تپه های ماسه ای در باختر مغولستان Sand Dunes in Har Nuur (Black Lake), Western Mongolia

Har Nuur (“Black Lake”) is located in western Mongolia’s Valley of Lakes, part of a system of closed basins stretching across central Asia. These basins are the remnants of larger paleolakes (paleo- means “ancient”) that began to shrink approximately five thousand years ago as regional climate became drier. Like other lakes in the region, Har Nuur relies on precipitation, growing in the spring and shrinking in the summer. This process of growth and shrinkage produces a variety of wetland habitats, as well as resting points for large numbers of migratory birds.

This oblique (looking at an angle) astronaut photograph captures the dynamic nature of the landscape of Har Nuur. The lake is encircled by sand dune fields that encroach on the lower slopes of the Tobhata Mountains to the west and south. Gaps in the mountains have been exploited by sand dunes moving eastward, indicating westerly winds. The most striking example is a series of dunes entering Har Nuur along its southwestern shoreline. Here, the dune forms reflect the channeling of winds through the break in the mountain ridgeline, leading to dune crests lying perpendicular to northwesterly winds. Another well-developed line of dunes appears between Har and Baga Lakes; while these dunes appear to cut across a lake surface, the dunes have in fact moved across a narrow stream channel.

Astronaut photograph ISS013-E-78506 was acquired September 7, 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 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.

Instrument: 

زخم ِ بر جای مانده از آتش سوزی بر زمین Burn Scar from Fourmile Canyon Fire

In September 2010, the Fourmile Canyon Fire broke out in the foothills west of Boulder, Colorado, scorching more than 6,000 acres (2,500 hectares) and forcing residents to evacuate. Ten months later, residents had to evacuate again, this time to flee floods. Stripped of vegetation, the slopes along Fourmile Canyon soaked up little of the water dropped by a thunderstorm. Instead, the runoff surged into local stream channels.

On June 7, 2011, the Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite observed the Fourmile Canyon burn scar. The top image is made from a combination of shortwave infrared and visible light. The bottom image is natural color.

The scar is more easily detected in the false-color image, where the burned area appears in shades of red and orange. Creek valleys, which generally escaped the flames in September 2010, form winding corridors of green through the scar. To the east and southeast, the city of Boulder lies on relatively flat land.

After the fire, the U.S. Geological Survey (USGS) warned residents to prepare for the possibility of flooding, even from small rainstorms. Late on July 13, 2011, such a storm occurred. As rain fell west of Boulder, Fourmile Creek rose rapidly. In fact, at one USGS gauge, the water discharge rate skyrocketed in a matter of minutes from 10 cubic feet per second to 350 cubic feet per second. The increased water flow translated into a 4-foot (1.2-meter) surge down the creek. Smaller surges followed later that night and over the next few days.

Fourmile Creek is a tributary of Boulder Creek, which flows eastward through the city. Water levels usually peak between mid-May and early July. But thanks to the melting of an unusually heavy snowpack, water levels on Boulder Creek were especially high when the July 13 thunderstorm struck. As residents in the Fourmile burn area were ordered to evacuate low-lying homes, emergency sirens also sounded in Boulder.

By late July 2011, water levels had receded along both the Fourmile and Boulder Creeks, although water levels in both remained above normal. Colorado’s monsoon season typically lasts from about mid-July to early September, so the possibility of more flooding remains.

Because of the angle of sunlight, these images may cause an optical illusion known as relief inversion.

1.   References

2.   Byars, M. (2011, July 13). Heavy rains hit Fourmile, prompt evacuations along Boulder Creek. Boulder Daily Camera.Accessed July 29, 2011.

3.   Colorado Mountain Club. Protecting Yourself from Mountain Hazards. Accessed July 29, 2011.

4.   Colorado Water Science Center. (2011, July 13). Video From Fourmile Creek at Orodell. USGS. Accessed July 29, 2011.

5.   Colorado’s Surface Water Conditions. (2011, July 29). Boulder Creek at Boulder, Colorado. State of Colorado. Accessed July 29, 2011.

6.   National Water and Climate Center. (2011, July 7). Weekly Report – Snowpack/Drought Monitor Update. U.S. Department of Agriculture. Accessed July 29, 2011.

7.   National Water Information System. (2011, July 29). USGS 06727410 Fourmile Creek at Logan Mill Road near Crisman, Colorado. USGS. Accessed July 29, 2011.

8.   National Water Information System. (2011, July 29). USGS 06727500 Fourmile Creek at Orodell, Colorado. USGS. Accessed July 29, 2011.

9.   News staff. (2011, July 13). Thunderstorms pound area; flood sirens sound in Boulder. The Denver Post. Accessed July 29, 2011.

10.          Ruddy, B.C., Stevens, M.R., Verdin, K.L., and Elliott, J.G. (2010). Probability and volume of potential postwildfire debris flows in the 2010 Fourmile burn area, Boulder County, Colorado: U.S. Geological Survey Open-File Report 2010–1244. Accessed July 29, 2011.

11.          Snider, L. (2011, June 8). Boulder Creek swells as warm weather melts snowpack. Boulder Daily Camera. Accessed July 29, 2011.

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

Instrument: 

EO-1 - ALI

رسوبات در جنبش و جابجایی در کناره ی اقیانوس Sediment in Motion at Ocean City

If you’ve ever stood in the water on an ocean beach, you’ve likely noticed a pattern in the way water and sand move across your feet. The direction oscillates between moving towards you (sometimes at an angle) carrying sand across the tops of your feet, and then away from you, removing sand from behind your heels and carrying it back out to sea. Your feet slowly begin to sink into the sand. Your feet are taking part in a micro version of a grand coastal process known as longshore transport.

Waves are generally steered ashore by the prevailing winds, often blowing at oblique (slanted) angles to the shoreline. Once a wave breaks, a shallow layer of water glides along the shore, carrying sediment with it. As the momentum from the wave deteriorates, gravity pulls the water downhill and back into the ocean—at least until the next wave moves in and carries the next load of sediment.

This process of longshore transport is responsible for moving sediment up and down coastlines. It can sometimes lead to the development of barrier islands and spits—thin strips of beach that generally form parallel to the mainland.

Before 1933, a single barrier stretched along the eastern seaboard of the Delmarva Peninsula in the United States. A major hurricane breached that barrier in August 1933 causing it to split into two islands: Fenwick Island to the north and Assateague Island to the south. The two islands are depicted in the image above, which was taken by an aerial survey plane on June 26, 2009. Various plumes of sediment are visible in the water both in the ocean and the bays.

Ocean City, Maryland—just north of the inlet—was already developing into a vacationer's paradise before the barrier breach. After the split in 1933, the local fishing industry flourished, too, particularly after a decision to stabilize the inlet by building jetties on either side. Completed in 1935, the jetties were designed to allow easy navigation between the ocean and the bay.

The jetties, however, interrupted natural coastal processes such as longshore transport. The inlet choked off the continuous flow of sediment along the coast to the north end of Assateague Island, accelerating beach erosion. The effects of the Ocean City inlet were initially overlooked. But they are hard to ignore now that the north end of Assateague Island has migrated nearly 700 meters (2,300 feet) landward.

Growing concern about the rapid deterioration of Assateague Island led to the North End Restoration Project. The first phase, completed in 2002, replenished the beach with a one-time supply of 1.4 million cubic meters of sand. The second phase, started in 2004, is addressing the long-term effects of the jetties and attempting to re-establish a natural sediment supply to mirror pre-inlet rates.

With or without human intervention, coastal processes continually morph coasts into different shapes, sizes, and colors. Changes can be observed in a day, a season, or a decade, such that there will always be something different about the sand beneath our toes from one visit to the next.

1.   References

2.   Environmental Protection Agency (2009, January). Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region (PDF). Accessed July 26, 2011.

3.   National Park Service (2008, November 21). Assateague Island National Seashore North End Restoration Project Introduction. Accessed July 25, 2011.

4.   National Parks Conservation Association (2007, August). State of the Parks: Assateague Island National Seashore.(PDF)

زمستان و بهار فصل های آتش سوزی است در شمال قاره ی استرالیا Fires in Arnhem Land, Australia

Winter and spring are fire seasons in northern Australia. During the dry winter months, plants that grew during the rainy summer dry up and become prone to fire. Aboriginal Australians have long used fire to manage land, and many native plants need fire to regenerate. Today, about half of the fires in Australia are started by people, and the other half are ignited by lightning.

The winter fire season often produces large wildfires in Northern Territory, but the most damaging fires in Australian history have been during the summer in the more populous south. This image, taken on July 30, 2011, by the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Aqua satellite, shows several fires burning in Arnhem Land, Northern Territory. The fires are marked in red. Smoke rises from the fires and blends into the clouds over Van Diemen Gulf to the west.

The fires are burning in the Murgenella Wildlife Sanctuary, which is adjacent to Kakadu National Park. Arnhem Land, including the park and the sanctuary, is owned and managed by Aboriginal Australians. The large image, which covers a wider area, shows fires throughout Arnhem Land.

1.   References

2.   Australian Government. (2010, November 24). Bushfire basics. Accessed July 31, 2011.

3.   Australian Government. (2011, July 8). Kakadu National Park. Accessed July 31, 2011.

سنگهای پوسته ی قدیمی و ژئو شیمی اولیه ی زمین Ancient Mantle Rocks and the Geochemistry of Early Earth

Landsat GeoCover image of Baffin Island. Light blue areas are ice cover

Ancient Mantle Rocks Under Baffin Island

 

Scientists have discovered a new window into the Earth's violent past. Geochemical evidence from volcanic rocks collected on Baffin Island in the Canadian Arctic suggests that beneath it lies a region of the Earth's mantle that has largely escaped the billions of years of melting and geological churning that has affected the rest of the planet. Researchers believe the discovery offers clues to the early chemical evolution of the Earth. 

Revealing the Composition of Earth's Early Mantle

The newly identified mantle "reservoir," as it is called, dates from just a few tens of million years after the Earth was first assembled from the collisions of smaller bodies. This reservoir likely represents the composition of the mantle shortly after formation of the core, but before the 4.5 billion years of crust formation and recycling modified the composition of most of the rest of Earth’s interior. 

"This was a key phase in the evolution of the Earth," says co-author Richard Carlson of the Carnegie Institution's Department of Terrestrial Magnetism. "It set the stage for everything that came after. Primitive mantle such as that we have identified would have been the ultimate source of all the magmas and all the different rock types we see on Earth today." 

Clues from Helium Isotopes

 

Carlson and lead author Matthew Jackson (a former Carnegie postdoctoral fellow, now at Boston University), with colleagues, using samples collected by coauthor Don Francis of McGill University, targeted the Baffin Island rocks, which are the earliest expression of the mantle hotspot now feeding volcanic eruptions on Iceland, because previous study of helium isotopes in these rocks showed them to have anomalously high ratios of helium-3 to helium-4. 

Helium-3 is generally extremely rare within the Earth; most of the mantle's supply has been outgassed by volcanic eruptions and lost to space over the planet's long geological history. In contrast, helium-4 has been constantly replenished within the Earth by the decay of radioactive uranium and thorium. The high proportion of helium-3 suggests that the Baffin Island lavas came from a reservoir in the mantle that had never previously outgassed its original helium-3, implying that it had not been subjected to the extensive chemical differentiation experienced by most of the mantle. 

دو ماه پس از فوران خاکستر و دود از شکاف آتشفشا ن های شیلی ، فوران ادامه دارد Puyehue-Cordón Caulle

Nearly two months after ash and steam began spewing from a fissure in Chile’s Puyehue-Cordón Caulle Volcanic Complex, the volcano continued erupting. The Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1)satellite captured this natural-color image on July 31, 2011.

A pale ash plume rises above erupting fissures, then fans out toward the north and east. The plume casts a shadow over the lava flow along the western (left) edge of the image. To the south of the plume, areas that have not been coated with lava sport instead a dendritic pattern of white snow and brown ash.

On July 31, SERNOGEOMIN, Chile’s geology and mineral agency, reported that a minor eruption was in progress at Puyehue-Cordón Caulle. The volcano released gas and ash, accompanied by a continuous volcanic tremor. In late July, an average of one low-magnitude earthquake per hour occurred beneath the volcano. Cameras installed around the site showed an eruption column height of 2 kilometers (1 mile) on July 31, and Chile’s Meteorological Office forecast that the plume would likely move toward the east-southeast overnight.

The eruption at Puyehue-Cordón Caulle began on June 4, 2011. The eruption sent an ash plume high into the atmosphere, and winds sent the ash around the Southern Hemisphere.

1.   References

2.   Global Volcanism Program. (n.d.) Puyehue-Cordón Caulle. Smithsonian National Museum of Natural History. Accessed August 1, 2011.

3.   Servicio Nacional de Geología y Minería. (2011, July 31). Reporte Especial de Actividad Volcánica No 90 Complejo Volcánico Puyehue – Cordón Caulle. (Spanish) Accessed August 1, 2011.

NASA Earth Observatory image created by Jesse Allen and Robert Simmon, using EO-1 ALI data provided courtesy ofthe NASA EO-1 team. Caption by Michon Scott and Robert Simmon.

آتش سوزی در باختر آفریقا FIRES IN WEST AFRICA

As fall moves toward winter, the continental-scale biomass burning across Africa shifts from areas south of the equator to northern areas. Biomass burning in southern Africa peaks in late summer, while burning season in the north peaks in January or February. Both the Sahel (a strip of transitional vegetation between the Sahara Desert to the north and the tropical savannas to the south) and the savannas are subject to agricultural burning as people clear land for farming and regenerate pasture lands.

This image of western Africa shows widespread biomass burning (red dots) detected by the Moderate Resolution Imaging Spect