Geology

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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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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Ocean Drilling science holiday programme

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The JOIDES Resolution drill ship is back in Wellington after spending the last two months recovering sediment cores from off the east coast of the South Island. The photo shows the ship being loaded with fresh supplies in the Port of Wellington. The expedition was very successful, with several holes being drilled, one of which was over 1900 metres deep. This is the deepest individual core drilled so far by the JOIDES Resolution. All of the rock retrieved has generated thousands of samples for analysis. In a few days the ship will depart for another trip, this time close to the coast of Antarctica. Check out the TV3 news video here. Also have a look at our own GNS video about the drilling programme: GNS Science is running a 7 day holiday programme for school students that is investigating the science of ocean floor geology. The students were amongst a priveleged few New Zealanders allowed to visit the ship today. They were able to ask all sorts of questions of a number of scientists and technicians. Young scientist Thomas Seaton is admiring thedrill teeth that cut through the solid rock of the ocean floor. Imaging specialist Bill Crawford explains the process for making high resolution digital images of the rock cores. Richard Levy of GNS Science and Christian Ohneiser of Otago University explain how the cores are analysed in the on board laboratory. Thanks to Victoria University, Capital E and the Museum of City and Sea for their collaboration with the Holiday Programme.

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