Mount Everest is 29,000 feet above current sea level. Your 500 feet above sea level is nothing. Google says 80 percent of dry land would still be above that higher sea level. Even if sea levels rose 5000 feet higher there would still be 15-20 percent dry land. Do you understand those physics?
I think tectonic plate movement has changed the earth's topography over the course of thousands of years.
One of the things that will happen near the end of the great tribulation will be a worldwide affect on the topography.
Revelation 16:
19 And the great city was divided into three parts, and
the cities of the nations fell: and great Babylon came in remembrance before God, to give unto her the cup of the wine of the fierceness of his wrath.
20 And
every island fled away, and the mountains were not found.
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I think it is best if we focus on Jesus's coming and not topography.