The Marianas trench .
The Marianas trench .
Oceanic trenches form where two tectonic plates converge, with one plate being forced beneath the other in a process known as subduction. This creates deep, narrow depressions in the ocean floor, some of which are the deepest parts of the ocean.
A basic answer is that the densest ocean water is the saltiest - a ship floats higher in salt water (sea) than in fresh water (lake). Also cold water tends to sink towards the ocean floor, or may form a layer mid way.
When two of Earth's oceanic plates collide, they can form a deep valley called a trench. Trenches are often found in subduction zones where one plate is forced beneath the other, creating a deep depression in the ocean floor.
A general deep area of the ocean will be called an abyssal deep, but a canyon-like structure will also be called a submarine canyon. e.g. the Clutha Submarine Canyonoff the mouth of the Clutha River on the east of New Zealand's South Island.Off the Kaikoura Peninsula, however is the Hikurangi Trench, a cleft-like canyon which has a relationship with subduction processes, not riverine. This Trench is over 3000 m deep.This structure continues broadly northwards to become the Tonga Trench in that vicinity.
The grand canyon
Sea Floor Spreading!
A deep-ocean trench is a long, narrow depression in the ocean floor where tectonic plates are being pulled into the Earth's mantle in a process called subduction. These trenches are some of the deepest parts of the ocean and are typically associated with intense seismic activity and volcanic processes.
Approximately 2.5% of the ocean bottom is covered by trenches, which are deep depressions in the ocean floor that form where tectonic plates collide and one plate is forced beneath the other. These trenches can be incredibly deep, with the Mariana Trench being the deepest known point in the ocean.
What causes ocean floor features to form
A lot of shells of marine organisms wind up on the ocean floor. Bones do not last on the ocean floor, they get eaten. But shells can last.
The place where the ocean floor suddenly plunges downward is called a submarine trench. These deep underwater valleys form at tectonic plate boundaries where one plate is being pushed beneath another in a process known as subduction. Submarine trenches can reach depths of over 10 kilometers and are some of the deepest parts of the ocean.