Topic: Cliffs - Three Sisters Beach
THREE SISTERS BEACH Rock cliffs
The Three Sisters beach is on the southern side of the Tongaporutu River. It extends south to the Point. It is roughly divided into two halves. The northern part has a substantial dune/beach area, while the southern part (past the first major arch) has no upper beach area, but is bounded by cliffs. They are composed of interbedded mudstones and sandstones. The top layer consists of yellow/brown material that is derived from sand and volcanic ash. This is generallytypical of the cliffs along the Tongaporutu coastline as a whole.
At the northern boundary, which is from Mammoth Rock to the first major cliff arch, there is a recessed dune/land area. This leads to cliffs that turn seaward to form a small promontory. This has a large arch at its base. The beach up to this point is well formed and clean of rock stacks (aside from Mammoth Rock at its northern boundary). From then on it continues south. The area south of the arch down to the Point is different in character. The cliffs are fractured with a number of blind caves, through passageway caves and arches. The cliffs are high and composed of interbedded mudstones and sandstones. There is one major cave, blind as of 2003 that has a huge open bowl above its northern entrance. The beach is usually well endowed with sand, but it does have sustained periods of bedrock exposure. There are five rock stacks. Namely, tracking north to south. Mammoth Rock, the Three Sisters and Elephant Rock.
8.7.2001 PHO2007-157, PHO2008-845, 853
This was the first time I had ever visited any of the beaches at Tongaporutu. While up at this fantastic place, I indulged myself photographically. I couldn’t foresee at the time the future opportunities that awaited, particularly of the dramatic changes that would occur, all before the unblinking ‘eye’ of my camera. Some of the rock stacks, White Cliffs and Mt Egmont are also featured here. PHO2007-157 looks towards the cliff and partial view of the Hole in the Rock rock stack that form part of the Point. The Point separates the Three Sisters beach from the Four Brothers beach. PHO2008-853 was taken from Pilot Point. It gives a general overview of the Three Sisters beach, its cliffs and rock stacks in relation to the greater environment.
PHO2007-157 shows part of the Point with a partially obscured Hole in the Rock rock stack to the rear. This is the southern part of the Three Sisters beach and forms the boundary between it and the Four Brothers beach. PHO2007-158 shows the Hole in the Rock more clearly with Mt Egmont in the background. These two images will also be repeated in the Point part of this section.
8.6.2003 PHO2007-318, 321 and PHO2008-900
The first two images show the first arch. Both views, close-up and distant are looking south. The Three Sisters rock stacks are located immediately south of the first arch. PHO2008-900 though primarily taken to show Elephant Rock, also highlights the cliffs from which it originally calved off from.
This is a repeat of PHO2008-900 which shows the cliff in relation to Elephant Rock. More importantly, it shows the difference that a change of light can make on the subjects.
This was my first sight of the Maori Carvings Cave. As the light wasn’t conducive, I didn’t take a photo at this stage. The cave itself is not large and is a through cave. I would classify it more towards being a through arch type cave. I have put it here in cliffs rather than caves because the sea-caves I have detailed separately have large, sound bowls or other unique features.
This shows a through-going arch or corridor cave that is immediately to the north of the Three Sisters Cave.
13.8.2003 PHO2008-116-121, 123-125, 131-135
CLIFF SEQUENCING. A low tide of 0.4m with a light south-easterly breeze. Nothing of note was recorded. That is, no cliff falls. Mammoth Rock, the Three Sisters and Elephant Rock rock stacks are also shown for reference purposes.
A photo I have taken shows the cliff section to the rear and north of the Three Sisters. It is interesting to note that the shadowed indentations on the cliff wall loosely resemble vertical waves. They are rounded on the southern side and flattened on the southern side.
An Alpha Storm struck Taranaki on Sunday, 28th September. It was still ferocious on the day of my visit. On the 3SB, lots of debris rocks were observed in the small caves and arches. Though the cliff faces looked really battered, no cliff falls were noted, but the LITTLE SISTER ROCK STACK WAS DESTROYED. (See Section Six on Rock Stacks). Near Mammoth Rock, waves had overtopped the dune area and caused a lot of damage. Salt foam was evident up to around 20 feet inland. I didn’t photograph the dune damage.
6.10.2003 PHO2008-250, 1043
Malcolm Arnott from GNS Science measuring gamma radiation in the different cliff rock strata. PHO2008-1043 shows the cliff face to the rear of the Three Sisters. The small through cave that houses the Maori carvings is just off to the left and out of frame of this image.
This image shows the cliffs of which Elephant Rock was once a part of.
Just before reaching the Three Sisters, I noticed a partial cliff-face collapse. The condition of a large debris field at the base indicated that it hadn’t occurred during the past couple of days. It was probably around two weeks old. Seeking shelter from a rain shower, I popped into a small blind cave close to Elephant Rock. While there I was aware of the deafening crescendo of noise from the sea, as if the enclosing rocks/cliff were acting as an amplifier.
These dawn images show the cliffs on the southern side of the Tongaporutu River that lead around to the Three Sisters beach. Mammoth Rock and one of the Three Sisters are fully visible in PHO2008-496.
5.4.2004 PHO2008-781, 1245
I observed a small ‘room’ or ‘window’ forming on the lower cliff wall just south of a blind passage cave. The actual location was between the Three Sisters and Elephant Rock. I also photographed a small cliff protrusion just north of the first arch. See PHO2008-1245.
18.7.2004 PHO2008-1305, 1309, 1312
The first image shows the well clothed cliff leading on from the dune area towards the first arch. The other two images show a partial cliff collapse between the Three Sisters and Elephant Rock.
The small room photographed in the cliff sequencing on 13.8.03 and individually on 5.4.04 has now been destroyed. (I didn’t note it in my diary at the time). The photo here shows a small arch.
Due to perfect light, I was finally able to get a good image of the Maori cave carvings with my 135 mm macro telephoto lens on my Pentax 6x7 medium format camera. (See also Section Three on Rock Strata and Section Five on Sea Caves).
19.9.2005 PHO2008-1454, 1459
An Alpha Storm coincided with a 3.9 m king tide, the highest of the year. From what little I could observe, there was no major cliff damage.
This aerial photo, taken during the film shoot of me by Sticky Pictures for Te Papa Museum, shows the cliffs on the Three Sisters beach. Unfortunately it is not sharp. I had been unable to purchase a roll of 200 ASA film which would have allowed me to shoot at a higher shutter speed to compensate for the low light levels.
A small chunk of cliff had been sloughed off at the base opposite the Three Sisters. Several rocks from this wallowed in a pool.
26.7.2006 PHO2008-1951, 1954
A full cliff-face collapse occurred just before Elephant Rock. The material looked fresh with vegetation sitting atop the soil/debris pile. I estimated that this had occurred with the last 48 hours, but more likely within 24 hours. Outside of this time window and the heavy surf would have dispersed it much more.
Just before I arrived at the Three Sisters Cave, I noticed a clean part of the cliff that looked like it had sheared off recently, although there was no debris evident. See PHO2008-1977. At through caves, most cliff fall debris tends to disappear very rapidly, often in as little as two weeks or less. (The Three Sisters cave was noted to have become a through cave on 24.7.2005. There is more on this in the section on Caves). I have also observed that after around three months, ‘clean’ cliff faces (following collapses), tend to get re-colonised by flora, thus making dating cliff fall events prior to this all but impossible. I then checked out the cliff collapse site I documented on 26.7.06 to see how it had evolved. It appeared pretty much intact and the topmost vegetation atop the debris pile was still there and surviving. See photos PHO2008-1978 and 1979.
The cliff collapse debris field near Elephant rock had all but disappeared now. Only the relative ‘newness’ of the cliff gave any indication of a recent cliff collapse.
At the cave that housed the Maori carvings, a wave had preferentially carved off the section of upper, inner cave wall where they had been carved. The MAORI CARVINGS ARE NOW COMPLETELY DESTROYED. Also, I recorded a small carved off piece of cliff wall, on the upper northern part of the destroyed ‘room’ in the cliff near Elephant Rock. When I say ‘destroyed’, this to mean that a hole remains where the intact room was before suffering demage impact by wave action. (See also Section Three on Rock Strata and Fossil Trees).
SUPER-STORM EVENT. Super-Storm One. Huge seas had monstered the beach. Great chunks of shoreline at the dune area had been gouged out. There was now a nearly three foot drop to access the beach from the bottom of Gibbs track, near where a cabbage tree stood. The cliff near the first arch also shed material.
SUPER-STORM EVENT. Super-Storm Two. Massive swells, tremendous energy, ‘high’ sea level. The sand-bar joining the dune area to Mammoth Rock is now gone. According to Russell Gibbs, it had probably been there for a minimum of 40 years. Approximately ten foot ‘sand cliffs’ had now been created by the stomping waves, and there was now a five foot drop to the beach. I couldn’t pass the first arch leading to the Three Sisters due to storm surge conditions.
SUPER-STORM EVENT. Super- Storm Three. I was amazed at how much additional destruction had occurred. Where there had been a three foot drop to the beach, then a five foot drop was now a ten foot drop and this part of the flat area was eating back towards the track. A frightened cabbage tree perched precariously close to the new boundary. The damage was truly tremendous. Large, ten foot sand clffs were joined by huge gouges that extended far up the cliffs leading towards the big arch just before the Three Sisters. More of the dune area was being carved off close to Mammoth Rock.
NOTE: Although I have concentrated on the sand dune as opposed to the cliffs, I have included them here as well as in Section Eight on Beaches and Section Nine on Flora and Fauna, because the three photos all cover roughly the same viewpoint. Namely looking towards the first arch and the Sisters rock stacks.
More of the dune area had been lost. The sand bank had been scoured back almost to the track. The cabbage tree had now gone and a white fence was now at the bottom of the sand bank. I estimated that around 30 feet of the sand dune had been carved off by the three successive storms. I now feared for the whole dune area here which included some large, old trees such as pohutukawa and karakas. The state of the beach – everything, I have never seen anything that comes close to this orgy of destruction. It really, really is mind-blowing. A large chunk of cliff-face (two large sandstone slabs), to the left (north) of the cave that once housed the Maori carvings had come away. Unfortunately, I didn’t photograph it.
There had been a large cliff roof collapse at the Three Sisters cave. It also took with it a good chunk of seaward facing cliff that forms the sea-ward side of the adjoining through passage cave. Judging by the debris, I estimated that it must have occurred within the past 12 hours. A flax bush sat atop the large soil pile and I could just see the top of a tree further back (inwards). Much of the soil was below the high tide mark and was staining the surrounding pools. Soil was also present on rocks that will be washed off when the tide comes back in.
12.11.2008 PHO2011-1367, 1398-1400
An ENTIRE CLIFF SECTION COLLAPSE. This occurred immediately to the rear of the Three Sisters and caused the total destruction of the Maori carvings cave. The carvings of which had been destroyed in July 2007.
The first inkling that a cliff collapse had occurred was when I was at Pilot Point in readiness for cliff sequencing at Rapanui. There was lots of plant material littering the beach. Mostly flaxes and coprosmas. No cliff falls were evident at Pilot Point, so I looked across the estuary towards the Three Sisters Beach, knowing that the prevailing currents would carry any plant material northward along the coast. I actually looked across to see if the sand was building up there. It didn’t appear to be, but what I did see totally stunned me. There was this huge, absolutely massive ‘flood’ of rock and soil that streamed down onto the beach to the rear of the Three Sisters. Even from this distance, across the Tongaporutu River, this was the most massive cliff collapse I have ever seen. Period. And it was the obvious source of all the washed up plant material. I endeavoured to complete the Rapanui cliff sequencing as quickly as possible and try to access the 3SB before the tide came in too far. The plant wash-ups reached as far north as the large arch just before the Rapanui River. I didn’t go further north than this, but assumed that more plants would be present further up the coast.
Finally, I accessed the 3SB. Before I even rounded the first arch I could see that this cliff collapse was like nothing I had seen previously. Rounding the arch, the full extent was jaw-dropping. It wasn’t a cliff-face collapse as such; rather, I had to think of another description for it. It was an entire cliff section or cliff wall collapse. That is, the entire cliff section from north of the Maori cave carvings to south of it, had collapsed in a mega-cliff collapse. That is, the northern and southern sections of the cliff wall, rounded out into small ‘horse-shoe’ coves. The northern one culminating in the first arch, and the southern one culminating in the large, open domed Three Sisters cave system.
Part of the Gibbs’ fence-line was hanging in mid-air; the collapse had gone back that far (around 30 feet). A mammoth debris field of boulders, rocks and soil reached almost right out to the innermost Sister. A massive amount of soil and plant material remained.
A new Sister appeared to be in the process of being carved off at the southern end. So much debris was present I couldn’t be sure if it had actually been carved off, but didn’t think so. Judging by the freshness, I assumed that the collapse had occurred within the past 48 hours. As I set up my tripod, three male teenage surfers came towards me. One of them was one of Russell Gibbs’ sons. He confirmed that they had been there two days ago and the cliff collapse hadn’t occurred then. I think it could have occurred in as little as 24 hours prior to my visit.
Lastly, of the large cliff roof collapse that occurred at the Three Sisters cave on 15 October, only a few rocks on the cave floor remained. If one hadn’t observed the cliff roof collapse during October, you would not know that a collapse had occurred.
23.11.2008 PHO2011-1406, 1410-1411, 1414-1417
At the cliff collapse site, dead flaxes and reeds were semi-buried with sand. A fair bit of soil had eroded away, exposing more of the new Sister. She still hadn’t calved off the mainland from what I could see. The large boulders were more rounded and being broken up more.
14.12.2008 PHO2011-1424-1426, 1428-1430, 1432-1434, 1436-1438, 1467
CLIFF SEQUENCING. The first thing I noticed was that the Middle Sister had lost her top. All the plants atop her had gone. There was more damage to the sand cliffs and cliffs along the dune area of the 3SB. More due to instability than anything else – things just sliding down and dropping off. Plants, rocks, etc.
At the cliff section collapse site, more material had washed away, but not a huge amount. A lot of heavy, sustained rain would be required to sluice it away, combined with the sea. A large boulder field from the cliff collapse had more or less joined up with a sizeable boulder field on the landward side of the middle Sister. Large boulders were being broken into smaller ones and becoming more rounded. More material had disappeared from the new, forming Sister, but she was still joined to the mainland.
There were people on the beach and they were useful as scales for my cliff sequencing. The cliff sequencing wasn’t as good as the 2003 series as firstly the weather was overcast, and because of the beach state at the wave-line in certain places, some of the images had to be taken at an angle.
11.1.2009 PHO2011-1487-1489, 1491-1492, 1503-1504, 1508, 1511
A lot of rain had sluiced away a massive amount of material from the November 08 cliff section collapse. (Viewed from cliff-top). Down at the beach, with most of the soil and debris being washed away, the true extent of the cliff section collapse can now be seen. Of the Maori carvings cave and original cliff-face, only part of the seaward cliff wall of the Maori carvings cave survived. This is now about 30 feet clear of the new cliff boundary.
To the rear and just south of Elephant Rock and just before the Point, there had been a full cliff-face collapse. Since 2003, this part of the Three Sisters Beach had been remarkably stable, i.e. no cliff collapses or partials had been observed. (I have recorded one cliff collapse just north of Elephant Rock on 26.7.06). As there was a large amount of soil in the debris pile, coupled with live flaxes, I assumed it may have occurred within 48 hours of my arrival. Though the weather is relatively calm, there are big tides which would quickly sluice the soil away by undercutting the debris field from below via washing and wicking.
On the return journey, I noticed that there had been a fresh rock fall to the rear of the newly forming Sister and at the northern entrance of a through passage-way arch on the immediate northern side of the Three Sisters Cave.
8.2.2009 PHO2011-1567, 1573
At the cliff section collapse site, a few large boulders remained, but most of the smaller stuff beyond the immediate cliff base was either buried with high sand cover, and/or smashed up. The cliff collapse site to the rear of Elephant Rock had significantly reduced, but some soil and large boulders still remained.
Such was the strength of the wind, I was mostly limited to photographing in the opposite direction (looking north) so as not to be sand blasted. I was actually more interested in showing the wind’s effect on the water pool at the base of the cliff than the cliff itself.
I photographed looking down the alleyway separating the newly forming Sister and the Maori carvings cave wall remnant. This seems to have settled down for the time being with all of the soft material having been removed back to harder fill. At the Elephant Rock cliff collapse site, the debris field was much smaller with all of the soil now gone, along with any remaining plant material. The large boulders have now been pretty much smashed up.
The coprosmas that had survived the super-storm event of July 2008 on the sand dune bank opposite Mammoth Rock had now vanished. The bank itself had been eaten into by recent big seas. Until recently the sand had begun to build up. So, at the present time, erosion forces are overwhelming any re-building attempts. Just before reaching the first arch, I noticed two cliff slides. These cliffs now mostly comprise of sand so this was not an unexpected event. The slide closest to the arch was akin to a three-quarters full cliff face collapse. Plants at the base were still alive. I didn’t photograph these two cliff slides.
Immediately to the rear of Elephant Rock, I observed a massive, full cliff-face collapse. After re-assuring two Chinese people that it was safe for the time being, I got them to stand close to some of the giant boulders for scale. The lady was Zheng Xiu Feng and the man was Zhou Pei Ao. This collapse occurred above the site of a blind passageway arch. Soil was evident along the beach north of the collapse and some of the rocks had reached Elephant Rock. I estimated that this had occurred during the past week. Two weeks at the outside, due to the large amount of soil still present, plus live flaxes. The rocks were sharp edged, apart from those smaller ones semi-buried in the sand.
From my observations since July 2008, THE THREE SISTERS BEACH IS IN A CURRENT STATE OF ONGOING COLLAPSE.
Though this photo was taken from Pilot Point, it shows the cliffs that lead around to the Three Sisters Beach from the Tongaporutu Reserve to Mammoth Rock.
22.7.2009 PHO2011-1619, 1621, 1626-1627
The cliff section collapse site is now relatively stable apart from a small, active area that is being carved out at the northern-most end of the collapse site and near the base. It is like a bowl is being hollowed out. Green algae is establishing on the rocks that remain on the beach. At the cliff collapse site to the rear of Elephant rock that I observed on 25.5.09, the debris field has spread out and most of the loose fill has gone. There was one live flax bush near the bottom. I didn’t observe any fresh cliff collapses. The dune area between Mammoth Rock and the first arch also appears to be relatively stable. That is, although there are big seas and big tides, the dunes are currently holding their own.
Had primarily come up to photograph the Gibbs family. As there was a high low tide of 1.1m due at 1.25 pm, coupled with big seas, I just checked out the cliff section collapse site to the rear of the Three Sisters to see if it warranted a visit in the near future. Yes it does. Due to heavy rains, all of the soil type material had now been sluice away leaving the cliffs totally naked. For the first time I was able to see how much or little the newly forming Sister was still co-joined to the main cliff. She is joined by a diagonal rock strata umbilical cord, approximately 15 feet in width. At the base of this and running the full length, was a fracture-line. In the not too distant future, the new Sister will be a free-standing one.
22.8.2009 PHO2011-1635, 1640, 1642
After re-examining the New Sister and how well or otherwise she is joined to the cliff, I see that she is quite firmly secured to the cliff below the diagonal rock strata umbilical cord. I now believe that she will not split off for some time unless the cliff is subject to more fracturing. This is quite possible as the new cliff section here is not stable. At the northern boundary a large bowl shaped cave is being punched out. It will either be the basis for a substantial new arch when finally punched through, or it will trigger another major cliff collapse. I think it will trigger a further cliff collapse.
The cliff collapse site to the rear of Elephant Rock is now hollowed out and free of loose material. A lot more of the debris field has broken up further and migrated out to Elephant Rock.
26.8.2009 PHO2011-1662, 1665
I came up to Tonga particularly to document the dune at high tide under storm surge conditions. However, I didn’t limit my photography to just that. PHO2011-1665 was taken on the cliff-top above the cliff section collapse site. The New Sister,( the high narrow rock promontory to the left) and the large, low rock immediately to her right are where the cliff extended out to prior to the 12th November 2008.
6.9.2009 PHO2011-1892-1893, 1895,
At the Gibbs, their daughter came in and said she had seen soil runoff in the sea. I had gone up to give the Gibbs their photos and to photograph at Te Kawau Pa for a photo competition run by NZ Geographic. I also wanted to try and get some photos on the beach of the recently split in half Middle Sister. I just had my digital camera and the panoramic camera.
I accessed the Three Sisters Beach via the Tongaporutu Reserve. The first thing I noticed while walking close to the cliff towards Mammoth Rock, was orange soil washed up on the banks. As I arrived at Mammoth Rock, the sea was markedly discoloured for some distance with bright orange soil. Also, the beach had a definite orange tinge like vat loads of orange paint had been splattered everywhere. Walking towards the Sisters, it was plainly obvious there had been a massive, full cliff collapse to the rear of the Sisters.
Specifically, it occurred precisely where I thought it would occur. At the cliff section collapse site that I observed on 12.11.2008, and at the cave being punched through at the base of the northern end of the cliff section collapse site. I was hoping to photograph the cave before it either formed a new arch, or more likely, a cliff collapse. It was sobering to realize that where I had both sat and stood on the cliff top on the 26 August photographing the Sisters, had collapsed. And, where I had stood on some high rocks at the cliff base on 22 August, again photographing the Sisters, had I been there at the time I would have been buried under tonnes of rock and soil.
Judging by the huge amount of fill, some live flaxes, copious orange soil on the beach rocks and everywhere. And importantly, lots of tiny soil balls, this latest collapse could be no more than 48 hours old, tops. Most probably though, even allowing for calm sea conditions, less than 24 hours old. It’s almost as if the cliffs are saying: “Look we won’t collapse until just before Pat comes up. We have to keep her interested in us. If we don’t put on a show, she’ll get bored and won’t bother coming up. We need her to keep on telling our story.”
This is the first time that I have observed two massive cliff collapses at the same location within a relatively short time-frame. Specifically, apart from the soil cliffs on Beach One, cave sites and known erosion hotspots, in the six years I have been observing cliff collapses, multiple cliff collapses occurring at the same location have not occurred within this space of time. This doesn’t mean that they never occur in the same location, only that I haven’t as yet observed any. My definition of single collapse sites is that they are (apparently) randomly located anywhere along the cliffs as a whole.
I took a number of photos with the digital camera from different angles. At least one has people in for scale.
The beach area between here and Elephant Rock is still scoured out to bedrock. It has been for some time and now appears to have bedrock exposed for lengthy periods, more so than in the past. Talking to Adam Buckle, he raised an interesting point about the passage of water over surfaces. Water slides more easily over smooth bedrock, (allowing for undulation), so it can extend further up the beach. Where a beach is composed of sand, then this will act as a drag and absorb water. Also, water passing over rock has a different resonance to water passing over sand. Sand would act as a partial vibration absorber, whereas smooth rock could act as an amplifier. The smoother the surface water passes over, the less resistance and friction to it.
Waves travelling over rock, particularly smooth bedrock, could be louder – greater vibration, and have more punch than waves travelling over sand. The topography of the beach could therefore affect how the waves impact on the cliffs – a change of frequency that perhaps has a significantly more adverse affect on the cliffs on the Three Sisters beach than normal. Another factor may be the speed and power of the wave travelling. In storm surge conditions, the wave might be travelling so fast that any drag from wet sand may be minimised. The vibration produced though should still be different.
19.9.2009 PHO2011-1667, 1669, 1676, 1679
I wanted to photograph the cliff collapse that I observed on 6th September with my Pentax 6x7 camera. On the 6th I only had my digital camera with me. I also wanted to see if the recent rain had removed a lot of the loose fill. The day was calm with a mix of cloud and blue sky. A low tide of 0.1m promised good access.
The beach had built up a little more at the cliff collapse site. A lot of the loose fill, particularly at the base, had washed clear. The flaxes had gone. The rocks are smoothed off more and broken up more. No sluiced soil was present. Higher up there is a huge boulder, around half the size of a bus that will come down when more of the debris pile around it washes away. I think this is a public hazard as it could potentially come down at any time. I can’t tell, but think the cave may still be intact at the base, as it still bulges out a bit at the extreme northern boundary. Overall, the cliff section collapse site still looks unstable. I think more material has yet to come down – it could still re-collapse, but perhaps in smaller chunks. More cliff material had also come away to the rear of the New Sister. I presume this occurred at the same time (6th September). The New Sister however, is still firmly attached at the base to the parent cliff. I photographed from on top of the cliff. This was mostly to document the Sisters, but some of the collapse material should be visible. It is sobering to note that where I stood and sat on the cliff edge on the 6th is now at the bottom of the cliff.
Though I photographed with the Pentax 6x7 at both the front and rear of the New Sister, I also took some more distant images with the digital camera. These mostly included the Sisters.
I also photographed the cliff collapse site to the rear of Elephant Rock. This is quite hollowed out now and appears to be reasonably settled.
18.10.2009 PHO2011-1926-1927, 1929
At the cliff section collapse site, the huge boulder situated part way up the northern end of the cliff, has, as I expected, now toppled down to the beach in another cliff collapse. I estimate that this occurred within the past couple of weeks. There is still loose fill immediately above the forming arch/cave at the base of the cliff to come away. I don’t know as yet if the arch/cave has survived or not. The New Sister is still attached to the cliff. The whole cliff section site still looks unstable. Some soil runoff was present, radiating away from the base of the debris field, but not much.
On the dune part of the beach. That is between Mammoth Rock and the arch, the cliff face leading around to the arch continues to erode away and is now nude of plants. The seaward side of the dune consists of fairly high sand cliffs and the dune itself continues to be carved out by the sea.
The weather was wet with a north-westerly wind. I had three members of the Taranaki Geological Society with me. They would prove great for scale purposes! This day had been arranged some time back. Under normal circumstances I wouldn’t have come up under such horrible conditions.
At the cliff section collapse site, it appeared little changed. However, it still remains in an unstable state. On the extreme northern boundary, we, that is, Pam Murdoch, Dawn Bowen, Mark Robbins and me, observed a large fault-line that extended high up the cliff. Small stuff was dribbling down from this area in the rain. To the right of this fault-line, the cliff wall protruded outwards. This section of cliff resides over the forming blind arch that I observed earlier. I had planned to photograph it when I visited Tongaporutu on 6.9.09, but a fresh cliff collapse had beaten me to it. The large boulders at the base of the collapse site are becoming more rounded and are slowly being dismembered and destroyed.
To the rear of the New Sister, fresh material is evident at her base where she is still joined to the parent cliff.
At the cliff face collapse site to the rear of Elephant Rock, it too appears little changed, but like the cliff section collapse site, there is still more fill to come away. Also, like at the cliff section collapse site, a blind arch is being preferentially carved out by waves in a south to north handed direction. It is a smaller version of the one at the cliff section collapse site. And like that one, it too will eventually evolve to be a through going arch. The large boulders at the base are continuing to reduce.
I differentiate between blind/through arches and blind/through caves as such: Arches are formed on promontories of varying sizes that protrude out from the cliff wall proper. Further, they are generally, (but not always,) located at an end point where the cliff turns around into a bay of varying size. Caves are formed in the cliff wall proper. Caves are therefore ‘internal cliff’ formations, whereas arches are predominantly ‘external cliff promontory’ formations.
The weather was unusual. Sea fog and low cloud that had persisted for several days.
Immediately north of the cliff section collapse site, I observed a fresh cliff collapse. This was located in a small horseshoe type bay that leads north into the first arch. At the cliff section collapse site itself, more material had come away. There is a lot of loose fill still to come down. This site remains in a highly unstable state. At the southern base of the through forming arch (not currently visible due to fill), more material has joined what is already there.
The Maori cave carvings remnant cliff wall is being split apart by wave action. To the rear of the new Sister, more material has come away and the narrow umbilical cord that keeps her attached to the parent cliff is being carved out.
16.1.2010 PHO2011-1713, 1717
Just before the first arch that leads south from the dune, a large portion of the cliff was virtually denuded of vegetation. It appeared to be currently in a soil bleed state. This has been slipping for some time.
Debris still remains from the cliff collapse that I observed on 2.12.09. This collapse occurred between the first arch and the cliff section collapse site. Of the cliff section collapse site itself, no new material appears to have come away, although overall it still remains in an unstable state. The new Sister remains attached to her parent cliff. The debris field overall continues to shrink in size with the large remnants becoming increasingly rounded by the abrasive action of water and sand.
The Maori cave wall remnant is still there, but it is gradually succumbing to the sea.
At the cliff collapse site to the rear of Elephant Rock, there doesn’t appear to have been any further collapses since my last visit on 2.12.09. However, it remains in an unstable state. The debris field continues to shrink. The arch that is forming at the cliff collapse site’s northern base still has not been punched through.
It is interesting to note that the cliffs between Elephant Rock and the Point are mostly wet, courtesy of a stream plus other water sources that keep them in a constantly dripping state. Above them, there was a raw area of sand that was bereft of vegetation. The strong southerly was whipping sand from this site into the air.
At the cliff section collapse site it appeared as if little had changed. The same too at the large cliff collapse site to the rear of Elephant Rock. There had however, been a medium cliff-face collapse immediately south of the cliff collapse site to the rear of Elephant Rock. This is most likely a daughter collapse. The cliffs in this particular location up to the Point are very wet due to stream activity. This collapse was at the northern end of that ‘wet section’. It appeared to be quite fresh as the rocks were sharp and intact. Internally there was a largish cave with quite a high ceiling. This cave extended internally for some distance. It wasn’t a blind corridor type cave but a rounded type of cave.
After returning from the Four Brothers Beach, I changed my roll of film to photograph both this cliff collapse and the larger one opposite Elephant Rock. While changing my roll of film, three lots of material came splooshing down inside the cave to the immediate left of the main entrance (northern side). The first rock fall was the largest and made you jump. The new material was very wet and sloppy due to the constant flow of water pouring down off the top of the cliff. The braided stream of water flowing across the beach from it was stained grey with the liquified cliff debris.
(Digital camera). The weather had been calm for some time. It appeared that more material had been added to an earlier collapse that I first observed on 2.12.2009. This cliff collapse site is immediately to the north of the cliff section collapse site. There was also a fresh cliff collapse at the northern entrance to the Three Sisters’ cave. (PHO2011-1948).
At the cliff collapse site to the rear of Elephant Rock and immediately south of the massive cliff collapse I first observed on 25.5.2009, a lot more material had come down. THIS secondary collapse was much larger than the initial collapse. This is a daughter cliff collapse, triggered by the much larger cliff collapse immediately north of it that I recorded on 25.5.2009.
At the cliff section collapse site to the rear of the Sisters, it appeared to have stabilized. The only exception was at the northern end above the forming arch. Here, soil and some large rocks and boulders remain in a loose state and are thus prone to further slippage. Some large boulders from the original collapse remain and they now provide a home for green algae.
At the full cliff collapse site to the rear of Elephant Rock, there had been a further major collapse as evidenced by large grey unweathered boulders. Due to there being little sign of the boulders having yet been dismembered by waves, I estimated that this collapse occurred during the past couple of weeks.
These weren’t photographed. As I only had the panoramic camera, I was limited in what I could photograph and I wanted to take advantages of the wonderful weather.