Landform

Oparara Limestone Arches

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On a recent trip up to Karamea on the west coast of the South Island, I went to visit the Oparara Caves. These are a few kilometers inland, and not far from the end of the Heaphy Track. They are an amazing example of limestone erosion… Huge archways have been cut through the limestone by the Oparara River. The limestone was laid down in the ocean during the Oligocene Epoch, about 34 million years ago. The third photo shows the largest of the arches (the Oparara Arch). You can see the clear boundary between the limestone and the underlying Karamea Granite. This is about 350 million years old, much older than the limestone. The arch is an impressive 200 metres long and 50 metres across. There are several accessible caves in the area. The unique geology and ecology is a ‘must see’ if you ever make the trip to Karamea.

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Caves and Moa Bones

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Takaka limestone landscape On a recent trip up Takaka Hill near Nelson, I went exploring over the limestone landscape with my daughter Sophie (with permission from the landowner). The area is riddled with sink holes and caves. The most well known is Harwood’s Hole – a huge vertical shaft about 50 metres across and over 180 metres deep. However most of them are much smaller – many only a few metres deep and blocked with debris. Moa Trap – the cave entrance In this second picture you can see a typical example. A small cave entrance half concealed by vegetation. Inside it, a few metres from the surface and half buried in the clay floor Sophie discovered a moa bone . With a bit of digging we eventually uncovered a variety of bones from several individual skeletons. They were jumbled up with blocks of rockfall debris and many of them were covered in a thick layer of white cave deposit (calcite). This showed that they were likely to be pre – ice age (at least 70 thousand years old) as it takes a long time for the bones to become coated in this way. Finding a moa bone There were once atleast 9 species of moa in New Zealand, although only two of them were common on Takaka Hill. The limestone pot holes were a death trap for many that fell in and were unable to escape. The bone that Sophie is holding in the picture is a lower leg bone (metatarsus). If you would like to see the bones, they are now resident in Ngarua Cave. This is a very worthwhile show cave that has beautiful formations as well as other Moa remains found previously. I can definately recommend a visit if you are passing over the hill some time!

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White Island 2

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See the video of our visit to White Island: Here’s a bit more about what we did during our day on there: Karen and Agnes set off with their water monitoring equipment, whilst Brad, Steve and I started the elevation survey, measuring height differences between an extended series of fixed points that had been marked by wooden stakes driven into the ground. Whilst Steve held the survey pole, Brad aimed his leveler at it from an adjacent measurement station and was able to read off the height difference between the two points. By sighting between the points in this way, we continued our survey past some very loud and active fumaroles, in a broad area towards the crater lake. Occasionally we stopped to take photographs of interesting features, or discuss the history of the formations around us. Once or twice we were enveloped in steam and gas from the fumaroles, and rained on by acidic water droplets (acid rain) that gave a burning, prickling sensation to my eyes. Past measurements have shown that the ground near the crater has been rising by two or three centimeters every three months for several years, mainly due to an increase in heat in the ground. From our measurements we found that the hottest area of ground near the most active fumaroles had risen up to a maximum of 50mm since the last survey, with the amount of uplift reducing quickly a short distance away. These results show continuity with the long term trend of uplift. Almost towards the end of the survey, we met up with Karen and Agnes, and I watched them sampling the water from a very active hydrothermal spring that was gushing and splashing nearby. To make a variety of measurements of the water chemistry and isotopes, they scooped water out of the spring and put it into various sampling bottles. Once our survey was done, Brad and I walked over to the lower of two webcams to give the glass a wipe, as the photos had been getting quite fuzzy due to a build up of dust. There in front of the camera was ‘Dino’ in real life. He is a small dinosaur, apparently famous the world over for having arrived mysteriously to take up residence in full view of White Island’s Crater Webcam some years ago: see http://www.geonet.org.nz/volcano/activity/white-island/cameras/whiteisland-latest.html Before we returned to the helicopter, we walked through the ruins of the old sulphur mine, where there were rusted machines and derelict buildings. Finally we were ready to leave and as we turned in a wide loop above White Island, I was very impressed to have been able to have had such a close encounter with such a remarkable place.

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