Scientists Are Investigating the Source of More Than 5,200 Craters Discovered off the Coast of California. It May Have to Do With Gravitational Forces

These formations typically result from methane seepage, but this doesn’t appear to be the case in the Golden State.

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Pablo Martínez-Juarez

In 1998, scientists at the Monterey Bay Aquarium Research Institute (MBARI) discovered mysterious holes off the coast of California during a survey of the seafloor. These boreholes, which resemble small underwater craters, had an unknown origin, leading to much speculation. 25 years later, a new theory has emerged to explain these curious underwater features.

New hypothesis. A recent exploration of the Sur Pockmark Field boreholes has prompted a team of experts to put forward a new hypothesis regarding their formation. The MBARI researchers have proposed a simple explanation: gravity.

Sur Pockmark Field. The area where the mysterious holes are located is known as the Sur Pockmark Field. Situated off the coast of Big Sur, California, this field comprises more than 5,200 of these small depressions.

The holes are situated between 1,600 and 5,200 feet below sea level, measuring about 500 feet across and around 16 feet deep, although they vary in size.

No traces of methane. Previously, scientists believed that the holes in the seafloor were caused by methane. Their research work had linked similar pockmarks elsewhere to this gas. In those instances, methane bubbles would rise from below the surface, bringing with them seafloor sediments.

More recently, the MBARI researchers wanted to determine if this was the case in the Californian pockmark field because of plans to install offshore wind power in the area. Methane leakage could potentially lead to unstable soil, posing a threat to these developments.

Gravity doesn’t stop. However, the studies conducted revealed no presence of methane in the area. Instead, there were signs indicating that the holes may have been formed by “sediment gravity flows,” which are underwater avalanches carrying sediment deeper into the ocean.

Scientists believe these flows have occurred repeatedly over the past 280,000 years. According to a new study by researchers at MBARI, these movements seem to erode the centers of the holes, contributing to their persistence over time.

“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… we’ve gained new insight into how and why these features have persisted on the seafloor for hundreds of thousands of years,” study co-author Eve Lundsten told EurekAlert.

Unmanned underwater vehicles. The recent MBARI study utilized advanced underwater technology to explore the seafloor. Initially, the team used autonomous underwater vehicles to create detailed seafloor maps using sonar technology.

These maps were then used by remotely operated vehicles to collect samples and study the area’s geological history.

Image | MBARI

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