Rootless cones on Mars

EDIT: Original thread title was "small, round structures on Mars" - now it is solved.
...
on CTX imagery strip firstly I have spotted three, 100 meters diameter, perfectly round, ringed outcrops (as if were parked UFOs),
then swarms of smaller ones, ending a cluster of both type.



later, on another CTX slice I have found similar objects again and image title seemed to solve the mistery:
"Ring/cone structures" - however these studied objects are much bigger.

in attached kmz folder, placemarks for 4 sites can be found. (keep GMars / Primary Database / Featured Satellite Imagery layer enabled) 
small round structures on Mars.kmz (1.16 KB)

can these be some martian kinds of Pingos?

dimensions and concentric structure make them similar to this smaller one in Canada:
small pingo Canada.kmz (805 B)


thanks!
g

Comet impact.


meteorites create non-round  impact craters, as the gas pressure is created by a non-round object,  giving the gas pressure a shape, overlayed on the  shapes  produced by  the varying  mechanical properties  rock strata it hit,  and then its gone.


 circular impacts  are from comets.  The comet fragment creates gas pressure for a while, a lot longer than from an asteroid rock thing,  and that flow of gas wipes out any feature.. (erosion occurs faster at corners.)  It doesnt much matter as to the angle of impact with comet fragments.

On Mars there are 600,000    craters larger than 600 metres diamater.   Imagine how many smaller craters there are... 

These ones appear to be a an erosion zone..  a process that may also change the crater ? Or at least remove the streaks from high speed impacts.
Meteors and errant Keiper belt objects may well hit at such a high speed, a small bit of rock makes a large explosion.. a gas based explosion  ,circular, and fresh ones have the streaks.


Straying  asteroids make for a far slower impact speed. perhaps  creating an asteroid shaped dent,   showing the differences of mechanic properties of the Mars strata, and with debris acculation   at the rim perhaps more to one side.

hi leong !

so you say that these hundreds of "small" domes are eroded impact craters of comet debris?

en.wikipedia.org/wiki/Rootless_cone

These are very numerous on the plains of Mars and are caused by lava moving over frozen groundwater, causing a massive steam explosion and an associated crater. They are not pingos as pingos lack central craters.

That is it! Thanks for solving shadowdragon! - I have edited post title also my whaddahecks list. (;

Do not you think btw., the same geological features can be seen around here in Mali?