Not sure how ya'll link to other threads so I apologize this isn't cleaner and easier.
Skip to 1:30 to avoid non relevant intro.
This guy says Tesla type tech (frequency) used (against Tartaria) to liquefy sand into mud. So rather than idea of mud flooding down a hill and burying the buildings perhaps the ground was turned to mud and they simply sank. Oh and also touches on Cleopatra, Civil War, Orphan Trains and Robber Barons. Just came across and figured would share as he presents as decent a theory as I've heard really that (potentially) ties many threads and subjects discussed here together.