Osborn(e) Bank Caves (225 fsw)

The original plan was to dive the USS Burns on Sept 2, 2020.

Alas, it was not to be. Two days before our scheduled trip, the military shut down access to that part of San Clemente island. We considered trying to go find the Grumman Goose but then figured we could go to Catalina Island at any time and that we wanted a bigger adventure. We settled on going to explore an area off Santa Barbara Island called Osborne Bank (or possibly Osborn depending upon which map you use).

A short history lesson

Southern California Bight (SCB) during the last Ice Age

During the last Ice Age in the Pleistocene Epoch (which began 2.6 million years ago and lasted until about 11,700 years ago), a large part of the water on the Earth’s surface was ice. The net effect is that the ocean surface was 300-400 feet below where it is today. Essentially, underwater structures that are considered “deep” underwater today were the tops of small islands on top of the ocean.

Today Osborn Bank is underwater with the top of the structure around 150-180 feet deep.

Underwater caves & structures – Andros Island

I’ve always had a fascination with underwater geological caves & formations. One of my favorite dive locations is Andros Island, Bahamas. It is not only the great people and the fun atmosphere, but also the incredible diversity of geology and diving. There are inland blue holes, inland caves, ocean caves, ocean blue holes, etc.

It really highlights what the Earth might have looked like during the ice age and the subsequent melting. You can imagine places where immense amounts of water carved holes and features into the rock. I’ve uploaded a couple sample videos from my dives in Andros to give you an idea of what I mean:

Elevator Shaft – An interesting “shaft” that leads down the side of the wall from about 120′ to about 185′. You can then turn right, go around the outcropping and then back up the wall. There are numerous “ledges” that were created during the ice melting in the last ice age.

Hole In The Wall – This is super interesting dive site that was lost for a long time until the local dive guid Fede and I found it again in 2015. It is an area that starts around 150′ deep with a big hole on the top of a plateau. It then leads down to about 180 feet where you can imagine a waterfall was. There are two exits out to the wall. One is deep at about 190′ and the other is shallow at 150′ or so.

Osborne Bank Cave

Ben, Justin, and I dropped down into the crystal clear blue water and followed the down line. It was incredible to see how clear the water can be once you get offshore. The visibility was virtually unlimited. The picture below is from about 180 feet deep looking down to the sandy bottom which is about 220′ deep. Note the Torpedo Ray (aka Pacific Electric Ray) in the middle of the frame.

Looking down onto the sandy flats

We oriented ourselves and decided to explore a little to see if we could find one of the caves that we knew were somewhere in the area. We quickly found the mouth of a cave that had clearly been explored in the past. This was likely placed by the Nautilus Live organization when they surveyed the area in 2019.

Entrance to one of the submerged caves

We had decided ahead of time that I would be the “reel man” and deploy the line into the cave. After tying off the scooters, I tied into one of them outside the cave and proceeded to run a line into the cave.

Running the line. Photo Credit: Ben Lair

Unfortunately, the “cave” ended up being more like a tunnel that was probably about 150′ long and we soon ran into daylight at the other end and turned around to reel back in the line. Oh well.

Me returning into the tunnel. Photo Credit: Ben Lair.
The light at the “entrance” end of the tunnel is my camera that I left on when I started running the line.

After retrieving the line, we got re-organized and set about exploring some of the other areas around the cave entrance. There was a nice arch and a bunch of the cool geologic features. We spend another 10 minutes or so before starting our way back up the wall to the down line for our long decompression profile.

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