Airedale Reef

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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Tongariro North Crater

Earlier this week I decided to spend the night camping up on the North Crater of Tongariro. This is the large flat crater that is off to the north and west of the main track of the Tongariro Crossing. For access information have a look at the GeoTrip page here: www.geotrips.org.nz/trip.html?id=279Here is a view across to it from near to the Red Crater: The crater is about 1 km across, and is believed to have once been a lava lake several thousand years ago. In the distance you can see the crater rim to the right of the cone of Ngauruhoe. The surface of the ground is uniformly covered with scattered blocks of lava. This windswept area feels isolated and rarely visited, even though it is so near to the Tongariro Crossing track. There is a spectacular explosion crater within the North Crater itself, over 300 metres across and about 50 or more metres deep. It has broken through and partly obliterated the surface of the solidified lava lake. A low angle valley cutting across the main crater represents the line of a fault. Debris from the explosion crater to the left of the image has partly filled the valley. This photo taken by Lloyd Homer in 1984 shows two more faults (dark lines) crossing the slopes on the western flank of Tongariro. They are normal faults, indicating extension of the crust that is associated with the volcanism in the North Island. They have been active since the Taupo eruption 1800 years ago The Tongariro Crossing passes just below and east of North Crater. There is a barrier prohibiting closer access to the Te Maari Crater / Ketetahi area  . This is the 2 km exclusion zone due to continued volcanic eruption hazard. From the edge of North Crater, there is a view down to Ketetahi Hut and across to Upper Te Maari. It is sobering to think that the hut was damaged by large flying rocks erupted from Te Maari about 2 km away during the August eruption. If you click on the image to enlarge it you can see the hut near the left side of the photo. This was the view at sunrise, looking down on to the steam plume coming from Upper Te Maari.Crater.

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Fossil Favourites from GNS Scientists

GNS Science recently produced a new “Photographic Guide to Fossils of New Zealand”. It is a small, pocket sized booklet, packed with photos and information about many of our characteristic fossils. It also contains a very readable introduction to New Zealand geology, the fossilisation process and the geological history of New Zealand. You can find more information about the book, including how to get hold of a copy; here. It is published by New Holland Publishers. Here is the team that created the guide, from left to right: James Crampton, Marianna Terezow, Alan Beu, Liz Kennedy and Hamish Campbell. I asked each of them to choose their favourite image from the book and say a few words about it. Here are their comments: James Crampton: Cretaceous ammonite, scalebar is 1cm My favourite fossil is the small Cretaceous ammonite on the bottom of page 62.  Ammonites are very rare in New Zealand Cretaceous rocks, although they are extremely common in other parts of the world.  This one came from the coastline of Raukumara Peninsula, north of Gisborne, from a lovely, wind-swept, wild, and pohutakawa-lined rocky shore.  This specimen is well preserved and shows how some species deviated from the typical, simple, flat spiral shell form of most ammonites – in this case, as the animal grew, the shell became partially uncoiled to end up looking like a hook.  In life, the animal had many tentacles and extended out of an opening in the shell at the point where the label is fixed (this opening is now filled with rock).  This ammonite was found with many fossils of strange clams that were specialised to live on deep-sea seeps – places where methane was naturally bubbling out of the sea-floor during the Cretaceous Period.  These clams probably ate bacteria that, in turn, survived by using chemical reactions to ‘feed’ on the methane. Fossil shells from Hakateramea, New Zealand Marianna Terezow My favourite photo is the one that resides on the title page. It’s an image of a late Oligocene-Miocene limestone block from Hakateramea, South Canterbury. I love this photograph because it showcases some of the great variety of marine life-forms found throughout New Zealand’s fossil record. From small filter-feeders like the clam Limopsis to the large, carnivorous snails such as Magnatica, this image is a snap-shot of a once-living, thriving marine community. I find these life stories of community dynamics that fossils tell us very fascinating. Struthiolaria frazeri – scalebar is 1cm Alan Beu My favourite image is Struthiolaria frazeri, on page 122. This is the largest, most spectacular and most elaborately sculptured of the “ostrich foot shells”, family Struthiolariidae, which are almost entirely limited to New Zealand, and are one of the really characteristic elements of our fauna. They display a long, complicated history of evolution and extinction, with more than 35 species occurring as fossils over more than 40 million years, and yet only two species still live here now – Struthiolaria papulosa (top of p. 123) and Pelicaria vermis (p. 123, lower on the page). Struthiolaria frazeri provides a clear example of extinction, as it is a key fossil for identifying the end of the Nukumaruan Stage, becoming extinct suddenly 1.6 million years ago, at a cooling spell.  Presumably it was a warm-water species, as it is mainly found in shallow-water rocks in central and northern Hawke’s Bay, with a few specimens found near Whanganui. The very obvious sculpture of prominent, square-section spiral ribs, the tall spire, and the short, oval aperture with thick, smooth lips and a deep sinus in the top of the outer lip make it easy to identify. Cretaceous broadleaf – scalebar is 5cm Liz Kennedy My favourite image is of an undescribed Cretaceous broadleaf angiosperm leaf base and podocarp foliage on page 54. These beautiful leaf impressions, along with many other leaf specimens, came from very hard grey sandstone overlying a thick coal seam which was mined at the Strongman Mine opencast near Greymouth. They are a glimpse of the vegetation which made up New Zealand’s Late Cretaceous forests which were very different to those of today, a time when dinosaurs still wandered about, perhaps even eating this kind of angiosperm leaf. These leaf impressions are generally well-preserved, with the ridges of prominent veins providing texture to the impressions. An assemblage of leaves such as these can provide us with a fascinating picture of the past including what kinds of plants covered the Late Cretaceous New Zealand landscape, how diverse the vegetation was and what the climate was like when the plants were growing. Historic fossil locality in the Chatham Islands Hamish Campbell: “My favourite image is on p.25. It captures not only fossils but also a ‘fossil moment’. After all, photographs are fossils of a kind…preserving a record of things that happened long ago. This beach on the north coast of Chatham Island is famous because this locality, with fossil oysters that are 50 to 55 million years old, is the very first fossil locality to be formally recorded in the scientific literature from New Zealand. It was collected by Ernst Dieffenbach in 1839 and he sent the fossils to the Natural History Museum in London. Oddly enough, this locality was ‘lost’ for more than a century because it was buried beneath a sand dune. It was only rediscovered by us paleontologists at the time of this photograph in 1995.”

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Fossil Whale Hunting

Last weekend I returned  to our fossil whale locality in Palliser Bay with John Simes, the paleontology collections manager at GNS Science. This is where I had found three large jaw bone fragments of a fossil baleen whale last November. We decided to have a good look through some of the loose debris in the area where I had already made some finds.After some time. John spotted another large piece of mandible, very similar to the ones that we had from the previous visit. I decided to try the direct route up the cliff, to get closer to the source of the bones. The ice axe proved to be quite useful for making progress up   the very crumbly mudstone. This got me about half way up the gully, to a point that I had reached last time and where I had found one of the three original bones. On this first re-inspection I didn’t come up with any more fossils. The next plan was to abseil down into the gully from the top, in order to have a very close look at the steep headwall which seems to be the actual source of the fossil whale. I had to take care not to dislodge any large rocks with the rope. Unfortunately this inspection of the cliff didn’t reveal anything even with careful scrutiny. Back in the bed of the gully, I dug around with my ice axe some more and did at last come up with three smaller pieces of bone. Here you can see one of them – we think it is the end of a jaw bone, although it is much thinner than the other pieces. Back in the macropaleontology lab at GNS Science, the thin layer of mudstone coating the bones was quite easily cleaned away with the help of a pneumatic air scribe. The 30 cm long piece shown here turns out to fit perfectly with the previously found  segments of the mandible, giving us a combined total length of 1.5 metres for it. The missing link puts it all together. The latest piece in the puzzle is second from right. The rest were found on the previous trip. Here are the smaller pieces after a bit of cleaning. It is tantalising to think that there must be a lot more of them waiting to be discovered in the mudstone of Palliser Bay.

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Titahi Bay Geology

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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Volcano Gas Flights Video

If you had to work out the daily quantities of different gases coming out of a volcano and spreading across the sky in a huge, mostly invisible plume, where would you begin? This video gives a brief introduction to how New Zealand’s GeoNet scientists go about it: The information is combined with other evidence such as seismic monitoring to judge the risk of future volcanic eruptions.

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Flight over Tongariro and Ruapehu

My next experience of a GeoNet gas monitoring flight was over Tongariro and Ruapehu. This time Karen Britten and I were joined by Fiona Atkinson (left in photo) who is part of the GeoNet volcano monitoring team. As we approached the volcanoes from over Lake Taupo, the small gas plume from Te Maari was visible. Because the plume is quite low against the mountain side, GeoNet cannot always monitor it by plane. They sometimes use a road vehicle instead, traversing under the plume along a nearby road.Our flight took us past the Red Crater (left) and the Emerald Lakes, where I had been tramping a few days before. North Crater on the right skyline is a solidified lava lake, whilst the dark lava flow in the middle distance on the right originated out of Red Crater. We circled Ngauruhoe several times just in case there was some evidence of gas emission, although non could be determined. If you click on the photo to enlarge it you can just see some people on the left hand side of the inner crater rim. The crater lake of Ruapehu was a uniform pale blue colour, with no visible upwellings. Our gas measurements showed about 670 tonnes per day of CO2 , a little H2S (0.5 t/day) and about 28 tonnes per day of SO2. These figures are in a similar range to those from the end of January, but somewhat elevated compared to December. On the way back we decided to take a closer look at the Upper Te Maari crater area. There is still a lot of grey ash covering the area from the November 21st eruption, and yellow sulphur deposits around the fumeroles. Having landed back in Taupo, I drove down to Whakapapa Village, and was able to look at the Te Maari area from the road on the way. The area affected by ash can be seen extending across the mountain side.I decided that I just had time at the end of the day to walk up Te Heuheu peak on Ruapehu. It is on  the north edge of the summit plateau.  The crater lake is just beyond the sunlit snow in the centre of the photo, out of sight behind the ridgeIn case you haven’t seen in yet, here is a video of the Te Maari eruption made from the webcam shots on November 21st:

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White Island Gas Flight

Yesterday I joined Karen Britten on  a GeoNet gas monitoring flight over White Island. This was to check the flux of volcanic gas emissions following an ash eruption a few days ago.Check this GeoTrip page if you are interested to visit White Island / Whakaari yourself: www.geotrips.org.nz/trip.html?id=541 ) The plane is modified to allow the equipment to extend outside so that the measurements can be made. carbon dioxide (CO2), hydrogen sulphide (H2S) and sulphur dioxide (SO2) are the most common volcanic gases and are all measured during a gas flight. Approaching White Island, we could see the plume extending first vertically, then off to the West at an altitude of about 2 000 feet. In the distance you can see a grey haze in the sky which is the extension of the plume. Our first task was to fly in circles at constant (neutral) throttle. Through using our GPS to measure our ground speed, we could calculate the effect of the wind on the plane, and thus work out the wind direction and velocity. The track of the plane is visible on the computer screen. Next we flew under the plume at right angles to the wind direction and at the lowest permissible altitude of 200 feet. A Correlation Spectrometer (COSPEC) looks upwards through the plume and measures the amount of ultra violet light being absorbed by the sulphur dioxide. We passed under the plume several times in order to get an average reading. The wind speed is also taken into account to calculate the SO2 flux with this method. Next we flew in wide arcs through the plume, at a radius of about 3 kilometres from the crater. We worked our way contouring back and forth, rising 200 feet each time to get a total profile of the gases through the whole plume. Later in the day Karen was able to process the data to show that the daily flux of SO2 was about 600 tonnes. This is at a relatively elevated level compared to mid January, but has not changed much in the last month. Here are the complete data that Karen processed after the flight, comparing them also to the two previous gas flights: Lastly we flew close to the main crater to get a look at the changes that had occurred in recent days. Most of the gas emission was coming from a small crater or tuff cone, and there seemed to be an area of red brown which is probably ash from the recent eruption. Back in Taupo after a total flight time of about 4 hours, I had this evening view across the lake to Tongariro. The Te Maari crater was producing a thin plume of its own extending across the sunset.

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Saddle Cone

On my way back to civilisation from Tama Lakes, I decided to take a detour to visit Saddle Cone, ( GeoTrip page here: www.geotrips.org.nz/trip.html?id=53 ) a small isolated crater on the northern slopes of Ruapehu. You can see the tilted rim of the cone in the centre of the photo: The second image is looking into the crater of Saddle Cone, which is about 100 metres across.In spite of its small dimensions, Saddle Cone produced a huge lava field that spreads out over an area of several square kilometres. These lava flows are visible in the distance. On the right side of this photo you can see a moraine ridge, showing that this valley was glaciated until about 10 000 years ago. This provides a maximum age for these lava flows, and many others in Tongariro National Park’s glaciated valleys. Hot arid summers, and freezing blizzards in winter are not too much for hardy alpine plants such as these: After several hours of wandering the semi-desert of the Tama Saddle, I descended to a river less than an hour from the road – a perfect oasis to end my hike on the mountain.

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Ngauruhoe’s Far Side

Climbing Ngauruhoe from the South is well off the tourist route, and involves scrambling up unstable blocks of lava for about 700 vertical metres up the face of the cone. I chose to go up more or less up the centre of the view you can see here, and it took me about an hour and a half of steady plodding to the top. The crater of Ngauruhoe was last erupting from 1973 to 1975, during which time it occasionally threw out blocks of lava to a distance of about 3 kilometres. If you click on the image to enlarge it you will see people on the crater rim that give an idea of the scale of the image. Ngauruhoe’s crater rim provides what to me is one of New Zealand’s finest landscape views. On the far left is Tongariro peak, then the flat top of North Crater and the Blue Lake (with steam from Te Maari just behind it). Just below the Blue Lake is the top of Red Crater and on the right side are old lava flows in the Oturere Valley. The Tongariro crossing track passes through South Crater as a white line in the centre of the photo. Descending the northern slope of Ngauruhoe, I then climbed a rocky ridge up to Tongariro peak, seen running from the centre to the right side of this photo: Next on my route was Red Crater, followed by a swift run down grey coloured soft scree just visible on the right of the photo. This took me into the Oturere Valley from where I turned back in the direction of my campsite. In the area to the east of Ngauruhoe I cut across country around the base of the volcano. This is a relatively rarely explored area. It took me a few more hours tramping across a variety of moraine ridges and blocky lava flows to reach my tent after a very satisfying day.

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