Archive for November, 2012

November Puzzler

November 12th, 2012 by Adam Voiland

Every month, NASA Earth Observatory will offer up a puzzling satellite image here on Earth Matters. The sixth puzzler is above. Your challenge is to use the comments section below to tell us what part of the world we’re looking at, when the image was acquired, and what’s happening in the scene.

How to answer. Your answer can be a few words or several paragraphs. (Just try to keep it shorter than 300-400 words). You might simply tell us what part of the world an image shows. Or you can dig deeper and explain what satellite and instrument produced the image, what bands were used to create it, and what’s interesting about the geologic history of some obscure speck of color in the far corner of an image. If you think something is interesting or noteworthy about a scene, tell us about it.

The prize. We can’t offer prize money for being the first to respond or for digging up the most interesting kernels of information. But, we can promise you credit and glory (well, maybe just credit). Roughly one week after a “mystery image” appears on the blog, we will post an annotated and captioned version as our Image of the Day. In the credits, we’ll acknowledge the person who was first to correctly ID an image. We’ll also recognize people who offer the most interesting tidbits of information. Please include your preferred name or alias with your comment. If you work for an institution that you want us to recognize, please mention that as well.

Recent winners. If you’ve won the puzzler in the last few months, please sit on your hands for at least a few days to give others a chance to play.

You can read more about the origins of the satellite puzzler here. Good luck!

Dune Gallery

November 2nd, 2012 by Michon Scott

The November 2012 issue of National Geographic features an article, “Sailing the Dunes,” about aerial trips over sandy deserts. The author, George Steinmetz, has flown in light aircraft in high winds—a dangerous combination. Yet the same winds that make the flying so dangerous also sculpt some of the world’s most beautiful landscapes. Several of the places mentioned in the article have also been covered by the Earth Observatory. Here is a sampling of some of those places, plus some additional dune-rich landscapes.

The Sahara Desert spans northern Africa, covering about 9.4 million square kilometers (3.6 million square miles). Within the Sahara are multiple sand seas, or ergs — big, windswept landscapes of shifting sands. The ergs can be as photogenic as they are forbidding.

Issaouane Erg in Algeria holds multiple crescent-shaped (barchan) dunes and star dunes. Winds blowing mostly from one direction create barchan dunes while variable winds create star dunes. Low-angled sunlight highlights the varied dune shapes in this region. Story: Issaouane Erg, Algeria

Besides barchan dunes and star dunes, Issaouane Erg is also home to mega-dunes. Mega-dunes likely take hundreds of thousands of years to form, and may have started their formation when the Sahara—once a more hospitable place—began to dry. In between the big dunes, winds have swept sand away from the desert surface altogether, revealing gray-beige mud and salts. Story: Dune Types in the Issaouane Erg, Eastern Algeria

The flat areas between dunes are known as dune streets, and they are unmistakable in Algeria’s Erg Oriental. In between the streets, star dunes sit atop linear dunes. Story: Erg Oriental, Algeria

Nearly sand-free basins also separate complex dunes in the Marzuq Sand Sea of southwestern Libya. The big sand masses are known as “draa” dunes, Arabic for “arm.” Extending from some of the draa dunes are snakelike linear dunes. Story: Sand Dunes, Marzuq Sand Sea, Southwest Libya

Dunes form in arid conditions, but conditions can change. The manmade Toshka Lakes of Egypt flooded old dune landscapes. Depending on lake levels and the underlying topography, some dunes are completely flooded while the crests of others poke above the water surface. Story: Toshka Lakes, Egypt

Although it covers an area much smaller than the Sahara Desert, the Arabian Peninsula’s Empty Quarter, also known as Rub’ al Khali, holds half as much sand as the entire Sahara. Salt flats—sebkhas or sabkhas—separate the towering dunes. Story: Empty Quarter

Though it lacks the massive sand seas of the Sahara and the Arabian Peninsula, the United States sports some impressive dune fields of its own. White Sands National Monument holds gleaming white sands formed from gypsum. These brilliant white dunes occur at the northern edge of the Chihuahuan Desert, which extends across the U.S.-Mexico border. Story: White Sands National Monument

The Algodones Dunes of southeastern California lack the snowy look of White Sands, but make up for it by hosting a complex assortment of dune formations. Smaller dunes sit on top of giant crescent-shaped dunes. Wind does not act alone in shaping this landscape; water flows off the Cargo Muchacho Mountains to the east, making its way into the dune field and sustaining some plant life. Story: The Algodones Dunes

Some of the world’s most complex dune formations occur in the Badain Jaran Desert of Inner Mongolia. Small lakes dot flat areas in between dunes, which have been characterized as “complex reversing mega-dunes developed from compound barchanoid mega-dunes.” Story: Elevation Map of the Badain Jaran Desert

And sometimes a single desert can host completely different landscapes. Identified by satellite data as the hottest place on Earth, Iran’s Lut Desert contains two completely different landscapes. The central portion is home to wind-sculpted linear ridges known as yardangs. The southeastern part of the desert hosts dunes that soar to 300 meters (1,000 feet) alternating with salt pans. Story: Diverse Terrain of Iran’s Dasht-e Lut

Note that due to the angle of sunlight, some of these images produce an optical illusion known as relief inversion.

Crane Glacier Terminus Retreat

November 2nd, 2012 by Adam Voiland

On October 25, 2012, we published a set of images that shows how the Hektoria and Green glaciers on the Antarctic Peninsula have continued thinning since the Larsen-B ice shelf’s collapse in 2002.  Though those two glaciers have been some of the fastest changing in recent years, they aren’t the only Larsen-B tributary glaciers that have lost ice over the last decade.

In all, the 15 glaciers that flow into the ice shelf have lost more than 10 gigatons (one gigaton equals one billion tons) of mass per year, according to research published in the Journal of Glaciology. Some of the most dramatic changes have occurred at Crane, the longest of the Larsen B tributary glaciers. Since the collapse of the ice shelf, Crane Glacier has retreated by more than 12 kilometers (7 miles).

This visualization, based on an image captured by the Advanced Land Imager (ALI) instrument on the Earth Observing-1 (EO-1) satellite, shows the location of the terminus in April 2002, February 2003, and February 2006. Since 2006, the terminus has stayed in the same general position. The image was acquired on February 24, 2012.  For another view of Crane glacier’s retreating terminus, please see this image.

NASA Earth Observatory image created by Jesse Allen and Robert Simmon, using EO-1 ALI data provided courtesy of the NASA EO-1 team.