Volcanoes

Volcano City

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Mangere Mountain, L. Homer / GNS Science Volcanic cones, explosion craters and lava flows form much of Auckland’s natural topography. All of these, apart from one (Rangitoto Island) are from vents that erupted once only (monogenetic), with eruptions lasting a few weeks or months and then ceasing completely.  There are many accessible and beautiful locations that can be visited to uncover the geological history of the area. Auckland volcanoes, GNS Science Although there are about 50 volcanoes within a 20km radius of the city, there is a similar eruption process that generated them, with three main possible styles of eruption. Knowing the difference between these eruption styles allows you to interpret the different features and rock types of each of the volcanoes that you might wish to explore. The magma that erupts in the Auckland Volcanic Field (AVF) is generated in a ‘hotspot’ about 80 to 100 kilometres below the surface. It is a very fluid type of basalt that is known to rise quickly to the surface (at up to 5km / hour) from the magma source. Tuff outcrop at North Head, J..Thomson / GNS Science Once at the surface, the style of eruption depends largely on the amount of groundwater or sea water present. If there is a lot of water near the vent, its interaction with the hot magma (1000 plus deg C) causes it to instantly vaporise.  This, along with the expansion of gases within the lava itself, creates extremely violent eruptions that fragment the lava into small particles and blasts them upwards and sideways from a wide, flat explosion crater. This becomes surrounded by a ring of ash. Such deposits are known as tuff (pronounced ‘toof’ as in ‘woof’). You can see outcrops of this in Auckland, for example around the shoreline at North Head. Each individual layer represents an explosion from the vent. Surtsey eruption, courtesy NOAA This type of eruption is known as a phreatomagmatic or wet eruption, and a classic example occurred off the coast of Iceland from 1963-67 when the island of Surtsey was born. Mount Eden Crater, J.Thomson / GNS Science Scoria outcrop, Mount Wellington, J.Thomson / GNS If the magma reaches the surface where there is little interaction with water there is a different type of eruption. This includes eruptions in areas of dry land, as well as those that start off as wet eruptions, but where the water supply near the vent gets used up before the supply of erupting magma runs out. The magma then erupts in a fountain of lava, driven up by gases within it that are expanding as the pressure is reduced.The lava fountains might be several hundreds of metres high, with blobs of lava partially solidifying in mid-flight, and landing as scoria in a ring around the vent. This is a bit like the froth coming out of a soda bottle once the lid has been removed.  The scoria pieces and lava bombs are relatively sticky and can build the steep sided cones that are very recognisable in the Auckland landscape. The reddish colour comes from the oxidation of iron in the magma as it cools during its flight through the air. Lava bomb approx 1/2 m in length, Mangere Mountain  If you look at the rock that makes up these cones, you will see that it is made of bombs and fragments that may be partially glued together or more or less loose and rubbly. Takapuna lava flow, J.Thomson / GNS Science If one of these eruptions gets to the stage where the gas has mostly been expelled, then there is less energy available and the fire-fountaining stage ends. Should the eruption continue (which is not always the case) then the third eruption style starts to dominate. Lava pours out of the vent and pushes through the sides of the scoria cone to spread out around the volcano. Because it is such a fluid type of lava, a  variety of flow structures are preserved when it finally solidifies. Lava tree mould with bark impression, J.Thomson / GNS A great example of such a lava flow can be found along Takapuna Beach. About 200,000 years ago lava poured out of the nearby Pupuki crater and flowed through a forest. The tree trunks and branches were surrounded by the lava which cooled around them. The trees then burnt, leaving tree shaped holes within the lava. Takapuna Fossil Forest and Rangitoto, J.Thomson / GNS For more information about where to go in Auckland to see some of these geological localities, have a look at our new online map of geological locations atwww.geotrips.org.nz Could a volcanic eruption occur in Auckland in the future? What are the probabilities in the short to medium term and what would the impacts be? The short answer to the first question is ‘Yes,  definitely!’ There is no reason to think that eruptions won’t occur again. In order to answer the last two questions (‘When?’ and ‘What?’) it is important to get as clear a picture as possible of the history of past events, their timing, duration and magnitude, and their geographic relationship to the housing and infrastructure in the wider Auckland area. Auckland Museum Volcanic Eruption Auckland City and Mount Victoria, J.Thomson / GNS These questions are the focus of a long term scientific programme called DEVORA (Determining  Volcanic Risk in Auckland). DEVORA is led by GNS Science and the University of Auckland, and is core-funded by the EQC and Auckland Council. The first part of this programme has been to further our knowledge of the eruption history of the Auckland Volcanic Field volcanoes. What this work has shown is that there is no simple pattern that we can project to help easily forecast the likelihood of eruptions in the future. The timeline of eruptions shows them to be clustered, with large gaps between phases of relatively high activity.  Graham Leonard, photo by Brad Scott / GNS Graham Leonard of GNS Science is a co-leader of the project. He comments

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Lahars on Ruapehu

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Ruapehu Eruption, Image: Lloyd Homer@GNS Science Ruapehu is very popular with skiers, trampers and other adventurers. As an active volcano with the potential for sudden eruptions through its crater lake, Ruapehu presents the Department of Conservation with a significant hazard management issue. Lahars on Ruapehu: Image: Lloyd Homer@GNS Science Obviously there is the possibility of people in the vicinity of the summit area being immediately affected by water, rocks and ash thrown out by an eruption. An additional hazard is that displaced water and sediment from the crater lake can mix with snow and loose volcanic material to create fast moving mudflows (lahars) which descend rapidly down valleys radiating away from the summit. The collapse of the crater wall can also cause a lahar to flow down the Whangaehu Valley to the east of Ruapehu, independently of an eruption. It was this type of lahar that caused the railway tragedy at Tangiwai in 1953. This video explains the basics of lahars at Ruapehu and the two ways they can be created: Image Graham Leonard@GNS Science Not surprisingly, due to the high number of mountain users, the lahar hazard has been studied in detail and measures put in place to give warnings and reduce the potential impact on people and infrastructure. This has involved a close collaboration between GNS Science (GeoNet), the Department of Conservation and Ruapehu Alpine Lifts who run the ski areas. First of all, regular monitoring of the crater lake’s physical and chemical properties is carried out by GNS volcanologists as part of the GeoNet project. This alerts them to changes of activity within the volcano: This information helps the GeoNet team to set the volcanic alert level for the mountain, which is important for a number of agencies such as the air industry, Regional Councils, local businesses and others. Because of the potential for some eruptions to occur with little or no warning, and the speed with which lahars travel down the slopes, there is also an Eruption Detection System (EDS) in place. This is triggered when both ground-shaking (seismic waves) and an air blast are detected within a short time of each other at a number of monitoring stations throughout the Tongariro National Park. This image shows the arrivals of volcanic earthquake tremors (top) and the air blast (bottom) of an eruption, at a station about 9 kilometres from the crater lake: You can see that there is a time lag of about 30 seconds between the onset of groundshaking and the arrival of the air blast at the same station. The EDS system has been developed by GeoNet and is unique in the world. A detected volcanic eruption will automatically set off the Lahar Warning System, consisting of loudspeakers that warn people in the ski areas to get out of valleys that could be affected, and onto high ground nearby. This video describes the system that has been set up to protect skiers on the mountain and how it is tested for its effectiveness: There is also a lot of information displayed visibly at key points in the ski areas and surrounding facilities and communities to explain the lahar hazard, and what to do or not to do if a warning alarm is sounded:

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NASA comes to Rotorua

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Last week I was involved in a NASA Spaceward Bound meeting in Te Takinga Marae in Rotorua. The purpose of the meeting was to promote interest in Planetary Geology and  Astrobiology, and it was attended by about 50 scientists, educators, undergraduates and school students  from New Zealand, Australia, the USA, Romania, the UK and Kazakhstan.  Image:  NASA / JPL A large focus for NASA at present is the Curiosity Rover that has been exploring the surface of Mars for the last couple of years. One of the questions for the scientists is whether there are any traces of simple life forms in rocks on the surface. If found, these would show that whilst there may be no life at present on the red planet, it did manage to evolve there in the past under previous conditions. Image:  NASA / JPL In order to understand some of the geological features that are being observed using Curiosity’s various probes, it is useful to get to know comparable geological sites on the Earth’s surface that can be investigated and understood at close quarters. During the Spaceward Bound week we made several field trips to visit hot springs and volcanic landscapes in the Taupo Volcanic Zone. The focus of these trips was to see how microbial life can take hold in extreme physical environments such as very hot,  acidic geothermal springs, and to see how these living communities leave physical and chemical evidence of their existence (biomarkers) in the mineral formations that build up at these locations. This image shows a silica terrace at Waimangu volcanic valley. The colours are created by different species of microbes that thrive in these harsh conditions. The colour distribution shows the tolerance of particular species to different water temperatures.  For more about extremophiles in New Zealand find out about  the 1000 Springs Project. Extremophile microbes inhabit the hot mineral rich water that creates the rock formations at Pariki Stream, Rotokawa. The bacteria leave visible biomarkers in the sinter left behind as the mineral laden water evaporates. Parag Vaishampayan, a research scientist at NASA, took a close look. Quadcopter meets Rover at Rotokawa This small radio controlled rover was designed by Steve Hobbs at the University of New South Wales. It is adapted for remotely investigating hot springs, and includes a number of sensors such as spectrometers, a camera and a non contact thermometer. the quadcopter that you can also see in the picture has been adapted by Matthew Reyes, (a technologist at NASA) to scoop up water samples that can’t otherwise be easily accessed. Part of the field investigations included a study of plant colonisation of lava flows in the Mangatepopo Valley in Tongariro National Park. This photo shows a young lava flow on the slopes of Ngauruhoe volcano at the head of the valley. We also went on an excursion over the bare volcanic landscape of the Tongariro complex. Mars, as seen by Curiosity.            Image:  NASA / JPL For more information about astrobiology have a look at the New Zealand Astrobiology Initiative website, and to find out about Spaceward Bound New Zealand have a look here. Finally here is a news clip from TVNZ about Spaceward Bound, and an interview with AUT scientist Steve Pointing on National Radio.

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Opunake

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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. information for you to visit this spot is on our GeoTrips website here: www.geotrips.org.nz/trip.html?id=56 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. Opunake 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.

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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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Tongariro North Crater

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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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Volcano Gas Flights Video

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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

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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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