Asked by Sonia Vegas
The Earth’s spin on its axis keeps water more or less balanced on all sides of the planet through what is known as a centrifugal force. The gravitational force of the Moon disrupts this balance, pulling a tidal bulge of water with it as it orbits our planet and as the Earth rotates, it too causes a tidal bulge on the opposite side. It is these bulges that are defined as high tide whereas other areas are low tide.
Now, moving the Moon closer to the Earth will increase the gravitational exertion of the satellite onto our planet. If the satellite were slightly closer, the tidal bulge would grow. Low tides would be lower and high tides would be higher and any low lying coastline would be flooded. If the Moon got much closer, say 20 times closer, it would exert a gravitational force 400 times greater than what we are used to. A mighty tidal bulge would be created, hitting the land and causing great flooding, with cities such as London and New York disappearing under water. When the Moon moves on however, the flooding subsides and the water will retreat.