Chaotic terrains are regions of the surface of Mars characterised by a complex morphology made of cracks, ridges, valleys, large and small angular blocks, which occur in different regions of the planet. They reach diameters of 20 to over 700 kilometers, consist in many cases of polygonal blocks, which can be several hundred meters high and have a very characteristic geometry. According to the most common thesis, the area was formed 3.7 to 2.9 billion years ago, when ice reservoirs under the surface suddenly melted due to heat and released large amounts of water. After the water drained away, the surface collapsed over the newly formed cavities, and the landscape crumbled in on itself.

In this new research, the team started from the new hypothesis that these complex terrains were generated by a volcanic process known as “piecemeal caldera collapse”. In this process, the surface of Mars is first uplifted by magma intrusion at depth, then collapsed by emptying of the magma chamber similarly to what happens in terrestrial calderas. Successive cycles of filling/uplifting and withdrawal/collapse determined the very complex structure of the Martian chaotic terrains.

To validate this hypothesis, the research team simulated the process of caldera collapse in a laboratory, through analogue modelling experiments performed at the Tectonic Modelling Lab of the CNR-IGG in Florence. In the experiments, researchers reproduced different cycles of magma inflation/uplift and deflation/collapse. In the laboratory, the Martial soil has been reproduced by using sand, whereas magma has been simulated by using polyglicerines.

For the first time, researchers were able to reproduce the characteristics of this region of Mars in an analogue experiment. Therefore, the experiments show that the development of these complex morphologies may have been created by volcanic processes rather than the action of water.

The research team also made a connection to very similar surface structures on the Moon: craters that formed by magmatic processes and later collapsed, called “Floor-Fractured Craters”. 


Erica Luzzi, Angelo Pio Rossi, Matteo Massironi, Riccardo Pozzobon, Giacomo Corti, Daniele Maestrelli (2021). Caldera collapse as the trigger of Chaos and fractured craters on the Moon and Mars. Geophysical Research Letters, 48, e2021GL092436.

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