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Aug 11, 2005
Richat Crater Revisited

Why do these three craters and a fourth line up and why are they so circular? We suggest these three craters are part of the same discharge event series. Circularity is an earmark of Birkeland-current machined craters.

See: TPOD for April 07, 2005 Earth's Richat Crater

Tenoumer crater, diameter 1.9 km, N 22°55' - W 10°24'

See: http://disc.gsfc.nasa.gov/geomorphology/GEO_2/geo_images_T-61/PlateT-61.K.jpeg

Satellites photos show this crater, located on top of the Pliocene (or younger) sediments overlaying Precambrian gneisses and granites in the western Sahara desert, Mauritania. to be quite circular. Projectiles found outside the crater are up to 20m long and consist of rock material containing altered gneiss and granite clasts with small fractured glass inclusions on the surface.

Temimichat crater, diameter 750 m, N 24°15' - W 9°39'

It is interesting to note that the Richat Crater is very slightly oval and its major axis is inline with the two other craters. We suggest that these three craters are part of the same discharge event series, conventional "dating" notwithstanding. Crater chains are a common result of electric arcs passing over a cathode surface because the arc "sticks" and machines out a circle and then jumps to repeat the process.

The excavated material is accelerated upwards, some into space, some to fall back down around the area, and some to just pile up along the edge forming the raised rims.  The twisted Birkeland current of the discharge channel usually doesn't machine as intensely in the center of the crater and it leaves a formation of undisturbed material ranging from a slightly elevated mound to a tall spike of rock. The type of central "peak" depends on many factors: the narrowness, focus and intensity of the Birkeland current, the type of material being excavated and the material's current carrying capacity.

When the current is narrow and intense, and the material is dense, most of the excavated material is accelerated away from the area. The result is deep canyons and/or craters with steep walls and central spikes. Conversely, broad, less intense currents machine out shallow craters with central mounds, less steep walls, and material piled up along the edge and strewn around the more immediate area.

Relatively flat floors are a feature of this Electric Discharge Machining  (EDM), and our modern industry uses tightly controlled EDM to produce extremely smooth surfaces on molds for "polished" surfaces on plastic parts or products. Those who have experience with machine shop EDM have no difficulty in relating to this model of crater formation.

Composed by Shaun Bourke and Michael Armstrong

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