The Arsia Mons Elongated Cloud forms when Mars’ atmosphere interacts with the tall volcano, creating a spectacular sight.

More info about it:

https://phys.org/news/2024-09-cloud-atlas-mars-showcases-array.html

https://www.sciencealert.com/we-finally-know-what-s-going-on-with-that-weird-long-recurring-cloud-on-mars

https://www.space.com/mars-weird-long-cloud-arsia-mons-secrets