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
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.