"|God| spared not the old world, but saved Noah the eighth person, a preacher of righteousness, bringing in the flood upon the world of the ungodly; And turning the cities of Sodom and Gomorrah into ashes condemned them with an overthrow, making them an ensample unto those that after should live ungodly." (2 Peter 2:5, 6)
These two verses speak graphically of two different kinds of terrible physical convulsions, both of which were divine judgments. The volcanic upheaval that sent fire from heaven pouring over the wicked cities of the plains was called an "overthrow" (Greek katastrophe, from which, obviously, we get our English word "catastrophe"). Great upheavals such as volcanic eruptions, earthquakes, and hurricanes are rightly called catastrophes.
But such events are only local or regional in extent, and occur relatively often. There was one event, however, which was unique in all history. When God brought the "flood" upon the ungodly antediluvian world, the word used to describe it was the Greek kataklusmos, and this word is never applied in Scripture to any event except the terrible Genesis flood, when "the world that then was, being overflowed |Greek, katakluzo| with water, perished" (2 Peter 3:6). From these Greek words we derive the English word "cataclysm".
There was never any flood like this flood! It covered all the world’s mountains, and everything on the land died, leaving great fossil deposits and great beds of lithified sediments all over the world.
There has been only one worldwide cataclysm in the past, but another is coming global fire instead of global water. Jesus said, "For as in the days that were before the flood they knew not until the flood came, and took them all away; so shall also the coming of the Son of man be. (Matthew 24:38, 39).