Dasht-e Kavir, or Great Salt Desert.

Roughly 300 kilometers (200 miles) east-southeast of Tehran lies Iran’s Dasht-e Kavir, or Great Salt Desert. To the untrained eye, Dasht-e Kavir looks like a place that has been bone-dry since the dawn of time. But to the well-trained eyes of a geologist, this desert tells a tale of wetter times. Tens of millions of years ago, a salt-rich ocean likely occupied this region, surrounding a microcontinent in what is now central Iran.

The Thematic Mapper on the Landsat 5 satellite captured this natural-color image of Dasht-e Kavir on October 15, 2011. The top image is a wide-area view, and the area outlined in white is then shown in the close-up view below.

Dasht-e Kavir is a complex landscape, but it can be mostly explained by the invasion and subsequent evaporation of an ancient ocean. As the ocean dried up, it left behind a layer of salt as much as 6 to 7 kilometers (4 miles) thick. Salt has a fairly low density, so if a layer of new rock buries the salt layer—and if that overlying rock is soft enough—the salt can slowly push up through it and form domes.

As its name implies, the Great Salt Desert is rich in salt domes, or diapirs. Geologists have identified about 50 large salt diapirs in this region. Like any other surface feature, a salt dome is subject to erosion. Wind and rain scrape away particles of rock, gradually wearing away the top of the dome and exposing it in cross-section.

But erosion is not the only force at work in this region. In the close-up view, we can see north-south-trending structures, some raised and some lowered. Callan Bentley, a geologist at Northern Virginia Community College, identifies them as folds or fault zones that run parallel to the trend of the region’s mountains. Bentley attributes the deformation of the salt domes to plate tectonic activity that has occurred since the salt domes formed. Bentley describes the landscape as a “a palimpsest tale that helps constrain the age of the diapirism to pre-folding.”

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In southern Iran, the collision between the Asian landmass and the Arabian platform has folded rocks and pushed up the rugged Zagros Mountains. In places, underlying deposits of salt have ascended in fluid-like plumes. Some of these plumes have pushed through the rock above, like toothpaste from a tube, and they are now visible as darkish irregular patches. This image shows a few of over 200 similar features—called diapirs, or salt plugs—that are scattered about this part of the Zagros Mountains.

Gravity has caused the salt to flow like glaciers into adjacent valleys. The resulting tongue-shaped bodies are more than 5 kilometers long, with repeating bow-shaped ridges separated by crevasse-like gullies and with steep sides and fronts. The darker tones are due to clays brought up with the salt, as well as the probable accumulation of airborne dust. This ASTER perspective view was created by draping a band 3-2-1 (RGB) image over an ASTER-derived Digital Elevation Model (2x vertical exaggeration), and was acquired on August 10, 2001.

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Not everyone knows that not all the white surfaces in the Andes are ice or snow.

Everyone knows that the Andes Mountains contain rugged, snow-capped peaks. Not everyone knows that not all the white surfaces in the Andes are ice or snow. Some of the bright spots in this part of the world get their color from salt.

On December 1, 2001, the Enhanced Thematic Mapper on NASA’s Landsat 7 satellite took this picture of part of the Atacama Desert. On the lee side of the Andes, away from prevailing winds and precipitation-making weather, reside salt pans—vast expanses of salt-covered soil. This image shows one such salt pan, Bolton de Pipanaco, tens of kilometers long. Besides the pale color of the salt pan, other features in this photo give clues to the region’s aridity. The sharp ridges around the salt pan appear in shades of beige and brown, indicating land that supports little vegetation. Two small water bodies appear in this image, one in the northwest and the other in the southwest.

The salt plains of the Atacama Desert were once underwater, and research at Cornell University deduced that 15,000 years ago, the salt pans were great salt lakes. When a lake has no outlet, the minerals carried into it accumulate, increasing its salinity. If conditions dry out, the lake can evaporate, creating a salt pan. Harsh as this environment is, some plants and animals have adapted to living in it. A species of saltbush in this area concentrates salt in its stems and leaves, crystallizing the excess on its exterior. Rabbit-resembling viscacha rats, able to eat the saltbush, live nowhere else. Able to tolerate saline lakes, flamingoes congregate in this area to dance.

Dry as this area is, it does see the occasional torrent. Summertime monsoons and mountain runoff can inundate the region, but the water does not soak the area enough to erase the vast plains of

salt . 

The largest salar (salt flat) in the world

The largest salar (salt flat) in the world, Salar de Uyuni, is located within the Altiplano of Bolivia in South America. The Altiplano is a high plateau formed during uplift of the Andes Mountains. The plateau harbors fresh and saltwater lakes, together with salars, that are surrounded by mountains with no drainage outlets—all at elevations greater than 3,659 meters (12,000 feet) above mean sea level. The Salar de Uyuni covers approximately 8,000 square kilometers (3,100 square miles), and it is a major transport route across the Bolivian Altiplano due to its flatness.

This astronaut photograph features the northern end of the salar and the dormant volcano Mount Tunupa (image center). This mountain is high enough to support a summit glacier, and enough rain falls on the windward slopes to provide water for small communities along the base. The dark volcanic rocks comprising Mt. Tunupa are in sharp contrast with the white, mineral-crusted surface of the salar. The major minerals are halite—common table salt—and gypsum—a common component of drywall.

Relict shorelines visible in the surface salt deposits (lower right of the image) attest to the occasional presence of small amounts of water in the salar. Sediments in the salar basin record fluctuations in water levels that occurred as the lake that once occupied the salar evaporated. These sediments provide a valuable paleoclimate record for the region. The dynamic geological history of the Altiplano is recorded in isolated “islands” within the salt flat (image left); these islands are typically built from fossil coral reefs covered by Andean volcanic rocks.

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The largest salar (salt flat or playa) in the world, Salar de Uyuni, is located within the Altiplano of Bolivia. Covering 10,582 square kilometers (4,086 square miles), the mineral-crusted salar is about the same size as the “Big Island” of Hawaii.

While the almost perfectly flat expanse of white can seem endless in photographs from the ground, this unique photograph offers a view on the playa as seen from the vantage point of an astronaut on the International Space Station. The smaller Salar de Coipasa is also visible to the northwest. The flat, white surfaces are comprised mainly of halite (common table salt) and gypsum, a soft mineral that is widely used in plaster and fertilizer. Several mountains, including the dormant volcano Mount Tunupa, cast long shadows across the salars.

The salars owe their existence to several large, ancient lakes that covered the plateau several thousand years ago. During the Late Pleistocene, most of this area was covered by Lago Minchin. About 15,000 years ago, Minchin had shrunk significantly, depositing large quantities of calcium carbonate in the basin and enriching the remaining water with gypsum, halite, and other minerals. Since it was trapped in a closed basin with no outlets, this briny water evaporated slowly during dry periods, providing the perfect conditions for salts and other evaporites to form. Over several thousand years, thick crusts have built up. In many areas, the salt crusts are more than 10 meters (33 feet) thick.

In addition to providing an exotic backdrop for photographers, the unusually flat surface has served as an ideal location for testing newly-launched satellite sensors. For instance, scientists working with both ICESat and Envisat have taken advantage of Salar de Uyuni to calibrate sensors on board. Salt flats make ideal locations for calibration because they are large, stable surfaces with strong reflection, much like ice sheets.

Chile’s Atacama Desert

Chile’s Atacama Desert may be the driest place on Earth. Large stretches of the Atacama have gone without moisture for as long as people have been keeping track. Yet some precipitation does fall in the region, and that water helps shape the landscape.

Within this arid environment lies a salt flat, or playa, named Salar de Atacama. The Landsat 7 satellite acquired this false-color image on March 21, 2002. Red indicates vegetation, the most abundant of which occurs around springs that dot the northern edge of the saltpan. Nearby soils that support some vegetation appear tan and brown.

Although it sits at a much higher elevation, the Salar de Atacama resembles California’s Death Valley as a flat area in between mountain ranges. The little precipitation that has fallen has usually drained off the mountains and flowed into nearby valleys, creating alluvial fans.

The salt flat is a geologically young, dynamic system. Occasional floods do reach the saltpan, and flood waters carry gravel, sand, clay, and salt. Heavier materials such as gravel and sand tend to drop out of the water sooner, coming to rest outside the saltpan. Clays and salts can hitch a ride all the way to the playa.

Floods initially stir the sediments inside Salar de Atacama, but material eventually settles into layers of clay and salty water. Because the playa lacks drainage, water only leaves by evaporation. As it evaporates, salts remain behind and form crusts. Inside the saltpan, mottled light blue indicates surface salt crusts.

The white color around the perimeter of the saltpan indicates a zone of clay and carbonate-rich material that alternately forms a crust on the surface and re-dissolves with rising and falling groundwater. Northeast of the playa, white indicates something else: snow and ice on the volcanic peaks. Volcanic rocks and soils range in color from burnt orange to tan.

Around the playa, the false-color green indicates rocks that would appear red to human eyes. Blue indicates older sedimentary rocks (deposited by wind and water) and igneous rocks (formed from cooling lava or magma) that support no vegetation.

Not surprisingly, Salar de Atacama is now mined for salt, and evaporation ponds appear in the middle of the saltpan—rectangular shapes of bright turquoise and white. The salt flat also holds the potential for lithium production from its subsurface brine-bearing waters.

The Infrared Visible Andromeda

 This remarkable synthetic color composite image was assembled from archives of visible light and infrared astronomy image data. The field of view spans the Andromeda Galaxy (M31), a massive spiral a mere 2.5 million light-years away. In fact, with over twice the diameter of our own Milky Way, Andromeda is the largest nearby galaxy. Andromeda's population of bright young blue stars lie along its sweeping spiral arms, with the telltale reddish glow of star forming regions traced in space- and ground-based visible light data. But infrared data from the Spitzer Space Telescope, also blended directly into the detailed composite's red and green color channels, highlight the lumpy dust lanes warmed by the young stars as they wind ever closer to the galaxy's core. Otherwise invisible at optical wavelengths, the warm dust takes on orange hues. Two smaller companion galaxies, M110 (below) and M32 (above) are also included in the frame.

The Day After Mars

 October 31, 1938 was the day after Martians encountered planet Earth, and everything was calm. Reports of the invasion were revealed to be part of a Halloween radio drama, the now famous broadcast based on H.G. Wells' scifi novel War of the Worlds. On Mars October 20, 2014 was calm too, the day after its close encounter with Comet Siding Spring. Not a hoax, this comet really did come within 86,700 miles or so of Mars, about 1/3 the Earth-Moon distance. Earth's spacecraft and rovers in Mars orbit and on the surface reported no ill effects though, and had a ringside seat as a visitor from the outer solar system passed by. Spanning over 2 degrees against stars of the constellation Ophiuchus, this colorful telescopic snapshot captures our view of Mars on the day after. Bluish star 51 Ophiuchi is at the upper right and the comet is just emerging from the Red Planet's bright glare.

Climate and Earth’s Energy Budget

Climate and Earth’s Energy Budget

by Rebecca Lindsey

The Earth’s climate is a solar powered system. Globally, over the course of the year, the Earth system—land surfaces, oceans, and atmosphere—absorbs an average of about 240 watts of solar power per square meter (one watt is one joule of energy every second). The absorbed sunlight drives photosynthesis, fuels evaporation, melts snow and ice, and warms the Earth system.

The setting sun, photographed from the International Space Station.

Solar power drives Earth’s climate. Energy from the Sun heats the surface, warms the atmosphere, and powers the ocean currents. (Astronaut photograph ISS015-E-10469, courtesy NASA/JSC Gateway to Astronaut Photography of Earth.)

The Sun doesn’t heat the Earth evenly. Because the Earth is a sphere, the Sun heats equatorial regions more than polar regions. The atmosphere and ocean work non-stop to even out solar heating imbalances through evaporation of surface water, convection, rainfall, winds, and ocean circulation. This coupled atmosphere and ocean circulation is known as Earth’s heat engine.

The climate’s heat engine must not only redistribute solar heat from the equator toward the poles, but also from the Earth’s surface and lower atmosphere back to space. Otherwise, Earth would endlessly heat up. Earth’s temperature doesn’t infinitely rise because the surface and the atmosphere are simultaneously radiating heat to space. This net flow of energy into and out of the Earth system is Earth’s energy budget.