The Kermadec Trench is one of Earth's deepest oceanic trenches, reaching a depth of 10,047 metres (32,963 ft). Formed by the subduction of the Pacific Plate under the Indo-Australian Plate, it runs over a thousand kilometres parallel with and to the east of the Kermadec Ridge and island arc, from near the northeastern tip of New Zealand's North Island to the trench's junction with the Louisville seamount chain northeast of Monowai Seamount. The Tonga Trench marks the continuation of subduction beyond this point. Subduction south of the Kermadec Trench is marked by the shallower Hikurangi Trench. The Kermadec Trench is noted for its very abrupt slope.
In 2012, deep sea researchers discovered individuals of a species of giant amphipod at the trench's lowest depths. Unlike most amphipods, which are approximately 2,5 cm (1 inch) long, this species reaches up to 34 cm (11 inches) in length, and are milky-white.