St. George's Cave

On Monday and Tuesday we visited St. George’s Cave. When we arrived at the cave, we discovered that the water level had risen significantly since the last deployment 2 years ago. The land bridge that had previously connected a large rock hill was approximately 1 foot underwater, so we were forced to setup our control box and other equipment outside of the cave.

Rock hill on the right

More of the cave...Pictures just don't do it justice in scale

We quickly deployed with the Smart Tether and began taking sonar scans.  It took a couple of hours just to map the outer walls of the cave, and it was lunchtime before we knew it.

After lunch, we redeployed with the HOBO sensor. When we went to put the ROV in the water, we noticed that the water level had risen since the morning. This made us wonder if the cave is somehow connected to the sea. Our HOBO data may help us answer this question.

Andrew on tether

Tape for our "Slices of Pie"

We quickly ran into a number of Smart Tether issues. After about an hour of troubleshooting we decided to begin taking manual measurement by driving the VideoRay to a wall, marking the tether with tape, diving to the bottom, and marking again. We kept a log of time stamps and approximate locations in my journal, in addition to our usual log books. These timestamps will help us match up the corresponding HOBO data. We decided to call this our “Slices of Pie” method, since we were taking new readings ever few degrees around the semicircle cave.

By  By the end of the day, we had finished collecting dense HOBO data for about half of the cave. When we returned on Tuesday, we decided to continue our “Slices of Pie” method for the remaining half of the cave. Interestignly, about 1/3 of the cave was blocked from view by the rock hill mentioned above.

View from the cave entrance

I quickly volunteered to be the adventurer who would cross the submerged land bridge to assist with the measurements on this portion of the site. As soon as I had crossed the bridge, we began having some software issues, so I spent ~20 minutes alone in the dark cave. It was a little creepy at first, then quite peaceful, and then very fun, as my eyes slowly adjusted and I explored more. By the end, I felt like Gollum sitting inside a dark cave surrounded by water.

Once the ROV software was back up and running, we quickly finished our slices of pie. One of the slices had a deep channel below it. We dove about 20 meters and could not descend lower, but still saw pitch black below, indicating that it went much further!

I’m excited to see the results of this deployment. Even with our manual logging style I am hopeful that we will get some interesting results.