Arch + Kitchen

Tasmans Arch and Devils Kitchen
 
 
 
 
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Tasmans Arch is what’s left of the roof of a large sea cave, or tunnel, that was created by wave action over many thousands of years. The pressure of water and compressed air, sand and stones acted on vertical cracks [joints] in the cliff, dislodging slabs and boulders.
 
 
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Tasmans Arch seems to be old but it is still changing - is the arch growing or the roof thinning. In the cliff-face opposite there are many weak zones similar to those that gave way to create an arch when the cave wall collapsed. The arch will eventually collapse and another ‘Devils Kitchen will be formed. Looking to the edges we thought it almost looked man-made, the upright sandy colours and the horizontal dark greys.
 
 
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1. Ancient and Modern Seas Erode Siltstone Cliffs. About six thousand years, when the sea-level rose at the end of the last ice age, the sea further eroded the base of the old siltstone cliffs. Wave action cut a notch in the base of the cliffs, undermining the rock layers above. The wave action thus caused some collapse and the formation of a shore platform. Waves also worked into some of the vertical joints, dislodging more rock. So began the formation of sea caves. Tasmans Arch, Devils Kitchen and The Blowhole all began their development in this way.
 
 
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2. The Formation of a Sea Cave: Wave Action Erodes a Cliff. Wave action continued to erode the base of the cliff. Vertical joints were weakened further and slabs of rock collapsed into the sea. Water pressure, sand and stones acted on the openings [cracks, joints] which widened and deepened into a sea cave and later a tunnel with a cave behind it. Some of this erosion probably took place during a time of higher sea level.
 
3. The Back of the Tunnel Collapses and Tasmans Arch is Formed. Thousands of years of erosion deepened or lengthened the tunnel. Eventually the tunnel reached a fracture that runs parallel to the coastline. This fracture is linked at sea level to the Devils Kitchen. The roof collapsed at this joint leaving a pit behind an arch.
 
 
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During the Carboniferous and Permian geological periods [300 to 265 million years ago] this area was part of a cold sea. Sea ice, icebergs and streams carried blocks of rock, sand, silt and mud into the sea. As the sea finally retreated an extensive, sandy plain was formed. These flat-lying siltstone and sandstone rocks form the sea cliffs from Waterfall Bay to Eaglehawk Neck.
 
 
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After reading everything on the information board it was time to bimble over to the lookout.
 
 
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View from the lookout into the distance.
 
 
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Closer view.
 
 
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The cliffs nearest our vantage point.
 
 
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New plantings behind us.
 
 
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From the other side [Tasmans Arch now on the right] we could see Mabel on the left.
 
 
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From as far left as we could get.
 
 
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Despite being bone dry on the ledge in front of us these chaps seem to thrive.
 
 
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Our final stop was a short walk away.
 
 
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Beginning our walk was like a time warp – Bear, Mabel horizontal rock erosion........
 
 
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Then the view down – wow. If only a  person was standing at the bottom to get the perspective of how deep. The small cave at the bottom would tower over them. The sea is still wearing down Devils Kitchen, the small cave will get a bigger opening and the sea will erode an even greater area.
This is the final act of our circle of erosion – from a humble cave to a great gulch, what a good word......
 
 
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View out to sea from the Lookout. A person in the water would look like a tiny pin head. Our final picture is us in the way of the Lookout.
 
 
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ALL IN ALL WE’VE SEEN THE FULL CIRCLE
                     GEOLOGICAL WONDERS