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Volcanism attributed to the hotspot began approximately 15 million years ago in the western portion of the Plain, with lava fields becoming younger to the east. With lavas erupted approximately 4,100 years ago, Hell’s Half Acre is one of the youngest lava fields. This pattern—older lavas in the west and younger lavas in the east—reveals the direction the plate was moving. (If the plate had been moving the opposite direction over the hotspot, areas to the east would have encountered it first, and the eastern lavas would have been older.) Today, the center of hotspot volcanism is located in Yellowstone National Park, where it feeds the extensive geyser system.
Portions of the Hell’s Half Acre Lava Field are a National Natural Landmark and Wilderness Study Area. This detailed astronaut photograph illustrates the forbidding landscape of the basaltic lava field. The complex ridge patterns of the black to grey-green flow surfaces include both smooth, ropy Pahoehoe and blocky ’A’a lava. Regions of tan soil surrounded by lava are known as kipukas. These “islands” are windows onto the older underlying soil surface. The kipukas are used for agriculture (both crops and grazing); several green fields are visible to the northwest of Interstate Highway 15 (image right). Light to dark mottling in the kipukas is most likely due to variations in moisture and disturbance by agricultural activities.
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This portion of the Rocky Mountains also hosts the Niwot Ridge Long Term Ecological Research (LTER) Site. Part of the National Science Foundation’s LTER program, the Niwot Ridge site is used for studies of climate interactions with tundra and alpine ecosystems. Niwot Ridge is visible in this image as a large eastward spur off the central spine of the mountains (center right). The entire Niwot LTER site is located at elevations higher than 3000 meters, and it includes an active cirque glacier and glacial landforms, tarns (glacial lakes), and permafrost.
Lake Granby, located to the west of the Great Divide, is a reservoir on the Colorado River. It is the second-largest manmade body of water in the state of Colorado. Storage of water began in 1949. Today, the lake is popular location for fishing, boating, and camping.
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The present day village of Abusir is clearly visible as a grey-white irregular patch of urban surfaces that contrasts with green agricultural fields of the Nile Delta and tan desert sands and gravels to the west. The historic necropolis of Abusir is located to the northwest of the village at image top center. Three pyramids are readily visible in the image, all built by kings of the Fifth Dynasty (2,465–2,323 BC): Sahure, Niuserre, and Neferirkare. The site of Abusir was likely chosen due to the existence of a lake—now dry—that facilitated transport of building materials for the pyramids and other structures.
The northern portion of the large necropolis of Saqqara is also visible to the south-southwest (image right) of the village of Abusir. The largest pyramid in this complex is that of Djoser, a king of the Third Dynasty (2,650–2,575 BC). Other readily visible pyramids include that of Userkaf (Fifth Dynasty) and Teti (Sixth Dynasty: 2,323–2,150 BC), attesting to the long history of use of the Saqqara necropolis. Astronauts have also taken detailed imagery of other necropolis sites along the Nile River delta such as Giza and Dashur.
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The caldera has the classic shape: it formed as overlying rock and soil collapsed into the magma chamber after it was emptied by powerful eruptions. Shadows in this astronaut photograph throw the steep southern wall of the outer crater into sharp relief. Following the formation of the main outer crater, a second inner crater (image center) formed, most likely due to later uplift and eruption of fresh magma moving towards the surface. This inner crater is filled with water.
Because the walls of the inner crater are higher than the adjacent caldera floor, precipitation flowing inwards from the outer crater walls do not enter the inner crater lake. White stream bed sediments (image center) show the water pathway around the inner crater to a second lake located along the northeast wall of the outer crater. While Jebel Marra is high enough (3,042 meters) to have a temperate climate and high precipitation, these lakes may be fed by hot springs as well as rainwater. The inner crater lake has a mottled appearance caused by sunglint—light reflected off a roughened water surface back towards the astronaut onboard the International Space Station.
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The image covers much of one of the most densely populated parts of the United States, with about 20 million people within the parts of five counties shown here. The dense urban areas appear gray, with the largest conurbation (geographers’ term for an aggregation or continuous network of urban communities) in the north of the view, spanning the area of Long Beach-Los Angeles-San Bernardino. A smaller conurbation zone appears around San Diego-Tijuana in the south. Major highways with their associated strip development snake through these dense urban areas.
The topography of Southern California is defined by long, linear features that trace the path of large transform faults. [At transform faults, two blocks of the Earth’s crust (or two separate tectonic plates) slide past each other horizontally.] These faults, including the Elsinore and San Jacinto Faults seen here, are part of the San Andreas Fault System, the broad zone of tectonic faults that occurs at the plate boundary between North America to the east and the Pacific Ocean to the west.
The Elsinore Fault marks the steep eastern scarp of the Santa Ana Mountains as well as the precipitation boundary between the wetter mountains and the drier deserts to the east. The rainfall difference is reflected in the darker appearance (more vegetation) of the mountains and coastal regions. Inland of the mountains, climates are far drier, and the natural vegetation is scrubby and much less dense, which allows brown and yellow soils to show through.
Although the mountains are wetter than inland areas, the climate overall is a dry one, and water management is a critical issue for the large urban areas of the state. Several reservoirs that are visible east of the Santa Ana Mountains provide water for both cities and agriculture in southern California. According to the California Department of Water Resources, the state is facing the worst water crisis in its history, and in June 2008, the governor declared a statewide drought, including a state of emergency for the Central Valley.
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Astronauts aboard the International Space Station (ISS) routinely observe intensive land use and document their observations through imagery so that changes can be identified. These two photographs of the Bolivian forest along the Rio Parapetí in Bolivia (south of Santa Cruz, not shown) show different stages of the clearing process and agricultural field development. The top image, a wide panoramic view looking toward the west and the Andean foothills, was taken from the Space Shuttle in November 1995. The clearing efforts were just getting underway, evidenced by the crosshatched and herringbone pattern of clearing north of the river. On the south side of the river, old, abandoned stream channels show up as lighter regions with lesser forest cover.
The bottom view, a composite of two images taken from the ISS, provides a more detailed view of today’s landscape, showing completely cleared regions that stretch for more than 10 kilometers. For scale, the white line is about 12 kilometers (7.5 miles). The geographic area covered in the 2008 view is approximated on the top image by the white box.
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Astronauts aboard the International Space Station (ISS) routinely observe intensive land use and document their observations through imagery so that changes can be identified. These two photographs of the Bolivian forest along the Rio Parapetí in Bolivia (south of Santa Cruz, not shown) show different stages of the clearing process and agricultural field development. The top image, a wide panoramic view looking toward the west and the Andean foothills, was taken from the Space Shuttle in November 1995. The clearing efforts were just getting underway, evidenced by the crosshatched and herringbone pattern of clearing north of the river. On the south side of the river, old, abandoned stream channels show up as lighter regions with lesser forest cover.
The bottom view, a composite of two images taken from the ISS, provides a more detailed view of today’s landscape, showing completely cleared regions that stretch for more than 10 kilometers. For scale, the white line is about 12 kilometers (7.5 miles). The geographic area covered in the 2008 view is approximated on the top image by the white box.
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Astronauts aboard the International Space Station (ISS) routinely observe intensive land use and document their observations through imagery so that changes can be identified. These two photographs of the Bolivian forest along the Rio Parapetí in Bolivia (south of Santa Cruz, not shown) show different stages of the clearing process and agricultural field development. The top image, a wide panoramic view looking toward the west and the Andean foothills, was taken from the Space Shuttle in November 1995. The clearing efforts were just getting underway, evidenced by the crosshatched and herringbone pattern of clearing north of the river. On the south side of the river, old, abandoned stream channels show up as lighter regions with lesser forest cover.
The bottom view, a composite of two images taken from the ISS, provides a more detailed view of today’s landscape, showing completely cleared regions that stretch for more than 10 kilometers. For scale, the white line is about 12 kilometers (7.5 miles). The geographic area covered in the 2008 view is approximated on the top image by the white box.
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The snow-covered peaks clearly delineate the tree line at an elevation of around 3,350 meters (11,000 feet). Annual average snowfall ranges between 7.21 meters (284 inches) at Copper Mountain to 7.62 meters (300 inches) at Breckenridge. Before recreation became the main industry, miners were attracted to the area in the mid-1800s following discoveries of gold, silver, lead, and zinc. The towns of Breckenridge and Wheeler Junction (at the base of Copper Mountain ski area) were born out of the surge to settle the West during the Pike’s Peak Gold Rush.
While there was snow on the peaks of the Tenmile Range when this astronaut photo was captured on October 24, 2008, the months of October and November 2008 saw little accumulation in the area of Breckenridge. The situation changed in early December 2008, when more snow fell in eight days than in the preceding two months. The late, but significant, snowfall boosted the snow pack back to expected levels for that time of year. Snow pack in the Rockies is important not only for recreation, but also as a major part of the water supply for ecosystems and people.
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The creation of a national monument at the site has given scientists the chance to document and study how forests generate from such a major disturbance. Astronaut photographs, such as this one taken on October 28, 2008, collected over nearly three decades have helped to tell the story of the eruption and its long-term effects. Taken from an oblique (side angle) perspective, this photo has a striking three-dimensional quality. The astronaut was photographing the mountain from a vantage point in the east (i.e., looking west.) Mount St. Helens is at image left, and the blast/debris zone is to the right.
Nearly three decades after the eruption, the impact on the forest in the blast zone is still obvious. South of the mountain, lush green forests cover the landscape, while north of the mountain, vegetation remains sparse, particularly on higher elevations. Different areas of the blown down or buried forests are recovering at different speeds. Recovery is slower in forests that had been clear cut before the eruption, and faster in places where vegetation was protected from erosion, wind, drying, and temperature extremes by fallen giants—old growth Douglas fir trees blown down in the eruption—or by snow pack.
In the six years following the catastrophic eruption, more than 120 million cubic yards of lava oozed from vents in the summit crater, building a lava dome that rose to 876 feet above the crater floor. Dome growth stopped for many years, and then resumed in 2004. According to the USGS Cascades Volcano Observatory Website, “From October 2004 to late January 2008, about 125 million cubic yards of lava had erupted onto the crater floor to form a new dome.” In July 2008, after five months during which no new evidence of eruptive activity was detected, geologists declared the eruption over.
