The twin gaps are located on two ridges running parallel approximately 300 meters apart. The first and most seaward gap is about 20 meters wide and the second, most spectacular, gap is about 10 meters wide. When the rising or falling tide occurs, the water builds up in front of the gaps faster than it can flow through them. This in turn creates an amazing waterfall effect as the water rushes through and then down to the lower levels on the other side of the ridgelines. The process is reversed and it is repeated again in the opposite direction.
The tides in this area have a 10 meter variation which occurs over six and a half hours from low tide to high tide and vice versa. On a slack tide it is possible to drive boats through the two gaps to the bay behind.
The waterfall phenomena has been described by David Attenborough as "one of the greatest natural wonders of the world".
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