IPA: /səbˈmɜːrʒən/
KK: /səbˈmɜrʒən/
The act of putting something underwater or the condition of being completely covered by water.
The submersion of the city during the flood caused significant damage.
Submersion is formed from "sub-" (meaning under) and "mergere" (meaning to plunge or immerse). The word describes the act of plunging or immersing something under a surface, typically water.
Think of something being 'under' ('sub-') the water as it 'plunges' ('mergere') down — that's what submersion means.