"Visitors to this coast are humbled by a seascape that is both ancient in design and dynamic in form. The bone jarring slaps of leviathan waves an aural reminder of a distinct lack of permanency."Contemplate this spectacular theatre of stone, sea and sand from a network of National Parks trails and lookouts.
Limestone is a sedimentary rock. It forms in layers with the youngest rock closest to the surface. When you look at a cliff in this National Park you are looking at a vertical geological record of millions of years.
Port Campbell Limestone is generally dated at 15-20 million years old it is a common misconception that visitors are viewing an ancient seascape. The formations they are viewing have formed in the last 6000 years (the time that sea levels have been at their current height) Dr Eric Bird surmises that the evolution of a rock stack from headland to arch to stack and eventual collapse can take place in just 600 years on the Port Campbell coast.
The spectacular variety of seascape in the Port Campbell National Park and Bay of Islands Coastal Park is not due to a large inconsistency in the erosive forces. It occurs largely because of a range of inconsistencies in the density and durability of the strata. The Port Campbell National Park cliff line and offshore stacks are comprised of differing densities of limestone interspersed with softer mudstone (marl) and calcareous clays.
"Port Campbell Limestone is harder in its top layers than it is in its bottom layers. The softer base layers allow the initial undermining that creates overhangs, arches and eventually new stacks."
The erosive forces of wave, wind and rain have in effect found their own “path of least resistance.” Surviving rock stacks like the 12 Apostles are generally comprised of “harder stuff” than areas surrounding them.
Port Campbell Limestone is harder in its top layers than it is in its bottom layers. The softer base layers allow the initial undermining that creates overhangs, arches and eventually new stacks.
Factors affecting hardness of limestone are silt depositions (making it softer) and a higher concentration of calcium carbonate (which makes it harder) Calcium carbonate is provided by skeletons and shells of marine creatures deposited on the old ocean floor. Limestone only forms where ocean has once covered.
For further information visit www.parkweb.vic.gov.au
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