What is the name of the deep-sea trench that is the second deepest on Earth?

The second-deepest deep-sea trench on Earth is the Tonga Trench. Its deepest point, Horizon Deep, reaches roughly 10,800 meters below the surface, making it the deepest point in the Southern Hemisphere. Only Challenger Deep in the Mariana Trench is deeper.

The Tonga Trench lies in the southwestern Pacific Ocean, east of the Tonga island group. It formed where the Pacific Plate is forced beneath the Tonga Plate, a process called subduction. This is one of the fastest-moving subduction zones on Earth, helping explain the trench’s extreme depth and intense earthquake activity.

A common mix-up is the Kermadec Trench, which lies south of Tonga and forms part of the same broader Tonga–Kermadec subduction system. The Peru–Chile, Philippine, and Java trenches are also major oceanic trenches, but none is the accepted second-deepest trench by maximum depth. Horizon Deep was directly measured during a crewed descent in 2019.