The Earth Story

Of dams and mitigated results When the Aswan high dam was completed in 1970 it was seen as a triumph of socialist modernism and archaeological rescue, since it involved the dismantling and recreation off the giant statues of Abu Simbel, whose original site was drowned. Intended to provide electricity and irrigation water in order to turn the desert green, and also (successfully) tame the annual Nile flood that has been at the centre of Egyptian life since the dawn of its Civilisation (and too which the culture was adapted), it has also had unexpected consequences that could be devastating to the long term future of the country.

Milky Way timelapse over the Saharan Desert - viewable in 360, so you can click and reposition the camera.

Waw an Namus — A Saharan volcano From these images captured by the Operational Land Imager (OLI) on Landsat 8, the dormant volcano Waw an Namus looks like a drop of ink on a dusty piece of parchment. Located in Saharan region of southwestern Libya, the jet-black patch is made up of volcanic ash that was produced during the volcano’s last eruption. Although we don’t know the eruption's exact date, we know that it likely erupted some time during the past few thousand years, since the volcanic ash hasn’t yet been weathered and eroded away by wind or water. At the center of volcano lies a 4-km wide caldera — a depression that forms when a volcano with a shallow magma chamber collapses after a volcanic eruption.

The Mountain of Sourcelets

Within the expanse of the Eastern Sahara, where the borders of Egypt, Libya, and Sudan meet, a craggy mountainous range known as Jebel Uweinat stands tall, with its peak nearly 2,000 meters above sea level. Also known as the “Mountain of Sourcelets”, the massif is actually made of two distinct geologic features. The western side of the massif is the remains of a massive granite dome, with three seasonally dry riverbeds that extend westwards from the dome's center. Meanwhile, the eastern portion consists of sandstone and permanent oasis that may have served as refuge for desert inhabitants. It is on the more habitable eastern end where petroglyphs of ancient peoples have been found. The sandstone outcrops provided a canvas for these paintings and engravings that appear similar to other Bushmen-style petroglyphs at other sites in the Eastern Sahara. The Jebel Uweinat petroglyphs seem to mainly depict domestic cattle, but markings representing other domesticated animals such as camels and goats were also found. This ancient community seemed to have molded a mainly pastoral way of life, but engravings of human figures with dogs and antelopes meant they probably cultivated a hunting lifestyle as well.

Although Jebel Uweinat receives slightly more rainfall the surrounding desert, 100 mm/year is still a difficult survival situation for most living beings. The rock art at Jebel Uweinat gives us a look as to how the harsh desert environment molded this bygone society.

-DC

Photo credits: https://visibleearth.nasa.gov/view.php?id=80599 & http://bit.ly/1anEa3n

Further reading: http://bit.ly/1anEa3n

http://bit.ly/1CfqhcU

http://bit.ly/1anEa3n

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5 Days in Marrakesh to Merzouga

Libyan Desert Glass

This gemstone shown in the picture is 28.5 million year old silica desert glass, found in-between sand dunes on the border of Libya and Egypt in the Great Sand Sea. People used the glass in the pleistocene era to make tools and carvings, and since its scientific discovery and investigation began in 1932, researchers have been trying to find an origin, but ultimately the reason has remained a mystery.

Color varies from transparent, milky white, light yellow, to a light green or green-brown color. The pieces vary in size and mass, and are often sand and wind eroded smooth on one side, with slight etchings resembling pseudo-regmaglypts, or characteristic grooves like a meteorite, on the other side. This glass contains high levels of silica, at around 98%, and can include many bubbles, dark brown streaks, and/or cristobalite spherulites, which are high-temperature silica structures.

Trace elements found in dark streaks within the glass include iron, magnesium, and aluminum, while wisps of iridium and iron in a low oxidation state point to an extraterrestrial origin for these impurities.

Scientists thought that the glass was formed by the impact of an extraterrestrial body into a sandstone layer, but no crater was found. This led researchers to hypothesize that a low-altitude airburst by a meteorite could supply the necessary heat to melt the sandstone, forming the gems we see today. This tektite would be similar to Trinitite, a glass made from the desert sands in New Mexico during the atomic bomb trial (see this Earth Story post on Trinitite: http://on.fb.me/1JV0IWh ).

A possible crater named Kebira was discovered in 2007, though very little research has been published regarding this site. A study did investigate in 2011, analyzing oxygen isotopes of sandstone taken from glass-containing areas and the proposed Kebira zone. This study determined that the glass did not originate from the proposed impact crater, but that did not identify an alternative source.

In 2013, scientists reported on a meteorite called “Hypatia,” a very hard, black, shiny, carbonaceous material with many fractures and diamond inclusions. Tests suggested that components in this rock formed at temperatures comparable to those found in liquid nitrogen, possibly suggesting that this stone is some of the only comet material found on Earth. Though there are some questions, the team suggests that a cometary nuclei entered Earth’s atmosphere, lost its water content and volatile hydrocarbons while gaining atmospheric noble gases, and then the bolide exploded. A diamond similar to the ones found in Hypatia has been found embedded in Libyan desert glass, possibly suggesting that a comet exploding in the atmosphere was the original source for this material.

On the other hand, a more recent study examined grains found in brecciated rocks associated with the Libyan Desert Glass strewnfield. In those rocks they found minerals like shocked quartz, which require large pressures - up to 20 GPa - to form in the state they were observed in. These pressures were unilkely to be produced during an airburst, leading those authors to again suggest that the Libyan Desert Glass was produced during an impact, but that the remnant crater has been completely eroded away.

-MH

Image Credit: James St. John, http://bit.ly/1zZYj75 References: Aboud, T., 2009, Libyan desert glass: Has its enigma been solved?: Physics Procedia 2, (2009) p. 1425–1432. Kramers, J.D, Andreoli, M.A.G., Atanasova, M., Belyanin, G.A., Block, D.L., Franklyn, C. Harris, C., Lekgoathi, M., Montross, C.S., Ntsoane, T., Pischedda, V., Segonyane, P., Viljoen, K.S., and Westraadt, J.E., 2013, Unique chemistry of a diamond-bearing pebble from the Libyan Desert Glass strewnfield, SW Egypt: Evidence for a shocked comet fragment: Earth and Planetary Science Letters, v. 382, p. 21-31. Longinelli, A., Sighinolfi, G., Michele, V.D., and Selmo, E., 2011, O and chemical composition of Libyan Desert Glass, country rocks, and sand: New considerations on target material: Meteoritics & Planetary Science , v. 46, p. 218-227. https://gsa.confex.com/gsa/2018AM/webprogram/Paper322276.html

Read More: http://geology.com/meteorites/impactites.shtml https://www.temehu.com/libyan-desert-glass.htm http://bit.ly/1EDTy8P

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

Huge salt flat in Tunisia

Saharan Sand: A Hindrance & Initiation of Weather

There is an invisible element out there that has the power to erode mountaintops, change landscapes, and in some cases carry sand and dust particles thousands of kilometers across the world’s atmosphere. I speak of wind. Wind is a powerful and mysterious element that exists even on the most distant planets. We can only bear witness to its effects since air is invisible to the naked eye. However sometimes, such as in the featured image, we can witness wind in disguise. Notice that in the picture, there is a faint band that stretches across the sea. That band is actually airborne sand particles and dust particles from the Sahara Desert, being carried thousands of kilometers across the barren Atlantic. The sand becomes kicked up into the atmosphere and affects global weather patterns in many ways

Recent research from NASA suggests that these dust particles, once settled on the ocean water’s surface, block out some of the sunlight which in turn cools the water. In 2006, there were significantly more dust storms in the Sahara which scientists think may explain the generally quiet 2006 hurricane season. More dust storms would yield more airborne particles which in turn would settle on and cool the ocean surface. Since hurricanes thrive off of warm water, the cooler water would hinder the development of strong and more frequent hurricanes. However, some scientists debate on whether or not the Saharan dust is enough to influence such large storms and claim that the quiet 2006 hurricane season was due more to the effects of El Niño.

Nevertheless, airborne dust and sand that originated from the Sahara do in fact affect the planet’s weather. In addition to travelling west over the Atlantic, airborne dust is also known to travel east, out of the Sahara and eventually all the way across the Pacific Ocean where it ends its journey in California in the form of precipitation. In this case, the dust becomes airborne and somewhat trapped in the atmosphere where it acts as nuclei within clouds. The particles initiate the crystallization of ice and then once the cloud has reached its saturation point, the frozen particles are released as rain, snow, or hail.

So next time you witness a snowstorm, consider that at the center of each snowflake there may or may not be a tiny sand or dust particle that traveled from the Sahara, thousands of miles through the atmosphere and across the Pacific, just to land on your sleeve; a primal example of how our planet is interconnected even on the tiniest of levels.

--Pete D

Photo Credit: Andre Kuipers / ESA / NASA

References: 1. http://www.nasa.gov/mission_pages/hurricanes/archives/2007/hurricane_dust.html 2. http://scrippsnews.ucsd.edu/Releases/?releaseID=1327 3. https://www.scientificamerican.com/article.cfm?id=asian-and-african-dust-influences-north-american-weather 4. http://science.time.com/2013/01/22/a-room-with-a-view-scenes-from-the-international-space-station/photo/6832380432_461a2a58cf_b/

Sands across the ocean

This really cool image from NASA’s Aqua satellite captures the South Atlantic Ocean from a unique perspective; looking west from orbit over Africa.

The deserts of North Africa regularly send plumes of dust out over the Atlantic. Here a strong wind has driven a huge plume of dust all the way across the Atlantic to the mouth of the Amazon River in South America.

These plumes of dust can have a variety of impacts on the Western Hemisphere. These dust plumes help replenish the soil in the Amazon basin rainforest by bringing in nutrient elements, but also impact the breathing of people exposed to it. They can contribute to blooms of algae throughout the Atlantic, and even can impact the weather. Plumes of dust like these in the summer have been shown to inhibit hurricane formation out over the Atlantic.

-JBB Image credit: NASA/Aqua/EOhttp://earthobservatory.nasa.gov/IOTD/view.php?id=83966&eocn=home&eoci=iotd_readmore

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