Search This Blog


Wednesday, 24 September 2014

Wairarapa Fault - the Biggest Rupture on Earth

The Wairarapa Fault is one of New Zealand's large active faults running along the eastern edge of the Rimutaka range from Palliser Bay north into the Wairarapa. It was responsible for the massive magnitude 8.2 earthquake that violently shook the lower North Island in 1855 in New Zealand's largest historically recorded 'quake.

This Google Earth view shows the surface trace of the fault, with the Rimutaka Range to the west and the Tararuas in the distance. An interesting location called Pigeon Bush is indicated by the red circle. It is about 50 kilometres north-east of Wellington City.

The second photo is a view of the Pigeon Bush locality from the nearby road, showing a steep scarp uplifted by earthquake ruptures of the fault. The fault itself runs along the base of the scarp, which is the product of several earthquakes over the last few thousand years.
A close up view shows some interesting features beside the fault scarp. Two stream  channels (left and centre of image)  appear out of the scarp, with no sign of any catchment gully above them. Meanwhile offset to the right is a deep cut gully in the scarp itself. Geologists have long recognised that the stream that created the two small 'beheaded' channels has been shunted along horizontally by the last two ruptures of the fault.
In this photo, Rob Langridge, an earthquake geologist from GNS Science, is standing between the first (most recently beheaded) stream channel on the left, and the vegetated gully that was originally connected with it on the right. Some idea of the amount of offset that occurred in the 1855 earthquake can be appreciated from the image. There would also have been some uplift during that earthquake of perhaps one or two metres at this location.
We used a tape measure and recorded the distance along the fault between the centre of the now separated stream gullies, and came up with a figure of about 18 metres. This huge displacement is the largest offset to have been caused by a single earthquake on a land based fault known from anywhere in the world. (It is now known that subduction earthquakes such as the great 2011 Tohoku Earthquake of Japan can produce even greater displacements of the ocean floor)

We also measured the offset of the older stream channel which was about 15 metres away from the first beheaded channel.This previous earthquake is thought to have occurred about 1000 years ago. The average repeat interval for ruptures of the Wairarapa Fault is thought to be about 1200 years.

A view of the fault itself can be seen in a cutting of the Ruamahanga River near Masterton, about 45 kilometres further north than Pigeon Bush. In the photo you can see how older grey rock on the right (west) have been pushed up relative to the younger gravels on the left (east) in a reverse fault. The substantial horizontal movement may also have caused this juxtaposition of older rocks against younger ones.
Here is another view of the fault where it is known as the Wharekauhau Thrust in a cliff section at Thrust Creek on the Palliser Bay coast. Royal Society Teacher Fellow Phillip Robinson is inspecting the older shattered greywacke rocks that have been thrust over the gravels from the west (left), tilting the relatively young 50 000 year old gravel layers from a horizontal to a vertical orientation.

This is the view looking south from Thrust Creek along to the southern tip of the Rimutaka Range, with Turakirae Head in the far distance. During the 1855 earthquake, a maximum of 6 metres of uplift occurred along this coast. A 10 metre high tsunami also swept along this coastline. Check out this previous post to learn about the amazing uplifted beaches at Turakirae Head.

Wednesday, 27 August 2014

Geolocating GNS Science Outreach

Announcing our new Google Map that shows the locations of blog posts, videos and some of our website information within New Zealand. Zoom in and out to find a location and click on any icon to go straight to the online content.

If you enable full screen (by clicking on the square icon at the top right of the map, or simply by clicking here ) you can switch layers off or on and change the style of the base map.

We will be uploading more layers of GNS Science content onto this map in the future.

To access the map at any time you can find it in the menu on the right hand side of this page.

I hope you like our new GNS Science Outreach map!    Enjoy...

Friday, 25 July 2014

1000 Geothermal Springs

GNS Science and Waikato University are investigating one thousand of the geothermal hot springs in New Zealand's North Island.

The goal of this ambitious 1000 Springs Research Project is to understand and compare the microbiology of these springs along with their physical  and chemical make-up. That adds up to a lot of sampling trips, processing of data and investigation of the findings!

Some of these hot springs are scummy looking puddles like this one, that don't seem to have much to say about themselves apart from the obvious message to stay clear and avoid being swallowed up by scalding mud.

Bruce Mountain/ GNS Science
Others are of course very spectacular and beautiful iconic tourist attractions such as the Champagne Pool at Waiotapu...

A few days ago I joined some of the GNS Science team; Jean Power, Dave Evans and Matt Stott, (who leads the project)  on a sampling trip to Whakarewarewa village in Rotorua,

The village is an extraordinary place, where a community has learnt to live in close relationship to an ever changing geothermal environment.

Home heating, hot water, cooking and bathing is provided by the hot springs, although there are interesting downsides, such as occasional ground collapses and holes appearing next to houses

Safety first! Investigating hot springs is a potentially hazardous activity. Sometimes well known and well trodden areas have suddenly caved in because the ground gets eroded from below. Scientists use various safety techniques as well as a strong sense of caution when approaching the springs.

Dave Evans uses a long pole to reach into a hot pool to get a water sample, while Jean adds information to a tablet with an application that allows all the data to be quickly uploaded to the 1000 Springs database website. 

Several water samples are taken, and the team measures the temperature, pH, conductivity, turbidity, dissolved oxygen and the redox potential of each spring, as well as taking photographs and other metadata.

Geothermal ecosystems are globally rare and little is known about the unique populations of microorganisms (Bacteria and Archaea) that inhabit these environments or the ecological conditions that support them. Here Dave is carefully labellling the sample bottles.

Samples are filtered and prepared for analysis after returning to the lab. To identify all the different species, the DNA in the sample is extracted and analysed, and the chemical content of the water and the dissolved gases is measured.

Extremophiles are microorganisms that thrive in harsh environmental conditions - where temperatures can be as high as 122˚C, the pH can range from highly acidic to strongly alkaline, and there are elevated concentrations of salts and/or heavy metals.

Different microbes are responsible for the spectacular colours seen in hot springs. The colour zonation relates directly to particular temperature ranges which the resident species have tolerance for.

There are thought to be more than 15000 geothermal features in New Zealand, and each of them will have a distinct microbial community and often include many undiscovered species

The selected springs span the known pH ranges (pH 0-9) and temperature ranges (20°C-99°C) or have unusual geochemical or geophysical profiles. Sites with high cultural or conservation value are also included.

All this new knowledge will allow New Zealand to assess the conservation, cultural, recreational and resource development value of the microbes in geothermal ecosystems, and enable further future microbial ecology research and discovery.

Photo by Matt Stott / GNS Science
My role in these field trips is to visually document the scientific process and communicate about the research to all who are interested. Scientists are invariably passionate and enthusiastic about their work, and are keen for others to find out about what they do.

Here is our video of the 1000 Springs team in action:

Tuesday, 22 July 2014

Mount Cook Rockfall

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.

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.