Charles Ellicott Commentary Genesis 7:17-19

"And the flood was forty days upon the earth; and the waters increased, and bare up the ark, and it was lifted up above the earth. And the waters prevailed, and increased greatly upon the earth; and the ark went upon the face of the waters. And the waters prevailed exceedingly upon the earth; and all the high mountains that were under the whole heaven were covered." — Genesis 7:17-19 (ASV)

The waters increased ... — The swelling of the flood is described with great power in these verses. Every stage and detail relates to the ark, as if the author of the narrative was one of those on board.

First, the “waters increased” and raised up the ark until it floated. Next, “they became strong and increased exceedingly”—the word translated as “prevailed” actually meaning the setting in of mighty currents , as the waters sought the lower ground—and at this stage the ark began to move. Finally, they “became strong exceedingly, exceedingly,” rushing along with ever-increasing force and carrying the ark high above every hill in its course.

Of these events, it is said—

All the high hills, that were under the whole heaven, were covered. — Interpreting this from the English Version, many regard it as proof that the deluge was universal. But, setting aside the well-known fact that in the Bible the word “all” often has a more restricted meaning than it does for us, we must also remember that the Hebrew language has a very small vocabulary, and “the whole heaven” means simply the whole sky. We, with our composite language, borrow a word for it from Greek and say “the whole horizon”—that is, the whole heaven bounded by the line of the spectator's vision.

So it was here. Far and wide, in every direction, to the utmost reach of the beholder’s gaze, no mountain was in sight. All was a surging waste of flood. But there is no idea here of the mountains of Auvergne, with the ashes of ancient volcanoes still resting on their craters, extinct from a time probably long before the creation of humanity itself. The mountains mentioned were those of the Noachian world, as limited as the Roman world in Luke 2:1, or even more so.