NASA picture of the day

[tittenman]

Summit of Popocatepetl Volcano, Mexico

Volcan Popocatepetl, a large stratovolcano located approximately 70 kilometers southeast of Mexico City, is considered by many volcanologists to be “the planet’s riskiest volcano.” The volcano warrants this distinction because of how close it is to one of the most densely populated megacities on Earth: near 23 million people lived in Mexico City in 2009. The variety of potential volcanic hazards at Popocatepetl is also considerable, including explosive eruptions of ash, pyroclastic flows (hot, fluid avalanches of rock fragments and gas), and debris avalanches.

This detailed astronaut photograph of the summit crater of Popocatepetl (image center) also highlights Ventorillo and Noroccidental Glaciers. Together with the ice on nearby Iztaccíhuatl Volcano and Pico de Orizaba (Mexico’s highest peak and the highest volcano in North America), Popocatepetl’s glaciers are the only mountain glaciers in tropical North America. The glaciers create yet another volcanic hazard: dangerous mudflows, or lahars, if the ice were to melt during an eruption. At the time this image was taken, steam and ash plumes were observed at the volcano. A faint white steam plume is visible against gray ash deposits on the eastern and southern flanks of the volcano.

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[dadolfo]

Great thread, great pictures.

 

[tittenman]

Great Bitter Lake, Egypt

The Great Bitter Lake is one of several lakes located along the Suez Canal, which connects the eastern Mediterranean and Red Seas. As the canal is built only to allow ships to travel in a single lane, the Great Bitter Lake is a location where ships can change their position in line (like the passing lane on the highway) before proceeding to either Port Said to the north, or the port of Suez to the south. The lake also provides an intermediate harbor for ships traversing the Canal—a journey that typically takes 14 hours end to end. Several ships, some under power and some anchored, are visible at image right.

Prior to the opening of the Suez Canal in 1869, Great Bitter Lake was a large salt flat; in the arid climate, basins rarely accumulate enough water to become true lakes. Large expanses of white and tan sandy sediments at image left and top attest to the desert conditions surrounding the lake. Located at the approximate midpoint of the Suez Canal, Great Bitter Lake is now filled with water derived from both the Red and Mediterranean Seas, and this steady influx of water balances the water lost to evaporation. The town of Fayid (also spelled as Fayed), visible along the western shore of the lake (bottom) is a tourist destination for residents of Cairo, particularly in the summer months.

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[tittenman]

Denver, Colorado, USA

Exhibiting the street grid typical of large cities in the south western USA.

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[tittenman]

Sir Bani Yas Island, United Arab Emirates

Sir Bani Yas Island is located in the Persian Gulf near the western coastline of the United Arab Emirates (UAE). Roughly 14 kilometers (9.7 miles) by 9 kilometers (6 miles), the island is the surface expression of a salt dome, which is pocket of salt minerals that balloons upward into overlying layers of sedimentary rocks.

Salt domes start during past periods of alternating wet and dry climate. A common scenario is an enclosed basin that is alternately flooded and then subjected to extreme drying. High rates of evaporation deposit thick layers of salt minerals, such as common table salt and gypsum (a chalky mineral that is a major component of wallboard). These layers are eventually buried by sediments. If the salt layers are buried deeply enough, the pressure can cause them flow. Salt has lower density than the surrounding rock, so it tends to flow upwards, pushing up the overlying layers of rock to form a dome. While many salt domes retain a cap of the youngest rock layers at the surface, in some cases the underlying salt extrudes all the way to the surface.

This astronaut photograph illustrates the varying character of surfaces on Sir Bani Yas. The central mountains of Jebel Wahid (image center) mark the location of the Sir Bani Yas salt dome. The dome has breached the surface but exposed salt, primarily gypsum, is eroded, leaving a rugged, insoluble cap made of fragments of the overlaying sedimentary and volcanic rocks. Sand and silt derived from the Jebel Wahid and surrounding gravel-covered areas form beaches along the outer edge of the island.

Sir Bani Yas Island was the personal retreat of the late Sheikh Zayed Bin Sultan Al Nahyan who was president of the UAE from 1971-2004. He established a nature preserve on the island for animals native to the Arabian Peninsula (including striped hyena, cheetah, oryx, ostrich, and gazelle) that is now open to the public. The numerous orchard plots than cover much of the island were part of a desert agricultural research program also started by the late Sheikh. Tan graded areas along the western and northeastern coast of the island (image bottom and image left) may be revegetated with additional plots or developed for other land uses.


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[CadillacD]

Love the thread.

 

[tittenman]

Volcanoes near Usulután, El Salvador

The Pacific coastline of much of Central America is marked by a line of active and quiescent volcanoes known to geologists as the Central American Volcanic Arc. The volcanoes result from the upward movement of magma generated along the subduction zone between the Cocos and Caribbean tectonic plates. Frequent earthquakes also occur along the plate boundary. This astronaut photograph includes four stratovolcanoes—a type of volcano common in active subduction zones—in El Salvador, near the midpoint of the Central American Volcanic Arc.

While all of the volcanoes shown here have been active during the Holocene Epoch (from about 10,000 years ago to the present), only the 2,130-meter- (6,990-foot-) high San Miguel (also known as Chaparrastique) has been active during historical times. The most recent activity of San Miguel was a minor gas and ash emission in 2002. The stratovolcano’s steep cone shape and well-developed summit crater are evident, along with dark lava flows. Immediately to the northwest, the truncated summit of Chinameca Volcano (also known as El Pacayal) is marked by a two-kilometer- (one-mile-) wide caldera. The caldera formed when a powerful eruption emptied the volcano’s magma chamber, causing the chamber’s roof to collapse. Like its neighbor San Miguel, Chinameca’s slopes host coffee plantations.

Moving to the west, the eroded cone of El Tigre Volcano is visible. El Tigre formed during the Pleistocene Epoch (1.8 million to about 10,000 years ago), and it is likely the oldest of the stratovolcanoes in the image. Usulután Volcano is directly southwest of El Tigre. While the flanks of Usulután have been dissected by streams, the mountain still retains a summit crater that is breached on the eastern side. Several urban areas—recognizable as light gray to white regions contrasting with green vegetation and tan fallow agricultural fields—are located in the vicinity of these volcanoes, including the town of Usulután (lower left) and Santiago de Mara (upper left).

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[tittenman]

Ice Floes off the Northeastern Tip of Urup Island, Russia

From space, it is sometimes difficult to tell where land ends and sea ice begins in the southern Sea of Okhotsk. This is particularly evident in this detailed astronaut photograph of the north eastern tip of Urup Island, one of the many islands in the Kuril chain, which extends from northern Japan to the Kamchatka Peninsula of Russia.

The approximately 120-kilometre-long island extends to the south west from the point illustrated in the image; like the other Kuril Islands, Urup was formed from volcanic processes along the active subduction boundary between the Pacific and Okhotsk tectonic plates. The north eastern tip of the island and three small islands to the north east are recognizable by their uniform cover of white snow and shadowing along the north western coastlines.

Sea ice that formed to the north in the Sea of Okhotsk has been piled up against the islands by prevailing north westerly winds, forming an irregular mass connecting the islands (image centre). The orientation of patchy low clouds over Urup Island (image lower left) also suggests that north westerly winds are present.

Smaller ice floes are breaking off from the main ice mass at gaps between the islands and forming finger like projections of ice fragments that extend to the south east (image lower right). Surface winds may be channelled through these gaps and accelerated, hastening the breakup and movement of ice.



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[Skyraider22]

Ice Floes off the Northeastern Tip of Urup Island, Russia

From space, it is sometimes difficult to tell where land ends and sea ice begins in the southern Sea of Okhotsk. This is particularly evident in this detailed astronaut photograph of the north eastern tip of Urup Island, one of the many islands in the Kuril chain, which extends from northern Japan to the Kamchatka Peninsula of Russia.

The approximately 120-kilometre-long island extends to the south west from the point illustrated in the image; like the other Kuril Islands, Urup was formed from volcanic processes along the active subduction boundary between the Pacific and Okhotsk tectonic plates. The north eastern tip of the island and three small islands to the north east are recognizable by their uniform cover of white snow and shadowing along the north western coastlines.

Sea ice that formed to the north in the Sea of Okhotsk has been piled up against the islands by prevailing north westerly winds, forming an irregular mass connecting the islands (image centre). The orientation of patchy low clouds over Urup Island (image lower left) also suggests that north westerly winds are present.

Smaller ice floes are breaking off from the main ice mass at gaps between the islands and forming finger like projections of ice fragments that extend to the south east (image lower right). Surface winds may be channelled through these gaps and accelerated, hastening the breakup and movement of ice.



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Wow it looks likes two planes dogfighting in the air.Great picture:thumbsup:

 

[tittenman]

Panian Mine, Semirara Island, Philippines

This detailed astronaut photograph provides a rare cloud-free view of the northern end of Semirara Island, which is located approximately 280 kilometers to the south of Manila in the Philippines. The northern part of the island is dominated by the Panian Coalfield, the largest of three coalfields on the island. Most of the coal is used for energy generation in the Philippines, with some exported to India and China.

The Panian coalfield is being mined using open-pit methods. The rock and soil above the coal layers (or seams) is known as overburden. Overburden is removed from the pit and heaped into piles, several of which ring the northern half of the pit. Several of the dark coal seams are visible along the sunlit southern wall of the pit (these may be more visible in the larger image version). Plumes of sediment from the overburden piles enter the Sulu Sea along the northern and eastern coastline of the island.

The Semirara coalfields formed from 12–23 million years ago along what was then a coastal plain—similar to the current geologic environment of the southeastern Gulf Coast of the United States. Organic materials were deposited in sequences of sandstone and mudstone, which were then covered by limestones as the environment became progressively more marine. Over geologic time, increased pressure from the overlying rocks changed the layers of organic material into coal.



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[tittenman]

Gulf of Mexico Oil Spill Observed From the International Space Station

On April 20, 2010, the oil rig Deepwater Horizon suffered an explosion and sank two days later. Shortly thereafter, oil began leaking into the Gulf of Mexico from ruptured pipes deep on the ocean floor. NASA satellites have been tracking the growth of the oil spill as it has spread towards the northern Gulf Coast. This detailed astronaut photograph from May 4 provides a different viewing perspective on the ongoing event. The image is oblique, meaning that it was taken from a sideways viewing angle from the International Space Station (ISS), rather than from a “straight down” (or nadir) view, which is typical of automated satellite sensors. The view in this image is towards the west; the ISS was located over the eastern edge of the Gulf of Mexico when the image was taken.

The Mississippi River Delta and nearby Louisiana coast (image top) appear dark in the sunglint that illuminates most of the image. Sunglint is caused by sunlight reflecting off the water surface—much like a mirror—directly back towards the astronaut observer on the Space Station. The sunglint improves the identification of the oil spill. Oil on the water smoothes the surface texture, and the mirror-like reflection of the Sun accentuates the difference between the smooth, oil-covered water (dark to light gray ) and the rougher water of the reflective ocean surface (colored silver to white). Wind and water currents patterns have modified the oil spill’s original shape into streamers and elongated masses. Among the coastal ecosystems threatened by the spill are the Chandeleur Islands (image right center).

Other features visible in the image include a solid field of low cloud cover at the lower left corner of the image. V-shaped ship or boat wakes are visible in the large image. Wave patterns at image lower right are most likely caused by tidal effects.


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[tittenman]

Nevado del Ruiz Volcano, Colombia

Nevado del Ruiz Volcano (image center) is located approximately 140 kilometers (87 miles) to the northwest of Colombia’s capital, Bogotá. Covering over 200 square kilometers (77 square miles), Nevado del Ruiz is a large stratovolcano—a cone-shaped volcano built from successive layers of lava, ash, and pyroclastic flow deposits. The volcano is fed by magma generated above the boundary between the subducting Nazca and overriding South American tectonic plates. The historical record of eruptions at the volcano extends back to 1570, but the most damaging eruption in recent times took place in 1985.

On the November 13, 1985, an explosive eruption at the Arenas Crater (image center) melted ice and snow at the summit of the volcano. Mudflows (lahars) swept tens of kilometers down river valleys along the volcano’s flanks, killing at least 23,000 people. Most of the fatalities occurred in the town of Armero which was completely inundated by lahars. Eruptive activity at Nevado del Ruiz may have occurred in 1994, but this is not confirmed.

The volcano’s summit and upper flanks are covered by several glaciers that appear as a white mass surrounding the 1-kilometer- (0.6-mile-) wide Arenas Crater; meltwater from these glaciers has incised the gray to tan ash and pyroclastic flow deposits mantling the lower slopes. A well-defined lava flow is visible at image lower right. This astronaut photograph was taken at approximately 7:45 a.m. local time, when the Sun was still fairly low above the horizon, leading to shadowing to the west of topographic high points.

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[tittenman]

Kata Tjuta (The Olgas), Northern Territory, Australia

Located in the Northern Territory of Australia, Uluru-Kata Tjuta National Park hosts some of the world’s most spectacular examples of inselbergs, or isolated mountains. The most famous of these inselbergs is Uluru (also known as Ayers Rock). An equally massive inselberg located approximately 30 kilometers (20 miles) to the northwest is known as Kata Tjuta. Like Uluru, this is a sacred site to the native Anangu or Aboriginal people. An English-born explorer named the highest peak Mount Olga, with the entire grouping of rocks informally known as “the Olgas.” Mount Olga has a peak elevation of 1,069 meters (3,507 feet) above sea level, making it 206 meters (676 feet) higher than Uluru.

In this astronaut photograph, afternoon sunlight highlights the rounded summits of Kata Tjuta against the surrounding sandy plains. Sand dunes are visible at image lower left, while in other areas (image bottom and image right) sediments washed from the rocks have been anchored by a variety of grasses and bushes adapted to the arid climate. Green vegetation in the ephemeral stream channels that drain Kata Tjuta (image top center) provides colorful contrast with the red rocks and surrounding soils. Large gaps in the rocks (highlighted by shadows) are thought to be fractures that have been enlarged due to erosion.

Kata Tjuta is comprised of gently dipping Mount Currie Conglomerate, a sedimentary rock that includes rounded fragments of other rock types (here, primarily granite with less abundant basalt and rhyolite in a coarse sandy matrix. Geologists interpret the Mount Currie Conglomerate as a remnant of a large fan of material rapidly eroded from mountains uplifted approximately 550 million years ago. Subsequent burial under younger sediments consolidated the eroded materials to form the conglomerate exposed at the surface today.


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[tittenman]

Panorama of Central Andes Mountains, Salar de Arizaro, Argentina

This panorama was taken by an astronaut looking southeast across the South American continent when the International Space Station (ISS) was almost directly over the Atacama Desert near Chile’s Pacific coast. The high plains (3000–5000 meters, or 13,000–19,000 feet) of the Andes Mountains, also known as the Puna, appear in the foreground, with a line of young volcanoes (dashed line) facing the much lower Atacama Desert (1000–2000 m elevation). Several salt-crusted dry lakes (known as salars in Spanish) occupy the basins between major thrust faults in the Puna. Salar de Arizaro (foreground) is the largest of the dry lakes in this view. The Atlantic Ocean coastline, where Argentina’s capital city of Buenos Aires sits along the Río de la Plata, is dimly visible at image top left.

Near image center, the transition (solid line) between two distinct geological zones, the Puna and the Sierras Pampeanas, creates a striking landscape contrast. Compared to the Puna, the Sierras Pampeanas mountains are lower in elevation and have fewer young volcanoes. Sharp-crested ridges are separated by wide, low valleys in this region. The Salinas Grandes—ephemeral shallow salt lakes—occupies one of these valleys. The general color change from reds and browns in the foreground to blues and greens in the upper part of the image reflects the major climatic regions: the deserts of the Atacama and Puna versus the grassy plains of central Argentina, where rainfall is sufficient to promote lush prairie grass, known locally as the pampas. The Salinas Grandes mark an intermediate, semiarid region.

What accounts for the changes in topography between the Puna and the Sierras Pameanas? The geology of this part of the Andes is a result of the eastward subduction of the Nazca tectonic plate underneath South America. Seismic data suggest that beneath the Puna, the Nazca Plate is dipping down steeply. Beneath the Sierras Pampeanas zone, however, the underlying Nazca plate is almost horizontal. The levelness may be due to the subduction of a submarine mountain range known as the Juan Fernández Ridge. In the simplest terms, ridges are topographic highs that are difficult to stuff down into the subduction zone, and that has profound effects on the volcanism and structures of the overlying South America plate.


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