Decode thousands of mysterious craters on the California seabed

Thanks to underwater robots, researchers discovered more than 5,000 craters on the seafloor off the coast of California that were not caused by leaking methane gas.

Off the coast of Big Sur, California, beneath the sea surface are countless large and small craters in the clay, mud and sand. Decades after discovering the craters, scientists at the Monterey Bay Aquarium Research Institute (MBARI) and Stanford University think they have found the cause of a series of curious rings forming on the sea floor. .

Map of the Sur depression field on the seabed. (Photo: MBARI).

According to popular theories, the dent in the seafloor is the product of methane gas or even hot fluids, flowing upward from the Earth's interior, causing some of the fine sediment to wash away, leaving a crater. While this may be true of underwater craters elsewhere in the world, the situation on the California seafloor is different, according to research published in the journal Geophysical Research Earth Surface .

The Sur streak field off the coast of California is among the largest in North America. This area is the size of Los Angeles and contains more than 5,200 craters with an average size of 175m wide and 5m deep. It is expected that this place will be a potential offshore wind farm, but there are many concerns that the presence of methane gas will affect the stability of the infrastructure.

During a recent expedition to the Sur Rift Field, located at depths of 500 - 1500 m, an underwater robot controlled by the MBARI research team found almost no evidence of methane veins or other fluid flows. Instead, they suggest that the dent may have formed due to the effects of gravity . Large craters located on the continental slope and seafloor samples collected by robots reveal sediment sliding intermittently down the slope over at least the past 280,000 years. The most recent slip occurred 14,000 years ago, possibly due to an earthquake or landslide.

Researchers at MBARI suggest that such an event could lead to erosion in the center of each rut. When a large enough portion of sediment flows away, erosion causes the depression to widen. This may be the reason the dents appear in series.

"We collected a large amount of data, which helped us find an unexpected connection between the depression and the sediment drifting due to gravity," said MBARI technician Eve Lundsten. "We cannot determine how these ridges form in the first place, but with MBARI's advanced technology, we have gained new insights into why they persist on the seabed for hundreds of thousands of years." year". The Sur ridge field is one of the best-studied seafloor regions in western North America.