The great Flood of Noah's day was a time of unthinkable geological upheaval, such that "the world that then was, being overflowed with water, perished" (II Peter 3:6). No flood in human history has rivaled its destructive magnitude.
Though we are far from a full understanding of the Flood, the Bible does give us a clue when it says, on that "same day were all the fountains of the great deep broken up, and the windows of heaven were opened. And the rain was upon the earth forty days and forty nights" (Genesis 7:11_12). Geologists note three succinct mechanisms which God used that bear our consideration.
The trigger for the rest was that "all the fountains of the great deep" were ruptured. The fountains may have been underwater volcanos or materials from deep inside spewing out into the ocean basins.
Evidently there were great subterranean chambers of water which belched forth their contents causing volcanism and tectonism on a broad scale. After being emptied some collapsed to become deep sedimentary basins which uplifted later in the Flood to form mountain chains.
Today when a volcano erupts under water, or if there is an underwater earthquake or mud slide, it causes a tsunami or tidal wave; a dynamic energy wave which pushes water toward the continents, devastating coastal areas. At the start of the Flood all the fountains of the great deep were rent open sending repeated pulses of water toward the continents from every direction bringing sediments and marine fossils to the land. Cyclic ocean currents and tidal actions would have left their imprint on these sediments.
Along the mid-ocean ridges once molten rock and other super hot fluids would have encountered the relatively cold ocean waters, evaporating huge volumes of sea water, ultimately yielding intense rainfall and precipitating their dissolved solids.
Torrential rain poured down. This was a special rain for forty days and forty nights but it continued for a hundred and fifty days, through the first half of the Flood. This continually replenished source of water would have bombarded the earth, eroding and redepositing sediments on a global scale.
For the next six months, the waters "prevailed" (7:18) upon the earth with water driven back and forth on the world oceans. Tides were unchecked by shorelines and until the fountains were stopped and the flood gates closed (8:2_3) any unstable deposit would be susceptible to reworking in a high energy environment.
Finally, six months after the start of the Flood, the waters "returned from off the earth" (8:3). They "decreased continually" for the next several months until the tops of the mountains were seen (v.5) exposing and drying the land, making it fit for life. This implies both continental uplift, ocean basin sinking, and sea floor spreading. This redistribution of the topography implies extensive deformation of soft, freshly deposited sediments. A great wind aided this drainage (8:1).
The Flood was unmatched by any event in our experience, yet both Scripture and science demands it. Any attempt to reconstruct earth history which ignores the Genesis Flood is certain to be in gross error.