Stepping Over the Boundary

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This is a classic view of the Southern Alps from Lake Matheson on a still morning, showing the high peaks of Mount Tasman and Mount Cook.The Alpine Fault runs along the foot of the steep rangefront, extending right up the West Coast of the South Island. The mountains are therefore part of the Pacific Plate and all the flat land in front, made up of glacial outwash gravels, is on the Australian Plate. This graphic shows the Alpine Fault as a very distinct line dividing the high mountain topography to the East and from the coastal lowlands along the West Coast. Arrows show the horizontal directions of fault ruptures along the fault, but there is also a vertical component that is pushing up the Southern Alps. At Gaunt Creek near Whataroa, you can get right up close to a cliff exposure of the Alpine Fault.  The pale green rocks in the foreground have endured being crushed and uplifted along the  fault line. They have been altered into what is known as cataclasite, consisting of clay and lots of crushed rock fragments.You can visit this location by checking out our GeoTrips website here: www.geotrips.org.nz/trip.html?id=57 The low angled line of the Alpine Fault is very distinct on the right side of the photo, with the metamorphosed cataclastic rocks that have been uplifted from kilometres down in the crust being pushed over the much younger gravels to the West (right). You really can put your finger on New Zealand’s plate boundary here! The Pacific Plate is on the upper left, thrust over ice age gravels of the Australian Plate on the right hand side of the image. The photo gives a good impression of the nature of the crushed rocks. A more distant view of the cliff section from the creek shows how the uplifted rocks have over-ridden the gravels which are about 15 to 16 thousand years old. The two white arrows show the line of the fault. A short distance away is the Deep Fault Drilling Project (DFDP1) Observatory that was set up after two boreholes were drilled here in 2011. The fault is dipping at about a 40 degree angle, and the boreholes were positioned to intercept it at around 100m depth. Instruments down the boreholes include seismometers and other sensors that have been installed to better understand the physical conditions along the fault as it extends down below the surface. For a bit more background to the DFDP have a look at this previous post from 2011

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The Fox

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A visit to Fox Glacier shows that changes over the last 5 years are similar to those at the Franz Josef Glacier.  Here is a view of the Fox Glacier front in 2009:  And this year (March 2014): The terminal face from another angle in 2009… …and as it was recently in 2014. The grass covered hummock in the centre marks the previous limit of the ice. There is a good view down onto the glacier from the moraine wall that can be accessed via a well made track. It is apparent that the glacier has not just got shorter, but the whole surface has lowered by tens of metres. This view of the present terminus shows that unlike the Franz Josef glacier, the Fox can still be accessed by climbers and guided groups. However, the future outlook is similar to that of the Franz. Update March 2015 – timelapse video of Fox Glacier terminus retreat through 2014 by Brian Anderson (Victoria University Wellington).This amazing timelapse shows how the moraine walls of the glacier are affected when the buttressing effect of the ice is removed. Worth watching through a couple of times to catch the details: Fox Glacier’s spectacular retreat from Brian Anderson on Vimeo. Have a look here for information about visiting the Fox glacier, which is one of the locations on our GeoTrips website:  www.geotrips.org.nz/trip.html?id=244 

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Franz Josef Ice on the Retreat

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Franz Josef Glacier 2009 – Julian Thomson GNS Science Recently I visited the West Coast Glaciers and was interested to see their condition after my last visit 5 years ago in 2009. Franz Josef 2009- Photo Eric Burger These photos give and immediate comparison of Franz Josef Glacier over the last 5 years: In 2009 the glacier filled the head of the valley with its spectacular ice falls. It was easy to walk onto the glacier with the appropriate equipment – crampons and ice axe. Franz Josef 2014- Julian Thomson, GNS Science 2014 – a big difference! The ice is now no longer apparent on the floor of the main valley, and only the distant ice of the upper ice fall can be seen. The glacier terminus has melted back by about 500 metres. From closer up, this is where the terminus of the glacier was in 2009. You can see that rock debris now covers the area. The exposed wall of the valley on the left shows where the ice level was in the late 1990s. The mound on the right is actually an isolated heap of ‘dead’ (stationary) ice that has been protected from melting by the insulating effect of rock fall debris that fell onto part of the glacier several years ago. The hollowed out and unstable ice and rock is the reason why tourists are not allowed to go any further up the valley than this. Some of the boulders are smoothed and rounded, having been dragged along at the base of the glacier before being dumped where the ice melted. Huge jagged boulders like this one will have fallen onto the surface of the glacier from the adjacent cliffs. They have not been smoothed by any scraping action along the bed of the glacier. This ridge of boulders running from the foreground into the centre distance of the image is one of several small terminal moraines left recently by the retreating ice. The glacier is now away to the left of the image. Is this a view of the long term future of Franz Josef, or will this barren pile of debris be over-ridden again by the glacier again sometime soon? Measuring summer melting at Franz Josef 2009 To explore this question further we need to understand a bit about the dynamics of a glacier. (For more in depth information about processes of glacier formation have a look at our GNS glacier page here.) On  top of a general understanding, we also have to consider some of the unique characteristics of Franz Josef glacier, and its sister, the Fox.  Franz Neve,  Julian Thomson GNS Science Lloyd Homer GNS Science With extremely high snowfall over a large accumulation zone and a steep, narrow valley that funnels the ice quickly to a very low altitude, the Franz Josef and Fox glaciers are the most sensitive in the world to climate change. Residual snowfall at the top of the glacier at the end of the summer melt season has been measured at over 8 metres of water equivalent per year. Ice melt at the terminus is around 20m w.e./ year which is the highest annual melt rate known for any glacier. The loss of ice of the lower glacier is replaced by very rapid flow rates of up to 2.5 metres per day that transports the abundant accumulation to lower altitudes. This dynamism is the cause of the sensitivity of the glacier to changes in average snowfall or temperatures which are reflected in an adjustment of the terminus position (glacier front) in only about five to six years. From 1890 to about 1980 the Franz has retreated by over 3.5 kilometres, interspersed with 3 or 4 re-advances of several hundred metres lasting roughly 10 years each. However, from about 1980 to 2000, there was a more substantial re-advance of 1.5 kilometres. This has been associated with regionally wetter and cooler conditions brought about by a phase of more El Nino conditions. These in turn relate to a fluctuating climate cycle called the Inter-decadal Pacific Oscillation. However, while the Franz and Fox were re-advancing, other glaciers in the Southern Alps with longer response times,continued to lose ice as they were (and are) still responding to the general warming of the 20th Century. Mount Cook and Hooker Valley,   J. Thomson GNS Science Overall from the 1850s to about 2007, it has been calculated that 61% of the ice volume of the Southern Alps has been lost, and from 1977 to 2005 there was a 17% reduction in ice volume. mainly because of massive calving into lakes that have formed at the termini of the Tasman and other valley glaciers, and also the continued downwasting ( i.e. surface lowering due to high rates of melting) of these larger glaciers. Re-advances of the Franz Josef, when they occur, have to be understood against the underlying trend of a warming climate. In the light of this, we can expect that, subject to temporary fluctuations, our cherished view of the Franz Josef’s terminal ice face from the approach walk has a rocky future. An excellent information leaflet about the Franz and Fox glaciers is available from GNS Science: Franz Josef Glacier features on our GeoTrips website, in case you want to go there: www.geotrips.org.nz/trip.html?id=245

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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 Dart Landslide

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Simon Cox   GNS Science M. McSaveney GNS Science Slip Stream is a tributary to the Dart River in the South Island of New Zealand. There has been an active landslide here for several thousand years, periodically sending down lobes of debris to gradually build up a large fan in the Dart Valley. There was vegetation established right across the fan, but over the last few years the widespread cover of trees has been largely buried and killed off by a very active phase of erosion and deposition. Debris volumes of the order of 100 000 cubic metres have been coming down during heavy rains in the spring and summer periods. Simon Cox  GNS Science The debris gets mobilised into a wet mix of mud and boulders.  The latest large event occurred early in this month (4th January 2014), and the flows continued to build up over several days. M. McSaveney GNS Science The debris flows crossed right over the valley, blocking the Dart River with a low angled, shallow pile of soft sediment. M. McSaveney GNS Science A lake formed in the valley above the slip, becoming about 4 kilometres long. The river is cutting down into the debris, and it is expected that the depth of the lake will fluctuate during landslide activity. The Department of Conservation is diverting the affected part of the Dart Valley track so that trampers can continue to visit the area. Photo DoC/Vladka Kennett This image gives a good overview of the affected area.  It shows the fan with the darker coloured triangle of recent debris, as well as the length of the lake. This is a graph from the Otago Regional Council website showing 7 days’ rainfall recorded from the 9th to 16th January at the Hillocks, about 24 kilometres down the Dart Valley from Slip Stream. The second graph shows how the river flow responded to the rain, with a sharp peak and a gradual tailing off after the rain stopped falling. The tail is not entirely smooth with a dip when the flow gets below 100 cubic metres per second. This suggests that when the river level drops, the continuing input of debris at the slip impedes the flow for a while, until the blockage is overcome and the flow rate increases again. Mark Rattenbury (left), Simon Cox (right) and Mauri McSaveney (behind the camera) visited the area to assess the impact and any possible downstream hazard. Note that a special DOC permit is required to visit Slip Stream as it is in the sacred Te Koroka topuni area of Mount Aspiring National Park.  The slip is in a state of continual instability and the area is hazardous. In this video Simon explains some of the interesting features of the slip, including some very strange bubbles that release dry dust when they burst:

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The growth of Tasman Glacier Lake

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The Tasman Glacier is the largest glacier in New Zealand. Its upper section is mostly white as you would expect of a river of ice. However, the lower half is covered with a layer of rock debris about a metre thick. This forms an insulating layer that slows down surface melting and allows the glacier to descend a long way down the valley to warmer elevations. This photo, taken from the location of the the top of the moraine wall near the old Ball Shelter in 2007, shows what the debris covered surface of the lower Tasman Glacier looks like.The moraine walls show how much the glacier surface has lowered in the last century. Before about 1912 the glacier surface was higher than the lateral moraine. New Zealand’s other large valley glaciers have all been suffering a similar loss of ice. Tasman Moraine Wall.      Julian Thomson GNS Science This is what the moraine wall of the Tasman Glacier looks like close up. The unstable terrain is very hard to travel over, especially when you are carrying heavy gear like this group of glaciologists. For more information about fascinating processes of glaciation check out this GNS Science web page. On our flight up to the Grand Plateau for the height survey of Mount Cook recently, it was interesting to see the state of the terminal lake of the Tasman Glacier. This has been expanding rapidly in recent years.  Once the lake became well established, the water could undermine and erode the ice much more quickly. This photo illustrates the process of melting of the ice. The surface water cuts away into the ice face to create a notch at water level. Once this notch is several metres deep, the overhanging ice collapses, leaving buoyant ice underwater that eventually breaks off in big pieces to float up to the surface as a new iceberg. The icebergs will continue to be eroded by the water in the same way. As they get lighter, they rise up in the water, lifting the ice notch up to give a mushroom like profile. The bergs often get top heavy by this process and can unexpectedly roll over. This video that we made several years ago gives a dramatic illustration of this process seen from a boat at close quarters: Here is some information on our GeoTrips website if you want to visit the lower reaches of the Glacier for a closer look: www.geotrips.org.nz/trip.html?id=147 I have flown up the Tasman Glacier several times on various glacier field expeditions in recent years. This is a photo of the lower section in 2002, looking down valley. The glacier itself is about 2 kilometres wide and the lake is already extending up the east side of the glacier by about 5 kilometres. Two years later (November 2004) you can see that the lake has continued to expand. The large ponds that can be seen near to the lake have grown and started to join together as more and more of the ice melts. November 2007, after a large break out of ice bergs, the lake has greatly increased in size. November 2013 from our recent flight up to the Grand Plateau on Mount Cook. It is inevitable that the lake will continue to expand. Due to the overdeepening effect of the glacier on its bed, the deepest point of the lake will be some distance up from the terminus, probably below the  area in the foreground of the image. After expanding past the deepest point, the lake will get shallower and shallower as it progresses up the valley, potentially to the point where the bed of the glacier meets the lake surface. It has a long way still to go. This image (added as an update in early March 2015) shows that the basic shape of the lake hasn’t changed substantially since the previous photo was taken over a year ago. However, if you look at the position of scree slopes on the right of the photo you can see that the glacier’s retreat is continuing. In this last photo you can see that as the lake erodes further up the glacier, the terminal ice cliff at the edge of the lake is getting higher due to the increasing surface elevation of the ice. There is a very good view of the lateral moraine wall in the background, that used to be below the level of the glacier surface back in the nineteenth century.  The glacier ice in this area has thinned vertically by roughly 200 metres since that time.

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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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Global Catastophe in a thin rock layer

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K-Pg boundary layer – when the Earth changed forever The K-Pg Boundary (or Cretaceous Paleogene boundary, or K-T boundary as it is still sometimes called) is a layer in the Earth’s crust that marks a very dramatic moment in the history of life on earth about 65 million years ago. There is a huge change in the fossil communities of plants and animals across this boundary. Over half the species that are found in Cretaceous rocks are missing from the younger Paleogene rocks above them. Included amongst the creatures that vanished forever at this precise point in time are the ammonites, large marine reptiles (such as mosasaurs and plesiosaurs), large flying reptiles and of course the dinosaurs. New Zealand has a unique record of the K-Pg boundary. These eight localities in the northern South Island provide the only Southern Hemisphere record of how the catastrophe affected land plants (Moody Creek Mine) and marine life (Waipara River and six localities in near Blenheim).   An artists image of the impact by Don Davis of NASA The now well established explanation for this dramatic crisis in the history of life is that an asteroid, about 10 km across, struck the earth near Mexico, causing a huge tsunami and a global dust cloud that darkened the skies worldwide for months, thus killing plant and animal life. After a period of recovery that lasted several thousand years, the remaining plants and animals were able to diversify into the ecological niches made vacant by this mass extinction. Mammals were one of the groups that flourished and ultimately gave rise to humans.  The dark line of the K-Pg boundary at Chancet Rocks Recently I joined a group of scientists visiting several sites in Canterbury and Marlborough, where the K-Pg boundary is exposed. K-Pg boundary at Chancet Rocks centre left of photo At Chancet Rocks, just north of Ward Beach, the light coloured Cretaceous limestone contrasts with the darker grey Paleocene rocks on the right side of the photo. These rocks were laid down in several hundred metres of sea water, and the fossils found within them are mostly microscopic unicellular plants and animals. These have been studied in detail and are very different assemblages. This slab cut through a section of K-Pg boundary by John Simes and Chris Hollis was taken from the coast south of Chancet Rocks. If you click on the image to enlarge it you can see some of the features in more detail. You can see the thin layer of clay that precisely marks the boundary itself. This layer has been found at sites around the world, including drill cores from the ocean floor, and is remarkable for containing high levels of an element called iridium. Iridium is common in asteroids and its abundance at the boundary was a key part of the evidence that lead to the asteroid impact theory. We also visited Woodside Creek, the first K-Pg boundary locality in New Zealand that was found to be enriched in iridium. Here you can see that the river was quite high, making access a little bit difficult. This is the Woodside Creek section. It has been sampled a lot over the years so that quite a lot of the rock has been mined away. The drill holes you can see in the rock layers on either side of the boundary itself show where scientists took samples for the analyses that led to the discovery of iridium enrichment. The image at the top of this page was taken from here. This is a close up view of the very top surface of the Cretaceous at Woodside Creek, just beneath the iridium rich boundary clay. The masses of tiny pock marks in this surface are thought to have been caused by droplets of glassy impact ejecta raining down onto the sea floor from high in the atmosphere after the impact thousands of kilometres away. Chris Hollis at GNS Science has done very detailed studies of the Cretaceous and Paleogene rocks in New Zealand. He is a paleontologist who specialises in tiny microfossils called Radiolarians. Radiolarians are marine plankton that construct complex shells of glass (opaline silica); each species has a distinctly different shell. Radiolarians are one group of organism that didn’t go extinct at the K/Pg boundary. Instead, some species became very rare, while new species evolved and flourished.  These microfossil changes are clearly shown in rock samples from the K/Pg section at Flaxbourne River, where over the distance of a few millimetres one group of radiolarians (nassellarians) are almost completely replaced by another group (spumellarians). This change is thought be a consequence of rapid cooling of the ocean waters around New Zealand. In this video Chris tells us about the Woodside Creek K-Pg boundary section:

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Weather Station at Lake Ohau

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To quantify the linkage between weather events and sedimentation in Lake Ohau, a weather station has been set up in the valley at the head of the lake. This is only possible due to kind assistance from the Inkersell family at Lake Ohau Station. I accompanied Heidi Roop to the weather station as it needed a bit of maintenance. We had a few visitors join us while we were there. No doubt they have an interest in weather data. In fact, some of the maintenance we were doing was because the cattle had chewed through the wiring to the weather station! The weather station measures air temperature, relative humidity, solar radiation, wind speed, wind direction, and precipitation . Data is collected every 10 minutes and is recorded in the data logger below the mast.   Precipitation events that  produce surges of sediment transport into the lake are recorded and linked to data collected by other instruments in the lake and up in the Hopkins River valley. This is helping to build up a detailed understanding of erosion, transport and sedimentation processes  in action in Lake Ohau.

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