Science has demonstrated that continents which are now separated were likely once joined. Science has also demonstrated through the work of plate tecktonics expert Dr. John Beaumgartner, that tektonic events can happen extremely rapidly. The flood record does mention the 'fountains of the great deep' (Genesis 7:11) as their way of explaining one of the mechanisms connected with the flood. Whatever these were, they were 'opened' suggesting volcanic activity on a large scale.
One thing is certain, and that is that the earth before the flood was very different from what the earth is like today. The climate was also probably quite different, since the warmer oceans and colder land masses produced the post-flood ice-age, as the planet settled back to relative equilibrium. Such massive extremes of weather, and even rain itself were possibly unknown before this.