Mu is the name of a Lost Land, or hypothetical vanished continent, located in the Pacific Ocean but now, like Atlantis and Lemuria (with which it is sometimes identified), believed to have sunk beneath the waters.

Current knowledge of the mechanisms of plate tectonics rules out the possibility of a major continent having existed in the Pacific. Continental masses are composed of the lighter SiAl (silicon/aluminium) type rocks which literally float on the heavier SiMg (silicon/magnesium) rocks which constitute ocean bottoms. There is no evidence of SiAl rock in the Pacific basin.

Interesting..