The Blowhole:
Over thousands of years, the constant waves have eroded and weathered the surrounding rocks. The blowhole, is an example of a sea cave, where the waves have burrowed/eroded in and after hitting harder rock, then up. When a set of waves come into shore, the momentum and power behind them sends the water through, up and out the blowhole. Creating a fantastic visual phenomenon.
Hydraliuc Action is when water will splash upwards on the cavity walls. The water has small pockets of air (also known as whitewater) and accompanied with the strong wind & air currents entering and leaving the blowhole, it causes it to erode on the inside in stages. Essentially, the air bubbles infiltrate into tiny pores in the rock, causing it to erode quicker.
Foreign objects and other rocks, pebbles and sand being swept into the blowhole break off weaker pieces of rock upon collision. This is known as Abrasion Weathering.
Apart from shoreline erosion, blow holes can also be formed through volcanic, human or biological processes. This however, is not the case for the Newcastle area.
Local daredevils, swim/jump into the blowhole and get a thrill from the sudden impulse of water and sometimes, in the hope of being thrusted up and out of the blowhole. This is extremely dangerous and it poses the risk of drowning or serious injury.
Rocks of the Region
This coastline is dominanted by large amounts of large particled conglomerate, shale rocks, tuff rock and sandstone. See http://www.resources.nsw.gov.au/__data/assets/image/0020/349310/Newcastle100Geology.jpg for more information.
Questions
A What is the approximate diameter of the blowhole, looking from the top. (Be mindful you may get wet)
B What has been deposited at the bottom of the blowhole, look when the water exits it.
C Describe the colour, shape and texture of the rock surrounding the blow hole.
D Provide a photograph of yourself around the blowhole (optional)
Sources: Wikipedia, GC2YWAG, GC2JRRP, Resources.nsw.gov.au
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