Beyond these three uses, there is much disagreement over when to capitalize. Every major publication and publisher has its own standards, and many writers have their own preferences (which are generally overridden by in-house rules during publication).
Deep-sea trench. Deep-sea trench, also called oceanic trench , any long, narrow, steep-sided depression in the ocean bottom in which occur the maximum oceanic depths, approximately 7,300 to more than 11,000 metres (24,000 to 36,000 feet). They typically form in locations where one tectonic plate subducts under another.
Ocean trenches have relatively steep sides falling to the ocean floor. Ocean trenches are typically caused when an oceanic crustal plate slides under a lighter continental plate or another oceanic plate. It is believed to work by density.Where one plate slides under another, this is called subduction.t least five trenches are over 6 miles (10 km) deep. The greatest ocean depth to be sounded is in the Challenger Deep of the Mariana Trench, at a depth of 11,034 m (36,201 ft) below sea level.