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Bahamas Blue Holes 2016: Underwater, Underground, Making a Map


Steve Bogaerts is a cave diving instructor and explorer originally from London, England who has been living in Mexico for the last 18 years. Steve first visited the Bahamian island of Abaco in 2003 and has been making regular trips since then to explore and map the incredible Crystal Caves. In 2015 Steve and Brian Kakuk were able to complete a project years in the making by connecting Dan’s and Ralph’s Caves—two of the most beautiful and important caves on the island, and the caves that are the subject of our current survey project.

Expedition Blog 10 / Dec. 12 / By Steve Bogaerts

Today was my last day working on the National Geographic Abaco Blue Holes project. It has been a very rewarding experience both to work with this talented multidisciplinary team and to dive the amazing caves Crystal Caves of Abaco. As one of the original explorers of these caves, I am continually awed by the surpassing beauty Mother Nature can create. Unfortunately very few people will have the chance to experience the beauty of these caves firsthand. To be able to share that beauty and wonder with other people is one of our main aims in this project.

One of the best ways we can do this is through cartography. Bringing back a map of your exploration allows other explorers and scientists to follow your path, to study and learn more, and most importantly to raise awareness of the need to protect and preserve this unique and fragile environment. Over the years many people have contributed to the exploration of the caves of the Bahamas, but unfortunately much of the mapping data remains missing or of poor quality.

During this expedition, we are starting a complete resurvey of Dan’s and Ralph’s Caves, which Brian Kakuk and I finally managed to connect together after many years of effort in 2015. The resulting connected system is properly known now as Dan’s Cave and is one of the longest island cave systems in the world. The area surrounding Dan’s Cave has moreover recently been designated a protected conservation area by the government of the Bahamas. Producing a complete map of the caves will help in these continued efforts to protect and preserve this unique and fragile natural wonder.

A very colorful section of the cave know as Fangorn Forest. The dive plan involves swimming through alternately decorated and naked passages as deep as 146 feet to emerge in a thick grove of speleothems. Photo: Jill Heinerth
A very colorful section of the cave know as Fangorn Forest. The dive plan involves swimming through alternately decorated and naked passages as deep as 146 feet to emerge in a thick grove of speleothems. Photo: Jill Heinerth

Cave survey, however, is a long, detailed, and laborious process. In addition to all the complex equipment a cave diver requires to safely conduct dives normally, surveying specifically requires many additional tools and techniques. The survey process begins by taking a GPS location fix at the entrance of the cave, which is then connected to the beginning of the permanent guideline that runs throughout the cave underwater. The GPS fix allows us to plot the survey data and the location of the cave on surface topological maps.

From this initial fix, every point at which the permanent guideline in the cave changes direction or depth must be fixed in place with a locking line wrap. Each one of these tie-offs becomes a survey station. The surveyor records the depth at each of these stations using a digital depth gauge and shoots the azimuth to the next survey station along the guideline using an orienteering compass. They then measure the distance between the stations using a fiberglass tape or knotted line.

All this information together with any important features or comments is recorded on an underwater slate. This basic information allows the survey team to create a “stick map,” or skeleton outline of the permanent guidelines installed in the cave passageways. This basic map can be further fleshed out by measuring the distance to the walls, floor and ceiling at every station and creating a cross-sectional sketch. Photos and video may also be recorded along with further geo-referencing at selected sites using a ground penetrating radar location tool called a “pinger.” All of this information is then downloaded to a computer survey program that creates a 3-D rendering of the cave with embedded links to photo and video of significant areas of interest.

Surveying an underwater cave is inherently limited by the amount of time that can be spent underwater on any one dive. This is further complicated in these particular caves by the saw-tooth dive profiles of the cave passageways (zig-zagging up and down), the need to surface slowly to allow for decompression, and the fragility of the highly decorated passages. In addition these caves are extremely complex with maze-like passageways that create a complex three-dimensional jigsaw puzzle of intersecting permanent guidelines. The desire to survey the cave accurately has to be balanced very carefully against the need to protect both the cave and the survey diver from any harm.

Having said all of that, it is a very satisfying feeling to return to base camp with full survey slates and to watch the cave map grow as you input the data and gain greater insight into the hydrology and geomorphology of the area. As the map has grown, so too has my desire to discover more of the secrets of the Crystal Caves of Abaco. I hope to be back soon to continue this journey of exploration and survey.

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