Topic: Strata - Overview
This section is more eclectic than the others. Though it is titled Rock Strata, it encompasses a much broader palette than just the interbedded layers of mudstones and sandstones that make up Tongaporutu’s cliffs. It also highlights things/events that struck a personal chord.
The Maori petroglyphs, located in a small, through going cave located to the rear of the Three Sisters, was one such thing of interest. Another was the amazing fossilized trees. The four main sites where I have observed these are: Te Kawau Pa, the Three Sisters Beach, Gibbs’ Fishing Point and Twin Creeks.
The fossilized tree remnants located at Te Kawau Pa, the Three Sisters Beach and Twin Creeks are the remains of a podocarp forest drowned by a rise in sea level about 6,000 years ago. From what I and others have observed, is that the trees appeared to be predominantly totara. They are petrified, as if struck down by Medusa herself. To look at them, you’d think that they’d just been deposited by the most recent storm.
The fossilized tree remnants located high up in the cliffs above the fishing ledge proper at Gibbs Fishing Point, couldn’t be more different. Though they look solid, they are fragile to the touch and bits can easily be made to flake off like charcoal. These trees are presumed to have been destroyed by an eruption from Taranaki’s spectacular volcano, Mt Taranaki/Egmont.
Though I have highlighted the Maori petroglyphs and fossilized tree remains, I feel sure that you will find the other things to be just as interesting. Perhaps that’s because every ‘thing’ is inter-connected. We humans are not separate from or ‘above’ the environment, but a part of it. To think otherwise, in my opinion, is the height of arrogance. And ignorance.
TE KAWAU PA
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.