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Note: In this photograph from astronauts on the International Space Station, the image is rotated so that north is to the right.
Perito Moreno is perhaps the region’s most famous glacier because it periodically cuts off the major southern arm (known as Brazo Rico) of Lake Argentino. The glacier advances right across the lake until it meets the opposite shoreline, and the ice tongue is “grounded” (not floating) so that it forms a natural dam. The ice dam prevents lake water from circulating from one side to the other, which in turn causes muddier and “milkier” water to concentrate in Brazo Rico. Water flows down under the glacier from the mountains, not only carrying the mud into the lake but also helping lubricate the glacier’s downhill movement.
Because of this natural ice dam, meltwater from the south raises water levels in Brazo Rico by as much as 30 meters above the level of the water in Lago Argentino. The great pressure of this water ultimately causes the ice tongue to rupture catastrophically in a great natural spectacle. The last rupture occurred in March 2012, after this image was taken. The process repeats every four to five years as the glacier grows back towards the opposite shoreline. The repeated ruptures have made the glacier and lake a major tourist attraction in the region.
A more detailed astronaut view of the glacier tongue can be viewed here.
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The city was a central point for humanitarian aid, and the operations base for the United Nations and non-governmental organizations during the Sudanese conflicts. Today, a significant number of foreign aid workers remain in the city. During the conflict, city infrastructure and main transportation arteries suffered heavy damage. The city is still surrounded by army camps and squatter settlements (labeled “informal built-up areas” in the image). They appear as muted gray areas extending outward from the center of the city.
The city also hosts the Juba Game Reserve, a protected area of savannah and woodlands that is home to key bird species. Since independence, a variety of countries and international organizations have helped rebuild Juba’s roads, railroads, and airport. Unfortunately, South Sudan continues to experience local wars with a variety of armed groups, including on-going conflicts with Sudan over oil-rich territories.
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Other smaller lakes hold red and brown water, a result of the interplay of water depth and resident organisms such as algae. The algae color varies depending on water temperature and salinity. (A similar process is observed in pink and red floodwaters when they pond in Lake Eyre, a mostly dry lake in Australia. In Lake Eyre, researchers know that the color is indeed due to algae growth.)
Typically, little water or sediment reaches the floor of the Etosha Pan because the water seeps into the riverbeds along their courses. The floor of the pan itself is only rarely covered by even a thin sheet of water. In this image, there was enough surface flow to reach the pan, but too little to flow beyond the inlet bay. A prior flood event, when water entered the pan via the Oshigambo River, was documented in astronaut imagery in 2006.
The straight line that crosses the image is the northern fence line of Namibia’s Etosha National Park. This three-meter-high fence keeps wildlife from crossing into the numerous small farms of the relatively densely populated Owambo region of Namibia, north of the pan. The large Etosha lakebed (120 kilometers long, or 75 miles) is at the center of Namibia’s largest wildlife park and a major tourist attraction.
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Originally called Tindouf, the 3.5-kilometer wide crater (image center) has been heavily eroded since its formation; however, its circular morphology is highlighted by exposures of older sedimentary rock layers that form roughly northwest to southeast-trending ridgelines. From the vantage point of an astronaut on the International Space Station, the impact crater is clearly visible with a magnifying camera lens.
A geologist interpreting this image to build a geological history of the region would conclude that the Ouarkziz crater is younger than the sedimentary rocks, as the rock layers had to be already present for the meteor to hit them. Likewise, a stream channel is visible cutting across the center of the structure, indicating that the channel formed after the impact had occurred. This Principal of Cross-Cutting Relationships, usually attributed to the 19th century geologist Charles Lyell, is a basic logic tool used by geologists to build relative sequence and history of events when investigating a region.
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The dust plumes in this astronaut photograph stretch more than 120 kilometers (74 miles). The vigor of the winds also can be judged from the fact that they are lifting dust particles from the valley floor to more than 1200 meters over the mountains. The winds channel the dust through a low point in the mountains, about 800 meters lower than the ridge crests to north and south (image right). The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite also captured a wider, regional view of the plumes on the same day.
In most parts of the world, blowing dust is some shade of light brown or red. In this image, two different colors can be seen in the dust plume: redder dust from the hillsides north of White Sands and white dust from the dune field itself.
The sand dunes of this national monument are white because they are composed of gypsum, a relatively rare dune-forming mineral. The gypsum is deposited during the evaporation of mineral-rich waters in an ephemeral lake in the western part of the Monument. Erosion of the deposits, together with wind transport, provides the granular material for the dunes. The dunes’ brilliance, especially contrasted against the nearby dark mountain slopes, makes them easily identifiable to orbiting astronauts. The white speck of the dunes was even visible to astronaut crews looking back at Earth on the way to the Moon.
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The island is volcanic in origin and has a summit elevation of 775 meters (2,543 feet) above sea level. The Île aux Cochons stratovolcano is thought to have erupted within the past 12,000 years; however, no historical activity has been recorded.
The summit elevation is high enough for the land surface to interact with cloud layers and winds flowing past the island, and two major cloud layers are visible. The lower, more uniform layer consists of roughly parallel cloud “streets” that suggest a westerly flow pattern of air. When the air mass encounters the Île aux Cochons, moisture-laden air rises and cools, causing more water vapor to condense into clouds.
As the air mass passes over the summit and descends, it may encounter alternating moist and dry air layers, enabling the formation of the discontinuous, chevron-shaped wave clouds. While their appearance suggests that the clouds are forming in the wake of the island and moving eastwards, it is in fact the air mass that is moving, with clouds forming in regions of moist air and dissipating in dry regions.
Île aux Cochons is the westernmost of the islands in the sub-antarctic Crozet Archipelago, part of the French Southern and Antarctic Lands. Except for occasional research visits, the island is uninhabited. The island is an important breeding site for seabirds, including the world’s largest King Penguin colony.
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Many of China’s cities have grown at tremendous rates, but comparison between a 2012 night time image (above, top) and 2002 day time image (above, lower) taken from the International Space Station provides an indication of how much development has occurred in the Shanghai region over the past 10 years. The official census count in 2000 was 16.4 million; the city population has increased more than 35% since that time. Much of the growth has occurred in new satellite developments like areas to the west of the city (for example, Suzhou).
Shanghai’s history is also colorful. The area started as an agricultural community more than 1,000 years ago. A trading and merchant economy developed, growing into a trading port and exporting cotton, silk, and fertilizer during the 1700s and early 1800s. Shanghai also figured prominently in the First Opium War, and became a British treaty port after the Nanjing Treaty (1842).
The city’s rapid growth and development during the 20th and 21st centuries have come at a cost. Water availability is a key concern, and groundwater withdrawal has resulted in substantial subsidence in and around the city. Because it is built only a few meters above sea level—on the banks of the deltaic estuary of the Yangtze River—curbing subsidence rates is a critical concern.
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The irregular southeastern coastline of Kamchatka provokes large, circular eddy currents to spin off from the main southwestward-flowing Kamchatka current. Three such eddies are highlighted by surface ice floe patterns at image center. The patterns are very difficult (and dangerous) to navigate in an ocean vessel. While the floes may look thin and delicate from the ISS vantage point, even the smaller ice chunks are several meters across. White clouds (image top right) are distinguished from the sea ice and snow cover by their high brightness and discontinuous nature.
The Kamchatka Peninsula also hosts many currently and historically active stratovolcanoes. Kliuchevskoi Volcano, the highest in Kamchatka (summit elevation 4,835 meters) and one of the most active, had its most recent confirmed eruption in June 2011. Meanwhile, Kronotsky Volcano—a “textbook” symmetrical cone-shaped stratovolcano—last erupted in 1923.
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On one side of the rift lies the Nubian (or African) tectonic plate, which includes the older continental crust of Africa. The Somalian plate—which is moving away in the other direction—lies to the other side and includes the Horn of Africa. Together with the associated Ethiopian Rift, the tectonic boundary stretches from the southern Red Sea to central Mozambique.
Landscapes in the rift valley can appear confusing. The most striking features in this view are the numerous, nearly parallel, linear fault lines that occupy the floor of the valley. Shadows cast by the late afternoon Sun make the fault scarps more prominent. These steps in the landscape are caused by slip motion along individual faults and are aligned with the north-south axis of the valley (lower left to top right). A secondary trend of less linear faults cuts the main fault at an acute angle, with the fault steps throwing large shadows.
The Eastern Branch of the East African Rift is arid. (By contrast, the Western Branch lies on the border of the Congolese rainforest). Evidence of this can be seen in the red, salt-loving algae of the shallow and salty Lake Magadi (image center). A neighboring small lake to the north (to the left of Magadi in the image) has deeper water and appears dark. The white salt deposits on the dry part of the Lake Magadi floor host a few small commercial salt pans. The lakes appear to be located where the main and secondary fault trends intersect.
The East African rift system is marked by substantial volcanic activity, including lavas erupted from fissures along the rift in the region. Much of the faulting observed in this image cuts through such lavas. Elsewhere along the rift system, individual volcanoes form. Some of those volcanoes are very large, including Mount Kilimanjaro and Mount Kenya. In this image, a volcano (Lenderut) appears to be superimposed on the faults, indicating that it is younger than the faults it covers. Deeply eroded slopes also suggest that the volcano has not been active for a long time.
The largest vegetated area is the green floor of a valley that drains an area large enough for water to exist near the surface. For a sense of scale, the vegetated valley floor is 17 kilometers long (10.5 miles).
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The islands themselves mark the tectonic boundary where the old, cold Pacific plate is being subducted at the Marianas trench beneath the younger, less dense crust of the Philippine Sea. The subduction results in substantial volcanic activity on the upper plate, forming the island arc of the Marianas. Considered to be one of the classic examples of an oceanic subduction zone, the Marianas Trench includes the deepest spot in the Earth’s oceans (more than 10,000 meters).
The foreshortened appearance of the island is due to the viewing angle and distance from the space station. The ISS was located over the Pacific Ocean approximately 480 kilometers to the southeast of Pagan Island when the image was taken. Visit this page for another image of Pagan Island.
