oceanic trench; deep-sea trench
A long, narrow, deep depression in the ocean floor; a technical term in geology and oceanography.
マリアナ海溝は世界で最も深い海溝です。
The Mariana Trench is the deepest oceanic trench in the world.
Earthquakes frequently occur along the Japan Trench.
There is a deep trench called the Japan Trench in the Pacific Ocean.
The sunken ship sank down into the deep trench.
The researchers surveyed the trench using an unmanned probe.