Deep-Sea Mining Hazard: Ocean Floor Rocks Found to Spontaneously Ignite

Humanity's quest for new sources of wealth in the deep ocean has encountered an unexpected and particularly dangerous obstacle. A new study by the United States Geological Survey warns that certain mineral rocks from the sea floor can spontaneously ignite once brought to the surface, posing a real life-threatening hazard to ships and crews working in the developing marine mining industry.

On the ocean floor lie natural deposits containing valuable metals such as copper, zinc, and iron, and frequently also gold and silver. In recent years, global interest has grown in the possibility of extracting these metals through deep-sea mining, similar to traditional terrestrial mining.

The Danger of Spontaneous Combustion

However, the new study reveals that some of these rocks exhibit physical and chemical properties that cause them to behave completely differently from their terrestrial counterparts. In 2022, researchers from the US Geological Survey embarked on a research expedition to an area known as the Escanaba Trough, located in the Pacific Ocean off the border between Oregon and California. This area features extensive hydrothermal activity, where hot water rising from the sea floor creates deposits exceptionally rich in metals.

Using a remotely operated underwater vehicle from the Woods Hole Oceanographic Institution, the researchers collected 57 hydrothermal rock samples from four different areas in the trough. Most of these samples contained metallic sulfide as a primary mineral component.

When researchers in the laboratory freeze-dried and crushed the rock samples, a dramatic incident occurred: two of the samples completely spontaneously ignited.

Unstable Nanocrystalline Marcasite

To decipher what exactly makes these burning rocks unique, the researchers compared the mineralogy, chemical composition, and thermal behavior of all the collected samples. The tests ruled out the assumption that the problem stems from tar or hidden submarine petroleum, revealing instead that the rocks that ignited were composed primarily of nanocrystalline marcasite, an extremely unstable form of iron sulfide when exposed to oxygen.

The addition of heat and mechanical forces—such as crushing, breaking, and grinding that occur during rock processing—provides the energy required to trigger the oxidation process. The researchers emphasize that while not every ocean rock containing marcasite poses an immediate threat, it represents a significant risk that must be considered when designing safety standards for this new industry.

Implications for Deep-Sea Mining

The new discovery has broad implications for the deep-sea mining industry, which is currently undergoing organization and regulation. The International Seabed Authority has already granted exploration and mining contracts for sulfide minerals in two major areas – the Northern Mid-Atlantic Ridge and the Southwest Indian Ridge.

Alongside the new technological and safety risks for workers and vessels, the entire industry faces sharp criticism from environmental organizations and scientists. They warn that industrial activity in the deep ocean could deal a fatal blow to fragile marine ecosystems already at risk, proving that human intervention in the abyss can backfire in unpredictable ways.