The central California coast has a unique feature on its seafloor, known as the Sur Pockmark Field, which consists of over 5,200 round depressions, or pockmarks, stretching across 500 square miles. For decades, scientists believed these formations were caused by methane bubbles rising through the mud, but recent research has debunked this theory. A team of researchers from the Monterey Bay Aquarium Research Institute (MBARI), the U.S. Geological Survey (USGS), and Stanford University used advanced technology, including autonomous underwater vehicles and sonar, to map the seafloor and collect samples. The results showed that the pockmarks are not caused by methane, but rather by sediment gravity flows, which are underwater avalanches that occur when sediment is carried downslope by gravity.
The researchers found that the pockmarks are almost perfectly spaced apart, with each one averaging 656 feet across and 16 feet deep. The sediment cores collected from the pockmarks revealed layers of fine silt and coarser sand sheets, with no signs of methane. The team also found that the pockmarks have been shaped and preserved by these sediment gravity flows over hundreds of thousands of years. The most recent flow occurred around 14,000 years ago, and the sediment layers suggest that these events have been occurring for at least 280,000 years.
The discovery has significant implications for the development of offshore wind farms in the area, as it suggests that the seafloor is stable and unlikely to be affected by methane bubbles. The research also provides valuable insights into the geological processes that shape the seafloor and can inform the planning and development of future offshore infrastructure. The study’s findings have been published in the Journal of Geophysical Research Earth Surface, and the researchers hope that their work will contribute to a better understanding of the seafloor and its processes.
The Sur Pockmark Field is now considered one of the best-charted seafloor provinces on North America’s west coast, and it provides a unique opportunity for scientists to study the geological and ecological processes that occur in this environment. Future research will focus on understanding the origins of the pockmarks and the sediment gravity flows that shape them, as well as the potential environmental impacts of offshore wind energy development. The study’s lead author, Eve Lundsten, noted that “there are many unanswered questions about the seafloor and its processes,” and that this research provides important data for resource managers and others considering potential offshore sites for underwater infrastructure.