Just trying to understand how the Great Flood occurred and what the Bible meant by "the fountains of the great deep". Raining forty days and forty nights would have no effect on the rise of the sea level of the earth because whatever amount of water that is evaporated to form rain clouds will be the same amount of water that will rained down. The purpose of raining 40 days and 40 nights was probably to maintain a layer of fresh water above the saltish sea water so that fresh water creatures could survived. Even if all the ice on the mountains and at the poles were to be melted, it will only raise the sea level by about 300 feet. Therefore, the main determinant that would flood the earth to above the mountain tops were the fountains of the deep. But what were the fountains of the deep? Today's English Version gives a much better interpretation: "all the outlets of the vast body of water beneath the earth...". Recently, scientists have discovered vast ocean beneath the surface of the earth, that would probably means that this/these vast ocean/s of water ("Fountains of the deep") burst forth from the earth crust at extreme pressure and thus raise the sea level of the earth to above the mountain tops:
"Scientists scanning the deep interior of Earth have found evidence of a vast water reservoir beneath eastern Asia that is at least the volume of the Arctic Ocean.
The discovery marks the first time such a large body of water has found in the planet’s deep mantle."
Genesis 7:11In the six hundredth year of Noah's life, in the second month, the seventeenth day of the month, the same day were all the fountains of the great deep broken up, and the windows of heaven were opened.
12And the rain was upon the earth forty days and forty nights.
13In the selfsame day entered Noah, and Shem, and Ham, and Japheth, the sons of Noah, and Noah's wife, and the three wives of his sons with them, into the ark;
14They, and every beast after his kind, and all the cattle after their kind, and every creeping thing that creepeth upon the earth after his kind, and every fowl after his kind, every bird of every sort.
15And they went in unto Noah into the ark, two and two of all flesh, wherein is the breath of life.
16And they that went in, went in male and female of all flesh, as God had commanded him: and the LORD shut him in.
17And the flood was forty days upon the earth; and the waters increased, and bare up the ark, and it was lift up above the earth.
18And the waters prevailed, and were increased greatly upon the earth; and the ark went upon the face of the waters.
19And the waters prevailed exceedingly upon the earth; and all the high hills, that were under the whole heaven, were covered.
20Fifteen cubits upward did the waters prevail; and the mountains were covered.