FORMATION OF A BLOWHOLE
The Blowhole was once a sea cave and tunnel. The roof at the rear of the tunnel collapsed to create a broad arch with a blowhole behind it. The Blowhole point was originally an unbroken line of cliffs of siltstone. This flat lying rock was formed like a giant layer-cake when mud and silt were deposited into the sea about 270 million years ago. Earth movement cracked the rock, creating vertical joints which enabled the sea to erode caves and tunnels into the sea cliffs. The Blowhole only lives up to its name when the seas are rough and in the right direction. Swells enter the tunnel, and sea-spray and air are blasted through the funnel, creating an explosive effect in the small joints at the back of the ‘inlet’. The sound of the ‘thump’ is the impact of water on the rock and the expansion of air that had been compressed into cracks. When seas subside the Blowhole runs out of puff and it may then be described, although rarely, as a millpond.
Reference from, Department of Primary Industries, Parks, Water and Environment.
To log a find on this Earthcache please answer the following questions and send them via email through geocaching.com. Please do not post your answers in your online log. Once you have sent your email feel free to log your find, if there are any problems I will contact you.
1. What is the width of the crack?
2. Which cracks form blow holes? Why?
3. Provide a photograph of yourself near the blowhole (optional)
CITO - The practice of "cache in trash out" would be greatly appreciated from all cachers visiting this splendourous location. Take nothing but photos and leave nothing but footprints.
SAFETY - There are warnings about this being a severe hazard area, with large waves washing over the foreshore rocks regularly and uneven and slippery rock surfaces. Please take care when visiting this location and follow all safety precautions recommended on the warning signs.