Tldr: it's not traditional erosion from water or wind, nor is it tectonic in nature. The edge collapsed in a landslide. As the volcano erupted over time it built up more and more depositted material in layers, and eventually the mass became too heavy for the bottom material layer to support so it crumbled and caused a land slide.
(Paraphrasing and a little filling in of the blanks here, I honestly only skimmed it out of curiosity, I would suggest reading the article if you really want more details)
SayuriShigeko t1_iv9h4nh wrote
Reply to What is the cause of the steep escarpment at the base of Olympus Mons? by Strong-Ball-1089
Nasa apparently has an article about their understanding of this actually: https://www.nasa.gov/mission_pages/MRO/multimedia/pia12992.html#:~:text=Most%20scientists%20think%20the%20the,rocks%20it%20is%20built%20of.
Tldr: it's not traditional erosion from water or wind, nor is it tectonic in nature. The edge collapsed in a landslide. As the volcano erupted over time it built up more and more depositted material in layers, and eventually the mass became too heavy for the bottom material layer to support so it crumbled and caused a land slide.
(Paraphrasing and a little filling in of the blanks here, I honestly only skimmed it out of curiosity, I would suggest reading the article if you really want more details)