1. Citizen Science with Night Images

    Since the Mercury missions of the early 1960s, astronauts have taken more than 1.8 million photographs of the Earth from orbit, and about one-third of them have been taken at night. These images are freely available to the public through The Gateway to Astronaut Photography of Earth, which opens up a great opportunity for citizen science.

    Photographs taken by astronauts on the International Space Station (ISS) are the highest-resolution night imagery available, asserts William Stefanov, NASA’s associate program scientist for Earth observations from the space station. While satellites collect data on a more consistent basis, astronauts with cameras can often get a sharper view. What they cannot always get is the exact location they are viewing.

    Astronauts captured this photograph of south-central Japan on August 16, 2014, as the space station was passing over the western Pacific Ocean. The brightest spot in the center of the photo is the port city of Nagoya, the third largest metropolitan area in Japan. To the left, the lights of the Osaka and Wakayama urban areas pierce through clearings in the cloud cover. (Note that north is to the upper right in this image.) Much of the scene is obscured by cloud cover, though a lightning storm lights up the clouds to the north. Note how the lightning is much whiter than the yellow and orange hues of city lights.

    The Complutense University of Madrid (UCM) is leading Cities at Night, a citizen-science project to catalog such nighttime images. So far, hundreds of volunteers have classified nearly 20,000 images for the three-part project. In part one, “Dark Skies,” people are asked to sort photos based on whether they show cities, stars, or other objects. In “Night Cities,” participants use their knowledge of local geography to identify points of light and match them to positions on maps.

    Finally, “Lost at Night” asks people to identify the cities within a 310-mile circle. “We don’t know which direction the astronaut pointed the camera, only where the station was at the time the image was taken,” explains Alejandro Sanchez, a graduate student at UCM. “Some images are bright cities but others are small towns. It is like a puzzle with 300,000 pieces.”

    Congratulations to Bruce Boucek, who was the first to identify the cities in this puzzler image. James Titmas, Yumiko Stettler, and Jyo Sano also correctly identified the Nagoya area.

    1. References and Related Reading

    2. Complutense University of Madrid (2014) Cities at Night. Accessed August 29, 2014.
    3. NASA (2014, August) Space Station Sharper Images of Earth at Night Crowdsourced for Science. Accessed August 29, 2014.
    4. NASA Earth Observatory (2008, April 22) Cities at Night: The View from Space.
    5. NASA Earth Observatory (2012) Earth at Night 2012.

    Astronaut photograph ISS040-E-98889 was acquired on August 16, 2014, with a Nikon D3S digital camera using an effective 42 millimeter lens, and is provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit, Johnson Space Center. The image was taken by the Expedition 40 crew. It has been cropped and enhanced to improve contrast, and lens artifacts have been removed. The International Space Station Program supports the laboratory as part of the ISS National Lab 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. Caption by Mike Carlowicz, partly based on a release by Melissa Gaskill, NASA Johnson Space Center.

    Instrument(s): ISS - Digital Camera
  2. Hurricane Cristobal

    In the early afternoon on August 27, 2014, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aquasatellite acquired this natural-color image of Hurricane Cristobal. At the time, the storm had maximum sustained winds of 70 knots (80 miles per hour), making it a category 1 hurricane.

    Read more about Cristobal on the NASA Hurricane Page.

    NASA image by Jeff Schmaltz, LANCE/EOSDIS Rapid Response. Caption by Mike Carlowicz.

    Instrument(s): Aqua - MODIS
  3. Still Huffing and Puffing

    Nine months after a new island broke through the surface of the western Pacific Ocean, the volcanic eruption at Nishino-shima continues. The tiny new volcanic island (“Niijima” in Japanese) merged into Nishino-shima last winter and continued to grow. Steady flows of lava are enlarging the merged island, which is now 1.39 square kilometers (0.54 square miles).

    The Operational Land Imager on Landsat 8 captured this image of Nishino-shima on August 21, 2014. Part of the Ogasawara chain, the island lies about 1,000 kilometers (600 miles) south of Tokyo at 27°14’ North, 140°52’ East. In the natural-color image, a plume of volcanic gases and steam rises from the island; such plumes can promote the formation of clouds, though most of the marine cumulus in the wider scene probably formed in the usual way. Off the northeast shore, submarine volcanic activity discolors the water with gas, minerals, and sediment.

    According to observers, lava is still flowing on the east side of the island at a rate of 200,000 cubic meters per day and could eventually lead to some instability. “If lava continues to mount on the eastern area, it will be deposited on steep slopes,” wrote University of Tokyo scientist Fukashi Maeno in an email to Earth Observatory. “This could cause instability on the slope, so a partial collapse of the island may occur. We need to carefully observe the growth process.”

    After flights on August 26 (photo below), Japan Coast Guard officials told local media that there is also a mound of congealed lava inside a volcanic vent on the north side of the island. The officials suggested such a mound could “seal off passages of magma and raise interior pressure if it continues to grow, resulting in a large-scale explosion.” Though no such eruption is imminent, the Coast Guard warned mariners to keep their distance from the island.

    “The ideal way to monitor and avoid a natural disaster is to set up a new tsunami and earthquake detection system near the island,” Maeno told The Asahi Shimbun. “But it’s impossible for anyone to land on the island in the current situation.”

    To view aerial photographs of the growing island, visit this Japan Coast Guard page.

    1. References and Related Reading

    2. Agence France Presse, via Australian Broadcasting Corporation (2014, August 20) Japanese island formed by volcanic eruption could collapse and cause a tsunami, scientists warn. Accessed August 28, 2014.
    3. The Asahi Shimbun (2014, August 28) Coast guard warns explosion could occur on volcanic islet in Ogasawara chain. Accessed August 28, 2014.
    4. The Asahi Shimbun (2014, August 21) Growing volcanic island in Ogasawara may collapse, triggering tsunami.Accessed August 28, 2014.
    5. Eruptions Blog, Wired (2013, December 27) Nishino-shima. Accessed August 28, 2014.
    6. Global Volcanism Program, Smithsonian Institution (2014, January) Nishino-shima. Accessed August 28, 2014.
    7. NASA Earth Observatory (2013, December 18) New Island in the Ring of Fire.

    NASA Earth Observatory image by Jesse Allen, using Landsat data from the U.S. Geological Survey. Aerial photographs courtesy of the Hydrographic and Oceanographic Department, Japan Coast Guard. Caption by Mike Carlowicz, with reporting from Adam Voiland.

    Instrument(s): PhotographLandsat 8 - OLI


  4. Iron Mines in Michigan

    In 1844, government surveyors were exploring rugged, lake-filled terrain near Negaunee, Michigan, when they noticed their compasses swung erratically in certain areas. It did not take long to determine why: ancient Precambrian rock layers in the area were laced with bands of iron ore. The surveyors had discovered the Marquette Iron Range (called the Negaunee Iron Formation by geologists), and the area would eventually become one of the most productive sources of iron in the United States.

    Within a few years, several companies were competing to mine, ship, and process the magnetite and hematite ore in the area, which was so abundant and accessible that chunks could be pulled off the surface and shipped directly to steel mills with little or no processing. But by the 1950s, most of the easily accessible ore with high concentrations of iron was gone, and mining companies had to dig much deeper and develop new techniques to extract and concentrate iron from lower-grade ore.

    Today, mine operators in Michigan’s Upper Peninsula are generally after taconite, a low-grade ore that was once considered waste rock. To make it usable, mining companies blast it into small pieces with explosives, grind it into powder with powerful machinery, and then use magnets or flotation techniques to separate the iron minerals out from the surrounding rock. Iron-rich powder is then mixed with water and clay into a slurry that is shaped into pellets, heated, dried, and shipped to steel mills. The pulverized waste rock—known as tailings—is loaded into water-filled retention basins, where it eventually settles to the bottom and re-enters the rock cycle.

    The Operational Land Imager (OLI) on Landsat 8 captured this image of iron mines in northern Michigan on September 11, 2013. Although the mined areas look like one facility from a satellite perspective, there are two separate mines in this scene. The Empire Mine, which produces about 5.5 million tons of magnetite each year, is on the west side of the complex; Tilden Mine, which produces about 8 million tons of hematite and magnetite each year, is just to the east.

    Exposed rock and dirt in the mines appear gray compared to the surrounding forest. Large pits, piles of rock, processing facilities, roads, and railroad tracks are visible within both mines. The water in the tailings basin and water reuse pond serving Tilden Mine is orange due to its high concentration of hematite, a mineral that often has a rusty brown color. In contrast, the water in the tailings basin for Empire Mine is blue because that mine only produces magnetite. You can also see Palmer and West Ishpeming, nearby towns where many mine employees live.

    The two mines are boons for the local economy, generating about $775 million in economic activity every year and supporting 1,600 jobs, according to Cliffs Natural Resources, the company that operates the two mines. However, the mines also have significant environmental impacts. For instance, a report released by Michigan’s Department of Environmental Quality found that sediment in Goose Lake sediment and in some nearby streams have elevated levels of selenium due to mining. Though essential to life, selenium can be toxic to wildlife in high concentrations. In response to the elevated selenium levels, environmental authorities have issued fish consumption advisories for several waterways near the mines.

    NASA Earth Observatory image by Jesse Allen and Kevin Ward, using Landsat data from the U.S. Geological Survey. Caption by Adam Voiland.

    Instrument(s): Landsat 8 - OLI
  5. Curiosities of the Danakil Depression

    Like some fantastical land conjured by a storyteller, Ethiopia’s Danakil Depression (or Afar Depression) exhibits some uncommon wonders: lava that burns blue, bright yellow hot springs, and lakes of bubbling mud. These otherworldly oddities are all manifestations of a tectonic process called continental rifting. In other words, the Earth is pulling apart at the seams here.

    In northeastern Africa, the Arabian, Somali, and Nubian (or African) plates are separating, thinning Earth’s crust as they pull apart. Part of the Danakil Depression, for instance, lies between the Danakil Alps (east) and the Ethiopian Plateau (west), which were once joined until the rifting process tore them apart. The land surface is slowly sinking, and Danakil Depression will someday fill with water as a new ocean or great lake is born. But for now, the region is full of other interesting liquids.

    Acquired on June 27, 2014, the Landsat 8 image above shows a few of the diverse and compelling features of the Danakil Depression. Chief among them is Gada Ale, the northernmost volcano in the Erta Ale volcanic range. Gada Ale is a 287-meter (942-foot) stratovolcano built of lava and ash, and it has a crater lake full of boiling mud and sulfurous gases. Basalt lava from the volcano paints the surrounding terrain a dark hue, with the youngest flows being the darkest colors in the satellite image.

    Just southwest of Gada Ale, a 2-kilometer-wide salt dome has pushed ancient lava flows up to heights of 100 meters (330 feet). North of Gada Ale, a salt lake (Lake Karum) lies 116 meters (380 feet) below sea level. To the south lies the Catherine Volcano, a 120-meter (400-foot) circular shield surrounded by a tuff ring (an amalgamation of volcanic ash). With gently sloping sides of basaltic lava, the volcano has been dated at less than one million years old. In the center of that tuff ring is a small, salty lake fed by thermal springs.

    The Afar people have survived in this unforgiving region for at least 2,000 years, mining and selling the plain’s abundant salt, which was once used as currency in Ethiopia. The harsh desert also has created an ideal exposure for the tectonic rifting—a process that often occurs on the recesses of the ocean seafloor or elsewhere on land where younger sedimentary rocks obscure the geologic record.

    The first modern studies of the Danakil Depression did not occur until the winter of 1967–68, when a French-Italian expedition took place. At the time, developments in plate tectonic theory made the region a research hotspot. The tectonic processes visible in the Danakil Depression are like “the development of the proto-Atlantic by rifting of Pangea,” scientist Enrico Bonatti wrote in a 1971 Science article. Competing interpretations of the region’s geology and controversies about the tectonic implications were kicked about in the scientific literature for years.

    1. References

    2. Barberi, F., and Varet, J. (1970, December 1) The Erta Ale Volcanic Range (Danakil Depression, Northern Afar, Ethiopia). Bulletin Volcanologique 34 (4) 848–917.
    3. Bonatti, E., et al, (1971, April 30) Final Desiccation of the Afar Rift, Ethiopia. Science 172 (3982) 468–69.
    4. Global Volcanism Program, Smithsonian Institution (2013) Gada Ale. Accessed August 15, 2014.
    5. NASA Earth Observatory (2014, July 27) Lava Around Lake Afrera.
    6. NASA Earth Observatory (2005, September 6) Afar Depression, Ethiopia.
    7. Tazieff, H., et al, (1972, January 21) Tectonic Significance of the Afar (or Danakil) Depression. Nature 235 (5334) 144–47.
    8. Tesfaye, S. et al, (2003, September 1) Early Continental Breakup Boundary and Migration of the Afar Triple Junction, Ethiopia. Geological Society of America Bulletin 115 (9), 1053–67.
    9. Wolfenden, E. et al, (2004, July 30) Evolution of the Northern Main Ethiopian Rift: Birth of a Triple Junction. Earth and Planetary Science Letters 224 (1–2), 213–28.

    NASA Earth Observatory image by Jesse Allen and Robert Simmon, using Landsat data from the U.S. Geological Survey. Caption by Laura Rocchio.

    Instrument(s): Landsat 8 - OLI
  6. Fires in California

    With most of California in the grips of an unusually severe drought, the state’s fire management authorities are prepared for the worst. The state’s forests and grasslands are parched and primed to burn. All it would take is one stray cigarette or lightning strike—combined with strong winds and hot weather—to unleash a blaze so large or damaging that it ends up in the record books. And yet, so far, the 2014 season has been surprisingly free of such headline-grabbing fires.

    Californians have certainly seen plenty of fire in 2014. A total of 4,172 fires have burned 83,282 acres (33,703 hectares) since the beginning of the year—far more than usual. For comparison, during the previous five seasons, an average of 3,198 fires burned 57,444 acres (23,247 hectares) by mid-August, according to California Department of Forestry and Fire Protection statistics.

    But none of the 2014 blazes have grown to be particularly large or destructive. California’s list of largest fires includes several blazes that destroyed more than 250,000 acres (100,000 hectares), such as the Rim Fire in 2013, the Rush Fire in 2012, and the Cedar Fire in 2003. The largest in 2014 has been the Bald fire in Lassen National Forest, which charred about 40,000 acres (16,000 hectares). In 2014, several fires have destroyed structures here and there, but none have devastated entire neighborhoods. The state’s historical list of most damaging fires includes events that destroyed 1,000 structures or more.

    The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this image of wildfire activity in California on August 24, 2014. Red outlines indicate hot spots where MODIS detected unusually warm surface temperatures associated with fires. The Happy Camp ComplexMan Fire and July Complex are visible in northern California. Most of the large fires have been in northern California, while central and southern California have been largely free of fire to date.

    NASA image courtesy Jeff Schmaltz, LANCE/EOSDIS MODIS Rapid Response Team at NASA GSFC. Caption by Adam Voiland.

    Instrument(s): Aqua - MODIS
  7. Kulundra Steppes, Russia

    In June 2014, the crew aboard the International Space Station (ISS) called down to Houston to ask for an explanation of this strange pattern of spikes crossing the Kulunda Steppe in central Russia. The “spikes” are a prominent visual feature when the ISS is at the top of its orbit (52 degrees north, the highest latitude flown over by the spacecraft). Scientists at NASA’s Johnson Space Center were able to provide an answer.

    The linear zones in the image are gentle folds in the surface rocks of the area; they lie slightly lower than the surrounding, lighter-toned agricultural lands. The dark zones are forested with pines and dotted with salt-rich lakes. The image shows a distance of a little more than 300 kilometers (200 miles) from left to right, and the forested spikes are nearly that length.

    The green floodplain on the right includes the famous Ob River, the westernmost of Siberia’s three great rivers (the others being the Yenisei and Lena). The Ob flows north for another 2,000 kilometers (1,200 miles) to the Arctic Ocean.

    The city of Barnaul lies on the banks of the river, with riverboat, air, and rail links to the rest of the country. With a population of 612,000 people, Barnaul is a major center of industry, trade, and culture in Siberia. A broader image of the Kulunda geology and the Ob River in winter can be seen here.

    Astronaut photograph ISS040-E-27042 was acquired on June 30, 2014, with a Nikon D3S digital camera using an 80 millimeter lens, and is provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit, Johnson Space Center. The image was taken by the Expedition 40 crew. It has been cropped and enhanced to improve contrast, and lens artifacts have been removed. The International Space Station Program supports the laboratory as part of the ISS National Lab 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. Caption by M. Justin Wilkinson, Jacobs at NASA-JSC.

    Instrument(s): ISS - Digital Camera
  8. Sea Ice in the Greenland Sea

    On August 18, 2014, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this natural-color image of ice in the Greenland Sea. (The center of the image is roughly 77.5° north latitude and 9° west longitude.) Thick tongues of glacial ice stretch over the fjords on the Greenland coast at image left. Farther offshore, loosely packed floes of sea ice make swirling, paisley patterns in the Fram Strait between northeastern Greenland and Svalbard. The swirls of ice are caused by winds and currents that steer the ice around the sea.

    Sea ice in the Arctic Ocean and surrounding seas is now approaching its annual minimum extent, which typically occurs in September. In 2014, as in several recent years, the Greenland Sea has seen less ice and thinner ice passing through its waters. Walt Meier, a sea ice specialist at NASA’s Goddard Space Flight Center, noted: “Ice usually extends quite a bit further south in this region because the currents push older, thicker ice out from the Arctic. Even in the warmer, more southern region, it takes a while for that ice to melt. We’ve seen a few years recently with very little ice in the Greenland Sea. Thinner ice may be one factor, but it seems like the biggest issue is that winds have been blowing perpendicular to Fram Strait and limiting the amount of ice exiting the Arctic Ocean.”

    As of August 19, 2014, sea ice covered about 5.98 million square kilometers (2.31 million square miles) of Arctic waters. That extent is comparable to the same date in 2013, and above the record-setting low year of 2012. Still, sea ice is nearly 20 percent below the 1981 to 2010 average, which was 7.04 million square kilometers (2.72 million square miles). In an August 19 blog post, researchers at the National Snow and Ice Data Center wrote:

    Ice extent remains below average everywhere, except near Franz Joseph Land and in the northern part of the Barents Sea. Extent is particularly low in the Laptev Sea, where open water now extends to about 85 degrees latitude, less than 560 kilometers (350 miles) from the North Pole. This is the one region of the Arctic where ice loss has been exceptional in 2014 compared to recent summers. Ice extent is also very low in the East Greenland Sea, possibly as a result of reduced ice transport through Fram Strait.

    NASA’s chief cryospheric scientist, Tom Wagner, offered some perspective on the state of Arctic sea ice in this video.

    In addition to making satellite observations, NASA is sponsoring three airborne campaigns to study climate-driven change to Arctic ice. The Arctic Radiation-IceBridge Sea and Ice Experiment (ARISE) campaign is flying out of Greenland to measure how changing conditions in the region are affecting the formation of clouds and the exchange of heat between Earth’s surface, atmosphere, and space. The Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) is flying out of Fairbanks, Alaska, to measure the emissions of greenhouse gases from thawing tundra and permafrost. And the long-running Operation IceBridge campaign will add flights over Alaskan glaciers to measure how the thickness has changed from previous years.

    1. References and Related Reading

    2. NASA (2014, August 21) NASA Scientists Watching, Studying Arctic Changes This Summer. Accessed August 22, 2014.
    3. NASA Earth Observatory (2007, August 28) Greenland’s Ice Island Alarm.
    4. NASA Earth Observatory (2014, March) Arctic Sea Ice.
    5. National Snow and Ice Data Center (2014, August 19) Ice is low, but record unlikely. Accessed August 22, 2014.

    NASA image courtesy Jeff Schmaltz, LANCE/EOSDIS MODIS Rapid Response Team at NASA GSFC. Caption by Mike Carlowicz, with reporting from Steve Cole, Alan Buis, and Patrick Lynch. Thanks to Claire Parkinson, Kelly Brunt, and Walt Meier for image-interpretation help.

    Instrument(s): Aqua - MODIS
  9. Marion Island, South Africa

    A dusting of ice graced the summit of Marion Island in early May 2009 as waves breaking against the island’s shore formed a broken perimeter of white. Like its smaller neighbor, Prince Edward Island, Marion Island is volcanic, rising above the waves of the Indian Ocean off the southern coast of Africa. Prince Edward and Marion are part of South Africa’s Western Cape Province. (Both islands appear in the large image.)

    The Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite acquired this natural-color image on May 5, 2009. Sunlight illuminates the northern slopes of the volcanic island, leaving southern slopes in shadow. More than 100 small, reddish volcanic cones dot the island, some of the most conspicuous in the north and east. The island reaches its highest elevation, 1,230 meters (4,040 feet), near the center. Vegetation is generally sparse on Marion Island. Lichens live near the summit, and mosses and ferns grow elsewhere on the boggy surface, but trees don’t grow on the island.

    Occurring at the juncture between the African Continental Plate and the Antarctic Plate, Marion Island has been volcanically active for 18,000 years. The first historical eruption was recorded in November 1980 when researchers recorded two new volcanic hills and three lava flows. Researchers observed another small eruption in 2004.

    Besides volcanic cones, Marion Island is home to Marion Base, part of the South African National Antarctic Programme. Focusing on biological, environmental, and meteorological research, the base is situated on the island’s northeastern coast.

    1. References

    2. South African National Antarctic Programme. Marion Base. Accessed October 16, 2009.
    3. Seach, J. Marion Island Volcano. Volcano Live. Accessed October 16, 2009.

    NASA Earth Observatory image created by Jesse Allen, using EO-1 ALI data provided courtesy of the NASA EO-1 team and the United States Geological Survey. Caption by Michon Scott.

    Instrument(s): EO-1 - ALI
  10. Retreat of Yakutat Glacier

    Located in the Brabazon Range of southeastern Alaska, Yakutat Glacier is one of the fastest retreating glaciers in the world. It is the primary outlet for the 810-square kilometer (310-square mile) Yakutat ice field, which drains into Harlequin Lake and, ultimately, the Gulf of Alaska.

    Landsat satellites captured this pair of images showing changes in the glacier and lake. The Thematic Mapperon Landsat 5 acquired the top image on August 22, 1987; the Operational Land Imager on Landsat 8 captured the bottom image on August 13, 2013. Snow and ice appear white and forests are green. The brown streaks on the glaciers are lateral and medial moraines.

    Over the past 26 years, the glacier’s terminus has retreated more than 5 kilometers (3 miles). What is causing the rapid retreat? University of Alaska glaciologist Martin Truffer and colleagues pointed to a number of factors in their 2013 study published in the Journal of Glaciology. The chief cause is the long-term contraction of the Yakutat Ice Field, which has been shrinking since the height of the Little Ice Age.

    Once part of a much larger ice field, Yakutat has been contracting for hundreds of years. As other nearby glaciers retreated, Yakutat ice field was cut off from higher-elevation areas that once supplied a steady flow of ice from the north. With that flow cut off, there simply is not enough snow falling over the low-elevation Yakutat ice field to prevent it from retreating.

    Beyond this natural change, human-caused global warming has hastened the speed of the retreat. Between 1948–2000, mean annual temperatures in Yakutat increased by 1.38° Celsius (2.48° Fahrenheit). Between 2000 and 2010, they rose by another 0.48°C (0.86°F). The warmer temperatures encourage melting and sublimation at all ice surfaces exposed to the air.

    In the past few years, the breakdown of a long, floating ice tongue has triggered especially dramatic changes in the terminus of Yakutat glacier. For many years, Yakutat’s two main tributaries merged and formed a 5-kilometer (3-mile) calving face that extended far into Harlequin Lake. In the past decade, satellites observed a rapid terminus retreat and the breakup of the ice tongue in 2010. As a result, the calving front divided into two sections, with one running east-west and another running north-south. See Truffer’s blog for photos and field updates.

    “You can’t just look at the rapid retreat you see in these images and say that it is entirely natural or entirely due to human-caused global warming,” explained Truffer. “It’s a combination of both.”

    NASA Earth Observatory image by Robert Simmon, using Landsat data from the U.S. Geological Survey. Caption by Adam Voiland

    Instrument(s): Landsat 5 - TMLandsat 8 - OLI
  11. Hobet-21 Mine, West Virginia

    Over the past two decades, the scale of surface coal mines in the coalfields of Appalachia has grown dramatically, and the controversy over the social and environmental costs of this mining method has escalated as well. The largest of these mines are called mountaintop removal mines because coal operators literally remove the tops of mountains to reach coal seams. The waste rock and dirt is piled into nearby hollows and streams in huge earthen dams called valley fills.

    Most of the largest mountaintop removal mines occur in southern West Virginia. This pair of images shows the growth of a mountaintop removal in the headwaters of Mud River in Boone County, West Virginia, between 1987 (bottom) and 2002 (top). In 1987, most of the mountainous, heavily forested terrain in the Mud River watershed was still undisturbed, although mining had already occurred north of Rt. 119. By 2002, the Hobet-21 Mine, operated by Arch Coal and its subsidiaries, had expanded across a large area on either side of the Mud River. At least one stream, Connelly Branch, was turned into a valley fill.

    Areas to the northeast of the river appeared to have been partially reclaimed; these sites are generally planted with grass to control erosion. The partially re-vegetated land is a much lighter green than the surrounding forests. Other prominent features include a coal hauling road that runs between the active mine site and a coal slurry impoundment at the top right part of the scene. These impoundments contain the coal slurry (sludge) left over from washing the coal. Since the 2002 image was captured, the western section of the mine has continued to expand. In December 2007, its northern extent nearly reached Berry Branch.

    To learn more about mountaintop removal mining in Appalachia and its effect on communities and natural resources, please read the Earth Observatory feature article Coal Controversy in Appalachia.

    You can also download a 28.5-meter-resolution KMZ file comparing the Hobet-21 mine site in 1987 and 2002 suitable for use with Google Earth.

    NASA image created by Jesse Allen, using Landsat data provided by the University of Maryland’s Global Land Cover Facility. Caption by Rebecca Lindsey.

    Instrument(s): Landsat 7 - ETM+
  12. Lake Oahe, Dakotas

    The Missouri River and its surrounding ecosystems are struggling in the tight fist of a 6-year drought. In North Dakota, 374-kilometer-long Lake Oahe, the nation’s fourth largest reservoir, is so low that it has left the state. The long, thin reservoir extends upriver from the Oahe Dam on the Missouri from Pierre, South Dakota, to Bismarck, North Dakota. North of the state line, more than 100 kilometers of the lake that were formerly about 8 kilometers wide have reverted to a narrow river. The shrinking of the lake has left behind weedy mudflats and boat ramps stranded 2 kilometers from the water’s edge.

    These images of Lake Oahe show the reservoir on April 4, 2005, (right) compared to the level on May 18, 2000 (left). The Missouri runs through the center of the images in a dark blue line. The image on the left was captured by NASA’s Landsat 7 satellite, while the image on the right was captured by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite. In both images, vegetation appears in shades of red, while bare or sparsely vegetated ground are in shades of green (May 18 image) or tan (April 4 image). The already-thin reservoir has shrunk dramatically in the four years between the images. Both images cover an area of 28.7 by 65.6 kilometers, and they are centered along the North and South Dakota border.

    The drought’s list of effects is long and painful: shortage of drinking and irrigation water; reduction in hydroelectric capacity; decrease in tourism; reduction in shipping; threats to endangered wildlife. The cause is the continuing yearly shortage of snowpack in the Rocky Mountains in Montana, where the Missouri River has its headwaters.

    NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team

  13. Great Flood of the Mississippi River, 1993

    During the first half of 1993, the U.S. Midwest experienced unusually heavy rains. Much of the United States in the upper reaches of the Mississippi River drainage basin received more than 1.5 times their average rainfall in the first six months of the year, and parts of North Dakota, Iowa, and Kansas experienced more than double. The rains often arrived in very intense storms. Floods overwhelmed the elaborate system of dykes and other water control structures in the Mississippi River basin, leading to the greatest flood ever recorded on the Upper Mississippi. In St. Louis, the Mississippi remained above flood stage for 144 days between April 1 and September 30, 1993.

    This image pair shows the area around St. Louis, Missouri, in August 1991 and 1993. The 1993 image was captured slightly after the peak water levels in this part of the Mississippi River. Flood waters had started to recede, but remained well above normal. This false-color image was created by combining infrared, near infrared, and green wavelengths of light observed by the Thematic Mapper (TM) instrument onboard the Landsat 5 satellite (TM bands 5, 4, and 2 respectively). Water appears dark blue, healthy vegetation is green, bare fields and freshly exposed soil are pink, and concrete is grey. The scale of flooding in the river basins of the Illinois, Missouri, and Mississippi Rivers in 1993 is immense. The deep pink scars in the 1993 image show where flood waters have drawn back to reveal the scoured land.

    Other factors contributed to the severity of the flooding that year. The previous year had been cooler than average, which decreased evaporation from the soil and allowed the heavy rains to saturate the ground rapidly. In addition, widespread landcover change along rivers and streams has dramatically altered the natural flood control systems: wetlands that can absorb large amounts of water and release it slowly over time. The network of levees, canals, and dams in the Upper Mississippi Basin was unable to control the floods of 1993.

    Spurred by this massive disaster, geologist Robert Brackenridge of Dartmouth College brought the tools of satellite remote sensing to bear on the issue of flood management, prediction, and monitoring. You can read about his work in the feature article High Water: Building A Global Flood Atlas.

    NASA images created by Jesse Allen, Earth Observatory, using data provided courtesy of the Landsat Project Science Office.

    Instrument(s): Landsat 5 - TM
  14. Eastern Mediterranean Coastline at Night

    This night photograph taken by astronauts aboard the International Space Station (ISS) shows the location and size of cities at the east end of the Mediterranean Sea. The largest, brightest cluster is the Israeli city of Tel Aviv, a port set against the blackness of the Mediterranean Sea. Jerusalem, Israel’s capital city, and Amman, Jordan’s capital, are the next largest (with Amman’s lights having a whiter tone), followed by Beersheba.

    Bright but narrow lines that snake between the cities are highways. The mostly dark areas with small towns are agricultural and pastoral areas of Israel, Sinai, Gaza, the West Bank, and Jordan. A wide, almost black zone between Jerusalem and Amman trends north-south across the right half of the image; it is the long valley that includes the Jordan River and the Dead Sea.

    Click here to view an astronaut image of the same area in daylight. And read more here about a new NASA crowd-sourcing project to identify cities and towns in night images from the space station.

    Astronaut photograph ISS040-E-74022 was acquired on July 22, 2014, with a Nikon D3S digital camera using an 85 millimeter lens, and is provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit, Johnson Space Center. The image was taken by the Expedition 40 crew. It has been cropped and enhanced to improve contrast, and lens artifacts have been removed. The International Space Station Program supports the laboratory as part of the ISS National Lab 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. Caption by M. Justin Wilkinson, Jacobs at NASA-JSC.

    Instrument(s): ISS - Digital Camera
  15. Where China and Kazakhstan Meet

    While people often say that borders aren’t visible from space, the line between Kazakhstan and China could not be more clear in this satellite image. Acquired by the Landsat 8 satellite on September 9, 2013, the image shows northwestern China around the city of Qoqek and far eastern Kazakhstan near Lake Balqash.

    The border between the two countries is defined by land-use policies. In China, land use is intense. Only 11.62 percent of China’s land is arable. Pressed by a need to produce food for more than 1.3 billion people, land that can be sustain agriculture is farmed intensely. Fields are dark green in contrast to the surrounding arid landscape, a sign that the agriculture is irrigated. As of 2006, about 65 percent of China’s fresh water goes to agriculture, irrigating 629,380 square kilometers (243,300 square miles) of farmland (an area slightly smaller than the state of Texas).

    The story is quite different in Kazakhstan. Here, large industrial-sized farms dominate, an artifact of Soviet-era agriculture. While agriculture is an important sector in the Kazakh economy, eastern Kazakhstan is a minor growing area. Only 0.03 percent of Kazakhstan’s land is devoted to permanent agriculture, with 20,660 square kilometers being irrigated. The land along the Chinese border is minimally used, though rectangular shapes show that farming does occur in the region. Much of the agriculture in this region is rain-fed, so the fields are tan much like the surrounding natural landscape.

    1. References

    2. BBC News (2010, January 30) Kazakhs protest against China farmland lease. Accessed July 9, 2014.
    3. Earth Observatory (2013, September 25) Fall harvest in Kazakhstan. Accessed July 9, 2014.
    4. Encyclopedia of Earth (2013, August 25) Land use profile of China. Accessed July 9, 2014.
    5. Fragile Oasis (2011, September 7) Borders from space. Accessed July 9, 2014.
    6. United States Central Intelligence Agency (2014, June 22) The world factbook: China. Accessed July 9, 2014.
    7. United States Central Intelligence Agency (2014, June 22) The world factbook: Kazakhstan. Accessed July 9, 2014.

    NASA Earth Observatory image by Robert Simmon, using Landsat data from the U.S. Geological Survey. Caption by Holli Riebeek.

    Instrument(s): Landsat 8 - OLI