Volcanoes

Adventures of the Sentry

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Sentry is the showpiece of our 2011 expedition to the Kermadec Arc Volcanoes. It is an autonomous underwater vehicle (AUV) that has been developed by the team at the Wood’s Hole Oceanographic Institution who are world leaders in submarine technology. Unlike the other devices that are put over the side of the ship and lowered towards the seafloor, Sentry travels independently and therefore has the capacity to make long journeys over the volcanoes covering a wide area.It has enough battery power to last for up to about 20 hours per mission.   All its missions are pre-programmed according to the bathymetry map that has been created from the ships multibeam sonar scanner. It moves at a constant height above the slopes of the volcanic cones, recording a range of measurements. Here you can see the track lines of a mission over Brothers Volcano yesterday, overlaid on the red contour lines. For the duration of each Sentry mission, a couple of transponders are sunk down to the sea floor nearby to provide extremely precise location reference points that greatly increase the spatial accuracy of the resulting maps and records.  At the end of the mission, these float back up to the surface for collection. Because it is able to travel so close to the sea floor and can move in any desired grid or spiral pattern, Sentry enables incredibly high resolution maps to be made with previously unachievable detail. With up to 10 different sensors including side scan sonar, temperature, pH and magnetics, Sentry is able to detect and measure widely distributed hydrothermal hot spots. Whilst Sentry is operating far below, the ship can move away and perform its other operations such as magnetic surveys, CTDO (water chemistry and cloudiness), TOWCAM and sled sampling, which all help to add layers of useful information to the total picture of these volcanic seamounts.The Sentry team monitor the progress of the AUV via short acoustic messages that are updated every few minutes. If necessary they can send commands back to it to redirect it or get it out of trouble. In this photo, Dana Yoerger, leader of the Sentry team, is at his workspace in the Sentry control centre. At the end of its mission, Sentry floats up to the surface, and the ship pulls alongside so that it can be winched back on board. Because it has a broad flat profile, it catches the wind, and these deployment and retrievals with the winch can be exciting to watch!  During this voyage, the team were faced with some major technical challenges, requiring new parts to be sent from the US to New Zealand and then dispatched to the ship via helicopter and boat. Al Duester and Andy Billings spent many hours involved in complex problem solving to allow the show to go on.

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Rock in the Boat

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Along with biological specimens, the sled brings a lot of rock off the sea floor. Christian Timm sorts through all the samples, cuts some of them up with a rock saw, and packs and labels them to be studied in detail back at GNS Science. The different minerals present in the samples will be analysed to give detailed information about the processes occurring deep down in the collision zone where the Pacific and Australian plates meet, as well as about the hydrothermal alteration of the rocks at the sea floor. Here is a selection of examples from off the cone of Rumble 2 West volcano that we have been checking out for the last few days: First up is a piece of volcanic rock (basalt) that comes from the cone of Rumble 2 West. It would have cooled rapidly as it encountered the sea water, which has preserved the flow structure running through the centre of the specimen. Hydrothermal fluid contains a lot of iron that it has dissolved from the basalt it has passed through down in the crust. As it reaches the sea floor and cools, it precipitates out the iron as an oxide called haematite, which has a deep red colour. Silicon is the most common element in the earth’s crust, along with oxygen with which it combines as silica (quartz). There are many other siliceous minerals too, some of which are precipitated around hydrothermal vents in association with microbes. These yellow and orange pieces contain several types of silica with different quantities of trace elements that give a wide colour range. The whitish stripes in this piece of basalt are from small crystals of barium sulphate or barite. As sea water flows down into a seamount and heats up, it loses a lot of calcium sulphate which precipitates out. The hot, sulphate poor fluid then dissolves barium from the surrounding rocks, bringing it back up to the sea floor. The barium then combines with the sulphate in the fresh sea water to give rise to these barite crystals. They tell us that hydrothermal fluids have been cycled through the crust in this area, and can even be dated to give a timescale for the process. This small piece is a jam packed mixture of rock fragments and minerals. It It is part of the debris from an old broken up black smoker chimney. It is loaded with valuable metal rich compounds that have crystallised as the hot hydrothermal fluid gushed out into the surrounding sea water.  Cornel de Ronde is checking out the finds and explaining some of their features to crew member Peter Morrison.

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The Magnetic Charms of the Sea Floor

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Fabio Caratori Tontini is interested in measuring the magnetic properties of the rocks on the sea floor. Because most of them are volcanic lavas that contain a lot of iron, they have become magnetised as they cooled and solidified in the presence of the Earth’s magnetic field. When the hot geothermal liquids pass through them, the rocks  become progressively demagnetised because the hot fluid dissolves and carries away the metal (iron) ions. This is of course why the hydrothermal fluids become enriched in these ions, and bring them up to be precipitated when they contact cold sea water. In the second photo you can see that there is a lot of red iron in this rock. Rocks that have been affected by hydrothermal activity will remain demagnetised even after the activity stops.  By mapping the magnetic intensity across a volcano, it is possible to locate areas of present or past hydrothermal activity (low magnetism). This adds a time dimension to the other surveys that focus on present day hydrothermal activity only, and potentially reveals other areas rich in hydrothermal deposits.   Fabio uses a magnetometer that is towed behind the ship in a grid pattern above the volcanoes. This measures the variations in magnetism which are then plotted on a map. His results can be compared to maps of present day hydrothermal activity, to tell us something about how the activity has changed over time.  There is also a magnetometer on board our yellow submarine SENTRY that is run much closer to the sea floor, and picks up a lot more close-up detail. Here is a high resolution image of the magnetic anomalies on Clark volcano that were recorded by SENTRY a few days ago, and shown graphically by Fabio. The blue lowly magnetised areas are the ‘ burn holes’ that will generally be centres of rich hydrothermal mineralization because the minerals that have been leached from the deeper rocks are now spread out in deposits at or near the surface. The orange and red areas retain their more of their original magnetism and will not have been strongly altered by hydrothermal fluids. In the second graphic, Fabio has added to the picture by overlaying the magnetic data onto a 3D image of the cone of Clark Volcano.   On a previous expedition, Fabio got some strange readings on his magnetometer, and noticed that there was extra tension on the cable. After pulling the device back on board, he found that it had been severely mauled by a shark, with nasty bite marks on two sides. In the photo you can see that there is even a small piece of white shark’s tooth left behind in one of the gashes. I guess that the magnetometer now has a lower level of attraction for the shark who will think twice before attacking a large fast moving goldfish again…

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Communal Living on a Kermadec Volcano

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The first image shows the depth profile created by the ship’s sonar as it passed over the summit of Clark Volcano. It has the classic cone shaped profile of a typical land volcano such as Taranaki. They stick up above the deeper plains of the ocean floor and provide quite different habitats for deep sea creatures. The plains are mainly very soft muddy sediments which contain an abundance of worms and other burrowing animals. The seamounts on the other hand are covered by harder volcanic rocks that provide a solid surface for a different living community. In order to gather actual samples of the rocks and animals that occur on the surface of these seamounts, a simple method is to use a sled. This is a crude metal cage with a net at the back. It is pulled along the sea floor for a short distance and then hauled up by winch. The second photo shows a fully laden sled just arriving back at the surface. Once the sled has been emptied onto the deck, the biologists quickly pick off the largest and most obvious specimens and put them into a bucket of sea water. Then the rocks are scooped up into the yellow bins and checked more carefully for smaller creatures. Once all the different finds have been sorted and given an initial identification, they are put into carefully labelled bottles and preserved for later more detailed research. These small lobster-like crustaceans probably all belong to the same species.They are often found tucked away into a rock crevice with just their claws showing, ready to catch some food. Rob Stewart, one of the team of NIWA biologists, showed me this large piece of coral that has come up with the sled. This branching coral often grows on seamounts and provides a living space for many other animals to hide in.This one had several residents, including the large worm that you can see, as well as a hydroid coral, a couple of large flower like solitary corals, and a brittle star or two. Rob has a camera set up in his lab to take a photographic record of such prize finds. The last photo shows another view of this sample in all its glory. Because the different seamounts along the Kermadec Arc are separated from each other by the deeper ocean plains, the biologists are interested to compare the living communities on them. This will help improve our knowledge of how these animals have spread and diversified through time along a line of active volcanoes.

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Mapping Volcanoes

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One of the amazing tools that is on the Tangaroa is a multibeam sonar scanner that maps the contours of the sea bed as the ship travels along. It sends high pitch sound waves downwards in a fan shape and calculates the shape of the sea floor from the complex acoustic reflections. Over the last hours the ship has been pulling a magnetometer (a device for measuring magnetism in the Earth’s crust) back and forth over Clark Volcano, so at the same time the multi-beam sonar was at work to make a new map. This will enlarge the map made 7 years ago on a previous expedition, and also be used as a comparison to see if there have been any major changes to the volcano caused by eruptions or landslides. The top photo is the early version, and the next one is the latest one, produced for the first time today. (pic 3) The new map represents roughly 8 kilometres square. You can see that Clark Volcano has two cones. The one to the north – east (top left) is relatively simple and is most likely much younger than the south – eastern one (bottom right of image). There are several interesting surface features such as fault lines where the south – eastern cone has rifted apart, possible lava flows and a large rockslide. The next operation is to send a camera down to have a close up look for any hydrothermal activity. This is a 3D version of the new scan of Clark Volcano, which makes its landforms stand out more clearly. These digital terrain models can easily be manipulated to show the sea floor geological features from any angle.

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Message in a bottle

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Here is a map of the ocean floor north of New Zealand. The different colours represent water depth, red and yellow are shallower than the blue and purple areas. The deep Kermadec Trench that marks the plate tectonic boundary is an obvious feature, with the Kermadec Ridge running parallel to the West (left) of the trench. The line of arc volcanoes look like pimples very close to the Kermadec Ridge. All of the named volcanoes shown in the second image except for Lillie, are booked for a visit from us on this expedition. For the last couple of days we have been traversing over the top of the first of these objectives, Clark volcano. Whilst the various science teams have been organising themselves and starting their first operations, I have been adjusting slowly to this new environment and the way things seem to work. This is my first cruise and, like anyone in a new place for the first time, I find myself amazed by ‘everyday’ aspects of life at sea, and my perceptions sharpened by things that must be insignificant for regular sea-goers. Things like: the endless changes in the rhythms of the waves, the effortlessness ease of an albatross skimming over the wavetops, flying fish skittering away from the bow of the ship, and the endless, flat, 360 degree horizon. On board the mysteries are more technical. It seems fantastic that the ship can navigate its way across this featureless ocean and then position itself so that it stays motionless above an invisible volcano deep below. Scientists stare at computer screens and announce that a piece of equipment they have lowered into the water precisely is three and a half metres above the bottom, or devise a solution when the un-manned submarine far below gets ‘confused’ and stuck beneath a rock overhang. These are things I hope to understand better over the next three weeks. One of the crew, Russel Jones, has been working on the Tangaroa for the past 10 years. One of his hobbies is to periodically drop a wine a bottle with a message inside, over the side of the ship. Over the years, several of his bottles have been discovered washed up on beaches around the Southern Ocean. One of them made TV news in NZ and Australia, having been found by Rod Davies on a beach in Western Australia after a five year circumnavigation of Antarctica! Russel showed me a bunch of letters from people in several different countries who had found his messages and subsequently become personal acquaintances. Yesterday he launched another of his messages as you can see. Keep a look out for this one when you are down on the beach some years from now. Russel will be delighted to hear from you…

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Off to the Kermadec Volcanoes

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For the next three weeks I will be at sea to the North of New Zealand, far away from the aftermath and unfolding ramifications of the events in Christchurch. I am on board the NIWA research vessel Tangaroa with a group of geologists and biologists, many of whom were involved with the recent discovery of the Pink Terraces under lake Rotomahana . We left Auckland Port yesterday, as the sun was setting beyond the city skyline, and have been travelling North East into the Pacific Ocean along the Kermadec Volcanic Arc.Our mission is to make detailed geological and biological surveys of several of the undersea volcanoes that lie parallel to the plate boundary as it runs north east of the North  Island. This boundary is a geographically distinct line of several parallel features. Have a look at our video of a computer simulated flyby of New Zealand under the ocean . To the east is the deep Kermadec Trench where the Pacific Plate dips below the Australian Plate. Just to the west of this is the Kermadec Ridge, uplifted by compression along the boundary. Near to the ridge are the Arc volcanoes that we will be investigating. West of the volcanoes is a “back arc basin” of deeper water which is a zone of extension. Further west again is the now inactive Colville Ridge. Right now we are approaching Clark Volcano,  the first of our objectives, the top of which is 850 metres below the surface. The various teams are sorting out the specialist tools for their particular research. I will be writing in more detail about how our explorations unfold over the next days.

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Pink Terraces found!

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The Pink Terraces of Rotomahana before the Tarawera Eruption of 1886 (Permission of the Alexander Turnbull Library, Wellington, New Zealand, must be obtained before any re-use of this image).  Devastation after the Tarawera eruption Yes – the unbelievable news is, that inspite of being located at the centre of New Zealand’s most violent eruption of historic times, shaken by volcanic earthquakes, covered by many metres of mud and ash and then flooded underneath a large lake, a large area of New Zealand’s iconic Pink Terraces of Rotomahana has been re-discovered!    Dan Fornari of WHOI Scientists involved in the Rotomahana Project announced their findings last night at a special meeting in the marae at Whakarewarewa, 125 years after the Tarawera Eruption. Thanks to the underwater vehicle and imaging technology and skills developed by the Wood’s Hole Oceanographic Institution (WHOI), and the expertise of marine scientists from Lamont-Doherty Earth Observatory (LDEO) and NOAA-PMEL in the USA, this discovery has been made possible. A key component of the expedition’s field approach was the use of the Remus100 autonomous underwater vehicles (AUVs) developed at WHOI.    Dr. Vicki Ferrini of LDEO observed the terrace formations as she was processing images from the sidescan sonar on one of the AUVs on Saturday. After checking details like water depth, location, orientation, shape and size of the features, Cornel de Ronde and the rest of the science team reached the conclusion that these can only be a part of the original Pink Terraces last seen on June the 9th 1886. The features show up as curved step like surfaces that are visible in the sonar images as bright reflectors due to their strong reflectivity, This means that they comprise a hard material, unlike the softer, therefore acoustically darker sediment that surrounds them. It is the steeply sloping or vertical sections that show up most brightly, probably because they are free from any overlying sediment. This early, pre-eruption photo of the lake shows the Pink Terraces on the left. In the middle distance you can see a hooked spit of land extending into the lake as a very distinct feature. This gives the lake shore a very identifiable contour just northeast of the Pink Terraces. In the compiled bathymetric map produced by Vicki from the AUV survey data, the same hooked-shaped peninsular can be seen in the lake bed, now several tens of metres under water. This is in the northern section of Lake Rotomahana, in the area that has been indentified as the probable location of the Pink Terraces by previous researchers. The close-up of the lake floor bathymetry shows this feature clearly (depths in the map at right are color coded- pink is deep and red is shallow). The main cascade of the Pink Terraces would fit in the green embayment in the top centre of the image, and the wide lower part of the terraces should extend down roughly in the centre along the green or pale blue band.When overlaid on top of the bathymetric map, Vicki’s step like rock features lie exactly on top of this location. This means that the lower portion of the Pink Terraces still remain. It is possible that they were covered in debris by the eruption, and that subsequent water erosion has exposed their edges again. The question still remains as to whether the upper section of the terraces is still intact underneath a layer of sediment. The sonar sensors used in this survey are unable to reveal adequate subsurface detail to answer this. However, a future expedition could settle this question using seismic reflection techniques. A further investigation was made by lowering an underwater camera, developed by Dr. Dan Fornari at WHOI, down to the bed of the lake to take a closer look. The following images are a selection from those taken. The first shows a small crater with a hazy cloud of bubbles and coming out of it. This depression is roughly a metre across. Because of disturbance caused by the high level of hydrothermal activity, the ranges of the camera images are only a few metres. * In the next photo you can see some vertical relief. On the right, the dark shadow is one of the terrace steps, whilst further to the left, across the sloping muddy lake floor there are some smaller exposed vertical sections of rock. These shapes are typical of hydrothermal silica deposits seen in other parts of the Rotorua geothermal area.* The last of the underwater photos, taken near the region identified by Vicki as being where the strong reflectors of the Pink Terraces are located, show the vertical edge of a terrace head on. The scaling is not exact but in the region of one or one and a half metres in height and could be an exposure of the lower part of the Pink Terraces. * These initial findings leave many questions that can be followed up in the future. But for now, to know that at least a part of the Pink Terraces of Lake Rotomahana are still there, hidden in the depths of the water, is a fantastic outcome of the Lake Rotomahana Project. Quite apart from this discovery, the analysis of the overall expedition findings will give the scientists plenty to do towards the goal of understanding the whole hydrothermal system  of Rotomahana.  Dr. Cornel de Ronde, of GNS and leader of the expedition has something to smile about. * “Digital underwater photographs taken by Dr. Dan Fornari – Woods Hole Oceanographic Institution (WHOI), Cape Cod, MA, USA, using equipment developed with funding from the US National Science Foundation and WHOI. Digital underwater camera developed by Mr. Mark Olsson of DeepSea Power & Light, San Diego, CA, USA. Copyright D. Fornari – Woods Hole Oceanographic Institution.”

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NZ Volcano Fact Sheets

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The GNS Science website now has 10 one page Fact Sheets on the main New Zealand volcanoes. They give details of the landforms, rock types and eruption histories, with colourful images and diagrams.These are great for a school project, or to print off and take with you when you go for a tramp up one of our volcanoes. Don’t forget that there is lots of detailed volcano information on our website as well as webcams and updates of volcano activity levels on our GeoNet site. Watch a video of scientists monitoring White Island Volcano, or follow some students whilst they check out the amazing Volcanic Landforms of Tongariro.

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