Monday, November 26, 2007

The Eye Of Africa - The Richat Structure

The Richat Structure is one of those geological features that are more clearly observed from space than from down on the ground. It was first observed from space by Gemini 4 astronauts McDivitt and White in June 1965.
Located in the center of Mauritania, the western end of the Sahara desert this prominent circular feature has attracted attention since the earliest space missions because it forms a conspicuous bull's-eye in the otherwise rather featureless expanse of the desert. Described by some as looking like an outsized ammonite in the desert, this 'eye of Africa' , which has a diameter of almost 50 kilometers (30 miles) has become a landmark astronauts since the earliest manned missions.

Credits: ESA

Most of the image looks yellowish, indicating sand desert. The dark brown part is bare sedimentary rocks, and within that you can see the Richat Structure, a gigantic ring structure of some 40 km in diameter.

The onion-like formation is formed by concentric bands of resistant paleozoic quartzite rocks form ridges, and between with valleys of less-resistant rock between them.

The part of the sedimentary rock corresponding to the white of the eye is a plateau standing some 200 m above the sand desert. The Richat Structure corresponding to the iris of the eye lies in a depression, and the peak of the outer rim is 485 m above sea level. The Richat Structure consists of Early Paleozoic rocks, some 600 million years old. Around the center, rocks resistant to weathering and erosion (purple and blue-green part) make 100 m high ridges, and nonresistant rocks (yellow and brown part) form valleys. These features alternate and are concentric.

Credit: Landsat 7, USGS, NASA

The Richat Structure was previously thought to have been formed by metorite impact or volcanic activity, but field surveys have demonstrated that neither are correct. The current thinking is that these features were formed by an uplift and subsequent erosion from wind and water.
However, why the structure is circular remains a mystery.

Friday, November 16, 2007

Weird Beauty

You can love them or hate them, but you can't be indifferent...
Here are some really strange and weird flowers you will probably never get from anyone (unless you live on some exotic island).

Amorphophallus titanum
Giant Voodoo Lily

Voodoo Lily has the world's largest inflorescence of any 8 feet tall, and they emit a foul odor.

Paeonia brownii
Brown's Peony

Sauromatum venosum


Clematis seeds

Daylily "Barracuda Bay"

Tricyrtis formosana
Toad Lily

Tacca integrifolia
White Bat Flower

Tacca chantrierei
Black Bat Flower, Cat's whiskers or Devil flower

Stapelia grandiflora

Stapelia Mutabilis




(This one looks like something from Harry Potter's Herbology class)

Dutchman's Pipe
Aristolochia trilobata


Passion Flower

Barringtonia asiatica
Commonly known as: barringtonia, fish-killer tree, queen of the shores, sea poison tree...

Dracunculus vulgaris
is variously called the Dragon Arum, Voodoo Lily, Ragons, Snake Lily, Black Arum, Black Dragon, Dragonwort, Stink Lily, Viagra Lily...

And here are some I'm not sure about the names...