Opunake

Another great geological venue on the South Taranaki coast is at the Opunake boat ramp, where we took our Geocamp participants recently. On two sides of the car park there are cliffs showing a spectacular sequence of strata.

It's a perfect spot to practice drawing a geological section and making detailed observations.
Drawing is very valuable as it forces you to be careful and attentive to details.

The observations lead to the next question. What can these rocks tell us about the processes that put them in place?

These colourful orange, grey and yellow bands contain numerous volcanic clasts (pebbles and boulders) suggesting that they have originated from the Taranaki / Egmont Volcano, an obvious source about 25 kms north-east of Opunake. Generally when you see stratification in a rock it suggests that it has been laid down in moving water (or from the air in some cases such as volcanic ash layers or sand dunes).  This layer shows well developed graded bedding - the larger particles were laid down first, followed by finer and finer material. The very coarse unit above indicates another very high energy phase of deposition.

In some places you can find very large boulders that have been deposited and left in scoured out hollows that have then been infilled with finer material.

In  this image you can see a channel on the right of centre that has cross cut the horizontal layers and been infilled with gravel. This also shows that the sedimentation process was occurring in a high energy environment.

So a fair interpretion of the Opunake sequences is that of volcanic material that has been eroded off Mount Taranaki and deposited in a fluvial (river) environment, possibly as reworked lahars or debris flows that have been mobilised by floods.

If you take a look at the landforms on the slopes of Mount Taranaki, you can see numerous gullies and larger valleys where the rocks have been eroded away, either by rivers, lahars or rock slides. Occasionally there have also been the massive debris avalanches such as the one that covered the forest at Airedale Reef)   Over time the mountain has produced the material that blankets hundreds of square kilometres of the surrounding plain.


Here is the geological Qmap for Taranaki. The red rocks are volcanic lavas and related rocks centred on Taranaki / Egmont Volcano, whilst the pink rocks are pyroclastic and debris flow deposits.
Opunaki is on the coast  half way up the map on the left.

You can see the profound effect of the volcano on the landscape, as it is at the centre of a radial arrangement of volcaniclastic deposits.  The volcanic rocks have been  spread across the landscape for large distances by the power of gravity and water.

Waihi Beach Taranaki

The South Coast of Taranaki near Hawera has extensive rocky beaches lined by high crumbling cliffs. It is a great place for geology, but you should be wary of the potential for cliff falls, especially after rain. This is the view east from the Ohawe beach access point.

A first look at the cliff from a safe distance shows that it is made of two main rock types; massive grey muddy sandstone at the bottom, with darker brown soft stratified layers above. The boundary between the two layers is very distinct and can be seen for many kilometres along the coastline.

If you take a closer look at some of the muddy sandstone boulders lying on the beach, you can find some nice fossils such as this scallop.

In places these rocks are very bioturbated. In other words they have been churned up by organisms that burrowed through them when they were part of the sea floor.

For a close up look at the boundary between the two layers that form these cliffs, a good place to go is the beach access track a few kilometres east at Waihi Beach (end of Denby Road). There, right before you reach the beach, is an easily accessible outcrop where you approach the boundary safely.

Here is a slightly closer view - you can see the change from the lower grey unit containing oysters and scallops with the shell rich layers above. The fossils in the lower unit indicate an environment of deposition about 20 to 50 metres deep. This layer is approximately 3.5 million years old.




Here is another image where can see the incredibly abrupt change from the lower muddy sandstone to a much looser sandstone packed with shells.

Just below the boundary there are some vertically positioned shells in a line. These have burrowed down into the sediment from above and have been preserved in life position. Although they are found within the 3.5 million year old sandstone, they are actually only as old as the overlying shelly layer, which is about 125 000 years old .

This means that the 3.5 million year sea floor sediment has been uplifted, eroded down to sea level, and then covered with shelly beach or estuarine deposits of much younger age. Nearly three and a half million years are missing from the sequence.

Interestingly the same unconformity is widespread across Taranaki. Here you can see it at Wai-iti Beach on the north coast. Here the time gap is even greater, as the underlying grey sediments are about 8 million years old and represent deposition at about 500 metres water depth. This shows that there has been greater uplift and erosion in the north compared to the south Taranaki coast.



Here is a video of Kyle Bland explaining the Waihi outcrop and the story revealed by fossils:

Power of the Planet Geocamp in Taranaki

Over the last two weeks, GNS Science, with support from the Todd Foundation, the Royal Society of New Zealand, and  Puke Ariki Museum in New Plymouth, has been running a hands on immersion geology course for teachers and years 7 to 9 students from 5 Taranaki schools. 24 students and about 10 teachers participated in this "Power of the Planet" Geocamp which culminated in a geoscience expo at Puke Ariki, that was created and run by the participants.

Richard Levy (paleoclimate scientist) and Kyle Bland (petroleum geologist) helped lead the camp along with myself.  This  was the second such event that we have organised, following last years' "Dinosaurs and Disasters" Geocamp in the Napier Aquarium.




The basic approach is that we encourage the participants to make very careful observations of a variety of rock outcrops and landforms at different field sites.





The video will give you an impression of the geological features that were researched by the participants:

Following each field trip, and with a series of guided questions and the use of simple models, the participants had to debate and interpret their findings to come up with understandings of the geological processes at work. This process of developing confidence in observation and thinking takes time, which is the value of having such an in-depth full time two week course.

In addition to the field trips, the participants also had the opportunity to visit local fossil collector Dave Allen, and to have a live video link with the ocean drilling ship Joides Resolution, presently working off the coast of Alaska.




Day by day a framework of understanding is built up. The final community / public expo event then requires the participants to become the educators, further re-inforcing the level of understanding of the geological concepts.

Through sharing the Geocamp experience with the participating students, the teachers are also able gain professional development in geoscience education with this inquiry learning approach. We hope that the ideas and  practices can be shared as the teachers return to their schools, to add longer term benefit.


This video shows the active engagement of the participants with members of the public during the expo. Their brief was to challenge the visitors to observe and think, in the same way that they had been challenged during their own Geocamp experience.



I would like to thank the teachers and students of Oakura School, Kaimata School, Eltham Primary, Makahu School and Sacred Heart Girls'  for their positive participation and response to the Geocamp.