Glacier

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 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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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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Beryllium-10 dating of moraines around Lake Ohau

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Lake Ohau is one of several very large lakes in the Southern Alps that fill valleys once carved out by huge glaciers during the Ice Age. As the ice retreated, it left spectacular and classic landforms in its wake, including concentric lines of moraines, erratic boulders, ‘U’ shaped valleys and extensive outwash plains. The rapid tectonic uplift of the Southern Alps, and extreme climatic conditions, have created the landscape we see today. The rock debris left behind as the ice retreated, has been mapped by geologists, and a lot of work has gone into dating the ages of the various moraines to gain a better understanding of how the landforms relate to specific changes in the climate as it gradually warmed up after the coldest phase (last glacial maximum or LGM) of the last ice age. This photo shows how Lake Ohau is dammed by a rim  of 18 000 year old moraines around its southern margin. They are the low lying hummocks you can see near to the lake, as well as in the foreground. The dark red lines on this map  show the extent of these moraine ridges, extending around the south end of the lake. The brown colours are river sediment (glacial outwash) that was spread across low lying areas by braided rivers. The lines crossing this mountainside above Lake Ohau are lateral moraines left behind as the glacier gradually lowered, and finally vanished at the end of the ice age. Richard Jones and Kevin Norton of Victoria University, Kevin Norton measuring the tilt on the surface of a boulder One of the best methods of dating these moraines is by measuring the concentration of the isotope beryllium-10 in the top surface of large boulders situated on them. The technique depends on the fact that the atoms in quartz (SiO2) in the rock are constantly being bombarded by cosmic ray neutrons. When such a neutron collides with the nucleus of a silicon or oxygen atom it splits the nucleus into fragments which will be smaller, different nuclides such as beryllium-10.  (Since they are produced by a cosmic ray interaction, all these products are known as cosmogenic nuclides). With time, a freshly exposed rock surface will gradually accumulate more and more beryllium-10 so that by careful measuring of its concentration in a boulder, the length of time that it has been exposed can be calculated. The accuracy of this method hinges on good callibration, and selection of a rock that hasn’t moved or been buried since it became exposed Richard Jones cutting out a rock sample as the glacier retreated. Lots of factors have to be taken in to consideration when sampling, including the angle of the surface of the boulder, the presence of nearby mountains that block some of the sky from view, the exact altitude and also the latitude of the sampled boulder. These photos show samples being collected around Lake Ohau this week. The boulders being sampled have already been dated. The purpose of re-sampling them is to test calibration between laboratories in New Zealand and the US. Richard Jones is cutting small 2cm thick pieces off the surface of a boulder with a rock saw. Albert Zondervan and David Barrell (GNS Science)  Once the sample has been labelled, bagged and transported to the laboratory, it needs a lot of physical and chemical processing. An accelerator mass spectrometer is used to make supersensitive measurements  of the the very small concentrations of beryllium-10 that allow the age to be calculated. This video gives a very good introduction to the use of this surface exposure dating method for dating glacial moraines in New Zealand, featuring David Barrell from GNS Science, along with colleagues from the US.

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