Basin Water Organization, run by nations with territory in the watershed. Some of the organization’s main efforts include accurate gauging of water use and repair of canals to reduce widespread water leakage.
Alexander the Great reached the Syr Darya in 329 BCE. On the north bank of the river (just beyond the lower left of this image) his army clashed with the local nomads. The river is consequently better known in the West by its Greek name, Jaxartes. From here, Alexander marched south through Afghanistan to the Indus River plains in Pakistan before starting the long march back. He died before reaching his homeland.
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The Nile River and its delta look like a brilliant, long-stemmed flower in this astronaut photograph of the southeastern Mediterranean Sea, as seen from the International Space Station. The Cairo metropolitan area forms a particularly bright base of the flower. The smaller cities and towns within the Nile Delta tend to be hard to see amidst the dense agricultural vegetation during the day. However, these settled areas and the connecting roads between them become clearly visible at night. Likewise, urbanized regions and infrastructure along the Nile River becomes apparent (see also The Great Bend of Nile, Day & Night.)
Another brightly lit region is visible along the eastern coastline of the Mediterranean—the Tel-Aviv metropolitan area in Israel (image right). To the east of Tel-Aviv lies Amman, Jordan. The two major water bodies that define the western and eastern coastlines of the Sinai Peninsula—the Gulf of Suez and the Gulf of Aqaba—are outlined by lights along their coastlines (image lower right). The city lights of Paphos, Limassol, Larnaca, and Nicosia are visible on the island of Cyprus (image top).
Scattered blue-grey clouds cover the Mediterranean Sea and the Sinai, while much of northeastern Africa is cloud-free. A thin yellow-brown band tracing the Earth’s curvature at image top is airglow, a faint band of light emission that results from the interaction of atmospheric atoms and molecules with solar radiation at approximately 100 kilometers (60 miles) altitude.
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Houston is home to the NASA Johnson Space Center and is notable among major U.S. metropolitan areas for its lack of formal zoning ordinances. (Other forms of regulation play a similar role here.) This leads to highly mixed land use within the city. Around Reliant Park you can find large asphalt parking lots, vacant lots with a mixture of grass and exposed topsoil, and both single- and multi-family residential areas. A forested area (dark green, lower left) is located less than two kilometers from the parking lots.
This subset of a handheld digital camera image has a spatial resolution of 2 to 3 meters per pixel (or picture element), making it one of the highest spatial resolution images ever obtained from the International Space Station (ISS). Such high resolution was made possible by using lens “doublers” to increase the optical magnification of camera lenses. Active ISS motion compensation is also important; the astronaut must pan the camera by hand at just the right rate, keeping the object at the same point in the viewfinder. The technique involves bracing yourself against the space station bulkhead to prevent movement related to weightlessness. Traditional short lens photography is easier because it does not require motion compensation.
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Coropuna also hosts several summit glaciers and ice fields that contrast sharply with the dark rock outcrops and surface deposits at lower elevations. Glacial deposits and lateral moraines on the flanks of Coropuna indicate that glaciers once extended to much lower elevations than observed today. Careful mapping and surface exposure age-dating of these deposits and landforms provides data on the timing of ice advances and retreats in the tropics near the end of the Pleistocene Epoch (extending from about 2.5 million to 12,000 years ago). This information can be compared with other paleoclimate records to obtain a better understanding of how Earth’s climate has changed over geologic time.
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The green, vegetated slopes that ring the Kathmandu metro area (light gray, image center) include both forest reserves and national parks. The metropolitan area is relatively flat compared to the surrounding mountains. Tribhuvan International Airport, near the eastern margin of the city, is the only international airport in Nepal.
Archeological evidence suggests that the human development of Kathmandu, together with the nearby “sister cities” of Lalitpur and Bhaktapur, began almost 2,000 years ago. Today, Kathmandu and its sister cities form the governmental, cultural, and—as a main access point to the Himalayas for tourism—economic center of the country.
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Kronotsky and Kizimen stratovolcanoes are distinguished by their symmetrical cones. Kizimen last erupted in 1928, while Kronotsky—one of the largest on the peninsula—last erupted in 1923.
Schmidt Volcano, to the north of Kronotsky, has the morphology of a shield volcano and is not known to have erupted since humans have been keeping records.
To the south (left) is Krasheninnikov, comprised of overlapping stratovolcanoes that formed within an earlier caldera. Krasheninnikov may have last erupted in 1550. Two summit craters are clearly visible.
Lake Kronotsky is Kamchatka’s largest lake. It formed when lava flows from Kronotsky Volcano dammed the Listvenichnaya River.
The Kamchatka Peninsula lies along the so-called Pacific "Ring of Fire." The ring is characterized by active volcanoes and frequent earthquakes associated with the many active subduction and transform boundary zones around the Pacific tectonic plate. There are 114 volcanoes on the Kamchatka Peninsula that have erupted during the Holocene Epoch (approximately 12,000 years ago to the present).
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Subsequent developments have sprouted progressively further from the ancient center, with ring roads concentrically arranged around it. The diplomatic quarter is reached via the waterfront Corniche promenade, north of the old city. Further away, an extensive marina known as West Bay Lagoon, with boating access to the Persian Gulf, stands out (image top).
Qatar’s new artificial island, known as the Pearl-Qatar, is under construction with 32 kilometers of new coastline just offshore of West Bay Lagoon. This development is intended mainly as a residential zone, with themes based on Arabic, Mediterranean, and European cultures. The Pearl-Qatar is so named because it is being built on one of Qatar’s historical pearl diving sites. A string of small islands built along the outer margin is intended to recall the pearl-diving culture of the nation’s past.
When compared to maps of the proposed project, the basic outline of the islands appears to be substantially complete. The distance from the entry causeway to the end of the string of small islands is 5 kilometers in a straight line. This image also shows the network of deep access channels—marked by darker blue water—leading to The Pearl-Qatar and West Bay Lagoon.
The population of Qatar is almost 1.7 million, with nearly 75 percent being migrant workers from south and southeast Asia. Ninety percent of Qatari citizens live in Doha. Qatar enjoys vast hydrocarbon wealth, thanks to the third largest gas reserves in the world. Consequently, the emirate has one of the highest per capita gross domestic products (GDP) in the world.
Qataris are known to be cricket, tennis, and soccer enthusiasts. On December 2, 2010, Qatar won the bid to host the 2022 FIFA World Cup. An underground soccer (football) stadium is being built, the first of its kind. The existing sports complex is based at the Khalifa Stadium, visible to the southwest of the city.
