Plizio Visual Lab

Horizon Deep

Plizio editorial teamUpdated: Oct 2026Data Sources

valley

Weather…

Horizon Deep is the deepest point within the Tonga Trench and is considered the second deepest spot on the Earth's surface after the Mariana Trench. It is located in the southern section of the trench and reaches an impressive depth of approximately 10,811 meters below sea level. This abyss was discovered in 1952 by the crew of the research vessel RV Horizon, after which it is named. Conditions at this depth are extreme: water pressure exceeds 1,000 bars, and temperatures are near freezing. It was not until 2019 that researcher Victor Vescovo succeeded in reaching the bottom of Horizon Deep with a special submersible. Geologically, this point is of the highest interest as it marks the maximum subsidence of the Earth's crust in the Southern Hemisphere. Scientific samples from this location help in researching life under extreme high-pressure conditions.

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📋 Practical info

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Getting there

Located at the bottom of the Tonga Trench, this site is only accessible to deep-sea submersibles and scientific research vessels departing from major international ports.

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Best season

Expeditions are typically planned during the Southern Hemisphere winter (May to October) to avoid the South Pacific cyclone season and ensure stable surface sea conditions.

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Terrain & paths

The terrain is an abyssal valley nearly 11 kilometers deep. It consists of a narrow trench floor with extreme water pressure and total darkness, accessible only via sensors.

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What to bring

Visiting requires multi-million dollar deep-sea technology, pressure-resistant hulls, and remote-operated vehicles. For surface observers, high-powered sonar is the primary tool.

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Parking

Research vessels dock at the Port of Nuku'alofa. There is no public parking or access for casual visitors; the site is situated hundreds of kilometers offshore.

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Safety

The extreme pressure at this depth makes it one of the most hostile environments on Earth. Only highly specialized, unmanned or manned submersibles can safely descend here.

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Time needed

Scientific missions to the deep can last several weeks. A descent and ascent by a manned submersible alone takes over 10 hours of continuous operation in a confined space.