Australia: The Land Where Time Began

A biography of the Australian continent 

Tasman Peninsula

The Tasman Peninsula is attached by a low, narrow isthmus, Eaglehawk Neck, which is only about 20 m wide at its narrowest point, to the Forestier Peninsula which is connected to mainland Tasmania. The constituent rocks of the Peninsula are sandstones deposited in the sea between about 300 and 200 Ma. About 165 Ma, the landmass that is Tasmania was raised violently from beneath the sea. During this process, molten dolerite was intruded between the sandstone strata. A feature of dolerite is that it contracts substantially as it cools, the resulting vertical cracks. The present state of the peninsula, after millions of years of erosion, during which a large part of the sandstone surrounding the dolerite intrusions has been eroded away, and the coastal areas have sunk and the sealevel has increased, is the black dolerite pillars now stand vertically above the sea, which pounds directly on the dolerite.

At the head of the peninsular, near Eaglehawk Neck, wave action has carved many blowholes and caves in the sandstone. In places the sea has worn deep coastal gorges intro the sandstone. Devil's Kitchen is the most dramatic of these, the thundering waves of the Southern Ocean surge up this 60 m gorge in what has been described as being like a cauldron that is on the point of boiling over. Tasman's Arch, not far from Devil's Kitchen, is a massive rock bridge across another large gorge, the underside of the bridge being 50 m above the sea.

The Blowhole is the feature where the power of the Southern Ocean can be best seen, especially on rough days, huge geysers of water being forced high into the air by every wave.

The waves have produced an uncommon effect,  tessellated pavements, on the marine platform at the base of Eaglehawk neck. The erosion has worked on joints in a fine-grained sandstone to produce pavements with the appearance of rectangular paving blocks.

An especially scenic feature of the peninsula is Waterfall Bay, a few kilometres south of Eaglehawk Neck. At this spot on the coast a waterfall cascades from the cliff directly into the sea.

Cape Pillar

At the southeastern tip of the Peninsula. Cape Pillar is the most spectacular of these formations, it is composed of a large cluster of dolerite columns soaring 300 m above the sea. A strait less than 1 km wide separates this structure from a small island of sheer cliffs, Tasman Island.

It was originally called South Cape by Tasman, but in 1789 Captain John Cox renamed it Cape Pillar when it was charted, along with the south and east coasts.

Cape Raoul 

The southwestern part of the Peninsula, Cape Raoul also has dolerite columns that rise up to 180 m above the sea. On the western side the columns are compact, but to the east they taper down to an appearance of craggy organ pipes.

Cape Hauy

North of Cape Pillar a several tall, thin columns of dolerite. At about 90 m, one of the tallest of these is named Needle. There are a couple of other very tall columns are the Candlestick and the Lanterns.

Remarkable Cave

Sandstones and mudstones are present in other parts of the Peninsula. Remarkable Cave has formed at the contact zone by erosion of wind and waves along the fault line that separates the dolerite from the sandstone. This is a narrow tunnel in the cliffs, about 40 m deep, that connects the sea to a chasm . A few days around Easter is the only time when the tides are low enough that water doesn't constantly move through the tunnel. At all other times the powerful waves passing through the cave make walking in it dangerous.

Sources & Further reading

Helen Grasswill & Reg Morrison, Australia, a Timeless Grandeur, Lansdowne, 1981

 

 
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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading