Local tucker

Tony (aka Kingfisher) comes up with the goods on the east Australian coastline ...

Yep - that's a cray.

North Head

Approaching the silhouette of South Head (Burra-wara) with the bold profile of this morning's destination -  North Head (Boree) - beyond.

Salmon Cove - where we scrambled ashore in our nimble kayaks and then walked up and over the rock fall at the base of the cove's northern cliff.

A compelling view of the rock platform with its stunning pool.

Note the distinctive NNE-aligned fractures associated with the Watsons Bay fault line.

Hey Peter - you might want to stand on this side of the fault.

The climb down the cliff's face to ...

... the olympian rock pool.

No underwater photos today ... sorry, forgot the waterproof camera.

Climbing out with flippers stashed in back of wet-suit.

Composition of rocks and figures.

The stunning landscape of North Head.

As we paddled southwards a lone vessel drifted along the eastern horizon ...

The Eora people of Sydney had a description for the British colonisers who sailed into Sydney with the First Fleet:

"Bèerewalgal" - people from the clouds.

Booderee

We've recently explored the Booderee Peninsula over 3 days.

A full account of this trip to follow soon ...

Paddle back in time

Today's little adventure began at the mouth of the Minnamurra River, about 100 kilometres south of Sydney.

With a flood tide to catch there was brilliantly clear sea water running uphill into the river's swollen mouth.

Further upstream, in the brackish water of the Minnamurra River, the Illawarra escarpment looms as a continuous backdrop along the western horizon.

This landscape is an excellent morphological analogy for the ancient topography that existed along the Sydney coastline during the last ice age.

That is, a ribbon of vertical sandstone cliffs tumbling down into a wooded plain braided with creeks and rivers feeling their way towards the sea many kilometres further to the east.

When you are next paddling along the base of the Sydney cliffs you may easily imagine that 10,000 years ago, with the sea levels much lower than today, you would have been thrashing through the ancient branches of a cold climate forest.

The Illawarra Escarpment.

Further up the Minnamurra River the woodland and waterways merge into a flooded forest.  An arcade of searching branches and interlocking canopies reflected in the water's calm surface.

Here scuttling beneath the kayak's hull like so many carapaced trilobites were dinner-plate-sized mud crabs. Sydney was once like this too.

Nor-easter

Sydney summer's favourite wind still blowing in March.

Trial of a prototype daggerboard

An addition to the kayaking kit - a carbon fibre blade.

Slot for blade retro-fitted to the Greenlander Pro.

View of the blade housing within the cockpit.

A crowded deck.

  Sailing to windward.

The blade improves the kayak's ability to sail higher into the wind and transfer that wind energy into lift. However on this trial run I found that despite bringing the V-sail in as tight as she would go the sail and mast system still tended to collapse before the kayak was pointing as high as I would like. 

Fltyng downwind under two sails.

Gullwing formation under a combined sail area of 2.5sqm in 12 to 15 knots of breeze.

The deep blade prevents the "yawl" effect that a large sail area generates when travelling directly downwind.

 

The blade.

Ancient topography

Paddling seaward on a Port Jackson ebb tide.

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And look who is paddling in the other direction ... Peter heading up-harbour and against the draining tide of the Port Jackson / Parramatta River valley.

A knot of tidal current gently sweeping around South Head and out to sea.

Mid-way between South and North Head a robust Bonito drags Tony's kayak backwards.

Today's destination : the rock platform at Salmon Cove.

This small section of the rock platform serves as a good analogy for the ancient sub-surface topography of Sydney Harbour.

In simple terms the harbour is formed by the erosive path that the Parramatta River has carved on its journey out to sea through its base of Hawkesbury sandstone and into which has flown the rising sea since the last ice age.

The image below shows a bathometric chart describing the path that the Parramatta River created for itself in the last ice age, when the sea level was much lower and the coast was consequently much further eastward ~15 or more kms.

The Parramatta River turned to the south at the Heads, travelling down to meet the "Bondi River" and then reorienting itself towards the east and before emptying into the ancient sea.

In the last ice age the view towards the eastern horizon from a position standing on either of the Heads would have been not unlike the present view from Katoomba towards the Jamison Valley. That is, sheer sandstone cliffs falling vertically into a cool climate forest v-shaped valley at the bottom of which travelled a modest river.

Source : Cainozoic Morphology of the Inner Continental Shelf near Sydney, NSW.

A.D.Albani et al. 1988

The chart above describes the path of the "Bondi River"which has been interpreted as the original way in which the Parramatta River found its way eastward - through what is now the Rose Bay Golf Course - before silting itself up and precipitating the carving of the modern river's path out to sea via the Heads. (See an earlier post on this topic).

There are other intriguing geological phenomenon that are observable above the current sea level along this section of coastline.

When east Gondwana began to break up under techtonic forces brought about by under-plate felsic intrusions around 120 million years ago there occured a series of near vertical "strike-slip" movements in the techtonic plates. In Sydney these strike faults took place along a north-northeast direction. The strike faults belonging to the "Watsons Bay Fault Zone" are clearly visible on the surface of the lower rock platform on the left side of the image shown above.

The southerly extent of this fault zone is visible at South Era Beach in the Royal National Park (see coloured chart below). This fault swarm is also clearly visible at Bottle & Glass Island and Shark Island.

Subsequent to the faults breaking up east Gondwana, igneous dykes exploited the weaknesses of the north-northeast strikes about 50 million years ago. A number of these dykes, including the examples at Salmon Cove and North Bondi, travel at an opposing angle to the faults - in a north-west orientation.

"Source : Timing of brittle faulting and thermal events, Sydney region: association with the early stages of extension of East Gondwana" D.J.Och et al (2009)

The strike faults passing through Sydney Harbour.

With the nor-easter filling in and the tide turning, we hoisted our sails and cruised back up the flooded ancient valley of Sydney Harbour.