Deep-Sea Sight
By Clara Moskowitz, The Monterey County Herald, Calif.
May 24–If only Mapquest covered the sea.
Fortunately, explorers of the deep are mapless no more, thanks to a project charting the ocean floor off California’s coast.
CSU-Monterey Bay scientists reflected sound and light off the ocean floor to trace the Earth’s underwater nooks and crannies. In addition to exposing canyons, landslides and even shipwrecks, the map recently revealed the secret behind the massive waves at Mavericks, Half Moon Bay’s notorious surf spot.
“We’ve never been able to look at the seafloor in this kind of detail before,” said project leader Rikk Kvitek, a CSUMB marine researcher. “It’s as though you could go out into the ocean, pull the plug, drain the water, and take a picture.” Kvitek said the map was detailed enough to spot a couch on the seafloor, up to 80 meters down.
The map that exposed the secret behind Mavericks was part of the Northern Central California Coast State Waters Mapping Project, a pilot program that covered 110 miles from A o Nuevo to Point Arena. The map extended from the shore to the edge of state waters three miles out.
The $3.5 million project, which began in 2006 and released its first images in April, was funded by the California Coastal Conservancy, the state Department of Fish and Game, and the California Ocean Protection Council. Kvitek’s team is hoping for more funding to map the rest of the coastal ocean, including Monterey Bay.
Scientists long suspected that unique terrain near Half Moon Bay creates Mavericks’ colossal waves, but the map provided the first detailed snapshot of what was really going on.
“Geologically, it’s an amazing spot,” said Moss Landing Marine Lab marine geologist Ivano Aiello. “We are in one of the most active tectonic areas on the planet.”
Aiello said the map revealed a series of bumpy layers of earth intersecting fault lines. Actively shifting plates have distorted and twisted the ground, creating jagged layers of rough and soft. The rutted ground stands higher than the ground around it, which is low and smooth.
“The topography of the seafloor is really influential in how waves react,” said H. Garry Greene, a marine geologist at the Monterey Bay Aquarium Research Institute.
Waves travel long distances across the ocean, Greene said, and can’t feel the seafloor deep below.
When a wave gets to shallow water close to shore, its bottom starts to slow from friction with the ground. But the wave’s top, which feels no drag, speeds on and grows larger. Eventually it gets so high, it outruns its base and crashes down on itself.
Because ground under Mavericks is higher and rougher than the terrain around it, wave bottoms slow down sooner, and the tops start to build earlier, Greene said. This allows waves to grow extremely large, eventually building up to 40 feet.
California is the first state to embark on an ocean-mapping project of this scale. Lawmakers are getting behind the project, Kvitek said, because they recognize how the map can help manage the state’s Marine Protected Areas and the ecosystems they preserve.
“Everyone’s on board, saying, ‘Yeah, we’ve got to do this,’” Kvitek said. “But we’ve only got a third of the state’s waters mapped, and two-thirds left to go.”
California in 1999 passed the Marine Life Protection Act, which called for a series of MPAs with restrictions on fishing and other human activities to protect marine life and habitats.
“If you’re going to set up refuges for species, you want to make sure you’re putting them in places that are suitable,” Kvitek said.
For example, he said, rockfish like rocky terrain, and halibut prefer coarse sediment. The map allows scientists to shape MPAs around specific spots that best suit the species they hope to preserve.
To probe the bottom of the sea, scientists bounced sound off the ocean floor. Their boat, equipped with new multi-beam sonar, blasted down a swath of sound, 1.5 degrees thin by 150 degrees wide.
Researchers measured the time sound took to bounce back, and the angle from which it came, to build a high-resolution topographical map of the ocean floor. Though sonar has been around for awhile, the swath, made of 101 separate beams, is a new technology that allows scientists to cover ground much faster, cheaper and in higher resolution than earlier versions.
The team used a new light-bouncing technique to map shallow areas that are difficult to reach with sonar. The light, whose travel time is measured similarly to that of sound, was beamed from an airplane that could avoid the turbulence of close-to-shore waves that plague sonar boats.
Kvitek said the mapping project revealed a dynamic world invisible from land.
“You stand on the shore, and it’s all blue,” he said. “You figure it’s all the same, but it’s extremely complex.”
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Copyright (c) 2007, The Monterey County Herald, Calif.
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