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The terminus of the Viedma Glacier, approximately 2 kilometers across where it enters Lake Viedma, is shown in this astronaut photograph. Moraines are accumulations of soil and rock debris that form along the sides and front of a glacier as it flows across the landscape (much like a bulldozer). Independent valley glaciers can merge together as they flow down slope, and the moraines become entrained in the center of the new ice mass. These medial moraines are visible as dark parallel lines within the white central mass of the glacier (image center and left). Crevasses—oriented at right angles to the medial moraines—are also visible in the grey-brown ice along the sides of the glacier. The canyon-like crevasses form as a result of stress between the slower moving ice along the valley sides (where there is greater friction) and the more rapidly moving ice in the center of the glacier. Calving of ice from the southwestern fork of the glacier terminus is visible at image lower left.
As they respond to regional climate change, the Patagonian glaciers are closely monitored using remotely sensed data. Scientists compare series of images collected over time to monitor the change in ice extent and position. Scientists have also estimated changes in volume using topographic data from NASA’s Shuttle Radar Topography Mission. The Global Land Ice Measurements from Space (GLIMS) Website is an excellent resource for glacier-monitoring information.
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This picture was taken as the International Space Station passed over the western border of Maryland and West Virginia. The resolution and spatial coverage of this image are similar to the 15-meter-per-pixel data obtained by sensors onboard the Landsat 7 and Terra satellites. Recognizable in this image are the Capitol Building, the Washington Monument (and its shadow), and the Lincoln Memorial, along the northeast bank of the Potomac River.
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This image was taken at 1:10 p.m. Mountain Daylight Time (19:10 Greenwich Mean Time), and low tide occurred later at 2:44 p.m. Mountain Daylight Time (20:44 Greenwich Mean Time). The outgoing, or ebb, current from Playa Colorado Bay is visible at upper right (the Bay itself is not shown). The current brings with it fresher and less dense water that appears as an elongated lens-shape as it flows on top of saltier Gulf water. This density difference causes obvious shear zones along the current boundary, and also a dampening of the ocean wave sets. Offshore, complex wave patterns, including intersecting wave sets, result from a variety of interactions of the moving water with the coastline. The sunglint allows identification of wave sets that are nearly perpendicular to the shoreline (bottom center), another wave pattern parallel to the shore (top center), and wave patterns caused by reflection and refraction (deflecting of the wave off a straight path) along a shoal area that also marks the boundary of the fresh water lens.
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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 19th century to irrigate their fields with water from the Salt River.
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On the left side of the second image, a thin, V-shaped wake curves back towards the shore (and appears near the lower left in the top image). This type of wake is typically created by a small, light craft such as a speedboat or sailboat under power. The third image shows similar tight-V-shaped wakes of other small craft. It also shows broad patterns of larger craft, probably large freighters carrying cargo, that displace and disturb more water during passage. These larger wakes are aligned with the direct course between Detroit (out of the image at lower right) and Cleveland (out of the image at top left). Some of the broad, ill-defined swaths of light and dark (aligned from lower left to upper right) are streaks of wind-roughened water, which reflect the Sun differently.
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Aves Island is small—only 0.5 by 0.2 kilometers (0.3 by 0.1 miles)—and its highest point stands just 4 meters (13 feet) above sea level. In hurricanes, the island can be completely submerged. In 1980, Hurricane Allen split the island in two, but subsequent coral reef growth reunited the two halves. This astronaut photograph is a rare, almost cloud-free, view of the island and the submerged fringing coral reef that surrounds it. The fringing reef is barely visible, appearing as a ring slightly lighter in color than the ocean water. The crosshatch-like pattern of roughness on the surrounding sea surface is most likely caused by variable winds at the time of image acquisition.
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The favorable location of the ancient city of Carthage is clear in this astronaut photograph. Bays along the coastline provide ready access to the Gulf of Tunis, which leads to the Mediterranean Sea. Docks along the coastline (lower right) support the shipping industry. Modern Carthage is a wealthy suburb of the Tunis metropolitan area (the center of which is located to the southwest of the image). Dense concentrations of white rooftops are obvious in the residential subdivisions to the north and south of the ancient city location. Large tracts of new developments appear to be in progress along the curving, light-colored roadways to the west of the historical city (lower image center). The green, shallow waters of an evaporating salty lake are visible at image left. Several such lakes are present in Tunisia and are centers for bird-watching tourism.
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This oblique astronaut photograph (oblique means the viewing angle is not vertical relative to the Earth’s surface beneath the International Space Station) captures the entire airport and portions of the surrounding Dallas-Fort Worth metropolitan area. The white rooftops of the new International Terminal D (completed in 2005) are also distinct from less reflective rooftops of the older terminals. A sense of the size of the airport is provided by the approximately 2,800-meter-long, northwest-southeast runway to the west of Terminal D (2,800 meters is about 1.7 miles). The oblique viewing angle also accentuates light reflection off of North Lake (upper right), giving the water surface a grey-green cast.
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The image shows the sandy atoll with 42 distinct patches of vegetation. These patches are located on the northeast and east portions of the atoll that face the dominant easterly winds. The detailed image (white box indicates area shown) shows the larger fields and settlements, which are on the inland side of the largest forest patch, protected from the wind. The land surface is probably slightly higher above sea level here because dunes build up preferentially on wind-facing slopes where beach sand is mobilized by wind. Swells driven by these winds approach from the east-southeast (right) and wrap around the atoll to produce an interference pattern on the downwind side. Water in the lagoon is notably calm in comparison. Coral heads appear in the lagoon, including one in the center of the image.
About 900 people live on Nukuoro, whose lagoon is 6 kilometers (about 3.7 miles) in diameter. Fishing, animal husbandry, and agriculture (taro and copra) are the main occupations. Nukuoro is remote. It has no airstrip, and a passenger boat calls irregularly only once a month. The tiny population speaks its own unique language.
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The Canal was built under the direction of Ferdinand de Lesseps of France using primarily Egyptian labor, and it was opened to traffic in 1869. Subsequent wars and skirmishes have passed control of the Canal to various powers including the United Kingdom, Egypt, Israel, and the United Nations. A multinational observer force including the United States, Israel, and Egypt currently oversees the Canal.
This is an oblique image of the canal, meaning it has been taken at an angle. Astronauts and cosmonauts on the International Space Station (ISS) can photograph the part of the Earth directly below the station as it passes overhead, or they can photograph different parts of the globe. When they photograph different parts of the globe, they take pictures at an angle to provide a sense of perspective. In this case, the ISS was located above the eastern coast of Cyprus, and the astronaut was looking at Egypt to the southwest. Regions of reduced clarity in the image result from thin cloud cover. The day this image was taken, the total number of Earth photographs acquired by astronauts aboard the ISS passed 200,000.
