The central California coast hides a dimpled and pockmarked seafloor region that is roughly the size of Los Angeles – five hundred square miles of soft‑edged pits stretching from Big Sur to Morro Bay.
For decades ocean scientists assumed these round depressions – a whopping six‑football‑field stretch from rim to rim and about 16 feet deep – were scars left by bubbles of methane burping up through the mud.
That tidy explanation raised eyebrows once plans for an offshore wind farm landed on the same patch of continental slope between 1,600 and 5,200 feet below the waves. If methane were still leaking, could turbine anchors stay put?
Curiosity turned urgent when more than 5,200 of the formations, known as pockmarks, appeared to be distributed with “eerie regularity.”
The pattern suggested an active force was sculpting and preserving the craters even today.
To settle the debate, a research team rolled out a fleet of high‑tech robots and a mountain of sensors – and overturned a favorite myth about how the seafloor breathes.
Seafloor full of large pockmarks
Autonomous underwater vehicles zipped barely yards above the bottom, beaming back sonar so sharp it mapped individual ripples of sand.
The survey refined ship‑based maps and revealed that most pockmarks sit almost perfectly spaced apart, each nearly circular and averaging 656 feet across.
Back at mission control aboard the research vessel, experts from the Monterey Bay Aquarium Research Institute (MBARI), the U.S. Geological Survey (USGS), and Stanford University watched the topography scroll across their monitors at one‑foot resolution.
The robots also carried a CHIRP sub‑bottom profiler, a sound cannon that peeks some 25 feet beneath the mud.
Instead of pockets of gas, profiles showed neat layers: thin bands of fine silt interrupted by coarser sand sheets. Those buried sand sheets hinted at something far more dramatic than gentle gas seepage.
Hellbound and Down 