Mud on the surface of Mars probably flows like lava does on Earth, which makes it difficult to tell whether Martian volcanoes are spewing lava or just mud
Source:
https://www.newscientist.com/article/2243570-mars-may-be-covered-in-mud-volcanoes-disguised-as-lava-flows/?utm_campaign=RSS%7CNSNS&utm_source=NSNS&utm_medium=RSS&utm_content=home