Topic: Cliffs - Te Kawau Pa
TE KAWAU PA. Highly folded rock cliffs.
Te Kawau Pa is at the northern end of the Tongaporutu coastline. It is a stand alone site.
The rocks that form the cliffs at Te Kawau Pa are more elaborately folded than further south. Also, there is a greater variety of types and textures. The undercut light grey layer at the base of the cliffs is fine-grained siltstone – often called papa and it is softer than the overlying sandstone. Folds in the sandstone formed before the sediments consolidated into rock, while they were still being carried into deep water. Above the sandstone is yellow-brown material derived from sand and volcanic ash in the last 125,000 years. Whatever their origins, none of these rocks are able to withstand the assaults meted out by the highly energetic Tasman Sea.
Generally, the interbedded mudstone (silt) and sandstone rock stratas form narrow bands, but in certain places the individual rock stratas can be quite wide. If one uses water as an analogy, then the narrow interbedded bands would represent showers, wider spaced bands more general rain, while particularly broad bands would be akin to extreme flooding events.
The height of the cliffs range from medium to high. Also, the upper soil type strata is particularly crumbly here. There is one major cave system. It has two entrances, one of which has a huge, open bowl on the northern side. Just south of the cave (looking from north to south), is a chain of rocks tumbling down to the low tide mark. I call these Chameleon Rocks, one of which has a through keyhole. There are also two rock stacks, Lion Rock and the Sphinx. (I later learned that ‘Lion Rock’ is Te Kawau Pa proper). Near the northern boundary is a large passageway cave cum arch. This leads round to the outer northern boundary. It is an impassable bluff which people fish from. The beach itself is usually well endowed with sand.
Another geologic feature at Te Kawau Pa, is the mudstone (papa) rock strata formations associated with the base of the Keyhole and the base of Lion Rock, have geometric patterned cracks. That is, these specific mudstone rock strata’s exhibit fractal honeycombing - geometric shaped bricks that combine to form a whole. On the one hand this makes them highly vulnerable to the smashing actions of waves where mudstone bricks are carved off on a regular basis. A key point to note, excuse the pun, is because of the numerous fracture-lines, the force being applied by a pounding wave is fractally diluted relative to the fracture-lines. That is, instead of one large force radiating out unhindered across a large plain area, the force’s full destructive power is reduced. Thus, while individual ‘geometric mud bricks’ are carved off on a semi-regular basis, dependent upon the Tasman Sea’s energy state, the destruction incurred at any particular time tends to be on a small, localised scale.
This ‘fractal honeycombing’ has also been observed at Twin Creeks.
4.11.2003 PHO2008-376- 378, 1098
My first visit to Te Kawau Pa. Very interesting rock formations. One in particular I named the Keyhole, located in what I later called the Chameleon Rocks. They are a ‘chain’ of highly decorative rocks that flow out to the low tide mark. The Keyhole at this stage was about four foot square with a width of about four inches. The Keyhole proper is situated in a mudstone (papa) rock stratum with fractal, geometric shapes. This makes it vulnerable to the smashing action of waves and sound. Water and sound being the twin architects on the coast. The rock stratum immediately above the Keyhole is comprised of sandstone. This has no fractalization; that is, it is seamless.
9.11.2003 PHO2008-391, 394, 404, 1100, 1103
Similar to 4.11.2003. I was struck by how the rock formations reminded me of some North American desert rock formations.
8.3.2004 PHO2007-214, PHO2008-724-730, 735-757, 1234-1236
CLIFF SEQUENCING. Some erosion noticed on top of the rock face above the Keyhole. It was more noticeable on the northern side of the Keyhole. With this cliff sequencing, I was able to access the beach beyond Lion Rock; that is, a 0.3m low tide combined with an offshore breeze extended the beach’s wave line around 30 feet beyond the seaward side of Lion Rock. The sand level was good. The rock stacks I later nick-named Lion Rock and the Sphinx are also shown for reference purposes.
21.3.2004 PHO2008-762-766, 1242
These images show different view of Te Kawau Pa, including Lion Rock, the Sphinx, the keyhole and the Chameleon Rocks. PHO2008-73 looks south from Te Kawau Pa towards Rapanui (obscured). This section of the coastline is inaccessible.
The Keyhole is enlarging.
A chunk of sandstone has been carved off just above the Keyhole (the sandstone rock strata).
16.8.2004 PHO2008-1346-1347, 1350-1352, 1354,1356-1357
Took various images of the keyhole from both the norther and southern sides with my backpack for scale. No new changes were noted. Ditto Chameleon Rocks.
The Keyhole and Chameleon Rocks in stormy weather. Some of the chimney structure above the Keyhole appears to have come away.
16.7.2005 PHO2008-1374,1375,1376,1377, 2378
The Keyhole has now enlarged to around 10 feet. That is the Keyhole proper – the mudstone geometric strata it has formed from. Also, a large rock fall had recently occurred opposite the Keyhole.
The Keyhole is still expanding. It is expanding on the landward end as opposed to the seaward end.
17.7.2006 PHO2008-1948, 1950
The Keyhole appears to have stabilized somewhat. Due to the sun being north for the winter, Lion Rock and the north facing cliff in the background, were well illuminated. I also took a good image of this same north facing cliff that clearly shows a through-going arch.
The Keyhole has enlarged a little more. It is still eroding primarily from the landward end.
28.10.2007 PHO2011-1087-1090, 1092, 1094-1096
Before rounding the cove to access the Keyhole, I observed that a fresh rock fall had occurred since the last high tide. At the Keyhole, it had grown in size such that a Morris Mini could all but drive through. A measurement I obtained with a tape measure was 11 foot 4 inches. It is eroding preferentially upwards along the mudstone strata (landwards). The Chameleon Rocks appeared little changed. There had been a fairly recent upper cliff collapse opposite Lion Rock.
The Keyhole appears relatively stable, but the large ‘V’ forming at the landward end of the Keyhole Chameleon rocks and the parent landward cliff could see them being sheared off in the future. Also, the southern cliff wall across from the roped access to the beach, appeared to be well eaten into.
SUPER-STORM EVENT. Super-Storm One. This was just a quick check on the health of the Keyhole.
On the northern side of the large cave, there is a channel that separates one cliff section from another, smaller cliff island. I noticed a boulder field at the base of the cliff, south side. A river flows past and out through the channel. This is a different entry point to Te Kawau Pa and is on its northern side. The Keyhole is on the southern side. It is little changed. PHO2011-1481-1483 and 1486 were taken atop Te Puia.
12.1.2009 PHO2011-1513-1520, 1523-1525, 1527, 1529-1534, 1537-1548, 1552-1554, 1556
CLIFF SEQUENCING. There was a low tide of 0.2m and a slight onshore breeze which resulted in a choppy sea but with no storm surge. The beach level was as built up as the first cliff sequencing on 8.3.2004. Some large rocks were observed on the seaward side of Lion Rock. The cliff sequencing was fairly uneventful. I heard lots of tinkling as small rocklets cascaded down the cliffs. Sandstone cliff shavings were present on the northern side of the Keyhole.
A crucial difference between this cliff sequencing and that of March 2004 is that despite it being a slightly lower, low tide and the beach level being similar, I was unable to access beyond Lion Rock. That is, the seaward side of Lion Rock was inaccessible due to the sea not going out beyond Lion Rock. My thoughts on this will be discussed in Section Two on Weather.
I noticed a fairly recent cliff fall on the southern side of the Keyhole and opposite a large rock. Everything else seemed more or less the same.
This view from the cliff-top shows the cliffs and Lion Rock and the Sphinx from a different perspective.
With the weather being fine, I took several standard images with the new panoramic camera. The cliff fall material I observed in April was still evident.
I particularly wanted to photograph this unusual cliff-top perspective, but couldn’t do so with my big film camera. Instead, I used the digital camera and took 4 successive images. Adam Buckle subsequently stitched them together for me as I am an ignoramus in the Photoshop department.
28.2.2010 PHO2011-1777, 1779-1782, 1787, 1790-1791
For the first time, I accessed the beach north of Te Kawau Pa. Moreover, I utilized my panoramic camera. I took full advantage of the day to photograph both immediately north of Te Kawau Pa and at Te Kawau Pa proper.
To the rear of the Keyhole where you access the beach down a roped part of the cliff, there had been a small cliff fall that had splooshed down into a mini-lake that had formed in this area. As the small amount of vegetation present was still alive, I presumed that the fall was quite recent.
I had stopped off at Te Kawau Pa after visiting Rodney White’s place to document the storm here and check on the Keyhole. While kneeling near the cliff edge that looks across to the Keyhole, I noticed that there had been a full cliff face collapse below me! Due to the large amount of soil still present, this collapse had only recently occurred. This massive storm was the obvious cause.