The vastness of this geological activity must have been in proportion to the huge depth of the flood. For Noah to be in the southern Euphrates valley before and after the flood, indicates a local flood in the Euphrates valley. Flood stories can be found in every part of the world and common to most of them is the recollection of a great flood which destroyed all but a tiny remnant of the human race. Many of these traditions tell of the building of a great boat which saved humans and animals and which finally landed on a mountain. This indicates that Noah's flood was global.
Flooding is experienced in every region of the earth where there are rivers.
Myths about flooding can therefore arise independently around the world. Over time, story elements from one local flood story gets mixed with other flood stories in distant lands. If one story had an unusually memorable story element, such as a boat saving a family from a flood, eventually some other local flood legends would absorb that story element. Similar stories in different parts of the world were the result of travelers and missionaries taking the Noachian story to different parts of the world. No single worldwide flood is needed to account for these flood stories, many of which are unrelated to Noah's story.