The discovery that surprised scientists: rocks from the seafloor ignited on their own

A study by the U.S. Geological Survey reveals an unexpected danger: hydrothermal rocks from the ocean floor, containing nanocrystalline marcasite, may spontaneously ignite when brought to the surface. Two samples collected from the Escanaba Trough in the Pacific Ocean ignited in the lab, with temperatures soaring above 100 degrees Celsius. Researchers warn of fire hazards on future mining ships.

A new study by the U.S. Geological Survey reveals an unexpected danger in the deep sea: hydrothermal rocks containing precious metals may spontaneously ignite when brought to the surface. In 2022, researchers collected 57 rock samples from the Escanaba Trough in the Pacific Ocean, off the Oregon-California border, using a submersible vehicle from the Woods Hole Oceanographic Institution. During drying and crushing in the lab, two of the samples spontaneously ignited, with temperatures rising above 100 degrees Celsius. Tests ruled out tar or submarine oil and showed the rocks are composed mainly of nanocrystalline marcasite, an unstable form of iron sulfide that reacts with oxygen. Heat and mechanical forces provide the energy to trigger the oxidation process leading to combustion. The discovery has implications for the developing deep-sea mining industry, which has already been awarded exploration contracts in the Mid-Atlantic Ridge and the Southwest Indian Ocean. Alongside safety risks, the industry faces environmental criticism over potential harm to marine ecosystems.