Thursday, July 02, 2009

Freaque current off La Jolla shores

Keith Darcé of Sign On San Diego reported today a strange deep water current off La Jolla shores that had occurred yesterday. Here's what happened:

— In more than 700 scuba dives off La Jolla Shores, Terry Strait had never encountered a deep-water current like the one that slammed into him and his buddies yesterday morning about 250 yards from the beach.

As the four divers swam roughly 60 feet below the surface along the edge of La Jolla Canyon, they noticed a wall of sand rushing toward them from the southwest.

“The current was really pushing us,” said Strait, 41, of Kensington. “We tried to swim lateral to it but couldn't get out of it.”

They held on to the edge of the cliff to avoid being pushed farther out to sea. The group slowly swam against the flow toward the surface and finally broke free at a depth of 15 feet, Strait said.

The strange and previously unknown current occurred in a normally placid area of water, said lifeguards and a marine expert at the nearby Scripps Institution of Oceanography. It was noticed by other divers in the area over several hours starting around 6 a.m., but not by swimmers on the surface of the water.

Here's a drawing of the local conditions:

and here's a plausible explanation of Dr. Seymour:

During normal current patterns, waves move up the coast from the south, Seymour said. Point La Jolla, which juts into the Pacific Ocean, serves as a natural breaker that largely protects the north-lying La Jolla Bay from those waves.

But the wave track shifted slightly yesterday morning — coming more from the southwest, Seymour said. The change was enough to allow waves to wrap around Point La Jolla and move into the bay, where they collided with a large pool of sedentary water that bounced them back out to sea.

Divers swimming around the edge of La Jolla Canyon were in the direct line of that deflection, Seymour said.

“The currents around La Jolla were very strong,” he said. “The intensity of this event was probably produced by a group of very big waves.”

It is of interest to note that there are not only freaque waves but also freaque currents as well and this freaque current took place at the door step of Scripps Institution of Oceanography, the world's premier ocean research center. We have built up a large knowledge base on ocean over the years and centuries, but we still know so little about the ocean. I think Seymour rightfully pointed out that the the currents might still be "produced by a group of very big waves" though the big waves were not observed. Perhaps as given in the article, Mr. Strait, the star of this story, gave the most sober of all possible comments:
“I have respect for the ocean. I constantly remind myself that I'm not really supposed to be out there underwater and that the ocean wants to kill me.”

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