Seabed maps reveal underwater caves, slopes and fault lines


Larry Mayer is left this week on a ship to explore the Channel Islands off the southern California coast. Well, he’s actually exploring the seabed formations near the islands, looking for evidence that ancient people might have camped in the caves when they migrated south about 15,000 years ago, at a time when the sea level was 600 feet lower than today.

To do this, Mayer and a team led by famous Titantic explorer Robert Ballard will use a new kind of technology to deliver three-dimensional images of the caves, a kind of acoustic camera. The device uses existing multibeam sonar technology, which has helped oceanographers digitize the seabed for the past 30 years, with improved resolution, computer processing speeds, and viewing software in a standard package.

“This device can now give you a view similar to an image taken with sound,” says Mayer, director of the Center for Coastal and Ocean Mapping at the University of New Hampshire. “The idea is to look for places that look like a beach and a cliff but are underwater. If there are sea caves there, this is where these people would live.

Researchers have made several trips to these formations already, but on this trip they will be examining them in more detail with the new acoustic camera mounted on a new surface drone. Once they find the caves, they will send a remote-controlled vehicle called the Hercules with a high-definition video camera and robotic arms to take samples.

The mission is just one of many recent missions in which oceanographers have deployed new seabed mapping technology and advanced autonomous vehicles to uncover startling new information on the ocean floor. There are finds like underwater sea caves, deep-water coral formations off the east coast, and new species of marine life clustered around hydrothermal vents spewing methane and other chemicals from the earth’s crust. . New mapping techniques also reveal dangers such as seabed faults, volcanoes or unstable underwater slopes that could generate deadly tsunamis near coastal towns.

This is what H. Gary Green and his colleagues at the Geological Survey of Canada discovered during a recent mapping of the Salish Sea, a waterway between the American mainland and Vancouver Island, in British Columbia. They detected two active fault zones – one of them newly discovered – that could trigger rockfall and sediment subsidence that could lead to tsunamis that could be directed towards the San Juan and Bellingham Islands, Washington. .

“You don’t want to scare the public, but it’s something that should be built into any hazard analysis,” says Greene, a marine geologist at Moss Marine Laboratories in Moss Landing, Calif. Greene and his colleagues explored the Salish Sea with multibeam sonar sensors attached to the bottom of the research vessel and seismic sensors on a small torpedo-like instrument towed 100 feet from the seabed. Their findings were reported in April at the annual meeting of the Seismological Society of America.

Although the surface of Mars is about 34 million kilometers away, scientists know more about the surface of this planet than the bottom of Earth’s oceans. Many marine scientists hope that could change over the next decade, mainly by using more robots and fewer human-staffed ships. “What you need to do is take the ship out of the equation,” says Carl Kaiser, program director at the Woods Hole Oceanographic Institution. Operating a large research vessel costs $ 25,000 to $ 60,000 per day, and research cruises can last up to six weeks for mid-ocean expeditions.


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