MYSTERY: Scientists Investigate Cause of 5,200 Craters Discovered off the Coast of California

Scientists at the Monterey Bay Aquarium Research Institute (MBARI) have put forward a new theory regarding the 5,200 mysterious craters on the seafloor off the coast of Big Sur, California.

Knewz.com has learned that the collection of craters, known as the Sur Pockmark Field, covers an area almost the size of the city of Los Angeles.

The Sur Pockmark Field covers an area almost the size of the city of Los Angeles. By: MBARI

MBARI scientists first discovered the craters in 1998, while conducting a survey of the seafloor using ship-mounted multibeam sonar.

Subsequent surveys carried out by MBARI collaborators at the United States Geological Survey and the National Oceanic and Atmospheric Administration in 2018 showed that the crater field covers an area of over 500 square miles, and contains over 5,200 depressions.

A press release published by the MBARI in May 2024 noted that the seafloor craters are "approximately 200 meters (656 feet) across, roughly the distance of two football fields, and five meters (16 feet) deep."

Previous research regarding seafloor craters in other parts of the world suggested that these depressions were formed—and maintained—by methane gas bubbling up through the sediments on the seafloor.

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"With wind farms slated for construction offshore of Central California, resource managers were concerned about how the presence of methane gas might impact the stability of the seafloor in this region," the press release mentioned.

However, MBARI scientists and researchers found no evidence of methane at the Sur Pockmark Field off the coast of California. Instead, their data pointed towards another factor that might be causing these depressions on the seafloor: sediment gravity.

"The research team has proposed that sediment gravity flows—similar to an avalanche of mud, sand, and water moving along the seafloor—that have occurred in this region intermittently for hundreds of thousands of years maintain these seafloor formations," the press release read.

"The research team deployed MBARI’s advanced underwater robots to study the Sur Pockmark Field. First, autonomous underwater vehicles (AUVs)—torpedo-shaped, self-guided robots—mapped the region."

Previous research suggested that these depressions were formed by methane gas bubbling up through the sediments on the seafloor. By: MEGA

"These maps then guided sampling with MBARI’s remotely operated vehicle (ROV) Doc Ricketts. Operated by the research team in the control room aboard an MBARI research vessel, the ROV Doc Ricketts collected sediment samples to reconstruct the history of individual pockmarks," the press release added.

Scientists at MBARI noted that the craters, or pockmarks, are located on the continental margin, a section of the seafloor connecting the relatively shallow continental shelf to the deep sea.

"Sediment gravity flows can move massive amounts of material through this region intermittently. The data and samples collected by MBARI technology helped the research team piece together the history of sediment movements over this part of the seafloor," the press release explained.

The team of scientists took sediment samples from the craters, the analysis of which indicated a significant flow of sediment gravity that occurred in this region "intermittently for at least the last 280,000 years."

One of the advanced underwater robots used by the researchers. By: MBARI

"These sediment gravity flows appear to cause erosion in the center of each pockmark, maintaining these unique underwater morphologic features over time," the press release mentioned.

MBARI Senior Research Technician Eve Lundsten, who led the research, commented on the findings, saying:

"We collected a massive amount of data, allowing us to make a surprising link between pockmarks and sediment gravity flows. We were unable to determine exactly how these pockmarks were initially formed, but with MBARI’s advanced underwater technology, we’ve gained new insight into how and why these features have persisted on the seafloor for hundreds of thousands of years."

"There are many unanswered questions about the seafloor and its processes... This research provides important data about the seafloor for resource managers and others considering potential offshore sites for underwater infrastructure to guide their decision-making," he added.