submersion - v.
1 tr. a place under water; flood; inundate. b flood or inundate with work, problems, etc.
2 intr. (of a submarine, its crew, a diver, etc.) dive below the surface of water.

the submerged tenth the supposed fraction of the population permanently living in poverty.

submergence n. submergible adj. submersion n. [L submergere (as SUB-, mergere mers- dip)]