On December 26, 2004, one of the largest earthquakes in recorded history reshaped the floor of the Indian Ocean.

On December 26, 2004, one of the largest earthquakes in recorded history reshaped the floor of the Indian Ocean. The magnitude 9.1 Sumatra-Andaman temblor generated tsunami waves that caused widespread damage to nations around the Indian Ocean, with most of the damage affecting Indonesia. One decade later, recovery is apparent in areas such as this stretch of coastline along the island of Sumatra in western Indonesia.

The series of natural-color images above shows a small area along the Sumatran coast in Aceh province, north of Meulaboah. In this region, the wave cut a swath of near-total destruction 1.5 kilometers (roughly one mile) in most places, but penetrating farther in many others.

The first two images, acquired with Landsat 7's Enhanced Thematic Mapper Plus (ETM+) on December 13, 2004 (top) and December 29, 2004 (middle), show the area before and after the tsunami crashed ashore. The third image, acquired by the Operational Land Imager (OLI) on Landsat 8, shows the same scene almost ten years later on November 15, 2014 (bottom).

According to research published in 2010, coastline along the Aceh coast eroded back about 500 meters (1,600 feet) during the tsunami. Along straight coastline north of Meulaboah, beach ridges running parallel to the shoreline eroded and streams became connected directly to the ocean. Within weeks, however, observations showed a new coastline beginning to emerge that closely resembled the old one. Within a few years, beach ridges were recovering and vegetation was returning.

The world’s saltiest body of water

The world’s saltiest body of water is tucked away in a valley in one of the most extreme environments on Earth. It rarely snows and never rains in the McMurdo Dry Valleys. Winter temperatures can drop to -50 degrees Celsius (-58 degrees Fahrenheit), and the few ponds and lakes in the valleys are capped by ice that is several meters thick.

Then there’s Don Juan Pond. The ankle-deep pond in the lowest part of Upper Wright Valley is so salty that its calcium-chloride rich waters rarely freeze. Salt particles lower the freezing point of water by moving between water molecules and impeding the formation of the crystal lattice structure of ice.

With a salinity level over 40 percent, Don Juan is significantly saltier than most of the other hypersaline lakes around the world. The Dead Sea has a salinity of 34 percent; the Great Salt Lake varies between 5 and 27 percent. Earth’s oceans have an average salinity of 3.5 percent.

The Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite captured this image on January 3, 2014. The ellipse-shaped lake is situated at the bottom of a basin between the Dais plateau and the Asgard Range to the south. It has a slightly darker hue than the salt-encrusted lake bottom around it.

The lower image shows a broader view of Wright Valley. Notice the network of channels just east of Wright Upper Glacier, an intricate feature eroded into dolerite bedrock known as the Labyrinth. Frozen Lake Vanda is visible to the northeast of Don Juan Pond.

While hydrologists have long thought that groundwater bubbled up from below to feed the pond, recent research by Brown University geologists Jay Dickson and James Head has shown that the water most likely comes from the atmosphere. By setting up cameras that took thousands of time-lapse photographs of the lake, the scientists observed that salts in the soil suck available moisture from the air through a process called deliquescence. These water-rich salts then trickle down slopes toward the pond, often mixing with small amounts of melt water from snow and ice. The process creates dark water tracks on the surface, some of which are visible in the ALI image.

For astrobiologists, one of the most tantalizing aspects of Don Juan Pond is the possibility that its salty water contains microscopic life. If life can survive in such an extreme environment, it would lend credence to the idea that life exists—or once existed—in hypersaline features on Mars. “There is certainly biology in the vicinity of the pond and some evidence for biologic activity in the pond itself, but this activity could be explained by abiotic processes,” said Dickson. ”Mars has a lot of salt and used to have a lot of water.”

Lake Mackay is Australia's fourth largest lake

Hundreds of salt lakes are sprinkled across the landscape of northern and western Australia. Most, including Lake Mackay, fill infrequently via seasonal rainfall that runs off of nearby lands and through minor drainage channels.

Lake Mackay is Australia's fourth largest lake—encompassing 4,737 square kilometers (1,829 square miles) along the border between Western Australia and Northern Territory. The image above, acquired on September 19, 2010, by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA's Terra satellite, shows about a quarter of the lake area. Dark areas indicate desert vegetation or algae, moisture within the soils, and the low elevations where water pools. Light browns indicate areas of higher elevation that occasionally form islands.

So, how deep is the water? That depends on when you measure. When full, some of the deeper lakes in the region can be several meters deep. Shallower lakes are less than 50 centimeters (20 inches) deep. The depth of Lake Mackay is uncertain, but is thought to be somewhere between the two extremes.

Water can persist in Lake Mackay for at least six months after a flood; when it does, the ephemeral lake provides an important habitat and breeding area for shorebirds and waterbirds. For example, researchers spotted at least 4,400 young banded stilts during an aerial survey of the wetlands in 2001

Milky Way over Yellowstone

Explanation: The Milky Way was not created by an evaporating lake. The colorful pool of water, about 10 meters across, is known as Silex Spring and is located in Yellowstone National Park in Wyoming, USA. Illuminated artificially, the colors are caused by layers of bacteria that grow in the hot spring. Steam rises off the spring, heated by a magma chamber deep underneath known as the Yellowstone hotspot. Unrelated and far in the distance, the central band of our Milky Way Galaxy arches high overhead, a band lit by billions of stars. The above picture is a 16-image panorama taken late last month. If the Yellowstone hotspot causes another supervolcanic eruption as it did 640,000 years ago, a large part of North America would be affected.

Ethiopia’s 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. The Danakil Depression 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.

Moonbow Beach

Like a rainbow at night, a beautiful moonbow shines above the western horizon in this deserted beach scene from Molokai Island, Hawaii, USA, planet Earth. Captured last June 17 in early morning hours, the lights along the horizon are from Honolulu and cities on the island of Oahu some 30 miles away. So where was the Moon? A rainbow is produced by sunlight internally reflected in rain drops from the direction opposite the Sun back toward the observer. As the light passes from air to water and back to air again, longer wavelengths are refracted (bent) less than shorter ones resulting in the separation of colors. And so the moonbow is produced as raindrops reflect moonlight from the direction opposite the Moon. That puts the Moon directly behind the photographer, still low and rising over the eastern horizon, a few days past its full phase.

The Cat's Eye Nebula from Hubble

To some, it may look like a cat's eye. The alluring Cat's Eye nebula, however, lies three thousand light-years from Earth across interstellar space. A classic planetary nebula, the Cat's Eye (NGC 6543) represents a final, brief yet glorious phase in the life of a sun-like star. This nebula's dying central star may have produced the simple, outer pattern of dusty concentric shells by shrugging off outer layers in a series of regular convulsions. But the formation of the beautiful, more complex inner structures is not well understood. Seen so clearly in this digitally sharpened Hubble Space Telescope image, the truly cosmic eye is over half a light-year across. Of course, gazing into this Cat's Eye, astronomers may well be seeing the fate of our sun, destined to enter its own planetary nebula phase of evolution ... in about 5 billion years.

Large and Small Magellanic Clouds

Featured above are the glows of the Large and Small Magellanic Clouds (at right), the Milky Way (at right center) and the zodiacal light (left) as observed from Reunion Island in the Indian Ocean. This panorama of 14 photos was taken on November 9, 2013. The Magellanic Clouds are satellite galaxies to the Milky Way. At a distance of approximately 160,000 light years, the larger cloud (LMC) is about 40,000 light years closer to us than the smaller cloud (SMC). Despite these enormous distances, they're visible with the naked eye throughout the entire Southern Hemisphere and from low latitudes in the Northern Hemisphere.

How did those big rocks end up on that strange terrain?

How did those big rocks end up on that strange terrain? One of the more unusual places here on Earth occurs inside Death Valley, California, USA. There a dried lakebed named Racetrack Playa exists that is almost perfectly flat, with the odd exception of some very large stones, one of which is pictured above. Now the flatness and texture of large playa like Racetrack are fascinating but not scientifically puzzling -- they are caused by mud flowing, drying, and cracking after a heavy rain. Only recently, however, has a viable scientific hypothesis been given to explain how 300-kilogram stones ended up near the middle of such a large flat surface. Unfortunately, as frequently happens in science, a seemingly surreal problem ends up having a relatively mundane solution. It turns out that high winds after a rain can push even heavy rocks across a momentarily slick lakebed.

Megadrought

This will be worse than anything seen during the last 2,000 years," says the lead author of the paper. Also: "Megadrought" is a real term.

A new study published as a joint effort by scientists at Cornell University, the University of Arizona, and the U.S. Geological Survey finds that the chances of the Southwest facing a “megadrought” are much higher than previously suspected.

According to the new study, “the chances of the southwestern United States experiencing a decade-long drought is at least 50 percent, and the chances of a ‘megadrought’ – one that lasts up to 35 years – ranges from 20 to 50 percent over the next century.” Not so crazy, according to Richard Seager, a climate scientist at Columbia University who has helped pen many studies of historical megadroughts: “By some measures the west has been in drought since 1998 so we might be approaching a megadrought classification!” he says. The study points to manmade global climate change as a possible cause for the drought, which would affect portions of California (where a drought is currently decimating farms), Arizona and New Mexico.

“This will be worse than anything seen during the last 2,000 years.”

“We know that megadroughts — droughts as severe as the ones in past century, but lasting much longer, up to a few decades – occurred over the past millennium in the southwest and the Great Plains,” says Seager. Megadroughts are commonly called “decades-long droughts” or “multi-decadal droughts,” and refer to length of time rather than severity. Seager says that the region hasn’t had a megadrought in several centuries; the Dust Bowl drought of The Grapes of Wrath, though incredibly severe, was not long enough to qualify.

Jason Smerdon, another climate scientist at Columbia University, spoke to us about what this specific paper does differently. “What is novel about the paper,” he says, “is that the authors use paleoclimate and observational evidence to inform statistical models of drought variability, which are in turn used to modify characterizations of future drought risks from climate model simulations.” The combination of traditional climate models as well as historical data and current observational data could give them much more insight into the future in the American Southwest — and their evidence points to a dry future indeed.

The thin outer surface of the Sun

ivid orange streamers of super-hot, electrically charged gas (plasma) arc from the surface of the Sun, revealing the structure of the solar magnetic field rising vertically from a sunspot. The thin outer surface of the Sun, the corona, is shaped by a complex network of magnetic fields. These magnetic fields are strongest inside sunspots, and their effect on plasma is visible in this image. The gas is drawn along the lines of force in the sunspot’s magnetic field like iron filings gather around a magnet. At the edges of the sunspot, the curving field lines, and thus the plasma, bend over to reconnect with magnetic fields of opposite polarity.

This extremely detailed image of the Sun was taken by the Solar Optical Telescope on the newly launched Hinode spacecraft on November 20, 2006. It and other images, which NASA released for the first time on March 21, 2007, reveal that the Sun’s magnetic field is much more turbulent and dynamic than previously known. “For the first time, we are now able to make out tiny granules of hot gas that rise and fall in the sun's magnetized atmosphere,” said Dick Fisher, director of NASA's Heliophyics Division, Science Mission Directorate, Washington.

Hinode, Japanese for “sunrise,” was launched September 23, 2006, to study the Sun’s magnetic field and how its explosive energy propagates through the different layers of the solar atmosphere. “Hinode is showing how changes in the structure of the magnetic field and the release of magnetic energy in the low atmosphere spread outward through the corona and into interplanetary space to create space weather,’ said John Davis, project scientist from NASA’s Marshall Space Flight Center. Space weather involves the production of energetic particles (coronal mass ejections) and emissions of electromagnetic radiation (solar flares), which can black out long-distance communications over entire continents and disrupt global navigational systems.

Scientists believe that space weather is driven by changes in the magnetic fields around sun spots, but the exact mechanisms that trigger flares and solar storms remain a mystery. “By following the evolution of the solar structures that outline the magnetic field before, during and after these explosive events, we hope to find clear evidence to establish that magnetic reconnection is the underlying cause for this explosive activity,’ said Leon Golub of the Smithsonian Astrophysical Observatory. Hinode will allow scientists study solar storms and flares by revealing changes in the

magnetic fields in unprecedented detail.

To read more about Hinode’s mission to study the Sun and to see additional images, please visit Hinode Mission to the Sun. Hinode is a collaborative mission led by the Japan Aerospace Exploration Agency and includes the European Space Agency and Britain's Particle Physics Astronomy Research Council.

Earth’s magnetic field

Launched in November 2013 by the European Space Agency (ESA), the three-satellite Swarm constellation is providing new insights into the workings of Earth’s global magnetic field. Generated by the motion of molten iron in Earth’s core, the magnetic field protects our planet from cosmic radiation and from the charged particles emitted by our Sun. It also provides the basis for navigation with a compass.

Based on data from Swarm, the top image shows the average strength of Earth’s magnetic field at the surface (measured in nanotesla) between January 1 and June 30, 2014. The second image shows changes in that field over the same period. Though the colors in the second image are just as bright as the first, note that the greatest changes were plus or minus 100 nanotesla, a minuscule but still detectable change in a field that reaches 60,000 nanotesla.

Geophysicists have noted that the strength of Earth’s magnetic field has been decaying—about 5 percent globally over the past century. However, it is not changing in a uniform way; it grows growing stronger in some places and weaker in others.

The changes are a natural variation due to processes in the deep interior of the Earth, explained Nils Olsen, a Swarm team member from the Technical University of Denmark. The movement of molten iron in the core creates electric currents, and electric currents create a magnetic field. So every change in the flow of the core means changes in the magnetic field.

“The magnetic field changes in a chaotic manner, and we do not know why it changes in the way it does nor how it will evolve in the future,” said Olsen. “There is no periodic behavior, and it is therefore rather difficult, if not impossible, to predict how the magnetic field evolves over time. We can just observe how it has changed in past and what it looks like today.”

Yosemite National Park

People come to Yosemite National Park expecting awe-inspiring views and great camping amidst the park’s granite peaks and forested lowlands. In September 2014, some visitors got much more than that.

A small wildfire had been burning in Yosemite for weeks before it suddenly quadrupled in size in early September due to strong winds and high temperatures. Park authorities needed helicopters to evacuate dozens of visitors from back-country locations on September 7, 2014, including 85 climbers airlifted from the summit of Half Dome and approximately 100 hikers picked up from campgrounds in Little Yosemite Valley. Several people posted photographs of the evacuation to social media sites as they were being ferried away.

A NASA satellite orbiting 725 kilometers (450 miles) overhead captured images of the Meadow fire from above on September 7, 2014. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured the top image of wildfire activity in Little Yosemite Valley. Red outlines indicate hot spots where MODIS detected the unusually warm land surface temperatures associated with fires. The lower image was taken by Yosemite National Park staff on September 7, 2014. Half Dome is on the left, with a smoke plume rising from Little Yosemite Valley to its right.

Lightning first ignited the Meadow fire on July 20. For several weeks, park officials let the small, high-altitude (8,000 feet or 2,440 meters) blaze burn in order to preserve the park’s natural fire patterns and because it posed no threat to public safety, according to The Los Angeles Times. Indeed, the fire had burned just 19 acres (8 hectares) over the first 49 days.

Then winds surged on September 7 and the Meadow fire suddenly flared up. By September 8, the fire had charred 2,582 acres (1,044 hectares). Though it is large enough to provoke dramatic photographs from the ground, the fire is small compared to California’s largest fires. For comparison, the Happy Camp Complex fire in northern California has burned more than 99,000 acres and was only partly contained as of the same date.

Visit Worldview, a satellite image-browsing tool maintained by the MODIS Rapid Response Team, to track the fires over time.

The view of the Holuhraun lava field

As an island in the moist, atmospherically turbulent North Atlantic, Iceland is often shrouded in cloud cover and hard to observe from space. And lately, the island is making some of its own cloud cover, as the Earth has split open between the Bardarbunga and Askja volcanoes and spewed lava and hot gas. The view of the Holuhraun lava field has been spectacular from the ground and from low-flying aircraft. Infrared imaging makes the view spectacular from space, too.

On September 6, 2014, the Operational Land Imager (OLI) on Landsat 8 captured this view of the ongoing eruption. The false-color images combine shortwave infrared, near infrared, and green light (OLI bands 6-5-3). Ice and the plume of steam and sulfur dioxide appear cyan and bright blue, while liquid water is navy blue. Bare or rocky ground around the Holuhraun lava field appears in shades of green or brown in this band combination. Fresh lava is bright orange and red. (Download this large image to see the same area in natural color.)

“Thermal imagery can be used to determine the extent of the lava flows and the heat loss,” noted Ashley Davies, a Jet Propulsion Laboratory scientist and leader of NASA’s Volcano Sensor Web team. Infrared imagery can help scientists estimate the effusion rate—the rate at which lava is pouring out of the Earth—as well as the sulfur dioxide content of the plume. “And high resolution imagery of this kind allows us to model the dynamics of the emplacement process. In this case, individual vents can be seen feeding separate lava flows that combine into a main channel feeding an expanding lava flow field.”

By some accounts, Holuhraun has spewed more lava this month that any Icelandic volcano since the 19th century. As of September 9, 2014, the new lava flow was 16 kilometers (10 miles) long and covered about 20 square kilometers (8 square miles), according to the University of Iceland.

The plume from Holuhraun is rich with sulfur dioxide (SO2), a rotten-smelling gas that can cause respiratory problems in humans and animals. A blue haze of SO2 and aerosols has been observed downwind over several towns and villages in eastern Iceland. Scientists and other observers working near the eruption site have been evacuated several times and cautioned to keep gas masks handy due to noxious gases and shifting winds. Elevated levels of SO2 have been detected as far as Ireland, Greenland, and Scandinavia.

The University of Iceland and Iceland Met Office have been providing regular updates on Holurhaun and Bardarbunga via Twitter and on their web site.

Short day. Long night

Late dawn. Early sunset. Short day. Long night. For us in the Northern Hemisphere, the December solstice marks the longest night and shortest day of the year. Meanwhile, on the day of the December solstice, the Southern Hemisphere has its longest day and shortest night. This special day is coming up on Sunday, December 21 at 23:03 UTC (5:03 p.m. CST). A fun fact about the coming solstice is that it occurs within about two-and-a-half hours of a new moon. No matter where you live on Earth’s globe, a solstice is your signal to celebrate. Follow the links below to learn more about the 2014 December solstice

“evening stars”

Venus, Mars, and other planets can appear as “evening stars”s in our skies, depending on your location and the time of year. On January 31, 2014, Earth played the same role for an earthling on Mars. NASA’s Curiosity rover turned its Mast Camera toward the horizon and snapped this photo of home.

Earth is just barely visible (image top-center-left), just above the dim glow of twilight near the Martian landscape. The image was captured about 80 minutes after sundown on the rover’s 529th day, or sol, on the red planet.

Curiosity and Mars were about 160 million kilometers (99 million miles) from Earth at the time, and the Big Blue Marble or Pale Blue Dot looked more like a faint white speck in this view. However, a human observer with normal vision, if standing on Mars, could easily see Earth and its moon as two distinct “evening stars.”

Across the atmosphere of Earth, lightning flashes about 50 times per second.

Across the atmosphere of Earth, lightning flashes about 50 times per second. That’s 4.3 million times a day and roughly 1.5 billion times a year. Using a new instrument on the International Space Station (ISS), scientists are hoping to observe and dissect at least a few of those lightning bolts every day.

Launched to the ISS in August 2013, the Firestation instrument includes photometers to measure lightning flashes, radio antennas to measure the static (a proxy for the strength of the electrical discharge), and a gamma-ray electron detector. Firestation could observe about 50 lightning strokes per day as it looks for brief bursts of gamma rays that are emitted by some of them.

Gamma radiation is usually associated with exploding stars or nuclear fusion, but scientists have found evidence that terrestrial gamma-ray flashes (TGFs) may occur in the atmosphere as often as 500 times a day. Atmospheric scientists are interested in the processes that trigger lightning within thunderstorms and what kinds of lightning produce gamma rays. TGFs may also be related to the atmospheric phenomena known as red sprites, electrical discharges that extend upward from thunderstorms.

“The fact that TGFs exist at all is amazing,” said Doug Rowland, the principal investigator for Firestation and a space physicist at NASA’s Goddard Space Flight Center. “The electron and gamma-ray energies in TGFs are usually the domain of nuclear explosions, solar flares, and supernovas. What a surprise to find them shooting out of the cold upper atmosphere of our own planet.”

The photograph above, snapped by an astronaut aboard the International Space Station on December 12, 2013, shows a white flash of lightning amidst the yellow city lights of Kuwait and Saudi Arabia. Another astronaut orbiting over Bolivia captured a close-up of a lightning flash beneath a thunderhead on January 9, 2011 (image below).

Moon and Earth from Chang'e 5-T1

 Described at times as a big blue marble, from some vantage points Earth looks more like a small blue marble. Such was the case in this iconic image of the Earth and Moon system taken by the Chang'e 5-T1 mission last week. The Moon appears larger than the Earth because it was much closer to the spacecraft's camera. Displaying much of a surface usually hidden from Earth, the Moon appears dark and gray when compared to the more reflective and colorful planet that it orbits. The robotic Chang'e 5-T1 spacecraft, predominantly on an engineering test mission, rounded the Moon last Tuesday returned to Earth on Friday.

A break in the clouds

A break in the clouds on October 29, 2014, allowed scientists the opportunity to fly over Pine Island Glacier—one of Antarctica’s most rapidly changing areas. The flight was part of NASA’s Operation IceBridge, a mission that makes annual surveys of Greenland and Antarctica with instrumented research aircraft.

After months of darkness in Antarctica, the Sun continues to rise a little higher each day. IceBridge project scientist Michael Studinger captured this photograph of late day sunlight striking glaciers and mountains in coastal West Antarctica at the end of the October 29 survey of Pine Island Glacier.

The recent, rapid changes at Pine Island have made it a high priority target for IceBridge. The weather, however, is not always agreeable. Paths flown in 2014 were last surveyed by IceBridge in 2012, and prior to that from 2002 to 2009. In 2013, satellite imagery found that a large iceberg had separated from the glacier's calving front. During the first 2014 flight, instruments found a new crack—a relatively common feature, according to scientists.

Repeat measurements of land and sea ice from aircraft extend the record of observations once made by NASA's Ice, Cloud, and Land Elevation Satellite, or ICESat, which stopped functioning in 2009. In addition to extending the

Thin sections of Limburgite

Shown above are thin sections of Limburgite, an augite composed of olivine and glass-bearing, tephritic volcanic rock. The top view is shown under plane polarized light and the bottom view under crossed polarized light. The study of microscopic features using a polarizing or petrographic microscope is called thin section petrography. Thin sections allow for more accurate characterization of minerals in rock samples.

These specimens, several millimeters across, date from the Miocene and were found in the Kaiserstuhl Hills of southwestern Germany. Both views portray what is called hourglass zoning. The occurrence of this mafic rock in close proximity to the Rhine River made it convenient to quarry during the 19th century.

Largest landslide

Largest landslide

Saidmarreh landslide is located in western Iran.

Landsat image of Saidmarreh Landslide in Saidmarreh, Iran. The source area of the slide is bounded on the southwest by the crest of the Kabir Kuh anticline. Debris from the slide travelled down the flank of the anticline, across the Karkheh River and continued across the valley floor. Some material in the slide was carried a distance of 14 kilometers (9 miles).

One of the largest landslides that can be easily recognized on satellite images is the Saidmarreh Landslide in western Iran. The slide occurred about 10,000 years ago when about 20 cubic kilometers (about 5 cubic miles) of Lower Miocene and Eocene limestone detached along bedding planes and slipped down the north flank of the Kabir Kuh anticline. The maximum vertical descent was about 1600 meters (5250 feet).

The sliding slab was about 15 kilometers (9 miles) wide and had a surface area of about 165 kilometers (64 square miles). Debris from the slide crossed the Karkheh River at the base of the slope and spread across the valley floor. Some material in the slide had a travel distance of over 14 kilometers (9 miles).

The slide debris dammed the Karkheh River, causing a large lake to form behind the dam. The lake persisted long enough for up to 150 meters of sediment to accumulate on its bottom (these sediments currently support several thousand acres of cultivated land). The lake then breached the dam and eroded a channel through it. The current landscape is shown in the Landsat image at the top of this page and in the Google satellite image in the right column.  

How did those big rocks end up on that strange terrain?

 How did those big rocks end up on that strange terrain? One of the more unusual places here on Earth occurs inside Death Valley, California, USA. There a dried lakebed named Racetrack Playa exists that is almost perfectly flat, with the odd exception of some very large stones, one of which is pictured above. Now the flatness and texture of large playa like Racetrack are fascinating but not scientifically puzzling -- they are caused by mud flowing, drying, and cracking after a heavy rain. Only recently, however, has a viable scientific hypothesis been given to explain how 300-kilogram stones ended up near the middle of such a large flat surface. Unfortunately, as frequently happens in science, a seemingly surreal problem ends up having a relatively mundane solution. It turns out that high winds after a rain can push even heavy rocks across a momentarily slick lakebed.

Zagros Mountains

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.

The Zagros Mountains in southwestern Iran

The Zagros Mountains in southwestern Iran present an impressive landscape of long linear ridges and valleys. Formed by collision of the Eurasian and Arabian tectonic plates, the ridges and valleys extend hundreds of kilometers. Stresses induced in the Earth’s crust by the collision caused extensive folding of the preexisting layered sedimentary rocks. Subsequent erosion removed softer rocks, such as mudstone (rock formed by consolidated mud) and siltstone (a slightly coarser-grained mudstone) while leaving harder rocks, such as limestone (calcium-rich rock consisting of the remains of marine organisms) and dolomite (rocks similar to limestone containing calcium and magnesium). This differential erosion formed the linear ridges of the Zagros Mountains. The depositional environment and tectonic history of the rocks were conducive to the formation and trapping of petroleum, and the Zagros region is an important part of Persian Gulf production.

This astronaut photograph of the southwestern edge of the Zagros mountain belt includes another common feature of the region—a salt dome (Kuh-e-Namak or “mountain of salt” in Farsi). Thick layers of minerals such as halite (common table salt) typically accumulate in closed basins during alternating wet and dry climatic conditions. Over geologic time, these layers of salt are buried under younger layers of rock. The pressure from overlying rock layers causes the lower-density salt to flow upwards, bending the overlying rock layers and creating a dome-like structure. Erosion has spectacularly revealed the uplifted tan and brown rock layers surrounding the white Kuh-e-Namak to the northwest and southeast (center of image). Radial drainage patterns indicate another salt dome is located to the southwest (image left center). If the rising plug of salt (called a salt diapir) breaches the surface, it can become a flowing salt glacier. Salt domes are an important target for oil exploration, as the impermeable salt frequently traps petroleum beneath other rock  layers