Cave Diving In Crystal Clear Water

Why Cave Water Is So Crystal Clear

• Jill Heinerth

I’ve just returned from the crystal caves of Abaco, and even after decades of diving, that first descent from the open water still takes my breath away. You slip below the surface, descending through a blurry halocline before the world sharpens in the blueish saltwater. Light travels amazingly far in the first room, brightening a yellow stop sign intended to deter the untrained. The water is so clear; it feels less like water and more like flying through liquid glass.

So what makes cave water so incredibly clear?

It all starts with geology. Most underwater caves, like those in Abaco, form in limestone, which is made from the remains of ancient sea life. When rainwater, made slightly acidic by carbon dioxide from the air and soil, seeps underground, it slowly dissolves the limestone. Over thousands or even millions of years, this water carves out tunnels and large chambers in a process called karst formation. When the water table drops and the cave dries out, slow drips from the ceiling create amazing formations called speleothems.

But carving the cave is just one part of the story. The real reason for the clear water is filtration.

Before groundwater reaches a cave, it usually passes through layers of soil, sand, and broken rock that are sponge-like. This acts like a very slow natural filter. Along the way, things like silt, bits of plant material, and tiny organisms are filtered out. By the time the water comes out in a spring or fills a cave tunnel, most of what would make it cloudy is already gone.

Another factor is hydrology, which is how water moves through these caves.

Caves are shielded from wind, waves, and other surface disturbances. There are no storms to stir up sediment, no boat wakes, and no shoreline erosion. In many caves, the water moves slowly and steadily, sometimes only a few meters each day. Because there is so little movement, particles settle on the cave floor and can stay there for an eternity. In Abaco, when I hover above the clean white silt, I always remember how delicate that stillness is and how a single careless kick can cloud the water in seconds.

Caves also have very little light and few nutrients. Without sunlight, algae cannot grow. Since not many nutrients get in and there are few openings to the surface, there is little plankton or other tiny life. With fewer organisms, there are fewer particles floating in the water.

The result is water so clear that you can see farther than your cave light can shine. The clarity feels almost sacred.

Every time I finish a dive in places like Dan’s Cave in Abaco, I feel like a guest in that quiet world, and I know it’s up to me to keep it undisturbed.

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Jill is featured on the latest CBC “The Nature of Things” episode, diving and studying the life of an iceberg as it is born among the glaciers of Greenland and meets its demise near Newfoundland’s Iceberg Alley. Here is the entire episode on Youtube. You can also watch it on the CBC Gem app in Canada.

“The Nature of Things” is a Canadian TV program similar to the UK David Attenborough nature documentaries. The show was hosted for decades by zoologist David Suzuki from 1979 to 2023. It is currently presented by David’s daughter, the marine biologist Sarika Cullis-Suzuki.

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Here’s a sneak peek at one of Robert’s art pieces in progress…more to be revealed.

“We Live In Public” collage on mannequin.

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HEALTH UPDATE:

Robert had a successful Cardioversion at the Heart Institute at Ottawa! He is now in a sinus rhythm - no longer atrial fibrillation. He feels better and his stamina is returning. He does have some BBQ skin burns on his back and chest but they are a small price to pay… He’ll stay on some cardiac meds and will be scheduled for an ablation which may be a more permanent solution for his arrhythmias. Thanks for your concern and good wishes.

Above: Robert’s artistic interpretation of his cardioversion.

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