Kiama blowhole

The Kiama blowhole is a famous feature of the coast south of Sydney.

You can find it on the rocky outcrop that is home to the lighthouse.

When you are used to what the shoreline in Sydney looks like, you will see that the rocks at Kiama are very different. They’re very dark, they’re unbelievably rough and sharp and you don’t get the little round depressions that fill up with water that you get on rock platforms in Sydney. This is because the rocks are not sandstone, as in Sydney, but they’re basalt.

Sandstone is a secondary stone that occurs in areas where there has been a lot of sediment from rivers. Basalt is primary volcanic rock, cooled lava.

Sandstone has a layered structure and will often also wear in layers.

Basalt responds to erosion by crumbling, and because the lava erupted unevenly, you can get deep fissures.

This is prime blowhole country.

You can read more about the area’s geology here.

A blowhole is where the ocean has undermined a cliff and where the waves come up from underneath in between the fissures. The wave gets trapped under there, and the pressure sends a spout of water up through the hole, somewhat like a geyser.

The blowhole works on most days. When we where there, the sea wasn’t particularly rough. When the waves are high, the blowhole can spout for up to 50m into the air.

The blow hole is within walking distance of the town’s centre, and the station is even closer.

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