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Flight over Tongariro and Ruapehu

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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

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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

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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

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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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Tama Lakes

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Last weekend I went to camp and tramp in the Tama Lakes area on the saddle between Ruapehu and Ngauruhoe. These lakes were created by several explosion craters within the last ten thousand years  giving them a circular or crescent form. The landscape is covered with blocks of lava and scoria as well as some fine ash  remaining from Ruapehu’s 1995 – 1996 eruptions. There are also some layers of pumice from the huge Taupo eruption about 1800 years ago. This photo shows some charcoal fragments – remains of some of the vegetation that was scorched during the most violent eruption on earth in the last 5000 years. The lower Tama lake is being slowly filled up by a river bringing in eroded ash and other volcanic debris from the surrounding area. You can see this delta on the far side of the lake in the image. Beyond it is a similar adjacent (sediment filled) crater of about the same size. The water is very clean and drinkable, and yes – it really was that blue! I set up my tent in a little hollow, sheltered from the wind and on a nice flat spot. The view north from my campsite shows the Upper Tama lake and the south face of Ngauruhoe, my planned hike for the next day.

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A dynamic landscape in Hawkes Bay

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Last week I was in Hawkes Bay with geologist Kyle Bland, who led a field trip for teachers, students and parents of Crownthorpe School. Hawkes Bay geology is a story of uplift along fault lines, combined with rapid erosion and deposition by rivers flowing from the inland mountain ranges. This story is etched into the geomorphology of the landscape. The Mohaka fault last ruptured between AD 1600 and 1850, and forms an amazingly straight scar across the landscape. Like many faults in New Zealand, it is an oblique strike slip fault, including both sideways and vertical movement.  If you click on the image to enlarge it you can see how streams crossing the fault have been offset by sideways movement from the last rupture. Combined sedimentation, uplift and erosion have produced stepped terraces alongside the Ngaruroro river flowing from the Ruahine range out towards the coast. There are many fossils to be found in the sedimentary rocks that have been uplifted and exposed. Fossil hunting Hawkes Bay style involves using a digger to get access to your specimens! Ancient greywacke sediments are exposed in the Ruahine Range, having been uplifted by tectonic movements of the North Island fault system (Mohaka and Ruahine faults). These rocks were deposited in a trough at the edge of Gondwanaland, long before New Zealand ever existed. In the video below, Kyle gives us a Hawkes Bay case study of landscape evolution.

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Fossil Whale

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Last week I visited Palliser Bay in the Wairarapa. Along the coastline there are many exposures of mudstone from the Hurupi Formation, about 11 to 8 million years old. These mudstones contain abundant marine shell fossils, but are also known for occasional whale bones.  After some time searching, as luck would have it, I found a large piece of bone sticking out of the mud near the base of one of the cliffs. The bone was embedded in soft sediment and was easy to remove with a bit of digging. Nearby I found two other large pieces. Back at GNS, Craig Jones identified them as fragments of mandible (jawbone) from a large baleen whale species. Two of the pieces matched together to give a combined length of 75 cms. Initially we thought that these are part of the left mandible, whilst the other single piece is part of the right mandible.    John Simes is the manager of the fossil collection at GNS Science. He  helped me to give them an initial clean to remove some of the mud that coated the bones. Here you can see the typical mottled texture and brown colour of fossil bone. This is the largest  piece, half a metre long and about 25 cms across. There is an epifauna of bivalve and barnacle fossils attached to the bones. This tells us that they would have been lying in calm, relatively shallow water before they were buried by sediment. There are also several wood fragments in the surrounding clay, which suggests that the whale died not far from land. After many hours of cleaning, some interesting grooves appeared in the bones. These show where blood vessels were embedded alongside the bone. For an update on additional whale bone discoveries from this locality check out this blog post.

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Artificial Earthquakes on an Active Volcano

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GNS Science volcanologists recently set up an experiment to test the seismic velocity of the rocks that make up White Island. Over the last few decades it has been New Zealand’s most active volcano and has produced minor eruptions in recent weeks. (For its present activity status click here.) Velocities of seismic waves through the Earth can vary considerably because of variations in the density and layout of different rock types. It is important for scientists to know these subsurface seismic velocities as they are used to calculate the locations of earthquakes under the volcano. These might indicate rising magma and therefore an impending eruption. It is for this reason that volcanic earthquakes are carefully monitored. For an explanation of how earthquakes can be located see this video, and for a look at White Island’s activity status, including the seismic drum, click here. There are various ways to generate seismic waves in order to measure velocities, such as by using explosives or air guns. These traditional methods can have environmental, safety or cost drawbacks. So in this case, a GNS Science team, led by volcano seismologist Art Jolly, used a novel method: First of all, The team set up 17 temporary seismometers around White Island, with six of those set up in a line across the volcano crater floor to record the shock waves, their travel times (hence velocity) and their intensities. Three large sacks were then filled up with about 700 kgs each of  beach sand… …whilst some of the team laid out large white crosses, held down by rocks or gravel to indicate the target zones for two of the drops. (The third target was the centre of the crater lake). A helicopter was then used to drop the bags of sand from about 400m onto the three target areas. The impacts when they hit the ground (or water) created the seismic waves required. They were also heard from a safe distance as  a very loud thwack!   The last image shows the seismic wave traces produced by the three impacts as recorded by the nearest seismometer to each impact. The drops were successfully recorded on the temporary stations giving scientists a new velocity model for White Island earthquake locations. Future tests might include heavier weights, greater drop heights and different seismometer locations to add more depth and breadth to the velocity model. (All images GNS Science)

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Filming on Ruapehu

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Last week I spent some time on Ruapehu with Bruno Cedat, a french documentary maker who is making a film about the geology and landscapes of New Zealand in collaboration with GNS Science. During the making of his film he has participated in challenging outdoor adventures such as climbing, caving and kayaking in a variety of wild places across New Zealand, Here he is climbing the Pinnacles next to Whakapapa ski field. We also tramped up the mountain to the summit plateau, with great views across to Ngauruhoe volcano further north. In this next picture you can see Bruno approaching the Dome, along the edge of the summit plateau.   The Dome Shelter was covered in rime ice. Inside the shelter there is a seismometer that is used to monitor volcanic earthquakes. Here is the GeoTrip page for you to climb up to the Dome: www.geotrips.org.nz/trip.html?id=646 Here is a view of the crater lake, surrounded by a winter blanket of snow. It is currently at Alert Level 1 as you can see on the GeoNet website. For  lots more information on Ruapehu have a look at our website here Here is a preview of Bruno’s Film: New Zealand, Land of Adventure:

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Whakataki

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Whakataki is a spectacular spot on the Wairarapa coast just north of Castlepoint. It features as one of the localities on our GeoTrips websiteThe shoreline is a large area of tilted rock strata that have been eroded into a broad, flat platform extending for hundreds of metres along the coast.  The rock layers are alternating sandstone and mudstone layers that stand out as distinct lines. It is believed that they formed as cyclically repeated turbulent flows of sand and mud that avalanched down and over the sides of an underwater channel about 500 to 1000 metres below the ocean surface. These sorts of deposits are know as turbidites. Here they are of early Miocene age (roughly 20 million years old) As the sediment laden water surged across the sea floor it laid down a deposit of sand and mud with several distinct layers. The base layer typically has very flat laminations, followed by a more convoluted and rippled layer above it. Above that the particles get finer as the remaining cloud of mud slowly settled on top of the coarser sandy layers below. It is interesting to look at the different structures and imagine how they formed in the dark depths of the sea so long ago. Here I am pointing at some climbing ripples in the upper sandstone layer, above a more regularly laminated base layer of the flow. They show that the current was moving from the left (south). Exploring the area shows up many interesting geological features. Here you can see that the beds are not only tilted up, but they have been dislocated by faults.   In this image you can see joints cutting across the beds at a right angle. They develop as the pressure on the sequence decreases due to erosion of overlying material. You can see how the spacing between the joints is wider for the thicker beds, and closer together on the thinner ones.   The rock layers are of interest to geologists because similar thin bedded fine grained deep sea sediments are often found to be important reservoirs for hydrocarbons which penetrate into the tiny pore spaces between the individual grains of sand.  By studying these beds where they are exposed at ground level, we can gain important information about similar but more inaccessible  sequences deep below the surface that may actually contain trapped oil or gas. During our visit, Garth Archibald was making a laser scan of the surface of the shore platform. This will be translated into a 3 dimensional computer image of the platform which can then be used for detailed analysis of the different layers in the sequence. Garth has used his laser scanner in a wide variety of settings, including a number of Christchurch cliffs that were seriously shattered by recent earthquakes, as you can see in this video.

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