How Blowholes Work
When the winds are coming from the South East then waves enter the mouth of the Blowhole & compress the air within the inner cavity. Contrary to popular belief the tides do not have any bearing on the performance of the blowhole.
The escaping air causes the loud "oomph", which accompanies the water spout. Over many years the Blowhole will become less vigorous, as the underground cavity erodes due to the pounding waves.As the retreating water leaves, it is forced upward by the compressed air, as the mouth is still blocked by the receding wave.
The main Kiama Blowhole was discovered by George Bass on his voyage of coastal exploration on December 6, 1797, after anchoring his whaleboat in the sheltered bay which became Kiama Harbour.
The shore Bass wrote, showed evidence of considerable volcanic fire and on the point he found: "The earth for a considerable distance round in the form approaching a circle seemed to have given way; it was now a green slope.....Towards the centre was a deep ragged hole of about 25 to 30 feet in diameter and on one side of it the sea washed in through a subterraneous passage...with a most tremendous noise..."
Bass was not, in fact, the first to discover the Kiama Blowhole, as local Aboriginals had for generations referred to it as Khanterintee.
In January 1889 a performer by the name of Charles Jackson attracted large crowds to see his crossings of the mouth of the Blowhole on a tightrope.
A smaller "Little Blowhole" is located a few minutes south of the main Blowhole in Tingira Crescent. The Little Blowhold performs best under moderate seas when the winds are coming from a northerly direction.