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Crater Formation


This research leads me to realise that most of the numerous craters on the Moon, Mercury and Mars as well as many asteroids have been produced endogenously and not by collision from asteroids.


Many craters are collapsed calderas, ex - Plinian type volcano structures, or kimberlite pipe structures.



Collapsed Calderas


A build up vaporised material within the crust often causes bulging upwards of the terrain. The vapour can be suddenly and violently released through a ring area - after-which the central area within the ring collapses downwards.


The vapour release is usually followed by a low energy exudation of magma residues either within the rim edge or at a central area to form a cone structure.


Ejections of gas from below the crust are even more violent and the crater formed from these eruptions resemble the exit damage of ballistics passing through materials. When a bullet passes through a material it vapourises the walls of the material creating a hole diameter much greater that the bullet itself. This hot vapour causes the surrounding material to be drawn along with it. Consequently when the bullet exits from the material it extrudes the walls outwards to form a characteristic rim structure. The orifice formed in this way is later filled with debris from the surrounding area.


Kimberlite pipes, in which diamonds are formed from compressed carbon dioxide form in this manner.


Craters with concentric rings


Many craters show concentric ring structures. These could not have been caused by asteroid impacts as the chances of asteroids impacting the same crater area perfectly centrally are impossible low.  
































The Richat structure in Mauritania would appear from outer space as an asteroid crater impact. However, there are numerous concentric rings. These must have been caused by regular violent de-gassings. This structure is in the Sahara desert and so the scarce population will have not witnessed any of these events - that is if they have happened in recent history.


One crater formation, however, has been witnessed. This was the formation of Nuovo Monte (New Mountain) in Italy near Naples which exploded in 1538.


This was a classic scenario where the terrain swelled up into a hill formation before it exploded violently, showering pumice everywhere in the vicinity.



Basin Formation
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