The Geology and Coastal Erosion of Piha, Auckland

The rocks of Piha beach near Auckland are the eroded remnants of the ancient Waitākere Volcano. This huge volcano extended over a vast area and consisted of a variety of rocks that were erupted over several million years. Whakaare / Lion Rock and the other cliffs of Piha Beach allow us to piece together some of the history of the volcano, and the cliffs also have an interesting variety of coastal erosion features.
In this video, geologist Bruce Hayward gives us a guided tour...
SAFETY: Please be aware of the tides when exploring around the rocks and caves to the south of beach. They can be cut off so are best visited on a falling tide.
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[@katedwek7785]

Absolutely brilliant! Thank you for making complex geology accessible.

[@OutThereLearning]

Thank you for watching and your nice feedback

[@nickburke5263]

Bruce is a true blue legend and a real authority for Auckland, coromandel and northland’s geology

[@OutThereLearning]

:-)

[@TheDalaiLamaCon]

I totally got the sand scribbles, he sure knows his subject. Thanks for the vid.

[@OutThereLearning]

Thank you for your comment!

[@carolineandrews7231]

This is so interesting. I have been out to Piha several times, and enjoy looking and noticing the rock formations. Now I can't wait to go again, and see them with fresh eyes ( amateur eyes) of knowledge. I think I will be running this video and pausing as I go. Thanks so much for sharing your wealth of knowledge with us.

[@OutThereLearning]

Thanks for your appreciation!

[@sixthsenseamelia4695]

😊This is amazing and exciting! I would want to stay for days and days and days exploring. It would be SO hard to leave! And I'd go home with little pebbles, pumice, sand, rock samples (again).

[@OutThereLearning]

:-)

[@wiregold8930]

Very informative. Bruce's drawings were helpful. I haven't been to NZ in 48 yrs and doubt I'll make it back. Thanks for the tour.

[@OutThereLearning]

Really great that you enjoyed the video, thanks for your comment

[@ElaineSmid]

Really nice work, Julian and Bruce! Really appreciate the important work you're doing and the stories you're capturing, Julian :)

[@OutThereLearning]

Thanks Elaine!

[@SeaSide420]

Another excellent video, thank you! Very interesting and amazing 👏

[@OutThereLearning]

Thanks - glad you enjoyed it!

[@user-ps1lv8yv9t]

Wow, I have lived in the Waitākere’s most of my life. Been going to the coast since a child. I never knew there was a massive volcano out to sea. Thanks for the sand drawings, very interesting! I’ve subscribed, so much to learn about the area that I call home 🙏🏻thank you!

[@OutThereLearning]

Thanks for sharing!

[@johnnylingo4686]

Fantastic

[@OutThereLearning]

Cheers!

[@RangieNZ]

Love the energy of both of them to explain things.

[@OutThereLearning]

Cheers!

[@George-xb5ey]

Lion Rock is awesome in person

[@Luubelaar]

Very interesting! Those columns inside the big cave at the end were very cool. Thanks for the video.

[@OutThereLearning]

Glad you think so! :-)

[@NZherewecome]

How awesome! More science I can share with my boys when we visit here now. Thank you

[@OutThereLearning]

Thanks for your appreciation!

[@davec5237]

Very interesting, thanks for sharing 👍

[@xe4743]

If i had a teacher at high school as enthusiastic as this man, i would have listened!

[@OutThereLearning]

Thank you!

[@matthewmellor2342]

These videos are great, very interesting. Love learning about NZs geology. Thanks! Keep them coming

[@OutThereLearning]

Thanks for watching and enjoying!!

[@chrissscottt]

Fascinating. I will view Piha's geology with new eyes next time I visit.

[@OutThereLearning]

That's great!

[@KiwiShellNZ1]

Awesome! Thank you 😀

[@OutThereLearning]

Thanks for watching!

[@robinsmith9734]

Magic you two semi-dryfooters, great energetic patter!.........

[@OutThereLearning]

🙂

[@IheartMount]

Top notch video team. I've often wondered how Lion Rock came to have it's varied compostion, but didn't realise it was an accumlation of material around a vent, seperate from the conglomerate of the rest of the surrounding area. It would be really cool if you could do a video on the formations around Maori Bay. So much interesting formations there with all the columnar jointing and lava pillows, and I'm sure Bruce could tell a tale about how those formations came to be there.

[@OutThereLearning]

Thanks for your comment and your suggestion. Watch this space :-)

[@barbarashikongo286]

Interesting and informative. Another great production. Keep them coming.

[@OutThereLearning]

Thanks for watching, and your encouragement!

[@gnrsgl]

Very cool thank you

[@janinekaretai4306]

So informative . It's great to learn about our own back yard. Thank you

[@OutThereLearning]

Thanks for watching!

[@tristanmelling410]

The sand itself deserves a mention! It’s a magnetite sand containing iron and titanium, and gets roasting hot in the summer! Burnt my feet a few times on the sprint down to the surf!

[@OutThereLearning]

Fair point!

[@Wildflower-xe8sn]

Fascinating

[@OutThereLearning]

Cheers!

[@hrtymongrel]

amazing fanX.

[@consciuosnesssoul]

Really good. I want to return and have a closer look.

[@OutThereLearning]

You must...

[@RS-bn9rx]

Riveting.. the enthusiasm is contagious

[@OutThereLearning]

🙂

[@Tokoroa3420]

Anawhata beach also had a good platform and huge caves, now I can annoy my mates with all these Geo-facts whenever we go fishing there.

[@OutThereLearning]

Haha - great!

[@tonybird4633]

Thanks, informative and entertaining

[@OutThereLearning]

Cheers!

[@robinhodgkinson]

As an Aucklander I’m familiar with pretty much all the rocks formations you’ve looked at - when at Piha I spend more time looking at the rocks than I do the sea. Thanks for making sense of the geological jumble there. Although it’s obvious that much of the formations are volcanic in origin, I had no idea that there existed a volcano that has been eroded away by the sea. All things succumb to time. One question though re the Piha conglomerate. I had always thought ( novice factor 10!) that it was sedimentary, since all the smooth rocks were contained in another “sand” medium. But I’m wondering now if these are in fact smooth due to the erosion of the whole conglomerate i.e. if you were to dig one out of the conglomerate it would be rough?

[@OutThereLearning]

Actually - although they are derived from volcanic activity, the conglomerates are sedimentary as they have been transported and deposited down the slopes of the volcano. The rounded cobbles were worn smooth by being moved and abraded during transport. The more angular fragments have been rolled around much less. If you were to dig into the conglomerate the rocks you pull out would be similar to what you see on the surface. Great question - thanks for asking.

[@TrailerYacht]

@@OutThereLearning - EXACTLY - I was surprised at how beautifully rounded those clasts were, obviously due to fluvial transport yet Bruce didn't mention this. You could clearly see the graded bedding too as the flows that deposited the clasts lost energy. Thanks for an interesting video. Will definitely check this place out on our next visit to NZ.

[@1969cmp]

Looks like a good fishing spot.

[@BoobyTrap8]

This is wonderful! I didn't know any of these things about Piha. Thank you both so much.

[@OutThereLearning]

Glad you enjoyed it!

[@leonakadir3833]

I was there last year but I had no idea! I just wanted to visit the beach 'The Piano' was filmed at!

[@ENZEEVIDS]

great vid! fantastic insight !

[@OutThereLearning]

Thanks!

[@alaskajdw]

Enjoy your videos sir 👊

[@OutThereLearning]

Thank you

[@yarraman8595]

so Lion Rock is a "plug" above an ancient volcanic vent below? also, at the southern end of Bethells beach is an obvious layer of conglomerate with a massive flow of lava layered above it.

[@OutThereLearning]

Yes - it is made of the contents of a choked up vent.

[@rosiepack1081]

Another fascinating explanation of NZ geology, wish I'd learned this at school

[@OutThereLearning]

Thank you!

[@mr0iz0]

Great information. You guys mentioned a visit to Mangere Mountain - when's that one coming? 😃👍

[@partlycloudy5049]

One to look forward to, my old playground.

[@OutThereLearning]

Yes - when time permits! ;-)

[@ohmpoingpoing]

I always stare at the formations at Piha and failed to understand how were they formed. This makes a bit more sense now.

[@OutThereLearning]

Great!

[@Seawithinyou]

How Amazing would love to explore this Too! 💖

[@OutThereLearning]

Cheers!!

[@salsmith1323]

I went here a long time ago while visiting some great NZ friends but never had a look at the geology. The Brian Cox of geology here!

[@barneymaurirere9592]

I LOVE ROCK STUFF NOW .

[@OutThereLearning]

That's great!

[@barneymaurirere9592]

In Piccasso footsteps . For real .

[@barron204]

Awesome video. I have learned many things from this video and I look forward to my next visit to Piha.

[@OutThereLearning]

Great, that's what we love to hear!

[@graemefindsen4001]

Good illistration my man .

[@OutThereLearning]

Glad you think so!

[@omekafalconburn9202]

Loving these videos looks like NZ is a geologists dream

[@OutThereLearning]

Thank you, and yes it is!

[@patrick247two]

Thank you.

[@OutThereLearning]

Our pleasure :-)

[@tigertiger1699]

🙏🙏🙏 Piha/ west coast.. so beautiful

[@OutThereLearning]

🙂

[@gasdive]

This is great. I was always more interested in the rocks while we watched 800 Words on telly.

[@OutThereLearning]

Thanks for watching and your interest

[@geofflewis8599]

..Please do Raglan Harbour next..

[@alantorrance6153]

One must pay particular attention to the tides when walking around the rocks on the southern end of the beach. It can be very easy to get "cut off" on an incoming tide, and then you are in real danger.

[@OutThereLearning]

Thank you for that information, I will add it to the description. Much appreciated

[@BruceHayward1]

The Tasman Lookout Track does provide an escape route above the cliffs if you are at The Gap and get cut off by rising tides.

[@jessebarlow1277]

I want to come to NZ just to get a geology tour from Bruce

[@OutThereLearning]

:-)

[@salsmith1323]

NZ is geology heaven.

[@ZebaKnight]

That was interesting, enlightening, and ... _exciting._ I wondered about the wisdom of walking into/through those tunnels, but I guess that Bruce Hayward is living proof that, at least for the past 45 years or so, that has been safe to do. I also wondered how the rocks that were of "different compositions" (at the 9:00 minute mark), could all come from the same volcano. I assume they were created at different times. Most of the hardened lava looked like basalt, but there was also mention of some andesite. Was the stratovolcano that produced these rocks over a rift system? Was it created by an oceanic plate subducting under what was once land but now is undersea? Perhaps it's obvious from these questions, I'm a recent student of geology. It's all pretty thrilling, actually! Thanks for a great tour.

[@BruceHayward1]

I only walk into the caves and through the tunnels and around the rocks around low tide and always check that there is no evidence of higher surges having recently passed into them. I ALWAYS check the time of low tide before I go out to west coast beaches and I recommend everyone else does too.

[@ZebaKnight]

@@BruceHayward1 I felt sure you didn't take foolish chances! I really enjoyed this video. (My "Reply" was delayed because I literally just figured out how to see past "Reply" posts without having to go back through the comments for each video.)

[@ocevicheband502]

Enthusiastic!!!!

[@OutThereLearning]

🙂

[@fb3rasp]

Thanks so much, super interesting. Does it mean that Lion Rock is still in/on the vent of the volcano?

[@OutThereLearning]

It is one of the infilled vents, but long extinct of course

[@andrewpetrie1355]

Looks very similar to the rocks in Whangaroa harbour

[@partlycloudy5049]

Boy, that’s a cool harbour to sail through, those cliffs are awesome. Reminded me of the Whangarei heads.

[@BruceHayward1]

Yes both are the eroded sides of stratovolcanoes of a similar age. The main difference is that at Piha the volcanic conglomerates were deposited under the sea on the largely submarine slopes of the Waitakere Volcano. At Whangaroa the volcanic conglomerates were deposited on land as part of the laharic ring plain, rather like the gentle ring plain that surrounds Mt Taranaki today or the Desert Rd area which is the ring plain of Mt Tongariro and Ruapehu.

[@orangudan3567]

Excellent video thanks; your time and effort is appreciated! I was at the south end of Piha beach today looking at that vertical section of conglomerate that had water running down it wondering why it was less eroded than the surrounding dry conglomerate. You have answered my question! My guess as to how the keyhole tunnel formed on Taitomo island was that there looked like there was a dyke (igneous intrusion) there but most of it had been eroded away. I would have expected the surrounding conglomerate to erode faster. Would this be because the border between the dyke and conglomerate served as an exposed crack for water/wave action to penetrate and then the dyke, being formed on a vertical plane, was more prone to sliding downwards with gravity?

[@OutThereLearning]

Your observations and thoughts about the eroded dyke are very astute. The dyke is much harder material as you point out, but is broken up into pieces along the cooling joints. This would have allowed loosened pieces to drop out under gravity. We did in fact have this in the original video but left it out for the sake of length / time. Great that you spotted it!

[@orangudan3567]

Thank you for the swift reply! Wow nice to have my thought process confirmed! We had a great day out gazing at this amazing geology! I missed the caves you went in to later in the video though - another time perhaps!

[@richardmorgan3093]

Thank you Julian and Bruce for inliighting me on the rocks of Pihia ...my wife and I were out there last month and we wondered how it all formed ....I did know of a large underwater volcano before today ....it really must have be humongous.... Question .....would this have slipped away into the sea around the time of lake Taupo exploding ..... Thanks again I love these videos of How new Zealand was formed ❤️❤️❤️❤️❤️

[@BruceHayward1]

The Waitakere Volcano became extinct 15 million years ago. It is the constant marine erosion by the Tasman Sea since then that has eroded most of it down to a stump just beneath the sea floor. Bruce

[@richardmorgan3093]

@@BruceHayward1 thank you Bruce, any chance of this volcano resurfacing or is it extinct ....

[@richardmorgan3093]

Have you got more videos I can tune into Bruce

[@BruceHayward1]

@@richardmorgan3093 See Out there Learnings' video library. I feature in Takapuna Fossil Forest and maybe a few more to come. Julian is doing a great job all around NZ.

[@richardmorgan3093]

@@BruceHayward1 champion Bruce , I learnt more in the last 6month about geography in nz than I ever did at Northote collage in 70s lol 😆

[@UnkleSi]

Very cool! Is this similar to the rock on sumner beach, chch that houses the old beach lookout?

[@OutThereLearning]

Very similar!! - those rocks are also volcanic breccias, ash and lavas

[@UnkleSi]

@@OutThereLearning thanks! And love your series, very interesting!

[@UnkleSi]

@@OutThereLearning do you think the Sumner one (being much smaller than lion rock) was one lava bomb that landed on the beach from the nearby volcanoes? (Maybe the lyttleton or halswell one for example?). Is it too small to be a lava cap of a plume erupting on the beach as per the wonderful lion rock beach drawing is that correct?

[@johnetherington6801]

very interesting indeed, so was all that caused by Rangitoto?

[@OutThereLearning]

These rocks were erupted from the ancient Waitākere Volcano which is long extinct and mostly eroded away.

[@johnetherington6801]

@@OutThereLearning Thanks for answering my question Bruce. Just out of curiosity I live in pukekohe and have always wondered about the big domain type half way up mill rd on the Auckland side reminds me of western springs,do you know if it was a volcano mate?

[@mrivantchernegovski3869]

Imfamous keyhole and on right tide its surfable and iv done it once and that was enough for me

[@OutThereLearning]

:-)

[@edsnack1181]

Would have been nice to mention why the tunnels follow the intrusive dikes of lava, it is because that lava, although considerably harder than the surrounding conglomerates, cools into a basically hexagonally jointed pattern which is very easy to erode in blocks. The Taitomo tunnel, blowhole, and the other tunnels shown all at least initially follow the line of these basaltic intrusions. There are some fascinating ones at Bethells Beach (Te Henga) as well, mostly at the Northern end, including a connected series running beneath one of the small peninsulas there. Just FWIW.

[@OutThereLearning]

Thanks for that, quite true and was nearly included!

[@adrianpilbrow]

where exactly are the last two caves? Is it between south piha and mercer bay? Is it accessed by foot from south piha?

[@OutThereLearning]

Walk past the gap, over the hill and down to a stream that flows into a sea cave. At low tide walk through the sea cave and the other caves are over to your left as you emerge.

[@jbennett3578]

This is why I want to marry a geologist. When I stop to ooh and ahh about some interesting rock formations, she can explain to me what I'm actually seeing. :)

[@OutThereLearning]

Good plan! :-)

[@edawg654]

Can’t wait to explain all this to the boys in the lineup 😂

[@OutThereLearning]

That's the spirit! 😁

[@michaelstott8402]

So why has the volcano out to sea eroded to the point that it's beneath the waves when the portion that makes up the Waitakeres hasn't?

[@BruceHayward1]

The Tasman Sea actually had eroded all of the volcano down to sea level by about 5 million years ago during a period of little tectonism. Then in the last 5 million years we have had another phase of tectonic activity that has progressively pushed up the Waitakere Ranges, more so in the east than the west so that it is tilted down towards the NW. If you look at the Waitakeres from a distance you can see their flat gently tilted top, which is the 5 million year old sea floor that has been pushed up. The flat top is actually just the ridge crests - in 5 myrs this uplifted surface has been deeply eroded into valleys by streams and the sea is once again carving away the west side forming the cliffs as it eats into the uplifted rocks.

[@user-ps1lv8yv9t]

I am in awe 😯

[@christenefaragher8821]

I have a question. Why doesn't NZ have diamonds crystals or gemstones. love the show by the way

[@paulmeersa7162]

Why is Taitomo island south east face so smooth in a circular type of shape, it is not a flat face at all, it is round - when all around it are rough scalloped out caves on other cliffs. Also, why is there a flat face facing north exactly on top of Taitomo Island above the fallen rocks 12:54. You can see the flat face at 19 seconds at the summit of Taitomo island not only is it facing north exactly but it is also perfectly perpendicular, and is a flat face - perfectly. Seems odd given it is created from lots of little stones held together in a matrix that it should fracture flat and perpendicular does it not...?

[@colinsmith2005]

The river rocks, the cliffs are full of them up and down the coast, must have been a huge river to deposit so much river rock sediment above todays sea level which then have deposits of rock atop. Everywhere the camera points it seems river rock is exposed, not being shaped by wave action, rounding, but being exposed as it is, imbedded and pre river rock rounded without a river. Maybe it’s a Magic underground river, I saw one once.

[@colinsmith2005]

Are you sure you know about dirt and rocks and sticks and stuff, or do you wear the backpack around and chameleon yourself to anyone with a camera in public, high, I’m an expert, I’ll explain, I’ll just get my stethoscope and little hammer out, roll it up, yes, oh yes, it’s the reflex bendy syndrome, not many people have that it’s an exciting day, your very lucky I came along, look at that lion, I think it’s hungry, quick RUN.

[@moped975]

- Übereinander geworfen in Minuten: eine Erd-Achsen-Verschiebung, bei der sich in wenigen Stunden der halbflüssige Globus unter der starren, zähen, trägen Erdkruste hinweg bewegte, ganze Kontinente, Gebirge, Gewässer verändernd, teils gekocht, gebacken unter vielen hundert Grad Hitze...

[@timway6839]

Taupo plug?

[@OutThereLearning]

Not really directly related to Taupo

[@leonakadir3833]

so is lion rock a volcanic plug?

[@OutThereLearning]

Yep

[@andrewdillon7837]

i thought Taupo was big,,, BUT wait there's more,,, 60km by 40 km ,,, yep,,thas big..

[@OutThereLearning]

Yep - it was a stratovolcano though - not a caldera like Taupo, so not as violent, and it built up over a looooong time!

[@minkelupa5763]

I found a twig fossil at the gap in piha. well I think it's a twig fossil it's just a short line of what I think is coal

[@OutThereLearning]

Never stop exploring, there's always more to discover!!

[@mozismobile]

Does the utube algorithm (all hail the mighty Al Gore Rhythm!) ever get upset at all this discussion of bombs and explosions?

[@OutThereLearning]

No idea! Doesn't seem to

[@paulbriggs3072]

I don't know- those volcanic conglomerates look composed of awfully water-rounded cobbles and boulders to me. And then deposited in very water sedimented strata. All this appears to be fairly level strata deposited by a fast moving debris flow thousands of feet thick and miles long. This is identical to thick stratified gravel deposits found in many places on earth that are in some places claimed to be from glaciers but in others from debris flows. Given that the debris flow theory has eye witnesses to modern examples with no one disputing it, I go with the obvious.

[@kiwi-eg5ld]

S

[@deborahtheredbrickchick468]

Looks like heat damaged red brick buildings of the old world to me ~ research meltology on YT

[@OutThereLearning]

It could give that impression superficially, but quite definitely not with close observation and understanding of geological processes. Thanks for your comment

[@weAreNotAloneHere]

He knows not. There not rocks, they where living creatures..

[@neilmarshall5087]

Using a feather quill to make maps on the beach.... 12/10 for that.

[@OutThereLearning]

😀 cheers!