The science of landslides, and why they’re so devastating in PNG



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A magnitude 7.5 earthquake took place on February 25, 81km southwest of Porgera, Papua New Guinea.
US Geological Survey

Benjy Marks, University of Sydney

A magnitude 7.5 earthquake struck the Southern Highlands region of Papua New Guinea on February 25, 2018. This was followed by a series of aftershocks, producing widespread landslides that have killed dozens and injured hundreds. The same landslides have cut off roads, telecommunications and power to the area.

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The PNG government has declared a state of emergency in the region. There is growing concern over several valleys that have been dammed by landslides and are beginning to fill with water – now ready to collapse and surge downstream, directly towards more villages.

Why is Papua New Guinea so susceptible to landslides? It’s a combination of factors – steep terrain, earthquakes and aftershocks plus recent seasonal rains have created an environment that is prone to collapse.




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How land becomes unstable

The Earth around us is generally pretty stable, but when the ground shakes during an earthquake it can start to move in ways we don’t expect.

Pressure changes during an earthquake create an effect in the soil called liquefaction, where the soil itself acts as a fluid.

When wet soil is exposed to physical pressure, other physical changes take place.

When lots of water is present in the soil, as is the case now during the monsoon season in Papua New Guinea, liquefaction can happen even more easily.

When liquefaction occurs, the earthquake creates changes due to friction. Imagine a visit to the greengrocer, where an accidental bumping of a carefully stacked pile of apples can cause cause them all to suddenly collapse. What was holding the pile together was friction between the individual apples – and when this disappears, so does the pile.

In an earthquake, two tectonic plates slip past one another deep underground, rubbing together and cracking the nearby rocks. The effects of this movement up at the surface can vary depending on the nature of the earthquake, but one feature is fairly common: small objects bounce around. The sand grains just below the surface do the same thing, but a bit less excitedly. A few metres down, grains could be bouncing around just enough to lose contact with each other, removing the friction, and becoming unstable.

A 2012 landslide in the southern highlands of Papua New Guinea.
dfataustralianaid/flickr, CC BY

Things are normally stable because they’re sitting on top of something else. When that support suddenly disappears, things tend to fall down – this is the classic dodgy folding chair problem experienced by many.

In engineering, we call this “failure” – and in the building industry it usually occurs immediately before the responsible engineer receives a call from a lawyer. Mechanically, this failure happens when the available friction isn’t enough to support the weight of the material above it.




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When soil acts like fluid

Once a slope fails, it starts to fall downhill. If it really slides, then we’re back to the same situation of grains bouncing around. Now, none of the grains are resting against each other, and the whole thing is acting like a fluid.

A couple of interesting things happen at this point. First, as the grains are bouncing around, small particles start to fall through all the newly formed holes that have opened up. This occurs for the same reason that you find all the crumbs at the bottom of your cereal box, and all of the unpopped kernels at the bottom of your bowl of popcorn. Once these smaller fragments accumulate at the bottom of the flowing landslide, they can help it slide more easily, accelerating everything and increasing its destructive power.

Second, landslides typically flow faster at the surface than below, so as large particles accumulate at the top they are also the ones moving the fastest, and they start to collect at the front of the landslide. These large particles, often boulders and trees, can be incredibly damaging for any people or structures in their path.

Simulation of a landslide impacting a structure.
Benjy Marks/USyd

The image above shows a laboratory simulation of a landslide flowing down a slope and hitting a fixed wall. The spherical particles are coloured by size (small is yellow; large is blue). Data from these sorts of studies can help predict the forces that an object will feel if it gets hit by a landslide.

Watching and waiting

These complex dynamics mean that we really need to know a lot about the geography and geology of a particular slope before any kind of reliable prediction could be made about the behaviour of a particular landslide.

In the remote areas of Papua New Guinea, accumulating this data at every point on every slope is a tough challenge. Luckily, huge advancements have recently been made in remote sensing, so that planes and satellites can be used to extract this vital information.

Using sophisticated sensors, they can see past foliage and map the ground surface in high resolution. As satellites orbit quite regularly, small changes in the surface topography can be monitored. Scientists hope that by using this information, unstable regions that haven’t yet failed can be identified and monitored.




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Papua New Guinea is located on an active fault line and has had nine major earthquakes in the past five years. Combined with the often remote and steep terrain, together with a monsoon season that delivers repeated heavy rainfall events, it is a particularly active area for landslides to develop.

The ConversationThe dry season in Papua New Guinea will not arrive until June. During the current wet season we may see even more slopes fail due to destabilisation by the recent earthquakes.

Benjy Marks, Lecturer in Geomechanics, University of Sydney

This article was originally published on The Conversation. Read the original article.

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Kokoda Track blockade alludes to deeper development issues in Papua New Guinea



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By preventing Australians from visiting a ‘sacred place’ like the Kokoda Track, it is more likely that local landowners grievances will be met.
ABC News/Eric Tlozek

Nicholas Ferns, Monash University

In recent days, several local landowners have blocked the Owers Corner end of the famed Kokoda Track in Papua New Guinea. They claimed they would stop tourists from accessing the track until the PNG government meets their demands.

According to their spokesman James Enage, government promises of economic benefits have not been fulfilled. Understaffed health centres and lack of education funding are causing great resentment among the local population. This is despite the establishment of the Kokoda Initiative, a joint undertaking between the Australian and Papua New Guinean governments that aims to “improve the livelihoods of communities along the track”.

The closure of the Kokoda Track by local landowners is not unprecedented; a similar closure took place at the Kokoda end in 2009.

The current blockade is a product of the complex political and economic issues affecting PNG, which is still dealing with the consequences of a controversial election late last year. It also highlights the complicated relationship between Australian war memory and its developmental assistance to a former colonial possession.

Australian aid preserving ‘hallowed ground’

The Kokoda Track experienced a resurgence of Australian attention following Prime Minister Paul Keating’s 1992 visit. He famously kissed the “hallowed ground” of the former battlefield.

In the 2000s, increasing numbers of Australian visitors sought to make the arduous trek, retracing the footsteps of former Australian soldiers. But with increased visitors came increased pressure on the local population.

In response to growing local discontent (which resulted in the 2009 blockade), the Kokoda Initiative Development Program was established in 2010 to improve living standards in areas along the track. The program includes educational services, provision of health supplies and infrastructure, and maintenance of the track itself.

Despite Australian government claims to have established several of these services, the protests at Owers Corner suggests that Australian aid is not making its way to the intended recipients. This is a common issue in aid delivery, particularly in remote areas such as those along the Kokoda Track.

Maintaining the Kokoda Initiative’s effective implementation is vital to ensuring the local population is able to enjoy the benefits of increased Australian visits to the track.

PNG’s health crisis

Compounding the problems with Australian aid are domestic issues related to the provision of health services throughout PNG. According to the country’s shadow minister for health and HIV/AIDS, Joseph Yopyyopi, PNG is suffering from a “health crisis”. Health workers are going without pay, and numerous hospitals are running out of basic supplies and medicines.

All of this comes despite Prime Minister Peter O’Neill’s promise of free education and health for all. But, if anything, the PNG population’s health has been in decline since O’Neill came to power. There is also little prospect of things changing quickly, given the unstable political situation following the 2017 election.

The Lowy Institute’s Jonathan Pryke and Paul Barker argue that Papua New Guineans experience lower health standards now than during the Australian colonial period prior to 1975. They suggest medical clinics are in crisis.

It is little surprise, then, that local communities suffering from the lack of health and education services have resorted to protests.

Striking a balance

Targeting the entry to a “sacred place” for Australians can be seen as a calculated move on the part of local PNG landowners. By preventing Australians from visiting the Kokoda Track, it is more likely that their grievances will be met.

It also points to a broader issue in PNG, as the problems people like Enage are facing are not isolated. Significant improvements are needed to improve basic services throughout PNG – not just along the Kokoda Track.

PNG continues to require significant amounts of Australian aid. According to 2017-18 budget estimates, PNG is to receive more than A$500 million, making it Australia’s largest aid recipient. This situation is very similar to the mid-1970s, when the colonial grant to PNG constituted two-thirds of Australian “aid”.

The ConversationAustralia’s Department of Foreign Affairs and Trade claims it is providing “tangible and lasting benefits” to the local communities surrounding the Kokoda Track. The blockade suggests this is not the case. Improved aid provision and governance within PNG is required to meet the needs of the people living near this “sacred place”.

Nicholas Ferns, Teaching Associate, Monash University

This article was originally published on The Conversation. Read the original article.

The good news and bad news about the rare birds of Papua New Guinea


Robert Davis, Edith Cowan University

The rainforests of Papua New Guinea are home to one of the richest bird populations in the world. But many are threatened by logging and palm oil farming.

Now, a team of researchers led by Edith Cowan University have surveyed the PNG island of New Britain to see how the bird population is faring.

The good news: several bird species, like the Blue-eyed Cockatoo, were found to be doing better than before.

The bad news: the researchers saw only a few New Britain Kingfishers, and some vulnerable species, like the New Britain Bronzewing, Golden Masked-owl and Bismarck Thicketbird, were not seen at all.

The ConversationTheir results, recently published in the journal Bird Conservation International, help to inform the International Union for Conservation of Nature and Natural Resources (IUCN) Red List of Threatened Species.

Robert Davis, Senior Lecturer in Vertebrate Biology, Edith Cowan University

This article was originally published on The Conversation. Read the original article.