Natural Hazards

Natural Hazards Science for East Coast Schools

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Natural Hazards Activities for Schools This article is about a science education project that I was involved in that was supported by MBIE’s Unlocking Curious Minds fund in 2018. It involved four three-day natural hazards science camps for intermediate level students in New Zealand’s rural Tairawhiti (Gisborne – East Cape) region. A total of 109 year 7 and 8 students and 16 teachers, from 19 schools were represented. The science camps were based at four different locations (Gisborne, Te Karaka, Tolaga Bay and Ruatoria / Te Araroa) with the activities and field trips tailored to suit each area. The events included lots of field trips and hands-on problem solving tasks. Here for the record is a summary of some of the activities and also a few of the places we visited: Introductory activities included observation and thinking exercises around the theme of science and natural hazards. These included demonstrations such as: earthquake P (longitudinal) and S (transverse) waves using slinky springs. A TC1 seismometer was used to demonstrate how ground shaking (created by participants jumping on the floor) can be captured as a wave trace on a projector screen, giving a record of the magnitude (energy) and duration of the vibrations. The TC1 can be used by schools and individuals who wish to detect earthquakes and interact with other enthusiasts online as part of the Ru programme in New Zealand Rock deformation: Alternating layers of flour and sand in a transparent container show how rocks can be faulted and folded by compression of the earth’s crust. For information about this demonstration have a look this earthlearningidea.com page. For a bit of a hands-on problem solving challenge, participants were invited to create some model structures to protect an area fromcoastal erosion. The models were set up in shallow storage containers. Once the ‘seawalls’ were built, the area behind them was backfilled with sand, the containers tilted at a shallow angle, and water added to within about 15cm of the ‘sea wall’. Here is one example: Testing involved using a plastic lid to push the water in waves up against the seawall, first gently, then with increasing energy. Different designs could then be compared and strengths and weaknesses discussed.   Following this exercise we travelled to Wainui Beach, Gisborne where there has been a variety of attempts to protect the foredunes which have properties built on them. Interestingly, many of the methods that had been used were similar to those that the students thought of with their model making. Here you can see the remains of a concrete wall that has been undermined by wave erosion    Another similar model making exercise, this time including a slope of cardboard at one end, was to design rockfall barriers.  These were also tested to destruction using varying quantities and sizes of rocks rolled down the slope. We were also able to do another activity associated with flooding which has been a big issue this year in the Gisborne area.The photo shows the sediment covering some of the farmland near Te Karaka following the floods. For this activity, participants had to design a stop-bank, and test how long it could retain water, by recording any pooling of water on the ‘dry’ side , every 30 seconds. If you are an educator wanting information sheets to run these activities they can be found on the GNS Science website learning pages here. Here are some of the field locations that we visited, and what we investigated at them: At Pouawa Beach, north of Gisborne, we made careful drawings of some deposits that are thought to have been laid down by a tsunami. Shells in these layers have been radiocarbon dated at about 2000 years old. The layers include gravel and shells that would have been transported from the sea floor. Using a  drone we could get a good view the top of a marine terrace (the flat surface upper left of pic) at the north end of the beach. The terrace was formed at sea level as a wave-cut platform during the last interglacial (about 80 thousand years ago), and has been uplifted since its formation by tectonic activity. There is a wide shore platform which you can see just covered by water in the photo. Another great example is nearby at Tatapouri –  for more information check out the GeoTrip here – these surfaces will also be uplifted eventually to form another step in the landscape. These marine terraces show that earthquakes and tsunamis have a long history on the East Coast! At the north end of the beach. we passed a landslide that had occurred during the very wet weather in June 2018. From the ground we could see the toe of the slip which included tree trunks, boulders and lots of muddy sediment. With our drone, we were able to get a much more complete view of the slip, including the source area, which was not visible from where we were standing. This shows clearly the value of drone technology as a tool to extend our view of this active landscape: Next stop Tolaga Bay, where the beach has been covered by logs, brought down from the forestry plantations by the recent heavy rainfall. The logs caused a lot of damage to properties, bridges and land as they travelled down the flooded rivers. Here we spent some time analysing the types of logs scattered on the beach, by counting the different species (pine, poplar, willow or other) within 10m square quadrats. The results showed that by far the majority came from pine forestry. We were able to visit a forestry area inland of Tolaga Bay, which showed that following harvesting of the pine trees, there is a period of time where the land is vulnerable to erosion before the next generation forest grows large enough to stabilise the soil. Following clear-felling, the slash (abandoned logs and branches) can get washed into rivers during heavy rainfall. Further North still we did a day trip

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Landslide Dam

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Seaward Slide, J.Thomson @ GNS science Rockfalls and landslides were one of the dramatic consequences of the M7.8 Kaikoura Quake. This first photo shows one that is actually so huge that you might not at first recognise it for what it is. The white cliff in the distance is the landslide scarp and the huge green capped pile of grey in the middle distance is the debris that fell away. This landslide was of course made famous on TV by the cows that became trapped on an isolated hummock in the debris pile. SH1 and Railway, Steve Lawson @ GNS Science A large number of coastal cliffs collapsed, causing spectacular damage to the coastal transport infrastructure. In this image you can see how the raiway line has been lifted up and dropped across the road and across the beach. J.Thomson @ GNS Science Another example of rockfall damage along the coast: Hapuku Landslide, Steve Lawson @ GNS Science In the Canterbury ranges, a short distance inland, a number of landslides have blocked river valleys and created landslide dammed lakes that are now filling up. This image shows the massive Hapuku landslide, which has buried the valley in over 150 metres of debris, weighing many millions of tonnes. The grey coloured lake in the centre of the image is a couple of hundred metres long Hapuku landslide, J. Thomson @ GNS Science This is a close up view of the lake taken a few days later. The lake is now near to the point of overflowing the dam. The problem with these dams is that they can fail catastrophically, sending a debris flow of water, mud and rock down the valley with potentially very destructive consequences. Linton landslide survey, J.Thomson @ GNS Science In this image you can see another landslide, this time in the Linton Valley. It has also dammed a small river. The team here are surveying the debris and the shape of the valley in order to calculate the possible downstream consequences of a breach of the dam. Linton landslide, J.Thomson @ GNS Science This photo shows the size of the landslide.  A large section of forest has slid down with it with many trees still standing. The debris has again blocked the valley to form a lake. Linton landslide dam, J.Thomson @ GNS Science The lake level is still about 10 metres below the rim of the dam: Linton landslide dammed lake, J.Thomson @ GNS Science In order to measure the lake’s water level safely, Chris Massey took a GPS reading from the helicopter whilst it hovered just above the water surface. Linton landslide, J.Thomson @ GNS Science Meanwhile at the base of the dam, some water is percolating through the debris, although the flow in the stream bed is much less than usual: Linton landslide, J.Thomson @ GNS Science This photo shows the toe of the landslide – a mass of rock debris and damaged trees. Linton landslide, J.Thomson @ GNS Science By the end of a few hours, we had lots of data in the form of laser scans of the slip from different locations, as well as hundreds of drone and aerial photos, which are combined to make a 3D digital image that can be used to model the possible consequences of the dam breaching in different ways. This video made by Steve Lawson is a virtual ‘fly through’ of the digital model: And here is a short video about these landslide dams: Finally, there is more information about landslides on the GeoNet website here

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The Kekerengu Fault

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Photo Tim Little @ VUW Whilst there were many faults that ruptured during the recent M7.8 Kaikoura Earthquake, the Kekerengu Fault is perhaps the most awe inspiring in terms of its effect on the landscape and infrastructure. As it ripped through the countryside, it displaced the land to either side by an astonishing 8 to 10 metres sideways and about 2 metres vertically over many kilometres of its length. Kekerengu Fault offset, J.Thomson @ GNS Science In places this horizontal offset is even more – up to a whopping 12 m. This is impressive on a global scale. In the first two images here you can see what this looks like where farm tracks have been sliced through at a right angle. Here is a drone’s eye view from above: Kekerengu Fault,   J.Thomson @ GNS Science As the trace of the fault passes through different locations, it expresses itself in a number of ways. Across the river from Bluff Station, it has opened up an enormous crevasse, not unlike the sort of thing that mountaineers often see on a glacier. This will be due to either a slight bend in the fault trace, and/or slumping of the downhill side of the fault where there is a slope. Kekerengu Fault,   J.Thomson @ GNS Science Slickensides is the name given to the scrape marks  on the surface of the wall of a fault. Here you can see that they are dipping down at about 28 degrees from the horizontal (towards the south-west). This is useful information to help understand the direction of movement of the rupture, and tells us that this fault moved obliquely (sideways and up).  When we looked across the fault we could see that the land on the far side had moved to the right. It is therefore a ‘dextral’ or ‘right lateral’ oblique slip fault. Kekerengu Fault,   J.Thomson @ GNS Science Fences are really useful markers to allow measurement of the fault offset, especially when they cross the fault at close to 90 degrees.as in this photo. Yes – those two lines of fencing used to join up! Kekerengu Fault,   J.Thomson @ GNS Science The hillside here appears scarred by a simple knife cut… Kekerengu Fault,   J.Thomson @ GNS Science …whereas in other places, the slip is distributed over a broad area of surface deformation. In this case it is likely that the groundshaking helped the hillside follow the call of gravity to spread the deformation over a large area. Kekerengu Fault,   J.Thomson @ GNS Science Near to the coast, the Kekerengu Fault tracks across this field towards the main state highway and the railway. Here the fault trace is a mound of huge clods of earth and ripped turf. We call this a “mole track”, and it results from some compression rather than extension along this part of the fault trace. Kekerengu Fault,   J.Thomson @ GNS Science Not far away, State Highway 1 has been pushed sideways in several pieces… Kekerengu Fault,   J.Thomson @ GNS Science and the nearby railway has been pulled so hard that it snapped. Kekerengu Fault,   J.Thomson @ GNS Science The fault runs right under this small bridge which is totally destroyed. Kekerengu Fault,   J.Thomson @ GNS Science Lots of food for thought and plenty of work ahead for earthquake scientist Russ van Dissen and his colleagues.

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A Ruptured Landscape

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J,.Thomson @ GNS Science On the ground in the Kaikoura Quake aftermath: Following the recent M7.8 Kaikoura Earthquake, a number of teams of scientists have been deployed to survey the geological impacts and assess the potential ongoing risks to people and infrastructure. This gallery of images shows some of the numerous dramatic impacts of the quake in the coastal area to the north of Kaikoura.  J.Thomson @ GNS Science Accessing the area by road involves careful driving. The road surfaces next to many of the bridges have subsided, creating a crack at either end of the bridge:  J.Thomson @ GNS Science Slumping has occurred along parts of the highway:  J.Thomson @ GNS Science This photo shows the now famous house at Bluff Station that had the mis-fortune to be built directly on top of the Kekerengu Fault. The house was shunted about 7 metres sideways leaving some of its foundations behind. J.Thomson @ GNS Science  The house was pushed across its own driveway… J.Thomson @ GNS Science  The coastal highway and railway have unfortunately been cut through in several places by fault ruptures. This view looking south at Waipapa Bay shows the northern branch of the Papatea Fault crossing SH1 and heading out to sea. J.Thomson @ GNS Science This is what the road now looks like on the ground. The fault scarp has been bulldozed to allow vehicle access. J.Thomson @ GNS Science A short distance away, the railway line was lifted up and dropped in the grass next to its original gravel bedding. J.Thomson @ GNS Science From the top of the fault rupture, you can see that the displaced railway tracks extend for about 300 metres into the distance. Will Ries @ GNS Science A few hundred metres further south, the southern branch of the Papatea Fault crosses the road and railway. J.Thomson @ GNS Science The earthquake ripped right through the concrete culvert that ran under the road, and again lifted the railway off its bed. J.Thomson @ GNS Science From the air, the scarp of the southern branch of the Papatea Fault is seen to extend like a knife-cut across the shore platform. In this image you can sea the uplifted coastline extending into the distance. The total uplift of the area left (east) of the fault is 5 to 6 metres, whilst the area to the right was uplifted by a smaller amount. Water has been ponded up against the new fault scarp. J.Thomson @ GNS Science A helicopter view showing the scarp of the Papatea Fault close up (across the top of image). The fault movement is thought to have been mostly horizontal with about 2 metres of vertical uplift in addition. J.Thomson @ GNS Science The Papatea Fault scarp is a sheer wall about 2 metres high. J.Thomson @ GNS Science Part of the task for scientists is to measure the uplift along the coast. The high and low water marks make a useful reference point that can be surveyed against the new sea level positions. J.Thomson @ GNS Science Sadly the raised shoreline stranded innumerable sea creatures that now litter the area amongst the seaweed. J.Thomson @ GNS Science Rockfalls have been numerous, and have caused a lot of damage where the road and railway are squeezed up close to the coastal cliffs. J.Thomson @ GNS Science The end of the road? The reason why you won’t be travelling into Kaikoura from the north anytime soon. This rockfall is at the south end of Okiwi Bay, and there are more slips like this further south. There are several GeoTrip locations that you can visit to see the changed landscape along the Kaikoura Coast such as this one 

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Lahars on Ruapehu

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Ruapehu Eruption, Image: Lloyd Homer@GNS Science Ruapehu is very popular with skiers, trampers and other adventurers. As an active volcano with the potential for sudden eruptions through its crater lake, Ruapehu presents the Department of Conservation with a significant hazard management issue. Lahars on Ruapehu: Image: Lloyd Homer@GNS Science Obviously there is the possibility of people in the vicinity of the summit area being immediately affected by water, rocks and ash thrown out by an eruption. An additional hazard is that displaced water and sediment from the crater lake can mix with snow and loose volcanic material to create fast moving mudflows (lahars) which descend rapidly down valleys radiating away from the summit. The collapse of the crater wall can also cause a lahar to flow down the Whangaehu Valley to the east of Ruapehu, independently of an eruption. It was this type of lahar that caused the railway tragedy at Tangiwai in 1953. This video explains the basics of lahars at Ruapehu and the two ways they can be created: Image Graham Leonard@GNS Science Not surprisingly, due to the high number of mountain users, the lahar hazard has been studied in detail and measures put in place to give warnings and reduce the potential impact on people and infrastructure. This has involved a close collaboration between GNS Science (GeoNet), the Department of Conservation and Ruapehu Alpine Lifts who run the ski areas. First of all, regular monitoring of the crater lake’s physical and chemical properties is carried out by GNS volcanologists as part of the GeoNet project. This alerts them to changes of activity within the volcano: This information helps the GeoNet team to set the volcanic alert level for the mountain, which is important for a number of agencies such as the air industry, Regional Councils, local businesses and others. Because of the potential for some eruptions to occur with little or no warning, and the speed with which lahars travel down the slopes, there is also an Eruption Detection System (EDS) in place. This is triggered when both ground-shaking (seismic waves) and an air blast are detected within a short time of each other at a number of monitoring stations throughout the Tongariro National Park. This image shows the arrivals of volcanic earthquake tremors (top) and the air blast (bottom) of an eruption, at a station about 9 kilometres from the crater lake: You can see that there is a time lag of about 30 seconds between the onset of groundshaking and the arrival of the air blast at the same station. The EDS system has been developed by GeoNet and is unique in the world. A detected volcanic eruption will automatically set off the Lahar Warning System, consisting of loudspeakers that warn people in the ski areas to get out of valleys that could be affected, and onto high ground nearby. This video describes the system that has been set up to protect skiers on the mountain and how it is tested for its effectiveness: There is also a lot of information displayed visibly at key points in the ski areas and surrounding facilities and communities to explain the lahar hazard, and what to do or not to do if a warning alarm is sounded:

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Disaster Risk Reduction in Indonesia

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GNS Science, in partnership with a team from the University Gadjah Mada (UGM) in Yogyakarta, is involved in a 5 year project to reduce the risks caused by natural disasters in Indonesia. Coastline, West Sumatra   J.Thomson@GNS Science Indonesia is a huge and very diverse country, made up of about 20 000 separate islands, with a total population of 250 000 000 people and hundreds of different local languages.  A very active plate boundary running alongside the country, along with its complex topography means that  much of Indonesia is susceptible to earthquakes, tsunamis, landslides, floods and volcanic eruptions. Population pressure forces many people to live in areas that are highly vulnerable to these hazards, such as coastlines, river banks and on the slopes of volcanoes. This small river in Palu, Sulawesi, can become a raging torrent in heavy rain. Several houses on the right bank were washed away in a flood some years ago, and yet people still live right next to the river on the opposite bank. Another disaster waiting to happen?  2004 Tsunami aftermath, G.Mackley In recent years some of the major natural disasters in Indonesia include the 2004 tsunami that devastated Banda Aceh, as well as several subsequent damaging earthquakes.  The Strengthened Indonesian Resilience – Reducing Risk from Disasters (StIRRRD) project aims to bring different agencies together in Indonesia to better prepare people and infrastructure from future such hazardous events.   Image; G. Mackley New Zealand has similar geological and environmental conditions to Indonesia, but a much smaller population. It is a much simpler matter for organisations in New Zealand to work together on common issues relating to hazards. For example science, engineering, planning, environmental management, civil defence, NGO and government agencies can share information to assist decision making processes around disaster risk reduction (DRR). This integrating capability and experience is what New Zealand can contribute to assist a larger more complex country like Indonesia in such a project. I joined the GNS Science team recently on a visit to some of the districts in Indonesia that are participating in the project. Michele Daly from GNS Science addresses a meeting in Palu. Over two weeks we travelled to Palu and Donggala (Central Sulawesi), Mataram (Lombok), and Bengkulu and Padang in West Sumatra (see project map here). We were involved in meetings and workshops with people from many agencies, and also went on several field trips to look at different environments and projects. In this video, Michele Daly from GNS Science, and Faisal Fathani from UGM, give and outline of the project:   J.Thomson @ GNS Science   Here are some images from the field trips: An active fault runs up the cliff between the brown coloured sandy rock on the left and the pale grey limestone on the right that has collapsed in a large rock fall. This is near Donggala, Central Sulawesi. J.Thomson @ GNS Science A year ago the village of Gol in Lombok was almost totally destroyed in an earthquake that lasted a few seconds. This newly rebuilt house stands next to the broken ruins of its predecessor that have yet to be cleared away. J.Thomson @ GNS Science This sea wall on the coast of North Lombok was built to protect the village next to it. Within a year of construction it was breached in a big storm and many houses were severely damaged. J.Thomson @ GNS Science This massive concrete structure being built near Bengkulu in West Sumatra is a tsunami vertical evacuation building. When completed it will be used as a community centre, with enough space and supplies on the top level for about 2000 people to escape from a tsunami at short notice. This example shows how the Indonesians are taking on significant Disaster Risk Reduction initiatives. For more information about this project and to be in touch with updates have a look at the StIRRRD Blog or ‘like’ the project on Facebook.

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Jumping Faults

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The Alpine Fault is divided into several segments based on changes in its tectonic structure and earthquake history along the plate boundary. The northern end of the Alpine Fault is much less straightforward in comparison to the southern and central sections. This is in the area where other faults of the Marlborough Fault System branch off the Alpine Fault and take up a large amount of the total slip. There is still a lot to find out in terms of their combined earthquake histories and how these faults interact in relation to each other. In 1964, a concrete wall was built across part of a paddock next to the Maruia River, near Springs Junction (see yellow dot on the map above). The wall is 24 metres long, about 1.5 metres high, and at first sight seems pointless, standing alone and unconnected with any other structure. I visited this location recently with Rob Langridge, earthquake scientist at GNS Science, 50 years after the wall was built. If you would like to go there have a look at our GeoTrips website: www.geotrips.org.nz/trip.html?id=59 The wall was built directly across the Alpine Fault by scientists who wanted to test whether it would be gradually pulled apart by slow sideways creep along the fault. As you can see – it has suffered no damage due to any gradual movement since it was built.This very clear finding is in accordance with our present understanding that most New Zealand active faults are locked. They do not gradually creep between rupture events, but do all their moving in sudden jumps – during earthquakes. Right next to the experimental wall, there is an overgrown stream channel that has been offset sideways by about 10 metres along the line of the fault. Some years ago, a series of pits were excavated to assess the age of the offset river features. In one pit a piece of buried wood was found and then radiocarbon dated, showing that the surface is about 1200 years old. This means that the 10 metre offset has occurred since this time, giving an annual slip rate (rate of movement) of the alpine fault about 8 mm at this location.  This compares with about 27mm per year for the central and southern sections of the Alpine Fault, further south. The last rupture here at Springs Junction in about AD 1600 offset a nearby river terrace by about 1.5 metres. This suggests that at least two earthquakes will have accumulated the 10 metres of offset of the stream channel.

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Mount Cook Rockfall

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Hooker Valley rockfall. – Simon Cox / GNS Science On the evening of Monday 14th July there was a large rockfall from the western slopes of Mount Cook into the Hooker Valley.   Staff from the Department of Conservation and GNS Scientist Simon Cox flew over the area  to make assessments of the  impact. The first photo shows the view towards Mount Cook with the dark shadow of the rockfall splaying out onto the Hooker Glacier on the left. Photo J Spencer / DoC Approaching the area, the scale of the rockfall starts to become apparent. As well as the debris fan there is a wide expanse of dust that settled on the opposite wall of the valley. Photo Simon Cox / GNS Science The devastated area of mountainside that was swept by the avalanche is well over a kilometre across. Photo Simon Cox / GNS Science Because of a prominent ridge in the path of the rockfall, the debris divided into two separate lobes as it poured down the mountain. This photo shows the smaller, upper branch and the white ridge (known as Pudding Rock) that obstructed the torrent of rock and ice debris. In the foreground is the dust covered icefall. Photo Simon Cox / GNS Science This is a view of the area from higher up, looking down the valley. Simon estimated that roughly 900 000 cubic metres of rock debris are scattered on the valley floor, having travelled  up to 3.9 kilometres and fallen a vertical distance of 1600 metres. On its journey down the mountain, the avalanche scooped up possibly three times as much snow and ice which mixed with the rock material. Photo Simon Cox / GNS Science A view upwards towards the low peak of Mount Cook, showing the source area and path of the rock avalanche Photo: DoC / J Spencer  Amazingly, the Gardiner Hut just avoided obliteration due to its favourable location on the tip of Pudding Rock. However it was badly damaged.   Photo: DoC / J Spencer The toilet block was crushed and the hut pushed off its foundations. Luckily no-one was inside. Photo DoC / D Dittmer Clinging to the mountain amongst a sea of debris. The Gardiner Hut was in the best possible position to (almost) avoid destruction in this rockfall event. Photo DoC / D Dittmer Finally here is a view of the headscarp with the 300 metre high x 100 – 150 metre wide grey rockfall scar on the cliff face, the source of all the devastation. You can visit the end of the Hooker Glacier, one of the spectacular day walks at Mount Cook: Here is the GeoTrips link: www.geotrips.org.nz/trip.html?id=685

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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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