It has been found that literally every culture on the planet has a flood story/myth/ account. Even ancient tribes that are isolated in remote places have them. ALL of them correspond closely to the same time period of around 10,500 BC to 12,000 BC. This period is the "Younger Dryas" sudden meltdown and warm up that lasted for around that long and then froze up again only to melt a relatively short period later. The great floods all happened after/during the meltdown. What precipitated that sudden melt down is under some debate.
My personal opinion is the following;
Around 12,000BC the Earth was impacted by several events at once. First to happen was either, or both, a SOLAR event where parts of the Earth literally caught fire, as some accounts tell of, and a celestial object impact of great size and speed. Also one of the common stories. Another story that is common is the planet seeming to stand still for a day and a half with the sun unmoving in the sky. In order for this to happen the planet would need to actually stop rotating, ( unlikely) be actually possible. The other way is for there to be a "crustal displacement" where the outer crust of the Earth breaks free from the core and the mantle shifts as a whole around globe. This has been proven ( to my satisfaction) to have happened. It explains many events very neatly. At the site called Gobekli Tepe in Turkey, a 12,500 year old dig, the stones tell a story of celestial object impact, a great flooding, and then visitation by two deities that imparted all lost knowledge in order to restart human civilization. These two "Gods" are thought to be two of the survivors of a destroyed advanced race, the survivors of which determined that in order for human kind to survive the cataclysms they would need to spread out in every direction and impart their knowledge of all things to whatever groups they encountered and then move on to the next. Thought to be survivors of Atlantis. All accounts, spread widely over the entire globe in a time when travel was by foot alone, give nearly exact descriptions and method of arrival. While accounts vary slightly, with probable embroidering by someone, they are alike enough to prove the global catastrophe.