Climate

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 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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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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Lake Ohau Sediments

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Ever since its creation by the retreat of a huge glacier at the end of the last ice age, Lake Ohau has been gradually filling up with sediments washed down from the nearby mountain ranges. This is the view looking north from the lake, up towards the Dobson Valley. The valley profile has the classic ‘U’ shape created by glacial erosion, and the flat valley floor is blanketed by sediments brought down by rivers, especially during floods when the water flows with high energy. Here you can see the lake inlet. You can see the delta created as the sediments fill the lake. Lake Ohau has been receiving a high level of scientific interest over the last few years, by scientists from GNS Science in collaboration with others from Victoria and Otago Universities. Gavin Dunbar of VUW preparing equipment They aim to understand the processes of sedimentation in the lake, and work out how these processes relate to weather patterns affecting the catchment. With that information, a study of the lake floor sediments will potentially give a detailed record of how the climate has changed in the area over the last 18 000 years, since the lake’s formation. A number of limnological (lake) measurements are being made to help understand the way water currents, water temperatures and water clarity vary seasonally in different parts of the lake. This is important because it allows for understanding of the factors that influence the deposition of mud on the lake floor. In this photo Heidi Roop (GNS Science PhD student) is helping pull a sediment trap out of the water at the end of the lake nearest to the outflow. At the bottom of the trap there is a bottle of sediments that have accumulated over the last 4 months. The 1 litre bottle is removed and replaced with an empty one. The bottle is quite full because it contains concentrated sediment that has fallen into the wide mouth of the trap. Careful recording is one of the most important parts of any scientific data collection. Marcus Vandergoes and Heidi Roop prepare to lower a gravity corer into the lake to sample a small core of the top layers of sediment. As the corer penetrates about 25cm into the lake floor, the mud enters the plastic tube. A cap then seals the top end of the tube so that the mud is held in place by a vacuum as the corer is pulled back up to the boat. Once at the surface, the lower end of the tube is sealed to prevent loss of the core which is then prepared for transport back to the lab for close study of the different layers, including thicknesses of the different layers, grain size and density. Heidi and Marcus pulled up a second core to show me what can be seen when it is sliced through to show a flat surface. Darker and lighter layers are visible, which have been shown to correlate with summer and winter deposition. The thickness of each layer is thought to be related to the number and size of storms and flood events. This core includes sediment accumulated over the last 25 to 30 years. Heidi has devised a way of comparing the sedimentation of particles from different depths in the lake water at each end of the lake. She has a line with several upside down cut plastic bottles that act as mini sediment traps attached at different levels in the water column. This shows whether the currents that deliver sediments to the lake are flowing at the surface, the bottom, or at intermediate depths. It turns out that this varies between summer and winter. In summer, the warm water entering the lake carries the sediment load at a high level, whilst in winter, the particles travel along with cold bottom currents. This is why the summer and winter layers of sediment have different physical characteristics. Clear as mud – a successful day’s sample collecting from Lake Ohau,

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Lake Tutira – tectonic uplift, ice ages, landslides and cyclones

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Lake Tutira is a scenic spot on the route between Napier and Wairoa in northern Hawkes Bay. It is in a very rural setting, surrounded by steep hillsides and farmland. The landscape around the lake contains several powerful geological stories. The first is that the hills themselves, made up of rocks that are about 1.8 million years old, reach a height of up to 800 metres above sea level. Before being uplifted and exposed by erosion, the rocks may have been buried to depths of 500 to 1000 metres. This means that they have been rising at an average rate of about a metre every 1000 years. When you look at this steep hillside, you can see lines of cliffs running almost horizontally across the slopes. These bluffs are made of relatively hard limestone, with softer muds and sandstones hidden beneath the grassy slopes separating the cliffs.The top limestone band that you can see correlates with the one on the top of Waipatiki Beach that I showed in a recent post. These cliff lines therefore represent the cycles of global change that repeated every 40000 years. The hard limestones were deposited as sea levels were slowly rising, while ice caps melted at the end of each glacial period, as shown also in my previous posts from Waipatiki and Darkeys Spur. The next landscape feature of interest is this area of grassy hummocks just beyond the pine plantation. These are the debris pile from a massive landslide that slid down from the nearby hills about 7200 years ago. It blocked the stream that flowed down the valley, thus forming the present day Lake Tutira.  Similar huge rock slides occurred in other parts of the region at the same time. Scientists believe that they may have all been triggered by a single massive earthquake. One of our activities on the recent ‘Dinosaurs and Disasters Geocamp” with Hawkes Bay schools was to drill a sediment core from Lake Tutira. Kyle and Richard used a PVC drainpipe which they pushed into a shallow part of the lake bed. Although only about half a metre in length of core was extracted, you can clearly see a number of layers. The top of the core is to the left of the photo, with several organic rich layers visible. The lower half consists of varying amounts of pumice that will have been washed into the lake from where they accumulated after the Taupo eruption 1800 years ago. The lakefloor sediment has in fact been studied in detail by researchers from GNS Science and other institutions . In 2003 a drill rig was set up that retrieved a 27 metre core right through to the base of the sediments. It revealed a detailed history of the environment around Lake Tutira over the last 7200 years: Almost 1400 storms were intense enough to leave their traces in the form of layers of mud washed down from the surrounding hills. Periods when storms were more common started abruptly and could last for several decades. Volcanic eruptions from the Taupo Volcanic Zone (including the well known ‘Taupo Eruption’ of 1800 years ago)  have left layers of ash that can be dated. Changes in land use from native forest to pasture due to human occupation, have increased the sedimentation rates tenfold.. During Cyclone Bola which passed over Hawkes Bay in 1988, over 750 mm of rain fell over four days.  A huge number of mudslides came off the hillsides over the whole region. In this photo, Richard Levy and I have exposed a buried soil layer next to Lake Tutira. It is beneath about metre of pale brown ‘Cyclone Bola Mud’  (top half of image). The dark soil layer below contained branches of wood. Further down there was another pale coloured mud layer from an earlier rainstorm.

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Waipatiki Beach

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Waipatiki Beach north of Napier is a great place for family holidays in the summer.  It is enclosed by cliffs at either end that happen to provide one of Hawkes Bay’s many classic geological sites. (for more geological and access information see also www.geotrips.org.nz/trip.html?id=24) A track leading south of the beach takes you to a good view of the cliffs. (Update: there have been very big big rockfalls in this area and it is likely to be safer to explore the north end of the  beach.) You can see several colour changes in the rock strata from the base of the cliff to the top. These are due to the fact that the water depth in which the rocks were laid down changed through time. The blue grey band in the middle of the cliff is fine grained mud with a few oyster fossils, that was deposited offshore in about 50 to 80 metres of water depth.The more orange coloured rocks were laid down in shallower water, with beach sand and many fossils. Because of erosion and rock falls, there are many boulders rich in fossils that have fallen down onto the beach below. This is where you can find lots of interesting specimens. In this photo, Richard Levy, a sedimentologist from GNS Science is looking at a slab full of bivalves and sand dollars. This is reminiscent of many modern New Zealand beach environments such as along the Kapiti Coast north of Wellington.  At the top of these orange beds the fossils have been washed around and damaged by wave action, indicating a very shallow environment of deposition.  A close look will show that the fossils here include very few actual shells. This is because many sea shells are made of aragonite, a form of calcium carbonate that differs in its structure from the other common alternative which is calcite. Aragonite tends to dissolve relatively easily during the rock forming process, and to re-precipitate as calcite in the matrix of the sediment. This makes these rocks very hard, but with many gaps where shells have disappeared, leaving only the internal casts. In this photo you can see some trace fossils made by some sea animals burrowing into the sediment about two million years ago.     So why do the rocks show this change from the grey muds, deposited in relatively deep water, to progressively shallower sandstone and limestone?  Either the land was going up or the sea level was going down, or perhaps both were happening at the same time. The rocks around Hawkes Bay and other parts of New Zealand show clearly that the main cause was sea level change, which in turn was due to global ice age cycles which themselves were driven by changes in the earth’s orbit around the sun (called Milankovitch Cycles). So if you ever go to Waipatiki for a holiday, you may like to look for some fossils and consider the relationship between Astronomy and the colours of the cliff.

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Our Changing World radio broadcast

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For those of you interested in the follow up of our ice core drilling expedition, here is the National Radio broadcast of the story as told on “Our Changing World” on Thursday 20th August. The broadcast is about 13 minutes long. http://podcast.radionz.co.nz/ocw/ocw-20090820-2120-Southern_Alps_Ice_Cores_Drilling-048.mp3

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Baker Glacier

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Out of our original top 3 favourite glaciers to check for ice cores there was still one left to go. This was the Baker Glacier, visible clearly from our previous site on Mount Hutton, almost directly across on the other side of the Murchison Glacier Valley. Baker Glacier is relatively low altitude at 2360 metres. None the less, because it is also east of the Main Divide, it will have relatively low accumulation rates and, with a depth of about 70m, potential for a longer core than we got on Mount Hutton. However the radar images showed a very strong reflector at about 30 – 40 metres, possibly due to the presence of water or rock debris about half way down, a potential indicator of trouble ahead. By now we had our gear preparation down to a tee, and were set for another blitz approach to get in and out before impending bad weather trapped us in. We flew in to the upper part of the Baker Glacier, directly opposite the imposing cliffs of the East Face of Malte Brun. Almost immediately an ice avalanche rumbled down the face, I guess as some sort of greeting to us.Within a couple of hours the drill was set to go and the tents were in place. After getting past the initial surface snow, we were soon pulling up nice quality ice cores, full of air bubbles trapped within a matrix of ice. As usual, Uwe helped Xinsheng at the drill control box and I worked with Dan bagging, labelling and packing the cores. Evening fell whilst we continued working, expecting to go on until the early hours, all being well with the ice. However at about 8.30pm, with 30 metres of core recovered, we suddenly started getting wet ice again. The strong reflector layer in the radar images was explained. One further drill section confirmed that the ice was getting wetter and Xinsheng again called a halt to the drilling. We were to get some sleep after all. In the photo, Dan is holding the final section of ice core that we drilled. We decided to pack up as much as possible in order to make a swift departure in the morning. Once the net load was more or less organised, we got out the dice and played a game of Zilch, sitting on ice core boxes with our head torched on. During the night occasional avalanches roared down the cliffs in the dark. A beautiful sunrise lit up the scene as we got ready for our final helicopter ride down to the valley floor.

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Bedrock

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After yet another day of sorting out and preparing our gear, the weather forecast looked quite promising for a few days. We decided to fly back up to Mount Hutton and drill non stop until we either came to bedrock of had to stop for other reasons, such as water in the ice. The four of us -Xinsheng, Dan, Uwe and myself, again flew up to the peak. It is a spectacular location with steep drop offs falling hundreds of metres down on all sides. Once up there you are committed! A sky of whispy clouds stretched above Mount Cook . Our heli put us safely on the landing spot, with our emergency survival gear (tents, food and extra warm clothing). This is standard procedure just in case something prevents the second load from being delivered – a sudden change in the weather or problems with the heli. Whilst the other three went up to the drill site (the same place that we had drilled our 10 metres core already), I walked across to a beautiful horizontal scoop in the snow that we had chosen for a campsite. Although the weather was sunny and calm, I made sure that the tents were well attached to the ground with snow stakes and shovel loads of snow on their snow flaps. We wanted to be able to go to bed very late without worrying about a change in the weather. By about lunchtime I could hear the humming of the generator at the site about 200 metres away telling me that the drilling had started. Once finished with the campsite I walked up to the others, feeling the effort more than usual due to the altitude. The drill site was now top notch. We had an upgraded snow wall to keep the wind off us, the drill pit was enlarged and the hot plate was on, melting snow for hot drinks and food. Uwe had decided to start a new core right next to the previous one to see if we could get a better quality first 10 metres that was less broken into sections than the first had been. Progress was very good, with no technical problems. The ice was mostly very bubbly glacier ice, immediately below this year’s winter snow. At the top there was a distinct layer of small pebbles and grit, but below that we saw little evidence of summer dirt layers. Sometimes there were clear areas in the ice, suggesting melting and re-freezing, but we found it difficult to interpret the age of the ice or what its features were telling us. Is it a remnant of old ice or all quite recent? Only the later analysis will tell. Uwe was measuring the ice temperature in the cores, which stayed consistently below freezing at about – 3 deg C. This was very promising! We had never drilled ice below 0 deg before. At last we had found some accessible cold ice in the Southern Alps! Once the routine of drilling and bagging the cores was established, there was time to look around, take pictures and chat. As the drill gets deeper, it takes longer and longer to winch up the core each time.  I took advantage of the opportunity to take an ice axe and climb the short distance up to the summit for a view from the top.Taking care not to slip I peered down the East face – a very long way down! After a few minutes I carefully cut steps back down off the summit to rejoin the others. The photo shows my tracks from near the top and you can see the drill site and our tents in the distance Just around 9pm we started to find bits of gravel in the ice cores at about 33 metres depth. Then suddenly Xinsheng said “Is finished!” – We could hear the drill clunking against rock down below in the hole. The first ever New Zealand ice core drilled to bedrock had just been drilled, a humble 35 metres from the surface.

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