Australia's ocean territory is vast and covers an area more than 1.5 times the nation's landmass. Within these waters is a diversity of resources, marine species and habitats. And they're deep. Excluding Antarctic waters, 70% of Australia's ocean territory is deeper than 1,000 meters (3,281 feet), and nearly 50% is deeper than 3,000 meters (9,843 feet).
So what are the deepest points of the ocean in our region, and how deep has RV Investigator mapped the seafloor?
Before we answer that, we need to understand how we map the seafloor.
1, 2, 3 seafloor mapping systems
Seafloor mapping is done by measuring the depth of the ocean above it. This measurement is called bathymetry, which literally means "measuring depth." By taking multiple ocean-depth measurements and combining them, a map of the shape of the seafloor beneath the ocean can be generated.
RV Investigator maps the seafloor using three separate multibeam echosounders (MBES), also known as sonar or acoustic systems. These systems use pulses of sound ("pings") to measure ocean depth, and the three systems are designed for use at different water depths and operate at different sound frequencies. The systems are all located in a special wing-shaped structure called a "gondola" under RV Investigator's bow.
The vessel has a shallow-water MBES that enables high-resolution seafloor mapping down to 200 meters (656 feet), a mid-water MBES that operates to 2,000 meters (6,562 feet) and a deep-water MBES that can operate to the full ocean depth of 11,000 meters (6.8 miles). This means that RV Investigator can map the deepest known point on the planet, which is 10,935 meters (6.8 miles) deep at a point called Challenger Deep in the Mariana Trench east of the Philippines.
At these depths, RV Investigator can map, in a single pass, a strip of seafloor called a "swath" that may be up to 40 kilometers (25 miles) wide. This means teams are mapping the seafloor well beyond the horizon visible from on board, which is about 5 kilometers (3 miles) away.
So how deep has RV Investigator mapped the seafloor?
Mapping the second-deepest point on the planet
In 2025, RV Investigator achieved its record depth for seabed mapping following a voyage to investigate the aftermath of the 2022 Hunga Volcano eruption. At the end of the voyage, equipment trials required the voyage team to seek out the deepest water they could find.
Conveniently, the second-deepest point on the planet was nearby.
East of the islands of the Kingdom of Tonga lies the Tonga Trench. It contains a point called Horizon Deep, which plunges to a crushing depth of 10,882 meters (6.8 miles). While passing over the Tonga Trench during the 2025 voyage, the team aboard RV Investigator put the vessel's sonar systems to the test and mapped the seafloor to a depth of 9,888 meters (6.1 miles).
It's not every day you're on a vessel with nearly 10 kilometers (6 miles) of ocean beneath you!
How deep is the ocean around Australia?
Within Australia's maritime territory, the deepest point in the ocean is approximately 7,000 meters (4.3 miles) in the Sunda Trench, also known as the Java Trench, off Christmas Island (RV Investigator mapped in this region in 2021 and 2022). This is a little-studied, arc-shaped deep-ocean trench that stretches from Christmas Island across a distance of around 3,200 kilometers (2,000 miles) offshore from the islands of Java and Sumatra.
Other deepest points within Australia's maritime territory include the Diamantina Fracture Zone off southwestern Australia at approximately 6,400 meters (4 miles) (RV Investigator mapped in this region in 2020) and the Macquarie Trench near Macquarie Island in the Southern Ocean, which plunges to depths beyond 6,300 meters (3.9 miles) (RV Investigator mapped in this region in 2020).
The Diamantina Fracture Zone recently made the news as the site of the world's biggest whale graveyard, found at depths of 7,000 meters (4.3 miles) outside Australia's ocean territory.
Even outside these extreme depths, there's no shortage of work for RV Investigator's deep-water mapping systems on voyages around the continent.
Upscaling Australia's seafloor mapping
RV Investigator is further increasing its contribution to seafloor mapping for Australia through the Australian Government's Resourcing Australia's Prosperity initiative. Led by Geoscience Australia, the initiative will produce Australia–wide foundational geoscience datasets and detailed seabed-feature maps. RV Investigator's deep-ocean mapping capabilities will be applied to update and replace lower-quality seafloor datasets.
The first voyage contributing to this initiative will take place in July 2026 through a collaboration between CSIRO, Geoscience Australia and James Cook University. Led by Dr. Rob Beaman AM from James Cook University, RV Investigator will undertake a targeted deep-ocean survey to improve a 2,200-kilometer (1,367-mile) strip of lower-quality seafloor mapping along Australia's east coast from Hobart to Brisbane.
The mapping will include ocean depths of 4,500 meters (2.8 miles) or more.
The new dataset will be used to update the flagship Australian Bathymetry and Topography (AusBathyTopo) dataset, specifically the annually released national 250-meter bathymetry grid. It will also be used to improve the General Bathymetric Chart of the Oceans (GEBCO), which seeks to provide the most authoritative publicly available bathymetry dataset for the world's oceans.
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Before: Low resolution bathymetry (AusBathyTopo2009 of northern NSW to southern Queensland) prior to seafloor mapping by RV Investigator. Credit: Rob Beaman, JCU. -
After: High resolution bathymetry (AusBathyTopo2024 of northern NSW to southern Queensland) following seafloor mapping by RV Investigator. Credit: Rob Beaman, JCU
Mapping to understand, manage and secure Australia's oceans
Seafloor mapping is critical to our understanding of the ocean. The seabed dictates how ocean currents move, how marine ecosystems function and how human infrastructure, such as undersea cables and coastal developments, is built. It helps inform safe navigation for shipping and protects coastal communities by modeling risks from natural hazards such as landslides on the seafloor that could generate a tsunami.
Equally important, it informs conservation planning and provides crucial information for Parks Australia, which manages the Australian Marine Parks network. Mapping seabed features is important for characterizing habitat types, which supports understanding of biodiversity, informs conservation efforts and guides marine park zoning.
With only 38.8% of Australia's maritime territory mapped in sufficient detail for effective ocean management, there's still much more work for the collaborative teams mapping the seafloor aboard RV Investigator.
Who's behind this story?
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Citation: Mapping the seafloor: How deep can we go? (2026, July 15) retrieved 16 July 2026 from https://phys.org/news/2026-07-seafloor-deep.html
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