Why Rocks Taken from the Seabed Suddenly Burst into Flames

Scientists were surprised by an unusual incident in a laboratory. Rocks collected from the floor of the Pacific Ocean suddenly heated up, began smoking and then spontaneously caught fire when broken open in the open air, CNBC Indonesia reported on Wednesday (14 October 2026).

The rocks were taken from waters off the border between the US states of Oregon and California, specifically the Escanaba Trough, an active volcanic ridge on the seabed. Samples were collected in 2022 using a remotely operated underwater vehicle.

After being brought to the surface and dried, two of the rocks displayed unusual properties. When they were broken open to examine their interiors, the newly exposed surfaces began to heat up and emit smoke, before burning completely and turning to ash.

The cause was a mineral contained in the rocks: a particular form of iron sulphide called marcasite, with grains measuring just 5 to 16 nanometres—thousands of times thinner than a human hair.

Because the mineral has an extremely large surface area, it reacts very quickly with oxygen in the air. The reaction produces heat. If the heat is generated faster than it can be absorbed by the surroundings, the temperature continues to rise on its own until the rock catches fire.

On the seabed, temperatures are around 2°C and oxygen levels are very low, so the reaction proceeds extremely slowly and the mineral remains stable. Once brought to the surface, however, the warmer, oxygen-rich air accelerates the chemical reaction until it becomes uncontrollable.

The discovery is more than a curiosity. Such seabed areas are rich in copper, zinc and other valuable metals. Mining is currently being planned on similar undersea ridges in the Atlantic and Indian Oceans.

The researchers warned that no safety regulations currently address rocks that can ignite spontaneously. The same phenomenon could occur aboard a mining vessel and put workers at risk.