Blue Hole Experience

March 2000 Table of Contents

OUR ABACO BLUE HOLE EXPERIENCE
by Brian & Carolyn McWilliams

30th July 1999
Treasure Cay Blue Hole
28 minutes, maximum depth 57 feet

After waving goodbye to our friends, we descended straight to the edge of visibility at 54 feet. At 57 feet it became very murky with only a few inches of visibility. Above 57 feet, however, visibility was about 30 feet. The only life we saw were small white crabs tucked away at the sides of the hole. Other than these little crabs it was devoid of visible marine life. During the first few minutes it felt a little creepy to be in there. Would it be full of eels or snakes? Would we see a dead body? After a few minutes our imaginations calmed down, we relaxed and had fun exploring.

The water was entirely fresh; there was no salt or brackish water in the hole. The limestone was extremely fragile and broke easily when we touched it. Silt lay everywhere. If we kicked our fins towards the limestone, silt would surround us and cloud our vision for about 30 seconds until it sank to the bottom, which acted as a giant sediment trap.

There were amazing 25 foot columns that hung down outside a few caves. These caves looked eerie. Their looming undercuts invited us in. We swam into a few of them until they became too small for us. We shone our flashlights in the caves. There seemed to be a system, but the caves became small very quickly. Between the caves, giant ravines sliced the hole from top to bottom. From our viewpoint underwater, the structure looked like a giant sand-dribble castle.

All of the limestone was extremely porous. As the name implies, it was very blue in the hole. Occasionally the limestone had small patches of red tinge. At first we thought it might be some form of lichen, but it was just some sort of ferrous compound on the limestone. The porous holes were everywhere - small holes, large holes, caves all around us!

We swam around the hole twice. At the far end of the hole, a thin yellow rope hung from the surface down to the bottom. When standing on land, the surface of the blue hole looked about 40 feet in diameter and seemed perfectly round. Below the water at about 10 feet, we looked up to the sky and could see the trees around the blue hole leaning over us. At about 30 feet underwater we felt a large thermocline. The surface temperature was 84 F and 77 F at the thermocline.

These blue holes are beautiful and offer scientists a geological history of the Caribbean. They use them as a time line for the rising sea levels in the last ice age. Also, the layered sediment on the bottom provides a record of atmospheric environmental changes over time. These blue holes used to be caves in which stalagmites and stalactites formed. When the last ice age ended, sea levels rose about 300 feet, flooding the caves. At the same time ceilings collapsed, leaving us these blue holes.

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