Topic: Cliffs - Pilot Point

Topic type:

PILOT POINT

Pilot Point starts at the southern end of Rapanui South beach, specifically at the southern cave.  That is, the cave is the boundary.

Pilot Point extends from this cave to a substantial arch immediately north of the Tongaporutu River.  It includes the south-facing cliffs around the corner from the arch and continues landward to include the large dune area.

The cliff face above the cave site is quite prone to erosion, while a wall-like section of the same cliff leading from just south of the cave to the arch is quite stable.  The cliffs leading round from Pilot Point towards the sand dunes are preferentially carved by the sea.  The presence of the Tongaporutu River adds to the erosive mix making these cliffs particularly prone to collapse.  At the cave, there are two arches.  One is a passageway cave/arch going through a promontory, while the other is a cliff carved arch.  On the Tongaporutu River side there are several blind caves.  Up until July 2008, there were no rock stacks at Pilot Point.

2002

12 May 2002   PHO2008-868

This is taken from the cliff top on the O’Sullivans’ farm and looks south towards the Pilot Point arch (obscured), the Tongaporutu River and White Cliffs in the distance.2003

18.5.2003   PHO2007-201, 203

These images show the cliffs at Pilot Point from the Tongaporutu River side of Pilot Point.

1.6.2003   PHO2008-892

This image, like those of the 18th May also features the cliffs on the Tongaporutu River side of Pilot Point, excepting that the light and perspective are different.

30.6.2003   PHO2008-036-037, 039, 046-047, 929-931

The area surrounding the Pilot Point arch has been excavated clean of sand and is filled with water, the rock base being uncovered.  I photographed the cliffs on either side to show the differences.  Close to the dune area there had been a recent rock fall.  I guessed it had occurred the day before.  (PHO2008-047)

13.7.2003   PHO2008-055, 058-059, 940, 943, 949-950

The arch is still ‘sitting high’ due to the bedrock and rocks still being exposed.  I also photographed the cliffs from various viewpoints on the beach, some in nice light.

27.7.2003   PHO2008-079, 974

The cliffs shown in PHO2008-079 house the Pilot Point cave system. The middle part of the cliff that ‘sticks out’ has an arch at its base, (obscured).  I also photographed the arch from its northern side.  See PHO2008-974.

28.8.2003   PHO2008-1006

This through view of the Pilot Point arch was taken hard up against a sheer cliff wall.  This photo almost cost me my life.  It was here that I learnt about wave bores generated by the nearby outflowing Tongaporutu River meeting up with incoming waves.  I had been too impatient to wait for the tide to drop to a safer level.  Had the water been just a few inches higher (to just above the knee), then I would have been gone, such was its power.

23.10.2003   PHO2008-304, 1076

This is on the cliff-top above the Pilot Point cave.  Both of these views taken at different times of the day looks south.  The Pilot Point arch is just beyond the wave splashing up the cliff.

 

26.10.2003   PHO2008-350, 352

CLIFF SEQUENCING.  I was primarily concerned with doing cliff sequencing at Rapanui South beach.  However, for my purposes, Rapanui South beach co-joins with Pilot Point down at the southern end.  I had already photographed the cliffs on the Tongaporutu River side of Pilot Point on 18 May 2003.  This was fortunate because for some reason I didn’t do any cliff sequencing photography around there today.

24.11.2003   PHO2010-0474

The arch remains high due to very low beach levels.  In a photo I took with my little camera – colour print film, clearly shows a distinctive fault line leading down from the cliff to the arch.

2004

7.3.2004   PHO2008-715-716

A full cliff face collapse occurred on the Tongaporutu River side of the arch.  There had been a blind cave at its base.

19.4.2004   PHO2008-795, 799, 1264

Most of the cliff fall debris of 7.3.04 remained intact.  I photographed someone standing in front of it for scale.  I also photographed the cliffs from the southern side of the Tonga River.  Though a distance shot, the cliff collapse can clearly be seen.  PHO2008-795 is a close-up of banding in one of the cliff walls.

2.5.2004   PHO2008-1269

Sea fog light gave a wet glow to the cliffs.  This view looks north through the Pilot Point arch.

18.7.2004   PHO2008-1306

Evolution of the 7.3.04 cliff collapse debris.

2005

24.7.2005   PHO2008-1382

This view looking south through the Pilot Point arch shows the Family of Rocks with the Three Sisters beach and White Cliffs in the distance.  Notice how the pool of water, present in the 2.5.2004 photo has long gone.

2006

15.5.2006   PHO2008-1621

A standard photo looking south towards the Pilot Point arch.

2008

6.4.2008   PHO2011-1205-1206

A double cliff face collapse on the Tongaporutu River side of the arch.  Just west of this (seaward) was another cliff collapse.  A huge chunk of cliff wall had carved off.  It is important to note that the cliff section from the arch back towards the dunes (west to east) are quite volatile compared to the cliff section from the arch to just before the cave (west to north).  This is due to them being more directly aligned to the prevailing south-western weather systems and currents, thus being exposed to preferential carving.

 

20.4.2008   PHO2011-1216-1217, 1223

I was able to access Pilot Point on this day to check on the cliff collapse that I observed from the Three Sisters Beach on 6.4.08.  The first cliff collapse, that nearest to the dunes, wasn’t as large as I first thought, unless some of the debris had washed away.  It wasn’t a double cliff face collapse;  rather, a single, full cliff face collapse.  The debris field was mostly intact.  Large, fresh cracks in the cliff face will yield future collapses.  The second, smaller cliff collapse, closer to the arch, was more of an internal collapse (roof), as most of the rocks were inside a partially formed blind cave.  At the arch itself, a small chunk had been carved off its base on the seaward side.

20.7.2008   PHO2011-1243, 1247, 1253-1255, 1257-1259

SUPER-STORM EVENT.  Super-Storm One.  The PILOT POINT ARCH has been COMPLETELY DESTROYED in a massive, full cliff face collapse.  I was stunned when I first observed this from the Gibbs farm overlook above Mammoth Rock.  There was also a smaller cliff collapse on the Tongaporutu River side of the arch collapse (eastward).  Upon arrival at the actual site, I deduced that this had occurred within the past 48 hours due to the large amount of soil present, live vegetation and hard edged rocks and boulders, plus live vegetation half buried in the sand.

As if that wasn’t enough, there was also a full cliff face collapse around at the cave.  This had collapsed the roof of the cliff formed arch, but due to the amount of cliff debris, I couldn’t tell if a free-standing rock stack had formed.  Due to the freshness and amount of cliff debris, I couldn’t tell how much of the cave and its three pillars had survived or not.  I estimated that both had occurred within 48 hours, and perhaps due to the size of the arch collapse, it had triggered a ‘ripple effect’ that caused the secondary collapses, one immediately to the east and the other at the cave, to the north.

I later discovered from the O’Sullivans that the arch collapse had occurred around 9.30 pm the previous night (19.7.08) and that the cave collapse had occurred around lunchtime on the day of my visit – the 20th).  They had felt like mini-earthquakes.

3.8.2008   PHO2011-1278-1279, 1281

SUPER-STORM EVENT.  Super-Storm Three.  I observed a new cliff collapse at the dune end of the cliffs but didn’t photograph it.  At the arch, all the soil had vanished and the rocks and boulders had rounded edges due to weathering.  The debris field ranged from hard up to the cliff to around 40 feet out.  These boulders joined the ‘family of rocks’ I have been documenting close by.  At the cave, most of the rocks and boulders remained, but the soil had gone.  The material at the cave site had cleared sufficiently to reveal a new rock stack had indeed formed from the defunct arch. I nicknamed it ‘Pat’s Stack’.

 

31.8.2008   PHO2011-1310, 1313-1314

The Pilot Point arch cliff collapse debris was spreading out more and rocks were getting smashed into smaller pieces.  The large ones remained intact.  At the cave site a similar thing was happening with some rocks having travelled some distance further out to sea.  The other cliff collapse debris was still around.  At the cave site, the top of the cliff, that is the soil part, was overhanging quite markedly.  The same at the arch site where shavings were plopping down on a regular basis.

12.10.2008   PHO2011-1351, 1353

PHO2011-1351 shows where the Pilot Point arch once was.   PHO2011-1353 was taken from the Pilot Point arch debris field and looks north towards the Pilot Point cave, (obscured to the rear of the cliff).

12.11.2008   PHO2011-1368, 1388-1391, 1393

Most of the cliff debris from the cave site had now gone, either been smashed up or travelled further out to sea.  Some large rocks remained.  At the Pilot Point arch debris site, the large boulders on the slightly south-eastern side of the collapse remained insitu, anchored in the sand.  Mostly the rock field was diminishing and fanning slowly outwards.  One of the large boulders has a nice strata pattern on it and I will be documenting its progress as well as the larger, plainer sibling on the southern seaward side of it.

As I was doing CLIFF SEQUENCING on Rapanui South Beach, I also continued to do Cliff Sequencing for Pilot Point.

2009

12.4.2009   PHO2011-1589

I photographed from the cliff top on the O’Sullivans’ farm, looking down on the cliff/cave and along to Pilot Point arch to record the cliff collapse debris from above.  It is still there and dissipating.  Pat’s Stack is also shown.

 

3.6.2009   PHO2011-1602, 1605-1607

 

Near the Pilot Point arch debris site, there had been a partial cliff fall.  That is, a large chunk of cliff face had carved off.  The cliff site was clean, although the debris was deep in the sand and rounded, so it probably occurred within the past month.  At the arch site itself, all of the rocks had moved away from the immediate cliff base so there was a clear, round area of about 12 feet.  The debris field had thinned out considerably.  What remains is fairly deeply ‘glued’ in place by a high sand level. 

The largest plain boulder and the fellow large rock with the nice strata pattern on one side were still there and were now being colonised by algae, mussels, limpets and barnacles.  The family of rocks is now enlarged and seems to prove that the original family of rocks originated from an earlier cliff/arch collapse.  I also believe that there are more rocks like them, but further out and buried out of sight.  In time a new arch will form.

 

At the cave, most of the debris has gone, but a few of the larger boulders remain.  The base of the cliff is mostly clear as the material gradually fans outwards.  High sand levels at present keeping what remains glued in place.

 

 

2.12.2009   PHO2011-1697

 

Enroute to Pilot Point, I saw some oldish, rounded sandstone boulders.  These are the remnants of the larger of the two cliff collapses that I first observed on 6.4.08.  At the Pilot Point arch collapse site, more material was still coming away.  At the base of the cliff gobs of soil had come down since that last high tide.  I photographed the new family of rocks from the northern side looking south.  A partial view of the still unstable cliff face is visible.

 

I also noted that a large, fairly open blind cave was quite close to the new Point proper.  This will in turn form the next Pilot Point arch in a process that is site specific.  It is an ongoing process due to the unique topography and location of the Tongaporutu River.

 

 

 

2010

 

 

11.8.2010   PHO2011-1830

 

I had come up for the day with the panoramic camera to primarily photograph Rapanui South.  The photo shown here looks towards the Pilot Point cave and Pat’s stack.  The promontory on the left is the boundary between Pilot Point and Rapanui South Beach.

 

Discuss This Topic

There are 0 comments in this discussion.

join this discussion