Technically it becomes a type of buoy known as a spar buoy: https://en.wikipedia.org/wiki/Spar_buoy https://en.wikipedia.org/wiki/Spar_buoy The surface wave mo

Technically it becomes a type of buoy known as a spar buoy: https://en.wikipedia.org/wiki/Spar_buoy https://en.wikipedia.org/wiki/Spar_buoy The surface wave motion decreases with depth, so having so much mass deep under water makes for a very stable platform.