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Tuesday, 22 July 2014

Mount Cook Rockfall

Hooker Valley rockfall. - Simon Cox / GNS Science
Sometime early last week 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 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 1 million cubic metres of rock debris are scattered on the valley floor. Some of the material travelled about 3.5 kilometres

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 the buttress. 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 perhaps 200 metre high grey rockfall scar on the cliff face, the source of all the devastation.

Tuesday, 24 June 2014

Drilling into New Zealand's most dangerous fault

The Alpine Fault forms the plate boundary in New Zealand's South Island, and is a very significant fault on a global scale. It last ruptured in 1717 AD and appears to produce large earthquakes on average every 330 years. Its next rupture has a high probability (28%)  of occurring in the next 50 years.

Each time the Alpine Fault ruptures, there is roughly 8 metres of sideways movement and about 1 to 2 metres of vertical uplift on the eastern side. These magnitude 8 (M8) earthquakes can rip the fault along about 400 kilometres of its length. Slowly, over millions of years, this is what has created the Southern Alps, and offset rock formations on each side of the fault sideways by a phenomenal 480 kilometres. Massive and continual erosion of the Southern Alps keeps them relatively small (below 4000m) inspite of about 20 kilometres of uplift over the last 12 million years. For a lot more information about the Alpine Fault and its earthquakes, check the GNS Science website.

Later this year, scientists plan to drill through the Alpine Fault at a depth of more than one kilometre  to sample the rocks and fluids of the fault at depth, and to make geophysical measurements down the borehole to better understand what a fault looks like as it evolves towards its next earthquake rupture. This is phase two of the Deep Fault Drilling Project (DFDP-2).

The first phase of the project (DFDP-1) was successfully carried out in 2011 when two shallow boreholes were drilled through the fault to about 150m and the first observatory set up at Gaunt Creek.  DFDP-2 will involve drilling a short distance away in the Whataroa River valley, not far upstream from the road bridge on State Highway 6.

This short video gives some background and information about the project:  You can also find out lots more detailed information about DFDP-2 at the GNS public wiki site here.

The prospect of drilling through a massive fault could  sound alarming to some people. Is there a possibility that this project could cause a damaging earthquake? Check this next video to hear about the safety review:

Thursday, 20 March 2014

Stepping Over the Boundary

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.

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

Wednesday, 19 March 2014

The Fox

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:

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.

Friday, 14 March 2014

Franz Josef Ice on the Retreat

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:

Wednesday, 5 March 2014

The Hot Bed of Rotomahana

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:

Saturday, 22 February 2014

Christchurch City Centre, Three Years On

Some images I took this morning, on an early walk through Christchurch City Centre.  I offer my  best wishes to the folk of Christchurch and other Canterbury towns who are still patiently rebuilding their livelihoods, three years on from the 22nd February 2011 aftershock.

We Remember: