Map of probably extent of the Great Flood in time of Noah
When we read of the flood of Noah’s time being over all the earth as Bereshith (Genesis) 8:9 says, it was over that portion of the earth that was known to Yahweh’s people and the people who had no love for Him. (See our Article “All of the Earth”)
To the East and North of the flood area and the land adjacent to the Mediterranean Sea is all very elevated and mountainous forming a huge basin. However the Arabian Peninsula was mostly hot and dry sandy desert with huge sand dunes forming a high sandy mountain range high enough to contain the flood, but over the millennia since then most of those dunes have eroded away to be the lower dunes of today.
The Strait at the entrance to the Persian Gulf probably opened up and the land scoured out when the flood waters broke out to end the inundation.