Topic: Strata - Te Kawau Pa

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As with the rest of the Tongaporutu coastline, the cliffs at Te Kawau Pa are primarily composed of interbedded mudstones and sandstones.  Specifically, the bottom layer is mudstone or papa.  This is softer than the overlying layer of sandstone. The top layer consists of yellow/brown material.  This is derived from sand and volcanic ash that has been deposited in the last 125,000 years.  At Te Kawau Pa, the rocks are more elaborately folded than those south of Rapanui North. 

My first impression was as follows:  “At the bottom, there were a number of rock islands and coves.  And the cliff faces were markedly different.  Reminded me of a small Grand Canyon or scenes out of the American West.  Bizarre land shapes.  The oddest being a keyhole ‘hole’ in the rock.  An arched, brownish cliff bottomed off with a different semi-geometric patterned whitish rock greeted me.”  This was what I later christened the Chameleon Rocks and they are situated immediately north of the roped cliff access site.

A unique feature is the Keyhole, located in what I call the Chameleon Rocks.  They are composed of distinctive broad bands of mudstone and sandstone.  At this site, as well as Lion Rock, the bottom mudstone band has distinctive fractal honeycombing.  This makes it vulnerable to mostly small-scale preferential wave carving.  Eventually though, particularly at beach level, this honeycombing is smoothed out and presents as a more stable 2-dimensional surface that is less susceptible to resistance and friction.  That is, water flows more smoothly over it.

On the northern side of the Kuwhatahi Stream, (this flows onto the beach immediately north of Te Kawau Pa’s huge through cave), there is an area that contains the fossilized remains of ancient trees.  These trees obviously thrived when the sea level was lower, then were killed off when the sea level rose.

2003

4 November 2003  

PHO2008-377, PHO2008-378, PHO2008-1098

My first visit to Te Kawau Pa.  The Chameleon Rocks are a chain of eroding rocks that become smaller the further out to sea they travel.  At the landward end there is a distinctive Keyhole which is approximately four foot across and about four inches wide at the base.  Rising above the Keyhole is a distinctive chimney formation that has been eroded out.  The evolution of the Chameleon Rocks and the Keyhole are detailed in Section Four on Cliffs.

 

9 November 2003  

PHO2008-397, PHO2008-405, PHO2008-1102

A couple of these images highlight the beautiful strata bands that make up Chameleon Rocks and the Keyhole.  If you think the colours appear to be more saturated in PHO2008-397, then you’d be right.  This is because I used an emergency roll of Velvia transparency film than my more usual Provia.  I prefer Provia because its colour palette more accurately represents how things really look.

 

2004

8 March 2004  

PHO2008-725, PHO2008-737, PHO2008-744, PHO2008-746.  Also, PHO2008-739

CLIFF SEQUENCING.  Detailed information with regards to cliff sequencing can be found in Section Four on Cliffs.  Photo number PHO2008-739 is shown as an example.  Cliff sequencing is only noted here for cross-referencing purposes.  As well as the Keyhole, more of the Chameleon Rocks are featured.

This was also the first time that I saw what I later discovered to be the remains of ancient trees.  The wood felt as hard as stone.  It was solid with no give.  The following was my initial observation.  “There were lots of driftwood and trunks upended in the sand ...”

 

21 March 2004  

PHO2008-766, 1242

These images show more of the Chameleon Rocks and the Keyhole as well as the high sand cover.

 

26 June 2004  

PHO2008-1296, PHO2008-1297, PHO2008-1298, PHO2008-1299, PHO2008-130, PHO2008-1301

More of the ancient trees were uncovered.  I photographed Rodney White who lives at Te Kawau Pa, sitting on one of the logs.  The trees looks so fresh it was hard to believe that they were thousands of years old.  They are usually buried, or mostly so, under a protective mantle of sand.  Severe sand scouring reveals more of them.

 

4 July 2004  

PHO2008-1302, PHO2008-1303

These two images show more detail of the Keyhole.  For the most part, further information concerning the Keyhole will be covered in Section Four on Cliffs.  This is where it more properly belongs.  I have just superficially covered it here because of its uniqueness.

 

2009

12 January 2009  

PHO2011-1539, PHO2011-1554, PHO2008-1555  (Examples)

CLIFF SEQUENCING.  The Keyhole by this time had expanded to about eleven feet across.  The Chameleon Rocks at the landward end have lost more material since 2003.  The distinctive chimney at the top has also shrunk.

 

Time was now marching on and I wanted to take some photos of the ancient logs part buried on the beach.  Most of the logs were now in the shade, but I managed to get a couple of shots showing some of them basking in the sun and wallowing in a shallow water filled channel.  I also liked how the verdant green algae at the splash line of the cliffs reflected in the water.

 

2010

28 February 2010

PHO2011-1777, PHO2011-1778, PHO2011-1780

PHO2011-1784, PHO2011-1785, PHO2011-1786, PHO2011-1787, PHO2011-1788

As I have decided to finish the Tongaporutu Project in June, this was to be the last time I would visit Te Kawau Pa.  I wanted to document the Keyhole, Chameleon Rocks and the ancient logs.  For this I had brought along my panoramic film camera.

At the Keyhole, the first thing I noticed was how exceptionally high the sand cover was.  It was so high that you could walk through the Keyhole.  In fact sand covered the lower part of it.  I have never seen this before.  The Keyhole had enlarged slightly in extent.  The cliff to landward of the Keyhole is preferentially eroding down towards the Keyhole.  I originally thought the Keyhole would eventually enlarge to the point where it would collapse, but I now think that it will be eroded out from landward.

The Chameleon Rocks continued to crumble away and a large crack was visible on the landward side of the chimney rock formation above the Keyhole.

On the northern side of the cave where the ancient logs are located, there was one area that was heavily populated with these logs.  Aside from this, individual log specimens of varying sizes pocked the sand belt seemingly at random.  Some were enveloped in pools of water.  They were coloured in various shades of brown.  Some also wore top hats of mussel spat.

One thing I noticed for the first time was an unusual low rock shelf formation located at the base of the cliff.  It was composed of two different coloured and distinct rock strata.  The reason I haven’t noticed it before was because I haven’t had cause to walk over it.  This time around, because I was wearing heavy gumboots and the sand belt was squishy with water, I wanted to walk on a firm platform that was less tiring.

It seems amazing that in seven years this is the first time I have noticed this rock strata.  I have probably come across before, but my mind was elsewhere.

While documenting the beach immediately north of Te Kawau Pa, I took a couple of close-ups of rock formations with algae that I liked.

 

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