The fall of a great city usually leaves behind ruins, but the doom facing Tyre is far more absolute. It is a promise of complete erasure, wiping away every memory of its glorious past. God declares that He will reduce the city to utter desolation [מצודת ציון]. The devastation will be so extreme that the area will look as though it had never been inhabited by humans. When the destruction is complete, the very rock upon which the city was built will be left entirely smooth and bare, stripping away any trace of human settlement.
The method of this total wipeout is depicted as a massive flood of deep waters rising up to cover the land, an image emphasizing the sheer scale of the disaster [רד״ק]. The primary approach among commentators is that this flood is a vivid metaphor. The deep waters represent massive armies from many nations sweeping over the city to destroy it entirely.
Conversely, other perspectives view the rising sea as a literal event. According to this understanding, after the city fell to Nebuchadnezzar, the actual ocean rose and drowned it [רש״י]. This physical flooding may have been a temporary surge where giant waves washed over the land, sweeping away everything on the surface before retreating to leave behind nothing but an empty, dry rock [רד״ק]. The cause of this literal flood could be understood in a few ways. It might have been a sudden act of God, a deliberate tactic by the conquering enemies, or simply the natural consequence of a deserted city. Once the inhabitants were gone and no longer maintained the local dams, the rising waters naturally broke through to swallow the ruins [ביאור שטיינזלץ].