Based on the results of several different analyses I believed that they were the result of igneous volcanism, but I was not sure. 

When I read a paper by Raack et al. (2017) describing the novel transport mechanism of sediments by levitation caused by the instability of liquid water in low pressure environments I started to wonder again how the environment would affect the way mud moves on Mars and hence what the resulting mud flows may look like. To satisfy my curiosity I wrote an email to Dr. Raack and asked him a simple question; do you know how mud would behave on the surface of Mars? He did not know and neither did anyone else whom I asked. But he made the best out of the situation. He suggested using the Europlanet society funding scheme to get access to a low pressure chamber situated at the Open University (United Kingdom) and to find out for myself.

A few months later I was in the lab of Dr. Manish Patel, playing with mud. He did not care too much how dirty his chamber would get, as long as the experiments had an interesting scientific question to answer. A rare situation…  I felt almost like a child again as me and my colleague, as well as the low pressure chamber, were covered in mud all day long. For four weeks we worked long days spending more than 10 hours per day in the lab. A lot of effort, but it was worth it. Even though the first couple days were full of failures, we realized very soon that we were on the verge of an interesting discovery. Even the failures were showing that the mud was behaving in very strange way compared to our everyday experience. It did not flow in the same way as, for example, when we accidentally spilt it over the lab bench or floor – not that this ever happened, of course…

Soon we mastered the experimental setup and we began to understand what we were observing. The mud was boiling as the atmospheric pressure in the chamber was low and soon after it started to freeze because of evaporative cooling. However, the freezing did not occur throughout the entire volume of the mud flow – it only froze at the surface and an icy-muddy crust was formed that protected the liquid mud underneath. We observed that mud movement over a cold surface under low atmospheric pressure in many ways resembled the movement of very mobile terrestrial pahoehoe lavas.

And this shook my world. I suddenly realized that many flow-like features on Mars which I believed to be lava flows based on their appearance might actually be mud flows. Therefore today, I am even less sure if something is mud flow or lava flow on Mars than I was 2 years ago. What a twist! I find myself having to rethink some of my previous interpretations and start again. But this time I am equipped with much better theoretical background, as I know what to expect from the movement of low viscosity mud on Mars.