Chaotic Terrain

Chaotic Terrain is a type of Martian surface feature. It is used in two ways by planetary scientists.

• The first is when a giant impactor on one side of a world causes massive shockwaves to travel thru the crust. When these shock waves collide on the opposite side of the world, the antipode, the shockwaves either cancel out, or combine chaotically, fracturing the curst, and making strange formations which planetary scientists call chaotic terrain.
• The second is when terrain saturated in ice, melts from below. The water turns to liquid and flows away, (sometimes emerging explosively downhill), leaving a strange area of collapses, shifted landforms, and gullies.

Both of these types of terrain have occurred on Mars.

Examples of Chaotic Terrain in the Solar System:

• On Mercury there is the Caloris Impact Basin which is about 1,550 km in diameter. On the exact antipode from this impact is chaotic terrain (also known as "a weird terrain"), which is made up of hilly, grooved terrain with few impact craters.

• On Earth, at the antipode of the Chicxulub Impact Event is India. At the time of the impact, the Deccan Traps formed. The Deccan Traps were caused when huge cracks opened in the Earth's surface and massive amounts of Lava flowed out, forming lava flows, in some areas, 2 km thick. (Approximately 1,000,000 cubic kilometres of lava were produced.) Gerta Keller, in a 2015 paper, has argued that the Chicxulub Impact created chaotic terrain in India, and the fractures produced in the crust allowed the Deccan Traps to form.

• On Luna, the largest impact crater is the South Pole-Aitken basin. Approximately opposite it are large lunar maria, and a concentration of the KREEP elements. (KREEP is from: K is the atomic symbol for Phosphorus, Rare Earth Elements, and Potassium.) It is currently thought that the impactor which formed the Aitken basin cracked the crust on the opposite side of the moon, and allowed the still liquid KREEP rich magma to form the 'seas' on the lunar northern near side.

• On Jupiter's moon, Europa there is the Conamara Chaos. No impact on the opposite side the world remains, but the ice plates over a liquid ocean may have erased a previous impact basin.

• On Pluto chaotic Terrain can be found at the antipode from the Sputnik Planitia impact basin.

Possible Impact(s) on Mars Formed Tharsis:

The Tharsis Bulge and the Hellas basin are at approximate antipodes from each other. In particular, Alba Mons, (an old, very large shield volcano north east of Olympus Mons), is exactly opposite from Hellas Planitia. It is possible that chaotic terrain caused by the Hellas impact weakened the crust at Tharsis and triggered, or aided, the formation of the Tharsis Bulge. Also note that the Isidis Impact basin (half the diameter of Hellas) is also opposite the southern parts of the Tharsis Bulge.

Water formed Chaotic Terrain on Mars:

The closest analog on Earth may be the mass wasting observed during permafrost melting.

On Mars, it is thought that a large area of soil saturated with ice may melt to create chaotic terrain. This melting may be caused by asteroid impact, gradual geothermal heating, a magma intrusion, seismic activity, increased pore pressure, or the dissociation of carbon dioxide & methane clathrates. (Different areas may well have had different forms of melting.) Some land near chaotic terrain appears undisturbed, and may be an area where the ground water did NOT melt.

However this water liquified, it flows downhill (causing collapses in the soil where it leaves), and may emerge to the surface lifting up and tilting huge blocks of rock. Chaos terrain is associated with a confusion of mesas, hills, valleys, gullies, & buttes. The chaotic terrain is often associated with the heads of large river systems on Mars, and it is theorized that massive amounts of water catastrophically emerged from some of these areas in sudden, huge floods.

By counting craters (old terrain has more craters), it is thought that these channels formed from 2.0 to 3.8 billion years ago.

Major areas of Chaotic Terrain:

• Chris Planitia
• Oxia Palus quadrangle
• Along the Martian Dichotomy (The border between the Martian lowlands to the north, and the southern highlands.)
• Margaritifer Sinus Quadrangle
• Phaethontis Quadrangle
• Lunea Palus Quadrangle
• Hydraotes Chaos
• Galaxias Chaos (this lacks an outflow river).

Noctis Labyrinthus is cool, but not chaotic terrain:

Note that Noctis Labyrinthus (the Labyrinth of the Night), west of Valles Marineris, was once thought to have been created by this process, but now is believed to have been created by faulting. (That is, this mesa and gully terrain is created when horsts remain still, and the corresponding gaben sink.)

Biography:

"Deccan Volcanism, the Chicxlub Impact, and the end-Cretaceous mass extinction: Coincidence? Cause and effect?" by Keller, G. Published in Volcanism, Impacts, and Mass Extinctions: Causes and Effects, GSA Special Paper 505. https://web.archive.org/web/20170618024315/http://specialpapers.gsapubs.org/content/early/2014/06/10/2014.2505_03.1.abstract

"Chaos Terrains on Pluto, Europa, and Mars -- Morphological Comparison of Blocks", Skjetne et. al. https://www.hou.usra.edu/meetings/lpsc2019/pdf/2146.pdf

"Martian Chaos Terrain on wikipedia. https://en.wikipedia.org/wiki/Martian_chaos_terrain

Noctis Labyrinthus on wikipedia. https://en.wikipedia.org/wiki/Noctis_Labyrinthus

"The Geology of Mars: Evidence from Earth-Based Analogs", published by Cambridge Planetary Science, Edited by Mary Chapman.