Here's why:

* Long and Narrow: Subduction zones are where one tectonic plate slides beneath another. This creates a long, narrow trench where the ocean floor dips downwards.

* Very Deep: The trenches formed at subduction zones are the deepest parts of the ocean. They can reach depths of over 10,000 meters (33,000 feet).

* Bends Down Toward the Mantle: The plate that is being subducted is forced down into the Earth's mantle.

While the term "canyon" can be used to describe some features in subduction zones, it's not the most precise term. The specific features you're describing are:

* Trench: The main depression where the ocean floor bends downwards.

* Subduction Zone: The broader area where the plates meet and one slides beneath the other.

Let me know if you have other questions!