With things like this happening in an average person's lifetime, why do we need to suppose that cultural memories are likely to be passed on for tens of thousands of years.
Why should we suppose it was forgotten?
There are many myths in many cultures, but the flood story seems pervasive in almost every culture, with many similarities between cultures that are widely spread apart.
We have an apparent genetic bottleneck in the human race. We have an apparent megadisater that happened about the time of the bottleneck. We have widespread myth that seems that it could be a orally passed-on account of that disaster. Why not suppose that is what it is?
I believe evolution has been the primary mechanism for the development of life on Earth. I do not believe in a six-thousand year old world and universe. However, I don't feel any need to go out of my way to debunk the Genesis account, particularly when I think Genesis can be interpreted to be in general accord with science.
I simply don't have a need in either/or. I have a belief in both. I try to make them mesh. And when they don't I'm quite content to shrug my shoulders and live with the contradiction, until I can resolve it to my satisfaction.
No one is going to be around to remember a supervolcano. There is hardly any orally transmitted history of the year without a summer, or the little ice age, or the seven mile wide tornado that ripped through the American midwest last century.
On the other hand, there are lots of vague stories and legends of catastrophes. There are plenty of them in every generation.