Are trenches caused from tectonic activity.
No they are not.
Sea mounts are underwater mountains that rise from the ocean floor but do not break the surface. They are formed by volcanic activity or tectonic plate movement, and are often rich in marine life due to the upwelling of nutrients they provide. These underwater features can play important roles in ocean ecosystems and biodiversity.
what happens is the ocean floor does not just keep spreading.instead, it sinks beneath deep underwater canyons called deep- ocean trenches
In the ocean floor.
probably..
Deep Trench in the ocean floor. It can sometimes be mistaken for a mid-ocean ridge.
the continental Margin, Ocean Basin Floor and Mid-Ocean ridge :D
an abyss
It is the Abyssal plain.
deep ocean trench
deep-ocean trench
deep-ocean trench