Field Trip

Waihi Beach Taranaki

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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 4.5 kilometres east at Waihi Beach (end of Denby Road see www.geotrips.org.nz/trip.html?id=55 for location and geological info). 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:

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Power of the Planet Geocamp in Taranaki

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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.

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Airedale Reef

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Earlier this week I was up in Taranaki, exploring the geology of the area  with two GNS Science researchers Kyle Bland and Richard Levy. One of the sites we visited was Airedale Reef, a short walk east along the coast from the mouth of the Waitara River. There are spectacular remnants of an ancient forest on the shore platform at low tide, with tree stumps in growth position and large logs sitting in a black layer of peaty soil. The forest layer reappears at the base of the nearby sea cliffs, with the roots and tree stumps gradually being eroded out. Just below the dark layer is an olive green bed of dune sands. The carbon rich forest layer is thickest in the depressions between the dunes. This  is one of the tree stumps emerging  from the cliff. But how long ago was this forest still living? How did it die and why was it preserved like this? The answers are in the layer just above it. This overlying layer is made of an unsorted mixture of different boulders and less coarse particles of rock. You can also find chunks of carbonaceous material scattered within the layer that must have been ripped up into it as it was emplaced. This 4 metre  thick layer of material has been mapped  over a minimum area of 255 km2 around north Taranaki, and has a total volume of at least 3.6 km3. It is believed that Mount Egmont (Taranaki) volcano is the source of this layer. Like some of our other andesitic volcanoes, Mount Egmont is made up of layers of unconsolidated volcanic deposits interbedded with more massive lava flows. Because the slope angle of the volcano is very steep, the cone is inherently unstable, resulting in occasional enormous avalanches of debris launching down the mountainside, spreading across the surrounding countryside and out into the sea for distances of up to 40 km from the source. For this reason Egmont is a significant geological hazard that is monitored by GeoNet. On our visit up the  mountain the following day, amidst the lava flows and ash layers we could see deposits such as these – not too different from the bouldery layer at Airedale Reef, although likely to be much younger. Back at Airedale Reef this photo shows a good view of  the layer that buried and destroyed the fossil forest. It is known as the Okawa debris avalanche deposit and has been dated at about 100 000 years old. This means the forest was growing during the last interglacial period. Pollen analyses shows a dense podocarp forest, but lacking specifically coastal plants. It seems that when the forest was alive, the coast was further out than its present position. Rimu Pollen  (Dacrydium cupressum) 43 microns across There is a lot of pollen preserved in the Airedale Reef cliff section. Scientists found over 10,000 pollen grains per cm3 in places.They were analysed to study the plant communities from the period of time represented by these layers. Cyathea treefern spore, diameter 30 microns  This allows research into climate variations through time, as different species appear and disappear up through the cliff section from the base to the top. The Rimu and tree fern species in these two images indicate a lush podocarp forest that grew in warm, wet conditions. In the next layer above, the species found represent a sub-alpine shrubland community that grew in a cooler climate. In this photo you can see two pale coloured tephra (volcanic ash) layers near the top of the carbon rich layer, showing periodic eruptive activity from the volcano. In the last image you can see that another carbon rich layer formed in a depression at the top of the Okawa Formation (centre left). Above that the rest of the section is made up of orange and pale brown soils.

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Titahi Bay Geology

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Titahi Bay is a great place to visit if you are interested to see some of the geology near Wellington. There are a number of very interesting features to look at and explore. The first thing to check out is the coastal landforms caused by a combination of the atmosphere and  the sea, as well as the variable resistance of the rock, and a history of earthquakes (uplift). The first image is taken from the Pa site, a few hundred metres north of Titahi Bay beach. If you are a teacher, this is an excellent place to encourage your students to observe some of these natural features, such as sea caves, sea stacks, arches, marine terraces and wave-cut platforms. There is more information about how these features form on coastlines generally on the GNS Science websiteYou can also have a look at this GeoTrips page for specific information if you would like to visit this area. This sea cave marks the line of weakness of a fault. It is no longer at sea level, having been uplifted out of range of the water by earthquakes. It is also a useful way through the rocks between two small embayments. A striking feature of some of the rocks at Titahi Bay is this type of weathering out of the spaces between joints to form distinctive criss cross box structures Having looked at the erosion and weathering features along the coast, the next thing to do is have a look at the structures and the rocks themselves. A good place for this is just south of the Pa site, accessed down a short very steep track from Terrace Road. www.geotrips.org.nz/trip.html?id=69 In this photo you can see that the rocks are made up of alternating bands of massive sandstone, with in-between layers of dark mudstone. These rocks were formed from sands and muds eroded from the margin of Gondwanaland, long before New Zealand existed. The material flowed down into the deep sea and settled over wide areas. The coarser sediment, at the base of each of these submarine landslides, is represented by the sandstone, whilst the mudstone gradually settled on top.After deposition, the sediments were squeezed and deformed by the bulldozing effect of plate collision along the edge of Gondwanaland. You can see how the originally horizontal layers are now  almost vertical at Titahi Bay. Many faults are easy to spot, as they displace the clearly defined rock layers.As well as faults there are also folds in the rocks such as the anticline (upfold) shown here. An interesting challenge is to look for sedimentary features such as graded bedding or cross bedding, in order to tell the direction of younging of the steeply tilted rocks.  In this photo you can see some cross bedding, showing where the rock above my finger cuts across some fine layers that must have been layed down first. If you have time whilst at Titahi Bay, and if the tide is out, you should have a look at the tree stumps of the fossil forest which are sometimes exposed, usually at the south end of the beach. It seems almost unbelievable that these wooden stumps date from a time before the last ice age, about 100 000 years ago. The fossil forest does actually extend right along the beach, but is mostly covered with sand. On rare occasions, about once a decade, storms clear the sand away to expose much more of the forest than you can see here.Look carefully and you can see the growth lines of these ancient tree stumps. Check out the GeoTrip location here: www.geotrips.org.nz/trip.html?id=32https://youtu.be/A2Jed7P-pQ0

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NZ’s First Reptile Discoverer returns to Mangahouanga

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In 1958, Petroleum Geologist Don Haw was mapping the rocks in the Mohaka river catchment of Western Hawkes Bay. The project was part of a wide ranging exercise to evaluate the hydrocarbon potential of the East Coast basin at that time for BP, Shell and Todd.  His discovery of reptile bones in the Cretaceous sediments was recorded on Company maps which subsequently caught the eye of Joan Wiffen in the early seventies. She ventured into the region to take a closer look. Remarkably this led to her eventual unearthing of New Zealand’s first dinosaur fossils, as well as many other new species of exciting Cretaceous reptiles. For her significant effort Joan became known as the “Dinosaur Lady”.  For his essential initial work, Don was awarded the Wellman Prize in 2001. On March 24th 2012, 54 years after his initial explorations,  Don returned to Mangahouanga along with the teachers and school children who were participants of our GNS Science “Dinosaurs and Disasters Geocamp“. This was a historic day as it was his first return to the valley in all that time. In the photo, Don (centre) is with Robyn Adams, one of Joan Wiffen’s long term fossil hunting assistants who still leads trips into the valley. In the following transcript, Don describes his experiences from all that time ago:   “We were mapping outcropping sediments in the Upper Mohaka river tributaries, observing for the first time, what might be there. Nobody had really mapped that steep isolated terrain before. We were keen to find what was present between the greywacke basement rocks and the overlapping Upper Tertiary sandstone section. Perhaps nothing – we just didn’t know – maybe the Upper Tertiary rested directly on basement.   Was there any Cretaceous section exposed?  This was so important to the assessment of the hydrocarbon prospectivity of the region.”   “It was high summer, February 1958 I think, and we were scrambling up this really difficult stream bed, huge boulders, and totally bush covered. We recognised we were stepping on boulders and outcrops of massive concretionary sandstones which we had not seen before. These appeared to be of marine origin, and had fine shell debris in them which was triggering off alert signals to me – There might be other important fossils here!  We should look carefully! I was with field assistant Ken Fink Jensen to whom I owe much for his support and encouragement in those days, Together we began to examine some odd protuberances on the surface of certain boulders, which I quickly recognised, because of their shape and texture, had to be organic and which were almost certainly bone remains from some marine creature.  I think my initial reaction was that they were fish remains. The rock was hard, very hard, and we extracted several and brought them back to Gisborne.“ “They were sent off to Jack Marwick, a retired NZGS chief palaeotologist,  who identified them as reptilean bones. Eventually they were recognised to be Mosasaur fossils, a type of  marine Plesiosaur.  It was a first for New Zealand.”   “This region became the hunting ground of Mrs Joan Wiffen who followed up our fossil discovery, with many years of hard work there, excavating numerous other finds from the same stream bed.  She, with her husband and family team, found many new fossils, some really exciting, including some terrestrial dinosaur remains which must have been washed into those early primeval seas. It has now become one of the most prolific fossil sites in New Zealand.”The final image shows a mosasaur skull that was found by Joan and her team and is now kept at GNS Science in Lower Hutt.

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Cape Kidnappers

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Cape Kidnappers and the Clifton Cliffs make for a spectacular geological site in Hawkes Bay. The cliffs extend for several kilometres southwards from Clifton, on the coast near Hastings. They  are very high and consist of quite loose rocks, so it is important not to go too close where possible. It is also important to start your visit on a falling tide which will give enough time for a return trip without being cut off by high water. At the start, near Clifton, the cliffs are made up of thick river gravels, with thin layers of white pumice (volcanic ash) and occasional dark layers of plant material.  Initially the beds are about 300 000 years old. Because they are dipping gently down to the north, you will pass further and further down the sequence as you walk along the beach to the south.and east. Here you can see the fluted erosion of the unconsolidated gravels caused by rainwater. In this photo, a layer of light coloured volcanic ash separates overlying river gravels from marine mudstones below. Just above the ash is a very thin dark organic layer with plant remains in it. There are many pale coloured ash layers in the sequence. They have been erupted from the Taupo Volcanic Zone in  the Central North Island, at least 150 kms away. The thickness of the layers even at this distance, testifies to the magnitude and violence of these past rhyolitic eruptions. In this photo you can also see how a fault has dislocated the beds by several metres. Further along the beach, towards Black Reef, there is a distinct change in the bedding, seen in this image about half way up the cliff. The lower gently dipping beds have been eroded flat with much younger beds deposited on top of them. This unconformity represents a time gap of about two and a half million years. The lower unit is three and a half million years old – the upper one starts at about 1 million. An exciting find on our visit was this fossil whalebone. It extended through the boulder for about one metre. Out on the reef itself were some well preserved shell fossils as well as another orange coloured whalebone fossil slowly being eroded away. Last but not least I should mention the gannets, for which Cape Kidnappers is most famous. The young birds here will take their first flight soon, and without looking back or touching down will travel all the way to Australia. Cape Kidnappers features on our GeoTrips website where you can also find lots of other locations to explore geology and landforms: www.geotrips.org.nz/trip.html?id=182

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Waipatiki Beach

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Waipatiki Beach north of Napier is a great place for family holidays in the summer.  It is enclosed by cliffs at either end that happen to provide one of Hawkes Bay’s many classic geological sites. (for more geological and access information see also www.geotrips.org.nz/trip.html?id=24) A track leading south of the beach takes you to a good view of the cliffs. (Update: there have been very big big rockfalls in this area and it is likely to be safer to explore the north end of the  beach.) You can see several colour changes in the rock strata from the base of the cliff to the top. These are due to the fact that the water depth in which the rocks were laid down changed through time. The blue grey band in the middle of the cliff is fine grained mud with a few oyster fossils, that was deposited offshore in about 50 to 80 metres of water depth.The more orange coloured rocks were laid down in shallower water, with beach sand and many fossils. Because of erosion and rock falls, there are many boulders rich in fossils that have fallen down onto the beach below. This is where you can find lots of interesting specimens. In this photo, Richard Levy, a sedimentologist from GNS Science is looking at a slab full of bivalves and sand dollars. This is reminiscent of many modern New Zealand beach environments such as along the Kapiti Coast north of Wellington.  At the top of these orange beds the fossils have been washed around and damaged by wave action, indicating a very shallow environment of deposition.  A close look will show that the fossils here include very few actual shells. This is because many sea shells are made of aragonite, a form of calcium carbonate that differs in its structure from the other common alternative which is calcite. Aragonite tends to dissolve relatively easily during the rock forming process, and to re-precipitate as calcite in the matrix of the sediment. This makes these rocks very hard, but with many gaps where shells have disappeared, leaving only the internal casts. In this photo you can see some trace fossils made by some sea animals burrowing into the sediment about two million years ago.     So why do the rocks show this change from the grey muds, deposited in relatively deep water, to progressively shallower sandstone and limestone?  Either the land was going up or the sea level was going down, or perhaps both were happening at the same time. The rocks around Hawkes Bay and other parts of New Zealand show clearly that the main cause was sea level change, which in turn was due to global ice age cycles which themselves were driven by changes in the earth’s orbit around the sun (called Milankovitch Cycles). So if you ever go to Waipatiki for a holiday, you may like to look for some fossils and consider the relationship between Astronomy and the colours of the cliff.

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GNS Science School Glacier Expedition – Fox Glacier

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This is our last glacier day of the trip. We visited the terminal face of the Fox Glacier, where we again made a short GPS survey, keeping about 10 metres in front of the ice. A large part of the ice front is high and unstable, making it a very hazardous to go near. Following our brief visit we headed North and home, and that was the end of our real life geology and glaciology adventure. Here is our video of the expedition:

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School Glacier Expedition – Franz Josef Glacier

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We packed early, walked down to the road and drove up to Franz Josef for a look at the lower part of the glacier. Brian had two 4 metre ablation stakes which needed to be redrilled and inserted deeper in the ice. We also wanted to record the position of the terminus with the GPS. The glacier is spectacular at any time. Walking towards it we had to negotiate a boulder field of flood debris. The true left of the glacier is covered with rock. This was from a time when dammed up water within the lake had burst out in a spectacular flood, spreading the debris all over the surface. Because of the debris cover, this part of the glacier has been protected from melting and has remained more or less static for a number of years whereas the true right of the glacier which has no rock cover, is retreating quite rapidly Jake is using a hand drill to make a hole for inserting an ablation stake on Franz Josef Glacier

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School Glacier Expedition- Brewster Glacier continued…

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Yesterday was a bad weather day which we spent mainly in the hut. Brian Anderson joined us in the evening. He is a glaciologist at the Antarctic Research Centre at Victoria University Wellington and has been studying the Brewster Glacier for several years. This morning we hiked across to the glacier again. While Brian went to check the stream gauge, I took the students along the front of the glacier with a GPS to mark its position. We kept a few metres of clearance from the ice as there were places where large blocks had fallen quite recently. Then we all roped up and walked the length of the glacier to look for the highest ablation stakes in the network. A couple were missing, but number 18 – right at the top, was there, melted out by 5.2 metres, a record for this altitude. On the way down we gathered as many stakes as we could. They will be redeployed again in the spring. It was fun trying to negotiate our way around the crevasses. By 6pm we were again off the ice.

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