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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 

Friday, 24 October 2014

Phase 2 Alpine Fault Drilling

Rupert Sutherland with DFDP-2 flags
Whilst researchers continue to pull together the history of past Alpine Fault earthquakes, the Deep Fault Drilling Programme is well underway in Whataroa on the West Coast of the South Island. For an introduction to this project have a look at my blog and video here, or check out the DFDP-2 Facebook page or project leader Rupert Sutherland's blog for updates over the next few weeks.
The first phase of the drilling process was to penetrate down through a thick sequence of gravel and mud left behind in the Whataroa Valley after the retreat of ice at the end of the last ice age. This was surprisingly challenging because of a thick sequence of very sticky mud that was deposited in the valley at a time when it was a deep fiord or lake.
DFDP-2 drill site   J.Thomson@GNS Science
Eventually the team struck bedrock 240 metres below the surface, and the second phase could commence. This involves drilling down towards the fault plane, thought to be about a kilometre below the rig, without trying to retrieve any large intact pieces of the rock at this stage. (That process is the goal of phase three, which will start when the geologists see from the minerals in the rock fragments that the drill is closing in on the Alpine Fault.)

DFDP-2 drill site   J.Thomson@GNS Science

This is a view of the drill site on a nice morning with Phase 2 well established and the drill at a depth of 340 metres. Behind the rig you can see the drilling mud ponds. The science labs are on the right and spare drilling rods that are added as the drill gets deeper are in the foreground.

The labsin the background are where the scientists  study the rocks being brought up by the drill, and make geophysical measurements taken by equipment that is lowered down the borehole.

Close up to the rig you can see the vertical drill rod (or pipe) that is rotating and gradually descending down the drill hole. The next rod is lined up ready for connecting when the drill is a few metres deeper. The speed of drilling is roughly 1 to 4 metres an hour at this stage, and a new drill rod is added about every 6 hours.

Next to the drill is this pond of muddy water, which is a vital part of the system used for cutting down into the rock. The mud is specially formulated to have the right viscosity and density and is sucked up by a very powerful pump. After having large particles sieved out of it, it is sent down the centre of the drilling pipe right down to the cutting face of the drill bit.

The drill bit on the right has cut through about a hundred and twenty metres of bedrock, and is about to be replaced by the nice shiny one on the left. The drilling mud is forced out of the holes that you can see, and then flows up the outside of the drill pipe back to the surface, bringing with it the rock chips and also carrying heat away from the cutting face at the same time.

This is the base of the drill rig, with a section of the rotating drill pipe visible. Drilling mud is flowing down the centre of it on its way down to the drill bit. After its return journey on the outside of the drill pipe, loaded with rock fragments, it emerges at ground level and is carried away in the pipe that extends to the right.

The drilling mud flows into a collection pond. The sieve that you see is for collecting samples of the rock fragments for analysis.
The samples are first carefully washed of fine mud or clay.
They are then sorted by hand.
After being glued to a microscope slide, the rock samples are ground down to a thickness of 30 microns. They are then transparent and can be analysed using an optical microscope. The mineral content can then be studied in detail. As the drill gets closer to the fault, the scientists expect to be able to see changes in the types of minerals present. In this way they will be able to judge the right time to change the drilling system to phase 3 and start retrieving intact rock cores.
DFDP-2 drill site   J.Thomson@GNS Science
Finally here are a couple more views of the DFDP-2 drill site looking up the Whataroa Valley.
DFDP-2 drill site   J.Thomson@GNS Science

Thursday, 23 October 2014

Nature's Earthquake Recorders

In order to make sense of the sediment cores that can be retrieved from lakes near to the Alpine Fault such as Lake Christabel, it is worth having a think about what happens to the environment when the fault ruptures in a large earthquake.
Under normal conditions, alpine lakes fill up very slowly with sediment that is fed into them by rivers. The particles settle onto the lake bed gradually, to create a sequence of finely layered mud.
When an earthquake occurs, a number of consequences affect the landscape. The soft surface sediment on the bed of the lake gets deformed and folded, and the shallower slopes at the side of the lake collapse to create flowing avalanches (turbidites) that sweep down and across the lake floor. In the nearby mountains, large landslides occur that choke the river valleys with a chaotic mix of large and small rock fragments.
In the months and years following the earthquake, the landslide debris is gradually washed into the lake, to form a recognisable layers on top of the turbidite deposit.
Eventually, conditions return to normal, with the finely layered sediments gradually covering over all of the evidence of the earthquake and its aftermath. It may be hundreds of years before another earthquake sttikes that is near enough and strong enough to leave its mark in new layers of the lake sediment.

Now lets have a look at the real thing - an example of a sediment core that has been retrieved from a New Zealand's alpine lake.

Back in the lab at the University of Otago in Dunedin, Jamie Howarth opens a core tube to reveal the layers of sand and mud from Lake Christabel.

Here is a section of the core that shows the finely laminated lake sediments formed in normal conditions (on the right). In the centre you can see that the layers are slightly folded - this is the indication of an earthquake that has deformed these layers. They would have been at or just below the surface of the lake floor at the time.

Here Jamie is indicating the remains of a leaf next to the blade of the knife. This is not far below the earthquake layer, and can be used to get a radiocarbon age which will help to date the earthquake event.

This dark coarse layer is the next layer that was added to the sequence on top of the folded sediment. It is the base of an earthquake generated turbidite deposit. The material gets gradually finer to the left ('upwards') as the cloud of particles slowly settled onto the lake floor.
The section shown here is the landscape recovery phase. Dating of the base and top of this layer in several cores has shown that it can take 50 years for the landscape to recover from an Alpine Fault earthquake. During that time, hillsides are destabilised, debris flows cover flat areas near to the mountains, and rivers are prone to changing course due to being overloaded with sediment.

Finally we see the thinly layered sediment  indicating that normal conditions have returned to the lake environment.
This map shows what can be done when this research is carried out at a number of lakes along the Alpine Fault. The coloured lines (purple, orange, green etc) show earthquake records that have been identified so far in some of the lakes along the length of the fault. You can see that the last earthquake rupture (in 1717 AD) was over 300 km long. The one prior to that around 1600 AD ruptured the northern end of the fault. Information about previous earthquakes is still incomplete, but the picture is starting to become clearer. With more research, Jamie and his colleagues will be able to show a more detailed history of the last 10 Alpine Fault earthquakes including the dates, lengths of rupture and magnitudes of the events.

Friday, 17 October 2014

Lake Christabel

Lake Christabel   J.Thomson@GNS Science
This is Lake Christabel in New Zealand's South Island. It is one of the many beautiful alpine lakes  to be found close to the Alpine Fault.
Lake Christabel was formed when a huge landslide blocked the valley, thus damming the river that then backed up to form the lake.The present day outlet runs over the old landslide deposit of large chaotic boulders.

Hidden beneath the waters of Lake Christabel are very distinctive sediment layers that tell the story of huge earthquakes that rocked the nearby mountains during ruptures of the Alpine Fault. Jamie Howarth from GNS Science, and Sean Fitzsimons from Otago University, have been investigating several such lakes to read the earthquake histories.
I joined them on a recent expedition along with Delia Strong and Rob Langridge from GNS Science. The aim was to retrieve sediment cores from the lake to investigate the earthquake records. First of all a seismic survey was undertaken to find the best spots to sample on the lake bed. Sean is in the lead boat, towing a second dinghy that carries the equipment.

The survey uses an acoustic source that sends pulses down into the water. The boat is towed along so that noise interference produced by a nearby motor is avoided.

As the sound pulses are reflected back from the lake bed and its layers of underlying sediment, they are translated into a two dimensional vertical section image of the lake floor. A number of survey lines are made across the lake to give some idea of the 3 dimensional structure of the lake sediments.
Once the best locations for sampling have been chosen from the survey results, the corer is prepared with a fresh 6 metre pipe that will be pushed into the lake floor to retrieve a sediment core.

The corer is transported to the chosen point on the lake surface, and then dropped off the side of the boat once it is in position.
After being connected with several airlines which are required to control the pressure coring process, the corer is lowered the 90 metres to the lake floor. The large barrel sits at the bottom, and is sucked into the mud to create a stable platform for coring.

High pressure air is then applied to the piston which pushes the 6 metre coring pipe into the mud, releasing clouds of bubbles up to the surface. These bubbles allow Sean and Jamie to monitor what is going on with the corer at depth.

Lake Christabel Corer Retrieval J.Thomson@GNS Science
When the coring is complete, an airbag is attached to the line and filled up with air so that it  pulls the whole assembly out of the mud. The airbag bursts up to the surface from below in a spectacular fashion.

Lake Christabel Corer Retrieval J.Thomson@GNS Science
About a minute later, the corer assembly also emerges from the depths. It is not a good idea to be too close to this as it could easily sink a boat that was in the wrong place.
The corer is then plugged and loaded into the boat to be brought back to shore, with its precious cargo of sediment.

The PVC tube containing the core is then cut into 1.5 metre lengths for ease of transport. Each tube is carefully labelled to avoid any confusion  about where it was taken from and its relationship to the other samples.

Lake Christabel Flight  J.Thomson@GNS Science
Once all the sampling has been completed, the expedition is over. It takes several helicopter loads to transport the two boats, safety gear, corers, generators, samples and all our personal equipment back to the road end. The samples are then taken to Otago University for analysis. My next post will describe how alpine lakes like Lake Christabel have shown themselves to be very useful natural seismometers through this research approach.