The Earth Story

Deadvlei, the dead marsh It is amazing the effect water can have in bringing life, and then taking it from an area. Deadvlei is a white clay pan in Namibia near the Tsauchab River. During an especially heavy period of rain, the river flooded leading to a shallow surface layer of water forming over the clay pan. This water allowed Camel Thorn trees to grow and then mature. However, during a drought the water dried up, and sand dunes around the edge of the clay pan blocked the river’s flood path into the area. This drought lead to the trees dying, approximately 700 years ago. Despite the death of the trees, the skeletons remain and despite being blackened by the sun, appear structurally as they would have when they died. This lack of decomposition has occurred, again, due to lack of water as the trees cannot decompose without it. ~SA Image credit: https://commons.wikimedia.org/wiki/File:Deadvlei_trees_dunes.JPG

Nebraska Sand Hills Extensive tracts of sand dunes are common throughout the central Great Plains and Rocky Mountains. The greatest among these is the Nebraska Sand Hills, which cover nearly 20,000 square miles (52,000km2) in north-central Nebraska and southernmost South Dakota.

White Sands Blonde mice and white lizards blend into the background in a desert of milk-white dunes.

Starry dunes Sandy formations of this type develop when there is no single dominant wind direction, a multiplicity of them combining instead to shape the landform. This process is not confined to our planet, as these examples, which could easily be in the Rub al Khali (the Empty Quarter) of the Arabian Peninsula, were actually snapped on the next planet out from the sun, namely Mars. Loz Image credit: NASA

Dune motion Sand dunes move due to wind. As air moves rapidly up the slope of a sand dune, it causes sand to saltate, bouncing upward with one grain hitting another until it reaches the crest of the dune. At the crest, sand piles up until the dune becomes too steep – the weight of the sand overcomes the frictional forces that hold the grains together. At that point, a small avalanche takes place – sand heads down the steep side of the dune, restoring the balance between friction and gravity. This shot of California’s Kelso Dunes captures a marvelous set of examples of this process; a series of sand grain avalanches, one after another, bringing material down from the crest of the dune. -JBB Image credit: http://bit.ly/1F6tmPl Read more: http://www.desertusa.com/geofacts/sanddune.html http://www.nps.gov/grsa/learn/nature/dune-types.htm

Dune motion Sand dunes move due to wind. As air moves rapidly up the slope of a sand dune, it causes sand to saltate, bouncing upward with one grain hitting another until it reaches the crest of the dune. At the crest, sand piles up until the dune becomes too steep – the weight of the sand overcomes the frictional forces that hold the grains together. At that point, a small avalanche takes place – sand heads down the steep side of the dune, restoring the balance between friction and gravity. This shot of California’s Kelso Dunes captures a marvelous set of examples of this process; a series of sand grain avalanches, one after another, bringing material down from the crest of the dune. -JBB Image credit: http://bit.ly/1F6tmPl Read more: http://www.desertusa.com/geofacts/sanddune.html http://www.nps.gov/grsa/learn/nature/dune-types.htm

Sightseeing in Namibia and the Namib desert

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A Dune that Swallowed the Town

It's difficult to miss the large green Michigan historical marker set up in the middle of the bustling tourist town of Saugatuck. Most people aren't disappointed, since it tells the rather romantic tale of the town of Singapore, Michigan. Named for the island country in the hopes of luring boat traffic, Singapore was once a hub of industry; the town boasted three lumber mills at one time, and even had a wildcat bank (a bank chartered and regulated by the state and known for their nefarious practices). The great Chicago fire of 1871 created a seemingly limitless demand for lumber, which the Singapore mills were more than happy to oblige. At the time, Allegan county was covered in forests. But as the demand for lumber increased, many of the forests in the area were logged out. They removed any suitable tree they could find, including the trees on the dunes that acted as a soil stabalizing buffer between them and the rampaging western winds of Lake Michigan.

The town was abandoned shortly after the forest resources gave out; by 1877 the bank and the town were defunct and everyone moved out (although some didn't go very far - just upriver a 1/4 of a mile to Saugatuck). While some of the buildings were moved, many of them were simply covered up over the years by the migration of Michigan's denuded dunes, and Singapore started it's new life as one of the more famous Michigan ghost towns.

While the disappearance of Singapore by sand might haunt the imagination like a Stephen King novel, the real star of this show is the sand dune. It seems the town was nearly completely buried with sand in about 4 years (1), although some parts of the town could still be seen as late as 1883(2). The burial of Singapore is a classic example of sand dune movement by the wind, particularly after a dune denuding event.

Shortly after the town was abandoned, Henry Chandler Cowles discovered the importance of dune vegetation to the growth and ultimate stability of the dunes. Cowles is famous for his research in dune succession, or how dunes “grow up” and become larger dunes. He was able to identify groups of plants that were the first to colonize dunes. Ultimately he was able to find a suite of plants that accompanied every stage of dune succession.

Perhaps one of the more interesting discoveries he made was how cottonwood trees could be responsible for building giant dunes. As cottonwoods are covered in sand they are able to grow taller because they send out roots from the buried trunk. Taller trees allow more sand to accumulate. This continual growth and accumulation leads to large, stable dunes that harbor other forms of plant life.

There are many reasons for severe soil denudation, including, but not limited to, strong storm surges, the quick accumulation of sand leading to smothering, fire, and people. This last caused the sudden burial of Singapore and still accounts for shifts in dunes to this day; a walk along any of Michigan's sand dunes will reveal signs asking hikers to stay on paths so that vegetation is not killed and the dunes remain stable.

(1) http://bit.ly/1s59vPQ… (2) http://bit.ly/1wrOdO1 Photographs courtesy of the Saugatuck-Douglas Historical Society Box 617, Douglas, MI 49406 Aritcle by Colter

Valley of Fire

These rocks are cross-bedded sandstones of the Aztec formation found in Valley of Fire State Park in Nevada.

This unit correlates in time with the Navajo Sandstone found in other parks throughout the Western U.S. The patterns of layers and cross bedding are similar to patterns we see forming in sand dunes today, implying that the rocks formed in giant sand dunes. In the early Jurassic when these rocks formed, this part of the North American continent was basically a giant sand sea known as an erg. The climate of the area gradually moistened during the Jurassic, allowing for preservation of these features. The colors are produced by iron oxides that were trapped in the sand dunes as they formed.

-JBB

Image credit: https://commons.wikimedia.org/wiki/File:Aztec_Sandstone_-_Valley_of_Fire1.jpg

Read more: http://digital-desert.com/valley-of-fire/geologic-history.html http://paleobiology.si.edu/geotime/main/htmlversion/jurassic5.html

Sahara meets sea The coastline in this astronaut photo from the space station looks almost as though it was carved by human hands in its near perfect linear regularity, the sharp contrast strengthened by the hues of sand and ocean and the surreal looking clouds over the Atlantic. Some drying patches of rain are visible thanks to the salt that they have dissolved and are now re-precipitating. Loz Image credit: Steve Swanson

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