Watch short videos about this expedition, and read deep-dive stories to learn more about the hydrothermal systems, marine geology, and critical minerals of Escanaba Trough.

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In May-June 2022, the U.S. Geological Survey, in cooperation with the Bureau of Ocean Energy Management (BOEM), the National Oceanic and Atmospheric Administration (NOAA), and others, embarked on a three-week research expedition to Escanaba Trough off the coast of northern California. The multidisciplinary crew collected extensive geologic, geochemical, and biological samples with the remotely operated vehicle Jason, as well as tested new seafloor mapping techniques using the autonomous underwater vehicle Sentry.

In addition to its unique geochemistry and geomorphology, Escanaba Trough is the only mid-ocean spreading center located within the U.S. Exclusive Economic Zone (EEZ). These zones extend 200 nautical miles from a country’s shores and gives that country control over the exploration and exploitation of marine resources in that area.

The USGS Global Marine Minerals Team, based out of the Pacific Coastal and Marine Science Center, led the research expedition. This team provides expertise to the U.S. regarding the geochemistry and distribution of marine minerals in the U.S. EEZ and beyond.

Escanaba Trough is a hydrothermal seafloor system located almost 200 miles off the coast of northern California. It lies at the divergence of two tectonic plates, where convection in the Earth’s mantle slowly pulls plates apart and allows new, less dense mantle material to rise, forming ridges on the seafloor.

Escanaba Trough is part of a tectonically and volcanically active plate boundary known as Gorda Ridge, a mid-ocean seafloor spreading center consisting of a deep, wide axial valley flanked by ridges. Escanaba Trough is 3,300 meters deep and 75 kilometers long. It is covered for most of this length by as much as 500 meters of sediment shed from the Pacific continental margin of the United States.

“The Escanaba Trough provides opportunities for scientists to learn details about tectonics, volcanism, mineral formation, and biological activity that are not normally observed at mid-ocean ridges,” said Randolph Koski, USGS Emeritus at the Geology, Minerals, Energy, and Geophysics Science Center. “It is a geological laboratory of grand proportions."

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At Escanaba Trough, the thick sediment layer traps geothermal heat, resulting in the formation of significant amounts of sulfide minerals. These minerals form when hot water from beneath the ocean floor escapes and mixes with cold seawater. As hot water travels through various rock and sediment layers, it pulls elements such as copper, zinc, and iron along with it, slowly depositing them in minerals as the water cools.

Sulfide minerals are sources of precious metals and critical minerals including gold, silver, platinum, antimony, bismuth, lead, nickel, and zinc. Critical minerals are resources considered essential to the economic or national security of the U.S. that are also vulnerable to supply-chain disruptions.

“Any inventory of global mineral resources is incomplete without considering marine minerals, which are distributed widely across the global seafloor and vary considerably in how and where they form,” said Amy Gartman, USGS Research Oceanographer with the Pacific Coastal and Marine Science Center and Global Marine Minerals Team lead. “In addition to mineral characterization, it is crucial to understand the environmental setting of these minerals and their interactions with the surrounding ecosystem.”

While terrestrial and coastal mineral deposits have been exploited for centuries, deep-sea geologic formations containing concentrations of minerals are largely untouched. A better understanding of marine mineral resources is of growing interest to nations worldwide—particularly those minerals used in the development and application of renewable energy technologies. Solar panels, wind turbines, and batteries for electric vehicles all require critical-mineral components; the transition to renewable energy will require a shift from fuel-intensive systems to material-intensive systems.

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Earlier studies in Escanaba Trough revealed the presence of polymetallic sulfide minerals that may contain high grades of gold, silver, copper, and zinc, as well as lesser amounts of metals such as antimony, bismuth, lead, cobalt, and tin.

“USGS and partners did quite a bit of research in that area in the 1980s,” Gartman said. “A lot of what we learned there has guided further research, and now it’s time for us to go back and apply what we have learned in the decades since.”

The last expedition to Escanaba Trough occurred in 2016, when researchers from the Monterey Bay Aquarium Research Institution used autonomous underwater vehicles to map the seafloor in finer detail. For the 2022 expedition, USGS worked with BOEM, NOAA, and partners to investigate the conditions leading to the enrichment of elements in sulfide minerals, and better understand the elements’ distribution in minerals and the surrounding ocean environment, including their relationship to vulnerable biological communities.

See the NOAA Ocean Explorer page for more information about the Escanaba Trough Expedition.

We hope you will join us for these discoveries by following along as the expedition progresses!

Archival photos taken during submersible dives to Escanaba Trough, 1985-1989

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