Richat Structure: Eye Of The Sahara

The Richat Structure, also known as the Eye of the Sahara, is a prominent circular feature in the Sahara desert of west–central Mauritania near Ouadane. Surrounded by thousands of square miles of nearly featureless desert, this 40-50 km in diameter series of concentric circles is readily visible from space. This prominent circular feature in the Sahara desert has attracted attention since the earliest space missions because it looks like a gigantic bull’s-eye.

Richat Structure is not the site of an ancient meteor crater, as many people originally postulated. These concentric circles are actually alternating layers of sedimentary, metamorphic, and igneous rocks that were pushed upward in a symmetrical anticline, geologic dome, from below due to a small incursion of magma. The structure is a deeply eroded. The sedimentary rock exposed in this dome range in age from Late Proterozoic (2.5 billion years) within the center of the dome to Ordovician (480 million years) sandstone around its edges.

Initially interpreted as an asteroid impact structure because of its high degree of circularity, it is now argued to be a highly symmetrical and deeply eroded geologic dome. Despite extensive field and laboratory studies, geologists have found a lack of any credible evidence for shock metamorphism or any type of deformation indicative of an extraterrestrial impact.

In addition, the Richat structure lacks the annular depression that characterize large extraterrestrial impact structures of this size. Also, it is quite different from large extraterrestrial impact structures in that the sedimentary strata comprising this structure is remarkably intact and "orderly" and lacking in overturned, steeply dipping strata or disoriented blocks. A more recent multianalytical study on the Richat megabreccias concluded that carbonates within the silica-rich megabreccias were created by low-temperature hydrothermal waters, and that the structure requires special protection and further investigation of its origin.

Exocoetidae: The Fish That Flies

Exocoetidae, commonly called Flying Fish, is a family of fishes aptly named for their ability to emerge out of the water and glide for long distances with their outstretched pectoral fins. Their streamlined torpedo shape helps them gather enough underwater speed to break the surface, and their large, wing-like fins get them airborne. Once in the air, these fishes can glide over considerable distances. Their flights are typically around 50 meters, but some fishes have been recorded to fly up to 200 meters or more. Some species of flying fish have enlarged pelvic fins as well as enlarged pectoral fins, which allows them to fly further than two winged gliders (up to 400 meters), and have far greater maneuverability. These fishes are known as four-winged flying fish.

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To glide upward out of the water, a flying fish moves its tail up to 70 times per second. It then spreads its pectoral fins and tilts them slightly upward to provide lift. At the end of a glide, it folds its pectoral fins to reenter the sea, or drops its tail into the water to push against the water to lift itself for another glide, possibly changing direction. The curved profile of the "wing" is comparable to the aerodynamic shape of a bird wing. The fish is known to take advantage of updrafts created by air currents to increase its time of flight.

Flying fish are thought to have evolved this remarkable gliding ability to escape predators, of which they have many. Their pursuers include mackerel, tuna, swordfish, marlin, and other larger fish. Unfortunately, this evasive maneuver is not enough to escape the biggest predator on earth – humans.

Flying fish is commercially fished in Asian countries such as Japan, Vietnam and China, including the Caribbean where it’s a coveted delicacy. In Japanese cuisine, the fish is used to make some types of sushi. It is also a staple in the diet of the Tao people of Taiwan. In Barbados, flying fish were threatened by pollution and overfishing, changing the occurrences of flying fish in the waters off of Barbados. This sparked a fishing controversy between Barbados, and Trinidad and Tobago.

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Sources: Wikipedia, Nat Geo, EOL

Psychedelic Stalactite Formation at Avshalom Cave, Israel

Avshalom Cave also known as Soreq Cave or Stalactites Cave is located on the western slopes of the Judean mountains near Bet Shemesh in Israel. The 5000 square meters cave has one of the most impressive collection of stalactites and stalagmites formed in a variety of patterns. Some of the stalactites hanging from the ceiling of the cave are up to four meters long, and in some cases they fuse with stalagmites growing from the floor. Other formations resemble shelves or sheets of cloth, branches, corals and clusters of grapes, among many other objects. The bizarre patterns at Avshalom Cave combined with the ghostly lightening creates a rather creepy ambience inside the cave.

Stalactites and stalagmites are formed by water flowing from the ceiling to the floor of the cave, melting limestone on the way. Over hundreds of thousands of years, each drop of mineral-laden water deposited a thin layer of calcite on the ceiling and on the ground. Given enough time these tiny layers add up to form columns of calcium carbonate called stalactites and stalagmites.

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The Avshalom Cave was discovered by accident in May 1968 when an explosion opened a crack to reveal the magical and fantastic cave hidden beneath. According to geologists, the Soreq cave was formed around 25 million-years ago, when the mountainous range of the Judean Hills rose up above the surface of the water. The layers of limestone and dolomite rock were displaced and folded with time, forming cracks which allowed water to enter and dissolve some of the rock. While seeping through the cracks and flowing through the soil this water absorbed increasing amounts of carbon dioxide from the roots of the plants and the surrounding decay. This process that turns the water acidic is called “Karst” and helped with the cave expansion process.

Years later, when the sea retreated and lowered the ground water level, the dissolution of rock stopped and the process was reversed. Drops of water saturated with limestone solution reached the ceiling of the cave the carbon dioxide escaped and the remaining limestone crystallized, creating the huge diversity of stalactites we see today. In several still-active areas of the cave, which maintains constant heat and humidity year-round, the stalactites and stalagmites continue to grow.

The cave is named after Avshalom Shoham, an Israeli soldier killed in the War of Attrition. After its discovery, the location of the cave was kept a secret for several years for fear of damage to its natural treasures. The cave which is in the heart of the 67-dunam Avshalom Nature Reserve, declared in 1975, is today open year round to visitors.

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Sources: Wikipedia, PerlaCopernik's Blog, Israel Nature and Parks Authority

Rare Weather Phenomenon Creates River of Clouds Over Grand Canyon

A rare weather phenomenon that affects the area only about once a decade, filled the Grand Canyon in the U.S. with a dense, white fog at the end of November. The phenomenon, known as "temperature inversion," happens when the temperature profile of the atmosphere is inverted from its usual state, and cooler air is trapped at the earth's surface by warmer air above.

Typically, the temperature of air in the atmosphere falls the higher up in altitude you go. This is because most of the suns energy is converted into heat at the ground, which in turn warms the air at the surface. The warm air rises in the atmosphere, where it expands and cools. When temperature inversion occurs, the temperature of air actually increases with height. The warm air above cooler air acts like a lid, trapping the cooler air and fog at the surface and preventing it from rising.

Temperature inversions happen once or twice a year, typically in the winter months. However, these inversions are partial and cover only few parts of the Grand Canyon. The most recent inversion happens only once every 10 years, because the fog filled up the entire canyon and it happened on a cloudless day.

AccuWeather.com Meteorologist Andy Mussoline explained the factors that contributed to the event.

"First, there was higher-than-normal moisture in the canyon," he said. "There was 0.75 of an inch of liquid precipitation that fell between Nov. 20 and Nov. 24 at the Grand Canyon National Park Airport [both snow and rain]. Normal precipitation during that time is only 0.19 of an inch, which converts to nearly 400 percent of normal precipitation within about a week of the event."

“Additionally, the average high temperature for this time of year is about 48 degrees Fahrenheit, which means there would be less evaporation of that precipitation than there would be in the summer months. This allowed more moisture to stay in the air inside the canyon.”

"A high pressure system settled into the region late last week and allowed for clear skies and calm winds, two important weather conditions that allow the air near the ground to cool rapidly," Mussoline said. "The rapid cooling of the ground allowed a temperature inversion to form."

Photos via Grand Canyon National Park Facebook page.

Dean's Blue Hole, World's Deepest Blue Hole

Dean's Blue Hole near Clarence Town on Long Island, Bahamas, is the world's deepest known “blue hole” - a term given to any deep, water filled, vertical caves or sinkholes with an entrance below the water surface. While most blue holes and sinkholes reach a maximum depth of 110 meters, Dean's Blue Hole plunges to more than 200 meters, which makes it quite exceptional. At the surface, Dean's Blue Hole is roughly circular, with a diameter ranging from 25 to 35 meters. After descending 20 meters, the hole widens considerably into a cavern with a diameter of 100 meters.

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Blue holes are so called for the dramatic contrast between the dark blue, deep waters of their depths and the lighter blue of the shallows around them. The intense blue color is created by high transparency of water and bright white carbonate sand. Blue light is the most enduring part of the spectrum; other parts of the spectrum - red, yellow, and green - are absorbed during their path through water, blue light manages to reach the white sand and return upon reflection.

Blue holes formed during past ice ages, when sea level was as much as 100–120 meters lower than at present. These holes were formed by deeper groundwater gradually dissolving the limestone until the ceiling of these voids collapsed. Later the sea level rose and filled the holes with water.

Dean's Blue Hole is a popular spot for diving ad snorkeling. At the 2012 freediving world cup in the Bahamas, New Zealand competitor William Trubridge set a world record when he dived to a depth of 121 meters without air in Dean’s Blue Hole.

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Pacu, The Fish With Very Human Teeth

Pacu is a South American freshwater fish found in most rivers and streams in the Amazon and Orinoco river basins of lowland Amazonia, but they have also been reported as far as Papua New Guinea, where it was artificially introduced to aid the local fishing industry. Pacu is related to the meat-eating piranha, both sharing the same subfamily Serrasalminae, although they have different food habits. The piranha is a carnivorous species while the pacu is omnivorous with vegetative tendencies. The difference is evident in the structure of their teeth. Piranha have pointed, razor-sharp teeth whereas pacu have squarer, straighter teeth, that eerily resemble those of humans.

Pacu uses its teeth mainly to crush nuts and fruits, but sometimes they also eat other fish and invertebrates. They usually eat floating fruits and nuts that drop from trees in the Amazon, and on a few occasions were reported to attack the testicles of male swimmers mistaking them to be floating nuts. This has earned them the name of "ball-cutter" after they castrated a couple of local fishermen in Papua New Guinea. So when the fish was spotted in a few odd lakes in Denmark and later in Washington, New Jersey and Illinois last year, a mild panic ensued.

While they are not aggressive carnivores like the piranha, their crushing jaw system can be hazardous. One toddler needed surgery after a pacu bit her finger at Edinburgh Butterfly and Insect World in Scotland. Commenting on the incident, Deep Sea World zoological manager Matthew Kane warned, "Pacus will eat anything, even children's wiggling fingers.

Pacus are legal to own in the United States, can be bought in aquarium stores and are easy to raise. The trouble is many aquarium owners are unaware that pacus can grow up to 4 feet long, which is way too large for a typical home aquarium. When pet pacus outgrow their fish tank, many owners end up dumping the fish in nearby lakes.

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Aside from pacu the Sheepshead fish (Archosargus probatocephalus) also has human teeth but a little too many.

Photo credit: Scientificamerican.com

A fully-grown adult sheepshead has well-defined incisors sitting at the front of the jaw, and molars set in three rows in the upper jaw and two rows in the lower jaw. It has strong, heavy grinders set in the rear of the jaw too, which are particularly important for crushing the shells of its prey. As with humans, this unique combination of teeth helps the sheepshead process a wide-ranging, omnivorous diet consisting of a variety of vertebrates, invertebrates and some plant material.

Sheepshead fish are also called convict fish due to the black and white bands that run down its silvery body. Photo credit