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Monday, 15 February 2016

Digging into the Alpine Fault

The Alpine Fault has been the focus of a lot of research over recent years, including the Deep Fault Drilling Project, Alpine Lake Sediment Research and the Earthquake Records at Hokuri Creek amongst them. These are building a much clearer picture of the history of previous fault ruptures, and allowing better estimates of the size and likelihood of future earthquakes.

The Alpine Fault is a long, straight, geologically  fast moving fault that typically produces very large earthquakes rupturing along large segments of its total length.

At its northern end the Alpine Fault branches into a number of different faults that cross Marlborough and are known as the Marlborough Fault System. This means that here the Alpine Fault only takes up a proportion of the total displacements in this region and is likely to have a different earthquake history compared to the
central and southern parts of the fault.

Recently a GNS Science expedition to the northern part of the Alpine Fault near Springs Junction, involved digging two trenches across it to better understand its local earthquake history through some careful investigation.

This image shows the trenches (left of centre foreground) from the air. The trace of the Alpine Fault passes through the trenches and into the distance between the hills.

Once the trench has been dug out,  the walls need to be cleaned up carefully so that the fine detail of the different sediments and structures can be observed and recorded.

A string grid is pinned against the walls of each trench to help map them out, and markers are placed to highlight significant features that can sometimes be very hard to discern. The leader of this project is Rob Langridge, shown here having a close look at the detail.

Many hours are spent drawing accurate maps of the trench walls as well as taking high resolution panoramic images of them. These are taken in order to document the excavation so that later interpretation of the data can continue once the trench has been filled up and the team has returned to the office.

This image shows the Alpine Fault in section with the line of the fault shown.  The scarp or slope at the ground surface has been produced by earthquakes uplifting the left hand (eastern) side.
You can also see the effect of fault movements on the river sediments below the ground. The grey clay layer on the left has been cut off at the fault and the overlying gravel layer has been dragged out of shape by repeated fault movements.
This is a close up view showing the complexity of the sediments and structures close to the fault. When earthquakes uplift ground on the left side of the fault, loose material at the surface collapses across the fault and forms a wedge shaped pile of sediment on the ground called a colluvial wedge.These earthquake associated layers later get buried by younger material. They can be very hard to identify, but are a critical record of past ruptures. They can form repeatedly, so that wedges from earlier earthquakes may have more recent colluvium laid over the top of them.

Once the colluvial wedges have been identified, the next step is to look for plant or animal material that has been trapped in them at the time they were created. These carbon rich specimens are carefully collected for dating in the lab using the radiocarbon dating method. (See below for a video that explains carbon dating)

When a major fault ruptures during an earthquake, it can branch out near the ground surface to produce a number of smaller faults close to the main fracture. Here is an example that showed up in the trench wall a few metres from the main fault. The layers on the right have been pushed up  relative to those on the left. By carefully observing which layers have, or have not been affected by these secondary faults, the earthquake record can be further clarified.
Once all the data and specimens have been gathered and logged, the trenches are filled in once more so that the surface can revegetate back to its original state.

Here is a 3 minute video of the project:

And this video explains radiocarbon dating:

Finally click here for the TVNZ news report on the trenching.

Monday, 19 October 2015

Lahars on Ruapehu

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:

Thursday, 23 April 2015

Precarious Boulders and Earthquakes

The National Seismic Hazard Model is the result of lots of work by scientists to indicate the likelihood of earthquakes happening in different parts of New Zealand.

It is made with reference to the historic record of earthquakes that have happened across the country, combined with research into the rupture histories of many individual active faults.

Work is done to continuously 'ground truth' and improve the Hazard Model through ongoing research and addition of data.

Mark Stirling has developed a way of testing the model at particular locations using ancient landforms known as tors that occur in places around the country.

These isolated boulders stand like statues. There are many of them near Clyde in Otago, occurring on the flat, uplifted surfaces of nearby ranges, such as the Old Man Range, shown here. You can see that some of these features are quite imposing and have a lot of character.

Although some of them are solid looking, there are others that are very delicate.These are the ones that Mark is interested in. The basic idea is to use the beryllium 10 exposure dating method to find out how old these fragile features are, and then to work out the amount of earthquake shaking it would take to knock them down. This tells Mark the minimum amount of time that has lapsed since the occurrence of an earthquake capable of knocking down the feature. This information is then matched with the National Seismic Hazard Model to see if the calculations give similar hazard estimates.

Making a numerical calculation of the fragility of the precarious feature is a matter of working out the angles between the centre of mass and the rocking points at the neck (narrowest point) of the tor.

For making these calculations with maximum precision, Mark makes a 3D computer model of the tor, by first taping key points on its surface, and then taking many photos from all angles, which are later stitched together.

This is what the model of the above tor looks like on the computer screen once completed .

During fieldwork with Mark last month, we were able to use a quadcopter drone to get good images of some of the more inaccessible fragile landforms.

Here is our video of the project:

Monday, 2 February 2015

NASA comes to Rotorua

Last week I was involved in a NASA Spaceward Bound meeting in Te Takinga Marae in Rotorua.

The purpose of the meeting was to promote interest in Planetary Geology and  Astrobiology, and it was attended by about 50 scientists, educators, undergraduates and school students  from New Zealand, Australia, the USA, Romania, the UK and Kazakhstan

Image:  NASA / JPL
A large focus for NASA at present is the Curiosity Rover that has been exploring the surface of Mars for the last couple of years. One of the questions for the scientists is whether there are any traces of simple life forms in rocks on the surface. If found, these would show that whilst there may be no life at present on the red planet, it did manage to evolve there in the past under previous conditions.

Image:  NASA / JPL

In order to understand some of the geological features that are being observed using Curiosity's various probes, it is useful to get to know comparable geological sites on the Earth's surface that can be investigated and understood at close quarters.

During the Spaceward Bound week we made several field trips to visit hot springs and volcanic landscapes in the Taupo Volcanic Zone. The focus of these trips was to see how microbial life can take hold in extreme physical environments such as very hot,  acidic geothermal springs, and to see how these living communities leave physical and chemical evidence of their existence (biomarkers) in the mineral formations that build up at these locations.

This image shows a silica terrace at Waimangu volcanic valley. The colours are created by different species of microbes that thrive in these harsh conditions. The colour distribution shows the tolerance of particular species to different water temperatures.  For more about extremophiles in New Zealand find out about  the 1000 Springs Project.

Extremophile microbes inhabit the hot mineral rich water that creates the rock formations at Pariki Stream, Rotokawa. The bacteria leave visible biomarkers in the sinter left behind as the mineral laden water evaporates.
Parag Vaishampayan, a research scientist at NASA, took a close look.

Quadcopter meets Rover at Rotokawa

This small radio controlled rover was designed by Steve Hobbs at the University of New South Wales. It is adapted for remotely investigating hot springs, and includes a number of sensors such as spectrometers, a camera and a non contact thermometer. the quadcopter that you can also see in the picture has been adapted by Matthew Reyes, (a technologist at NASA) to scoop up water samples that can't otherwise be easily accessed.

Part of the field investigations included a study of plant colonisation of lava flows in the Mangatepopo Valley in Tongariro National Park. This photo shows a young lava flow on the slopes of Ngauruhoe volcano at the head of the valley.

We also went on an excursion over the bare volcanic landscape of the Tongariro complex.

Mars, as seen by Curiosity.            Image:  NASA / JPL
For more information about astrobiology have a look at the New Zealand Astrobiology Initiative website, and to find out about Spaceward Bound New Zealand have a look here.

Finally here is a news clip from TVNZ about Spaceward Bound, and an interview with AUT scientist Steve Pointing on National Radio.

Tuesday, 16 December 2014

Disaster Risk Reduction in Indonesia

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.

Tuesday, 4 November 2014

Bottom Hole Assembly

About 10 days ago, drilling was stopped at the Alpine Fault drill site so that geophysical measurements could be made down the borehole, and the bit could be replaced.

This involved lifting all of the drill rods out one by one and stacking them next to the rig.

Next to come up was the bottom hole assembly (BHA) comprising these thick steel pipes that Rupert Sutherland is describing to the camera in this image.

Last to appear was the business end of the drill string including the drill bit itself.

This photo shows the bit being replaced using some impressive sized hand tools:

The view looking down into the top of the borehole - 400 metres deep and filled with mud.

Here is the video of Rupert explaining the Bottom Hole Assembly:
Once the geophysical measurements were taken down the hole (more about these later), the Bottom Hole Assembly was put back together and lowered back down the borehole. Unfortunately disaster struck when the wire snapped and 7 tonnes of unattached BHA dropped down the hole. To cut a long story short, this delayed progress for about a week, until finally the detached parts were fished out of the hole using a variety of highly specialised methods. You can read a little more about these events here in Rupert's Blog:
1.The Calamity.  
2. Landing the Fish