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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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Hot Water Plumes

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Hydrothermal activity in undersea volcanoes is largely the result of sea water descending into the crust, being heated up and then chemically breaking down the surrounding rocks as it rises back up to the sea bed. These mineral rich fluids then re-enter the water column either diffusely over a wide area, or out of one of many vents in a hydrothermal field. As the emerging hydrothermal fluids mix with the sea water and quickly cool down, the dissolved minerals within them precipitate out. Some (such as metal sulphides) will accumulate immediately around the vent to create vertical chimney like structure, whilst others (such as iron and manganese oxides) will form particles that get carried up in the hot water plume to form a sheet like cloud that is pulled sideways by water currents. The particles within the cloud will slowly rain out back to the sea floor over a wide area. Sharon Walker from NOAA (the National Ocean and Atmosphere Administration in the US) specialises in analysing the physical and chemical properties of sea water to locate hydrothermal plumes and the vents that have created them. She uses several tools mounted onto a CTDO (conductivity, temperature, depth and optical) recording device. In the photo you can see Cornel de Ronde and Matt Leybourne preparing the CTDO. It will be towed below the ship and lifted up and down to sample at different depths. On it there is a light scattering sensor which detects reflected light to give a measure of the water’s particle content. It will also take samples of water from different levels in the water column for chemical analysis. Yesterday Sharon and Matt collated some results to create this diagram of the hydrothermal plume above Rumble 2 West volcano. The green and yellow lines represent light scattering. You can see that near the bottom there is a large spike indicating a hydrothermal plume about 30 metres thick. Faint red lines across the graph show the depths at which water samples were taken. Finally here is a photo I took from the bridge during quite windy and choppy conditions the day before yesterday, just to show that it is not always flat as a mirror out here. For some of us landlubbers it meant spending a bit of time outside looking over the rail… just admiring the view of course.

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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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Help from above

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We have now been traversing above Clark Volcano for several days, and a variety of surveys have been operating, including dredging for mineral and biological specimens, photography of the sea floor, magnetic surveys and water chemistry sampling.  The technological centrepiece of our expedition to the Kermadec Arc is a strange object known as ‘Sentry’. Sentry is a bright yellow un-manned submarine that can be programmed to dive to the sea floor on journeys of up to 19 hours long, manoeuvre up and down over obstacles, and take a whole variety of close up readings with its many sensors. On Sentry’s initial dive a few days ago, its multibeam scanner stopped working. This feature is a very important part of the Sentry’s armoury of equipment. It is used to make very high resolution maps of the sea floor, which are extremely detailed because Sentry is travelling so close by. So while the other scientists have been very active with their own projects, the Sentry team have been working on solving this key problem, finally organising to get a replacement scanner. This was flown to New Zealand from the US, cleared through customs, and immediately flown to us yesterday by helicopter out of Auckland. The delivery was lowered down from the helicopter in a large container, whilst a crowd of us enjoyed the spectacle from the front of the ship. Shortly afterwards, these beautiful fish called mahimahi, each about one and a half to two metres long, paid us a visit from below. Gently cruising around the ship for about half an hour, their offering to us was just the simple appreciation of their presence. And as from last night, Sentry is on duty, now deep below us.

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Images from the Unknown

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TOWCAM is an underwater camera that is lowered down to the sea floor and pulled along just above the bottom on a long winch line. It has an altimeter on it that allows the scientists to pull it up or lower it to keep it just above the bed as the ship drags it along sideways. Here you can see TOWCAM being lowered into the water and down into the deep blue depths to over 1100 metres depth. Every ten seconds it takes a photo timed with a strobe flash to give a stream of images along the designated path.  The red line on the map shows yesterdays mission across the summit of the southern cone of Clark Volcano, where hydrothermal activity was expected to be occurring. The total length of the path shown is about 3 kilometres. Up on the ship’s bridge, the TOWCAM team from Woods Hole Oceanographic Institution in the US, manually adjusts the winch to keep the camera as close as possible to 4 metres above the sea bed. I watched Marshall Swartz as he continuously monitored the computer screen and adjusted the winch up and down in response to TOWCAMs signals of changing water depth. When TOWCAM has completed its mission after several hours, it is pulled up to the surface again. Tim Shank, the biologist in the WHOI team, was delighted to find that by chance TOWCAM had hauled up some specimens off the sea floor including a beautiful coral, some brittle stars, and a crinoid. Here are three of the three thousand photos that were taken on TOWCAMs first mission on Clark. They were downloaded after the camera had resurfaced, and Tim checked each one of them for signs of hydrothermal activity, variations in the geology, and evidence of interesting biological species. The first of the undersea pictures shown here includes a hard coral and some sea anemones living on hard volcanic basalt that was erupted from Clark Volcano. In the next photo, you can see the yellowish colour of softer sediments that have been altered by hydrothermal activity. Lastly here is an image of a steep face of volcanic lava that has also been stained by ongoing hydrothermal activity.

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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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