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Sources:  NASA, U.S. Geological Survey, National Science Foundation, NY Times     

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Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth.

Description:

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 rate at which Expedition 13 has been photographing the Earth has been record-setting, as they passed the 200,000^th image mark less than two months before. The 250,000^th image is an oblique view (the photograph was taken from a side angle) of the city of Christchurch, New Zealand. The oblique view provides a sense of perspective and accents topography, in contrast to nadir (directly downwards) views, such as this image of Christchurch acquired by the Landsat 7 satellite in 2001.

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.

Other interesting features in the image include the braided Waimakariri River to the north-northwest of the city, and the greenish brown waters of Lake Ellesmere at image left. The coloration of the water is due both to its shallow depth (1.4 meters on average) and its high concentrations of nitrogen and phosphorus, which fertilizes the growth of large amounts of green algae.

Astronaut photograph ISS013-E-67242 was acquired August 15, 2006, with a Kodak 760C digital camera using a 180 mm lens, and is provided by the ISS Crew Earth Observations experiment and the Image Science & Analysis Group, Johnson Space Center. The image in this article has been cropped and enhanced to improve contrast. Lens artifacts have also been removed. The International Space Station Program supports the laboratory to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet.

Credit:

NASA image created by Jesse Allen, Earth Observatory, using data obtained from the University of Maryland’s Global Land Cover Facility.

Description:

They may look like meteor craters, but the circular depressions in the surface of northern Canada’s Melville Island actually formed from geologic processes deep underground. The crater-like features on the island’s Sabine Peninsula are salt domes, or diapirs. When ancient seas evaporate, they leave behind salt deposits. The salt layers are buried by sediment, which eventually turns into rock. Because the salt deposit is less dense than the overlying rock, it’s buoyant. The buoyant mass of salt balloons upward and intrudes into the overlying rocks through weak spots. The intruding “salt bubble” is called a salt diaper. In most environments, salt diapirs that reach the surface erode rapidly, leaving behind craters such as the ones shown here.

This image from the Landsat 7 satellite shows two salt diapirs on Melville Island. The island’s rocky surface appears to be dusted with snow in places, even though summer had officially begun. Pale blue and white, sea ice surrounds the island like a carefully crafted stained-glass window. A few puffy clouds stretch across the northern tip of the island where it juts into the Hazen Strait. Hazen Strait is one of the interconnected pathways that weave through the northern Canadian islands that stretch between Baffin Bay to the southeast and the Arctic Ocean to the northwest.

Melville Island lies in a geologic formation known as the Sverdrup Basin, a southwest-northeast-trending basin about 1,300 kilometers long and 400 kilometers wide. The salt deposits in the basin are linked to a period in Earth’s past known as the Carboniferous, which spanned the time between about 359 to 299 million years ago.

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Credit:

Robert Simmon, based on data provided by the Landsat science team and the UMD Global Land Cover Facility.

Description:

Each year in July, close to 200 professional cyclists converge on France for the most prestigious and grueling bike race in the world: the Tour de France. The three-week stage race traverses France with excursions into neighboring countries, scaling peaks in both the Pyrenees in the south and the Alps in the east. The race always finishes in front of hundreds of thousands of fans along the Champs-Élysées, a famous Paris street.

This image from the Enhanced Thematic Mapper Plus sensor on NASA’s Landsat satellite shows the terrain of the 17^th stage of the race—the final day in the mountainous terrain of the Alps. Deep green forests line the lower slopes of mountains, while the summits of many of the peaks appear lighter green because they are beyond the elevation where trees can grow. Some of the summits are capped by glaciers. The rugged terrain is carved by gray ribbons of rivers and creeks.

Stage 17 starts in the town of Saint-Jean-de-Maurienne (lower left) and finishes in Morzine (upper right); the day’s ride is 200.5 kilometers (124.6 miles). The race organizers categorize the mountains on a scale of 1 to 4 (harder to easier), with a special “beyond category” (hors catégorie in French) for the absolute toughest mountain climbs. From Saint-Jean-de-Maurienne, the route takes riders north, roughly following the route of the Arc River, which flows northwest, where it eventually meets the Arly River. Beyond the Arly River, riders climb four steep passes more than 1,400 meters in altitude (1 meter is about 3.3 feet). The first, Col des Saises, is 1,650 meters tall. The last, Col de Joux-Plane, reaches 1,700 meters over 11.7 kilometers of road with an average gradient of 8.7 percent. From Col de Joux-Plane, riders race downhill into Morzine. Like other towns visible in the image, Morzine forms a gray spot against the green landscape of France’s Savoie and Haut-Savoie regions. Geneva, Switzerland, is the grey region on the shores of Lake Geneva in the upper left corner of the image.

This image was captured by Landsat on July 21, 2001

Credit:

Landsat 7, USGS

Description:

A series of rocky outcroppings are a prominent feature of this Sahara Desert landscape near the Terkezi Oasis in the country of Chad.

Ordering ID: PD-TERKEZI-OASIS
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Credit:

Landsat 7, USGS

Description:

The so-called Richat Structure is a geological formation in the Maur Adrar Desert in the African country of Mauritania. Although it resembles an impact crater, the Richat Structure formed when a volcanic dome hardened and gradually eroded, exposing the onion-like layers of rock.

High-resolution Images:
• May 10, 2006; ISS
• May 18, 1990; Landsat TM

Credit:

NASA/JSC Gateway to Astronaut Photography of Earth, Landsat, NASA

Description:

The Phoenix, Arizona, metropolitan area is the largest in the southwestern United States. The city is made up of 21 incorporated municipalities. When discrete political entities form a larger, integrated urban landscape, geographers call the arrangement a conurbation. This astronaut photograph (upper image) of the central metro region includes the boundary area between three of the municipalities included in the conurbation: the cities of Phoenix (left), Tempe (center and lower right), and Scottsdale (upper right). This high-resolution astronaut image has a spatial resolution (level of detail) of about 9 meters per image pixel. A regional view of the greater Phoenix metropolitan area is also available from the Earth Observatory.

The urban area is still expanding along its fringes, but significant redevelopment is also ongoing in “landlocked” municipalities in the center of the metro area, where expansion is not possible (such as Tempe). Residential areas are grey and gridded into blocks, commercial or industrial sectors often have highly reflective white rooftops, desert soils and rock exposures are brown, vegetation is dark green, and water is black. Comparison of the astronaut image with Landsat Thematic Mapper data (lower image) acquired in 1990 reveals changes in the region over 16 years.

Perhaps the most striking change visible in this image pair is the appearance of Tempe Town Lake, filled in 1999 (upper image, right). The lake was created in the usually dry Salt River channel (dry because the river has been impounded upstream behind Roosevelt Dam since 1911). The lake is part of a plan to develop the Tempe portion of the channel and adjacent floodplain. Contained by inflatable dams to accommodate releases from Roosevelt Dam, the lake holds a nominal water volume of approximately 1 billion gallons, with an estimated 620 million gallons lost to evaporation each year. Other visible changes between 1990 and 2006 include development of land surrounding Sky Harbor Airport, expansion of the airport itself (a third runway, begun in 1997, is visible in the astronaut photograph), and completion of major highways to the southwest of Papago Park and to the east of Tempe Town Lake (upper image, right boundary). Study of the effects of urban modifications in the Phoenix metro area and the surrounding Sonoran Desert ecosystem is the focus of the Central Arizona-Phoenix Long Term Ecological Research site based at Arizona State University.

While suburbs and skyscrapers are the latest expression of civilization in this portion of the Sonoran Desert, it is not the first large-scale modification of the area to serve human needs. The Hohokam society cultivated the region and created an extensive network of irrigation canals between AD 300 and 1450. The canals remained long after the Hohokam themselves quit the region, and settlers used them in the 19^th century to irrigate their fields with water from the Salt River.

Astronaut photograph ISS013-E-17394 was acquired May 10, 2006, with a Kodak 760C digital camera using a 400 mm lens, and is provided by the ISS Crew Earth Observations experiment and the Image Science & Analysis Group, Johnson Space Center. The image in this article has been cropped and enhanced to improve contrast. The International Space Station Program supports the laboratory to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth.

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When the Pleistocene Ice Age reached its peak around 22,000 years ago, continent-spanning glaciers covered large sections of North America and Eurasia like a sheet. As the Ice Age waned, the glaciers retreated. Occasionally large chunks of ice broke off from the glacier and became surrounded or even buried by soil and rock debris deposited by the melting ice sheet. Eventually, the blocks of ice also melted, leaving behind a depression in the ground. These depressions are called kettles; when they are filled with water, they are called kettle lakes, or pothole lakes.

This natural-color Landsat 7 image shows blue and green pothole lakes in northern Siberia, adjacent to the Ob Gulf (image right). The different colors of the lakes reflect different amounts of sediment or depth; the deeper or clearer the water, the bluer the lake. The arctic tundra in this area is permafrost: the top levels of the soil melt and warm in the summer, but the ground below is frozen solid year round. Rivers cut only shallowly into the hard, frozen ground, and they meander across the image like golden threads (upper right and lower left). The landscape is dominated by spongy peat bog, covered in shallow-growing vegetation such as moss that can survive the harsh winters.

Pothole lakes dot the landscape of the Northern Hemisphere in the American and Canadian prairies, the Russian steppes, and throughout northern Siberia. Scientists use satellite images of these glacial kettle lakes to measure water clarity and to make environmental assessments. These lakes are far from agricultural land and settled areas, so they have fairly clear and unpolluted waters. Scientists also monitor these lakes to study climate change. Researchers reported in Science that some glacial kettle lakes in northern Siberia have drained over the past 30 years as the region has warmed and the permafrost beneath the lakes has “cracked,�? allowing lake water to drain out.

NASA image created by Jesse Allen, Earth Observatory, using data obtained courtesy of the University of Maryland’s Global Land Cover Facility.