New Defender's Study Bible Notes
7:19 all the high hills. The double superlative precludes the use of “all” in a relative sense here. The obvious intent of the writer was to describe a universal inundation.
7:20 mountains. The words “high hills” and “mountains” are the same in the original Hebrew. The waters were 15 cubits (22.5 feet) above the highest mountains, patently including Mount Ararat, which is now 17,000 feet high. In the “local-flood” theory, Mt. Ararat would have had the same elevation before and after the Flood, but it should be obvious that a 17,000-foot flood is not a local flood!