That’s not lava, it’s mud

Lava-like flows on Mars are more likely caused by mud than lava, according to a new study.

A European team used the Mars Chamber at the Open University in the UK to recreate the surface temperature and atmospheric pressure on Mars and compare them with a simulation of conditions on Earth.

They observed that the mud flows on the Red Planet did not behave like typical Earth mud flows, but instead resembled ropy and jagged terrestrial lava flows with a frozen crust rapidly forming around lobes of mud.

This is because water is not stable and begins to boil and evaporate, they report in a paper in the journal Nature Geoscience. The evaporation removes latent heat from the mud, eventually causing it to freeze.

“We suggest that mud volcanism can explain the formation of some lava-like flow morphologies on Mars, and that similar processes may apply to eruptions of mud on icy bodies in the outer Solar System, like on Ceres,” says lead author Petr Brož, from the Czech Academy of Sciences.

There are thousands of volcano-like landforms on the Martian surface, often situated where there are massive channels scoured into the surface by ancient liquids flowing downstream.

These channels are extremely long, extending many hundreds of kilometres in length and usually more than dozens of kilometres wide. They are believed to be the result of massive floods involving huge bodies of water comparable to the largest floods ever known to have occurred on Earth. When the water seeps into the subsurface it can emerge again as mud.

Brož and colleagues from the Czech Republic, the UK, France, Germany and Norway performed experiments at low pressure and at extremely cold temperatures (–20 degrees Celsius) to recreate the Martian environment. 

Under Martian conditions, the experimental mud flows formed shapes similar to “pahoehoe” lava frequently occurring on Hawaii or Iceland on Earth, which cools down to form smooth undulating surfaces. In the experiment, this happened when liquid mud spilled from ruptures in the frozen crust, then refroze.

However, under terrestrial atmospheric pressure, the experimental mud flows did not form lava shapes, did not expand, and had no icy crust, even under very cold conditions.

“The same principles apply to other Solar System bodies and icy moons, and so our experimental results should be considered when interpreting effusive cryovolcanic surface features on these bodies,” the researchers write in their paper. 

“Our results show that it is vital to consider the effects of the differing environmental conditions on other planetary surfaces when comparing analogue landforms observed on Earth with apparently similar effusive morphologies on other bodies.”