Deep Ocean Trenches

Deep Ocean Trench A trench is any long, narrow, steep-sided depression in the ocean bottom. The deepest known depression of this kind is the Mariana Trench, which lies east of the Mariana Islands in the western North Pacific Ocean . Of the Earth's 20 major trenches, 17 are found in the Pacific. The only Atlantic trenches are the Puerto Rico Trench north of the Caribbean islands and the South Sandwich Trench east of Drake Passage between South America …

… along the shifted land. As well, quick cooling after the event, caused by water with high salt content (after expulsion the ocean water would cover the continents up to 12,000 feet, according to numerous sources) made the top magma too sluggish to fill up to the general level, thus leaving the trenches empty. If subduction did occur, there would be no trenches. They would be filled with the sedimentary debris of the ocean floor (Carey).