GeoPhysics

Earth’s Magnetism in Antarctica

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A blog post by Tanja Petersen and Neville Palmer from their recent GNS Science trip to Antarctica to measure the Earth’s Magnetic Field. It took 8 hours for the Hercules aircraft to fly from Christchurch to Williams airfield, a runway on the Ross ice shelf close to Scott Base. Both of us had never been to Antarctica before; we had a big smile on our faces when we stepped out from the airplane onto the ice being greeted by dry crisp cold air and what seemed like a never ending blanket of snow.  Read up on the Hercules – it is a quite fascinating aircraft and has been around since the 50s! The view from Crater Hill, a volcanic cinder cone on the foot hills of Mt Erebus, provides a fantastic overview of the settings of Scott Base. You can see Williams airfield (upper left corner); the boundary between the thick ice shelf and the thin sea ice meanders diagonally through the photo towards White Island in the distance. The pressure ridges on the sea ice are semi-circling the green painted buildings of Scott Base. 10pm at Scott Base. 24-hour sunlight! Looking out from the back towards the two geomag huts (left). We are here to measure the strength and direction of the Earth’s magnetic field at two locations in the Ross Sea area, Lake Vanda & Cape Evans, where people have been repeatedly measuring it since 1974 and 1911, respectively. And we also want to check up on our equipment inside the two little green huts outside the back of Scott Base, which is continuously recording the local variations of the Earth’s magnetic field.  The accommodation for the night at Scott Base: One of the many corridors inside Scott Base connecting the buildings of different sizes and shapes. Corner, stairs up, another corner, stairs down … a bit of a labyrinth for a newbie! Häglund snow vehicle to the left, Mt Erebus in the background, a toilet tent, two sleeping tents, some shelters built into the snow and a flag marking a safe route.The inside of Scott Base is being kept warm & cosy at T-shirt temperature, but outside it is more like -6 to -12 degrees C (including wind chill – important factor!). The Antarctic Field Training is giving us a good practice run on how to keep warm outside, before heading into the field. Antarctica New Zealand provided us with heaps of layers of warm clothes to wear. We then were ready to load up the helicopter that flies us from Ross Island to Lake Vanda, in the Dry Valleys, 125 km away on the Antarctic mainland. The Wright Valley with Lake Vanda in the distance. Our fieldwork in the Dry Valleys, Antarctica, begins. First thing is to set up the fluxgate magnetometer near the Lake Vanda camp, before we walk to the nearby repeat measurement sites to get readings of the strength and directions of the magnetic field. Neville is measuring the directions of the Earth’s magnetic field at Lake Vanda. In 1767 the South Magnetic Pole was located around here; now it is about 1720 km away. We are repeating these measurements several times over the course of four days. Tanja on a special mission – the “P bottle” is part of keeping the environment as we found it. After those four days working at Lake Vanda we continue to Cape Evans, Ross Island, Antarctica for a day. The historic magnetic hut there was constructed in 1911 as part of Scott’s Terra Nova expedition. It has asbestos in its wall panels; its structure is protected by a plywood construction around it. Inside that hut is the wooden pillar that Captain Robert Falcon Scott and his team of explorers used to take magnetic measurements before heading into their ill-fated expedition to the South Pole. Over 100 years later Neville performs the same type of measurements, but in a slightly different outfit. The Terra Nova Hut nearby. Captain Scott’s base for his explorations of the frozen continent, in the early 1900s. It was also used by Shackletons’s Ross Sea party. After completing our work successfully our flight back gets delayed and we have a bit of time for some recreational activities on the ice shelf close to Scott Base before heading home to New Zealand.

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Precarious Boulders and Earthquakes

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The National Seismic Hazard Model is the result of lots of work by scientists to indicate the likelihood of earthquakes happening in different parts of New Zealand. It is made with reference to the historic record of earthquakes that have happened across the country, combined with research into the rupture histories of many individual active faults. Work is done to continuously ‘ground truth’ and improve the Hazard Model through ongoing research and addition of data. Mark Stirling has developed a way of testing the model at particular locations using ancient landforms known as tors that occur in places around the country. These isolated boulders stand like statues. There are many of them near Clyde in Otago, occurring on the flat, uplifted surfaces of nearby ranges, such as the Old Man Range, shown here. You can see that some of these features are quite imposing and have a lot of character. Although some of them are solid looking, there are others that are very delicate.These are the ones that Mark is interested in. The basic idea is to use the beryllium 10 exposure dating method to find out how old these fragile features are, and then to work out the amount of earthquake shaking it would take to knock them down. This tells Mark the minimum amount of time that has lapsed since the occurrence of an earthquake capable of knocking down the feature. This information is then matched with the National Seismic Hazard Model to see if the calculations give similar hazard estimates. Making a numerical calculation of the fragility of the precarious feature is a matter of working out the angles between the centre of mass and the rocking points at the neck (narrowest point) of the tor. For making these calculations with maximum precision, Mark makes a 3D computer model of the tor, by first taping key points on its surface, and then taking many photos from all angles, which are later stitched together. This is what the model of the above tor looks like on the computer screen once completed . During fieldwork with Mark last month, we were able to use a quadcopter drone to get good images of some of the more inaccessible fragile landforms. Here is our video of the project:

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Bottom Hole Assembly

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About 10 days ago, drilling was stopped at the Alpine Fault drill site so that geophysical measurements could be made down the borehole, and the bit could be replaced. This involved lifting all of the drill rods out one by one and stacking them next to the rig. Next to come up was the bottom hole assembly (BHA) comprising these thick steel pipes that Rupert Sutherland is describing to the camera in this image. Last to appear was the business end of the drill string including the drill bit itself. This photo shows the bit being replaced using some impressive sized hand tools: The view looking down into the top of the borehole – 400 metres deep and filled with mud. Here is the video of Rupert explaining the Bottom Hole Assembly: Once the geophysical measurements were taken down the hole (more about these later), the Bottom Hole Assembly was put back together and lowered back down the borehole. Unfortunately disaster struck when the wire snapped and 7 tonnes of unattached BHA dropped down the hole. To cut a long story short, this delayed progress for about a week, until finally the detached parts were fished out of the hole using a variety of highly specialised methods. You can read a little more about these events here in Rupert’s Blog:1.The Calamity.  2. Landing the Fish 

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Phase 2 Alpine Fault Drilling

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Rupert Sutherland with DFDP-2 flags Whilst researchers continue to pull together the history of past Alpine Fault earthquakes, the Deep Fault Drilling Programme is well underway in Whataroa on the West Coast of the South Island. For an introduction to this project have a look at my blog and video here, or check out the DFDP-2 Facebook page or project leader Rupert Sutherland’s blog for updates over the next few weeks. The first phase of the drilling process was to penetrate down through a thick sequence of gravel and mud left behind in the Whataroa Valley after the retreat of ice at the end of the last ice age. This was surprisingly challenging because of a thick sequence of very sticky mud that was deposited in the valley at a time when it was a deep fiord or lake. DFDP-2 drill site   J.Thomson@GNS Science Eventually the team struck bedrock 240 metres below the surface, and the second phase could commence. This involves drilling down towards the fault plane, thought to be about a kilometre below the rig, without trying to retrieve any large intact pieces of the rock at this stage. (That process is the goal of phase three, which will start when the geologists see from the minerals in the rock fragments that the drill is closing in on the Alpine Fault.) DFDP-2 drill site   J.Thomson@GNS Science This is a view of the drill site on a nice morning with Phase 2 well established and the drill at a depth of 340 metres. Behind the rig you can see the drilling mud ponds. The science labs are on the right and spare drilling rods that are added as the drill gets deeper are in the foreground. The labsin the background are where the scientists  study the rocks being brought up by the drill, and make geophysical measurements taken by equipment that is lowered down the borehole. Close up to the rig you can see the vertical drill rod (or pipe) that is rotating and gradually descending down the drill hole. The next rod is lined up ready for connecting when the drill is a few metres deeper. The speed of drilling is roughly 1 to 4 metres an hour at this stage, and a new drill rod is added about every 6 hours. Next to the drill is this pond of muddy water, which is a vital part of the system used for cutting down into the rock. The mud is specially formulated to have the right viscosity and density and is sucked up by a very powerful pump. After having large particles sieved out of it, it is sent down the centre of the drilling pipe right down to the cutting face of the drill bit. The drill bit on the right has cut through about a hundred and twenty metres of bedrock, and is about to be replaced by the nice shiny one on the left. The drilling mud is forced out of the holes that you can see, and then flows up the outside of the drill pipe back to the surface, bringing with it the rock chips and also carrying heat away from the cutting face at the same time. This is the base of the drill rig, with a section of the rotating drill pipe visible. Drilling mud is flowing down the centre of it on its way down to the drill bit. After its return journey on the outside of the drill pipe, loaded with rock fragments, it emerges at ground level and is carried away in the pipe that extends to the right. The drilling mud flows into a collection pond. The sieve that you see is for collecting samples of the rock fragments for analysis. The samples are first carefully washed of fine mud or clay. They are then sorted by hand. After being glued to a microscope slide, the rock samples are ground down to a thickness of 30 microns. They are then transparent and can be analysed using an optical microscope. The mineral content can then be studied in detail. As the drill gets closer to the fault, the scientists expect to be able to see changes in the types of minerals present. In this way they will be able to judge the right time to change the drilling system to phase 3 and start retrieving intact rock cores. DFDP-2 drill site   J.Thomson@GNS Science Finally here are a couple more views of the DFDP-2 drill site looking up the Whataroa Valley. DFDP-2 drill site   J.Thomson@GNS Science

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Nature’s Earthquake Recorders

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In order to make sense of the sediment cores that can be retrieved from lakes near to the Alpine Fault such as Lake Christabel, it is worth having a think about what happens to the environment when the fault ruptures in a large earthquake. Under normal conditions, alpine lakes fill up very slowly with sediment that is fed into them by rivers. The particles settle onto the lake bed gradually, to create a sequence of finely layered mud. When an earthquake occurs, a number of consequences affect the landscape. The soft surface sediment on the bed of the lake gets deformed and folded, and the shallower slopes at the side of the lake collapse to create flowing avalanches (turbidites) that sweep down and across the lake floor. In the nearby mountains, large landslides occur that choke the river valleys with a chaotic mix of large and small rock fragments. In the months and years following the earthquake, the landslide debris is gradually washed into the lake, to form a recognisable layers on top of the turbidite deposit. Eventually, conditions return to normal, with the finely layered sediments gradually covering over all of the evidence of the earthquake and its aftermath. It may be hundreds of years before another earthquake sttikes that is near enough and strong enough to leave its mark in new layers of the lake sediment. Now lets have a look at the real thing – an example of a sediment core that has been retrieved from a New Zealand’s alpine lake. Back in the lab at the University of Otago in Dunedin, Jamie Howarth opens a core tube to reveal the layers of sand and mud from Lake Christabel. Here is a section of the core that shows the finely laminated lake sediments formed in normal conditions (on the right). In the centre you can see that the layers are slightly folded – this is the indication of an earthquake that has deformed these layers. They would have been at or just below the surface of the lake floor at the time. Here Jamie is indicating the remains of a leaf next to the blade of the knife. This is not far below the earthquake layer, and can be used to get a radiocarbon age which will help to date the earthquake event. This dark coarse layer is the next layer that was added to the sequence on top of the folded sediment. It is the base of an earthquake generated turbidite deposit. The material gets gradually finer to the left (‘upwards’) as the cloud of particles slowly settled onto the lake floor. The section shown here is the landscape recovery phase. Dating of the base and top of this layer in several cores has shown that it can take 50 years for the landscape to recover from an Alpine Fault earthquake. During that time, hillsides are destabilised, debris flows cover flat areas near to the mountains, and rivers are prone to changing course due to being overloaded with sediment. Finally we see the thinly layered sediment  indicating that normal conditions have returned to the lake environment. This map shows what can be done when this research is carried out at a number of lakes along the Alpine Fault. The coloured lines (purple, orange, green etc) show earthquake records that have been identified so far in some of the lakes along the length of the fault. You can see that the last earthquake rupture (in 1717 AD) was over 300 km long. The one prior to that around 1600 AD ruptured the northern end of the fault. Information about previous earthquakes is still incomplete, but the picture is starting to become clearer. With more research, Jamie and his colleagues will be able to show a more detailed history of the last 10 Alpine Fault earthquakes including the dates, lengths of rupture and magnitudes of the events.

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Lake Christabel

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Lake Christabel   J.Thomson@GNS Science This is Lake Christabel in New Zealand’s South Island. It is one of the many beautiful alpine lakes  to be found close to the Alpine Fault. Lake Christabel was formed when a huge landslide blocked the valley, thus damming the river that then backed up to form the lake.The present day outlet runs over the old landslide deposit of large chaotic boulders. Hidden beneath the waters of Lake Christabel are very distinctive sediment layers that tell the story of huge earthquakes that rocked the nearby mountains during ruptures of the Alpine Fault. Jamie Howarth from GNS Science, and Sean Fitzsimons from Otago University, have been investigating several such lakes to read the earthquake histories. I joined them on a recent expedition along with Delia Strong and Rob Langridge from GNS Science. The aim was to retrieve sediment cores from the lake to investigate the earthquake records. First of all a seismic survey was undertaken to find the best spots to sample on the lake bed. Sean is in the lead boat, towing a second dinghy that carries the equipment. The survey uses an acoustic source that sends pulses down into the water. The boat is towed along so that noise interference produced by a nearby motor is avoided. As the sound pulses are reflected back from the lake bed and its layers of underlying sediment, they are translated into a two dimensional vertical section image of the lake floor. A number of survey lines are made across the lake to give some idea of the 3 dimensional structure of the lake sediments. Once the best locations for sampling have been chosen from the survey results, the corer is prepared with a fresh 6 metre pipe that will be pushed into the lake floor to retrieve a sediment core. The corer is transported to the chosen point on the lake surface, and then dropped off the side of the boat once it is in position. After being connected with several airlines which are required to control the pressure coring process, the corer is lowered the 90 metres to the lake floor. The large barrel sits at the bottom, and is sucked into the mud to create a stable platform for coring. High pressure air is then applied to the piston which pushes the 6 metre coring pipe into the mud, releasing clouds of bubbles up to the surface. These bubbles allow Sean and Jamie to monitor what is going on with the corer at depth. Lake Christabel Corer Retrieval J.Thomson@GNS Science When the coring is complete, an airbag is attached to the line and filled up with air so that it  pulls the whole assembly out of the mud. The airbag bursts up to the surface from below in a spectacular fashion. Lake Christabel Corer Retrieval J.Thomson@GNS Science About a minute later, the corer assembly also emerges from the depths. It is not a good idea to be too close to this as it could easily sink a boat that was in the wrong place. The corer is then plugged and loaded into the boat to be brought back to shore, with its precious cargo of sediment. The PVC tube containing the core is then cut into 1.5 metre lengths for ease of transport. Each tube is carefully labelled to avoid any confusion  about where it was taken from and its relationship to the other samples. Lake Christabel Flight  J.Thomson@GNS Science Once all the sampling has been completed, the expedition is over. It takes several helicopter loads to transport the two boats, safety gear, corers, generators, samples and all our personal equipment back to the road end. The samples are then taken to Otago University for analysis. My next post will describe how alpine lakes like Lake Christabel have shown themselves to be very useful natural seismometers through this research approach.

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Imaging the Crust beneath Wellington

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Having had a close up look to the surface trace of the Wairarapa Fault (see recent post here), I thought it would be interesting to find out the latest about what such a major geological structure looks like below the earth’s surface. Stuart Henrys and colleagues at Victoria University, the University of Tokyo, Japan, and the University of Southern California, USA, have been busy working on the results of the SAHKE project that ran a large scale seismic survey across the Lower North Island in 2011. The purpose of this survey was to  gain a better understanding of the anatomy of the plate boundary and associated structures below the Lower North Island. This image shows the line of the survey that not only ran across the land surface, but also extended across the sea floor to West and East. Thousands of measurements were recorded, creating a huge dataset that had to be processed to create two dimensional seismic cross sections. SAHKE seismic survey. Stuart Henrys @GNS Science Here is an example of how about 80 kilometres of the section can be displayed to highlight some of the structures in the crust down to 35 kilometres depth SAHKE seismic survey. Stuart Henrys @GNS Science It takes a lot of work to be able to interpret the information to see some of the major structures. You can see that a coherent band of energy deeper than 20 km depth is interpreted to be the plate boundary and descends at a very shallow angle, Also how the Wairarapa and Wellington Faults show up as narrow bands of energy that become low angle thrusts from about 15 kilometres below the surface Stuart Henrys @GNS Science This is a simplified summary of the complete 250 km length of the SAHKE seismic survey: Initially the plate boundary dips at a very shallow angle below the Lower North Island. This angle steepens below the west coast (Kapiti). The blue area is rock that has been scraped off the surface of the Pacific Plate and stuck (“underplated”) onto the base of the Australian Plate. You can think of the Australian Plate acting a bit like a chisel as it scrapes the top off the Pacific Plate in this way, pushing the overlying crust upwards along the Wellington and Wairarapa Faults to give rise to the Rimutaka and Tararua Ranges.  The diagram also shows (in red) where the plate interface is locked (down to about 30 kilometres depth) and the (green) area where it produces slow slip events. Find out more about the potential for very large earthquakes to be generated on Wellington’s Stuck Plate Boundary and also about Slow Slip Events. Tararua Range,  J.Thomson@GNS Science The narrow, long form of the mountains of the Lower North Island may be related to their position above  where the plate boundary dives more steeply downwards with underplated sediments  pushing the ranges up. Cross section of SAHKE seismic survey. Stuart Henrys @GNS Science Here is a more detailed image for you to explore if you are interested, showing some examples of earthquake locations (grey dots) in relationship to the crustal structures: UPDATE 5th Feb 2015:  Have a look at this media release about further groundbreaking discoveries resulting from this research project – “Scientists discover slippery base on underside of Pacific Plate”

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Drilling into New Zealand’s most dangerous fault

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The Alpine Fault forms the plate boundary in New Zealand’s South Island, and is a very significant fault on a global scale. It last ruptured in 1717 AD and appears to produce large earthquakes on average every 330 years. Its next rupture has a high probability (28%)  of occurring in the next 50 years. Each time the Alpine Fault ruptures, there is roughly 8 metres of sideways movement and about 1 to 2 metres of vertical uplift on the eastern side. These magnitude 8 (M8) earthquakes can rip the fault along about 400 kilometres of its length. Slowly, over millions of years, this is what has created the Southern Alps, and offset rock formations on each side of the fault sideways by a phenomenal 480 kilometres. Massive and continual erosion of the Southern Alps keeps them relatively small (below 4000m) inspite of about 20 kilometres of uplift over the last 12 million years. For a lot more information about the Alpine Fault and its earthquakes, check the GNS Science website. Later this year, scientists plan to drill through the Alpine Fault at a depth of more than one kilometre  to sample the rocks and fluids of the fault at depth, and to make geophysical measurements down the borehole to better understand what a fault looks like as it evolves towards its next earthquake rupture. This is phase two of the Deep Fault Drilling Project (DFDP-2). The first phase of the project (DFDP-1) was successfully carried out in 2011 when two shallow boreholes were drilled through the fault to about 150m and the first observatory set up at Gaunt Creek.  DFDP-2 will involve drilling a short distance away in the Whataroa River valley, not far upstream from the road bridge on State Highway 6. This short video gives some background and information about the project:  You can also find out lots more detailed information about DFDP-2 at the GNS public wiki site here. The prospect of drilling through a massive fault could  sound alarming to some people. Is there a possibility that this project could cause a damaging earthquake? Check this next video to hear about the safety review:

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The Hot Bed of Rotomahana

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This week I have been with Cornel de Ronde and a group of ocean floor researchers applying more of their methods to expand the large amount of research of Lake Rotomahana done over recent years. This is the lake that used to be decorated by the famous Pink and White Terraces. It was excavated by the extreme violence of the Mount Tarawera eruption in June 1886. This photo of a cliff section in the nearby Waimangu Valley, shows a black horizontal soil layer that was buried by volcanic mud during the eruption. The area still has a lot of geothermal activity. One of the tasks for this expedition was to measure the heat flow coming up through the lake floor. Scientists from Woods Hole Oceanographic Institution (WHOI), the National Oceanic and Atmospheric Administration (NOAA) and the University of Waikato collaborated with the project. Maurice Tivey of WHOI provided the special blankets for measuring heat flow in the ocean. This was the first time they had ever been used on a freshwater lake. The blankets have a thermistor (thermometer) on the top and the bottom. They measure the temperature on the surface of the lake floor sediment and also of the water layer just above. The difference between the two measurements allows the amount of heat flow to be calculated in watts / square metre (w/m2). The heat blankets are lowered on to the lake floor in a pre-determined grid pattern and left for 24 hours to equilibrate with the prevailing temperatures. Then they are pulled up to the surface and re-deployed in a new position. Gradually the whole lake floor gets coverage in this way with the 10 available blankets. The thermistors take readings of the temperature every minute and store the data until they are eventually plugged in to a computer for it to be downloaded. In the image you can see the temperature curves for a blanket that has been deployed at 4 different locations over 4 days. The upper curve shows the data from the lake sediment recorded by thermistor under the blanket. The lower, darker curve is the (cooler) water temperature recorded by the top thermistor. You can see that it takes several hours for the readings to adjust to the lake floor temperature conditions. The last recording on the right hand side is very hot, so the thermistor records a rising temperature. The dots on this map of Rotomahana show the locations of the measurements. Maurice has outlined the hot areas identified initially, although the data had still to be fully processed. You can see how the areas of high heat flow in the map above correlate well with the map of gas bubbles recorded on the surface of the lake in 2012. This may seem obvious for a hydrothermal system, but gas plumes are not necessarily accompanied by heat. This is a map of a heat survey that was undertaken in the 1990s. This week’s survey is more detailed and uses a new method,  but it will be interesting to see how the results compare. In the earlier survey, areas of heat flow of up to 10 w/m2 were outlined. Some of Maurice’s recordings are several times hotter than these. In this video. Maurice describes the new heat flow survey method:

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The Changing Height of Mount Cook

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Mount Cook  rock avalanche 1991. Lloyd Homer, GNS Science On 14th  December 1991 a massive rock avalanche occurred from the East Face of Aoraki /Mount Cook, sending an estimated 14 million cubic metres of rock in a 1.5 kilometre wide cascade across the grand plateau and down onto the Tasman Glacier. It is thought that the avalanche travelled at speeds of 400 to 600 km per hour, and the resulting seismic recording at Twizel, 75 km away, lasted well over a minute, registering the equivalent of a magnitude 3.9 earthquake. Mt Cook Dec. 1991.  M. McSaveney, GNS Science Prior to the avalanche the surveyed height of New Zealand’s highest peak was 3764m. The Department of Survey and Land Information (now LINZ) calculated that this was reduced by 10 metres after the summit fell off with the rock fall. As you can see from the photo, the peak became extremely narrow and unstable. In the image taken by GNS geomorphologist Mauri McSaveney a few days after the event. A lone climber that can be seen as a tiny dot inside the red circle  gives some idea of the scale. The “new” summit was obviously highly unstable, and would be subject to quite rapid erosion following the rockfall. Since 1991, there has been no re-calculation of the revised elevation of 3754m until recently. At the end of November 2013, I flew up to Plateau Hut with a climbing team who planned to take direct GPS measurements of the summit ridge of the mountain, a short distance from and a few metres below the highest point. The measurement would then be used to validate a computer model made from recent aerial photos to give a precise calculation of the present height of the peak itself. The team was made up of (left to right): Geoff Wayatt, mountain guide; Nicolas Cullen from Otago University; Brian Weedon, mountain guide; Pascal Sirguey (project leader) from the National School of Surveying at the University of Otago; Jim Anderson from Survey Waitaki and myself. Geoff, Brian, Nicolas and Jim made up the climbing team. GNS Science provided support in terms of the helicopter flights.  I was able to accompany the team to Plateau Hut where I spent two days gathering a visual record whilst they were involved in their climb. Mount Cook East Face   Julian Thomson, GNS Science The plateau of Mount Cook is arguably the most spectacular alpine setting in New Zealand. This image shows the 1500m high East Face of Mount Cook in the early morning light seen from Plateau Hut. The normal route up the mountain follows the Linda Glacier, starting on the right hand side of the image and following into the shadow behind the long low angled rock ridge (Bowie Ridge) up to the summit rocks. As well as Mount Cook itself, the Grand Plateau has views of many other summits along the main divide, including Silberhorn, Tasman and Dixon. This image shows the top section of Syme Ridge on Mount Tasman. There are three climbers just visible on the ridge just above the centre of the photo, about 10 hours into their climb from the hut. This image shows the patterns of crevasses on the grand plateau, just above the Hochstetter Icefall. Plateau Hut at night.  Julian Thomson, GNS Science The climbing party left Plateau Hut just after midnight with clear, cold weather conditions that were perfect for the climb. Mt Cook Summit Rocks, Photo Geoff Wayatt Aoraki / Mount Cook is a challenging peak to climb, with very dynamic glaciers and steep rock and ice faces to negotiate. In this photo, the climbers are in the ice gullies that run through the summit rocks. Photo Nicolas Cullen View from the summit, with Mount Tasman in the background Photo Nicolas Cullen Looking along the summit ridge of Aoraki / Mount Cook, with the two GPS units in place. The very highest point is about 45 metres distant. The GPS units measured a height of 3719 metres at their position. This measurement was consistent with the height from the computer model which then allowed the height of the high peak to be calculated as 3724 metres above mean sea level. This means that Aoraki / Mount Cook is a full 30 metres lower than the 1991 estimate of its height, showing that the mountain peak has continued to erode significantly during the last 22 years. There is more information about the project at the Otago University School of Surveying website. Here is our video of the expedition : Mountaineers staying at Plateau Hut can get an incredible 360 view of the surroundings from nearby glacier dome. We have even created a GeoTrip for the location:  www.geotrips.org.nz/trip.html?id=450

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