SF Bay underwater dunes


San Francisco long has been renowned for its hills, bay and bridges — but not for expanses of sand dunes. That’s liable to change.

It turns out there are more than 2 square miles of dunes right next to the city, and world-class dunes at that: Only a few sites around the globe have larger dunes of this sort.

Access, however, will remain difficult unless you’re a sand dab or Dungeness crab. The dunes are just west of the Golden Gate, submerged in 100 to 350 feet of sea water.

Scientists grasped the extent and size of the underwater dunes — technically known as “sand waves” — only recently, aided by sophisticated, multiple-beam sonar that provides stunningly detailed images of the submarine topography.

“These are some of the largest sand waves in the world,” said Patrick Barnard, a coastal geologist with the Santa Cruz office of the U.S. Geological Survey. “They’re certainly in the upper 10 percent.”

The sand waves range up to 700 feet long and reach heights of more than 30 feet, Barnard said. It is a dynamic system, he said, with the configuration of the individual dunes changing significantly with each tidal cycle. But overall and over time, the net change to the entire field is slight.

[full story at SF Gate]  [via BLDGBLOG]

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