Genesis 7:10-12

"And it came to pass after the seven days that the waters of the flood were upon the earth. In the six hundredth year of Noah's life, in the second month, on the seventeenth day of the month, on the same day were all the fountains of the great deep broken up, and the windows of the heavens were opened. And the rain was upon the earth forty days and forty nights."

Genesis 7:11 here, is for the purpose of precisely dating the coming of the Flood. Of course, the exact manner of counting years referred to is unknowable in the light of what information we have; and, therefore, we do not know if it began in the Fall or the Spring. Even the duration of it is ambiguous. Willis' chart placing the duration at a period of one year and ten days is as good as any.[9]

"Were all the fountains of the great deep broken up ..." Some strange ideas surface with reference to this, for example, the understanding of these "fountains of the great deep" as being under the rivers and the earth generally. It appears, to the contrary, that "the great deep" could hardly refer to anything other than the ocean. Unger read this as "the primeval ocean"[10], and what is suggested seems to be that the waters of the great seas themselves were instrumental in such a super-colossal deluge. Such a thing might have been due to the sudden swelling and lifting of the ocean floor; which, if it returned later, would also have expedited the draining off of the flood waters. It is, of course, explicit that men cannot know HOW it happened.

"The windows of heaven were opened ..." The meaning of this is adequately explained in the very next line, "The rain was upon the earth forty days and forty nights!" The expression is a metaphor for the rain.