Some reflections on the Typhoon Morakot landslide disaster in Taiwan

For landslide scientists Taiwan has an almost mythical status, effectively being the nearest thing to a landslide laboratory. To my great benefit I have been able to work on landslides in Taiwan since 1991. As well as being a country of great beauty (there are good reasons why the Portuguese named it Ilha Formasa - Beautiful Island - in 1544), the combination of high rates of tectonic uplift, weak rocks, steep slopes, frequent earthquakes and extreme rainfall events renders the landscape highly susceptible to landslides and debris flows. Indeed, Taiwan has almost every type of landslide, although as an aside the number of known ancient rock avalanches remains surprisingly low given the prevailing conditions.


Of course the reason why Taiwan is of interest to landslide scientists is also the reason why it can be a challenging place in which to live. When the World Bank reported in 2005 on its "Disaster Hotspots" study it noted that "Taiwan may be the place on Earth most vulnerable to natural hazards, with 73 percent of its land and population exposed to three or more hazards". The last great disaster there, the Chi-Chi Earthquake, which happened almost exactly a decade ago, was a wake-up call to the hazards that mountain communities face in Taiwan. I think that a great deal has been achieved in Taiwan since this event, but the Typhoon Morakot disaster shows that there is so much more to do.

Inevitably, and frankly understandably, there is now a great deal of concern in Taiwan about the viability of its mountain communities. The issues are complex - many mountain villages are inhabited by indigenous populations that have strong ancestral links to their land. In other areas the communities were settled by retired soldiers who came to Taiwan with Chiang Kai-Shek in 1949. Both sets of mountain dwellers are poor, but they are often passionate in their desire to remain in their rural communities. There are high stakes here, with the possibility of a new wave of enviornmentally-damaging engineering works in the mountain areas.


Unfortunately, in Taiwan much of the development in mountain areas has been undertaken without fully considering the ways in which humans and natural processes interact in this sort of environment. In many cases this is quite understandable - the processes are so dynamic that our understanding of them is poor - but the consequences are tragic. The race of build mountain hotels is perhaps the most obvious case - as the typhoon so clearly showed - but there are many other examples. As roads, hydroelectric schemes, fruit farms, recreation areas and many other developments cause extensive environmental degradation, the landscape is responding with increased rates of erosion, mainly in the form of landslides, debris flows and floods, that puts the population at risk.

I should stress that I am not calling for a moratorium on development in the mountains in Taiwan, and nor am I advocating that the mountain populations are relocated. I do believe that development, including road construction and the building of hydroelectric power schemes, is viable. In addition, I also believe that it is possible for people to live, relax and work in the mountains with tolerable levels of risk, although as Shiaolin showed some of the existing communities are built in highly dangerous sites. I do think that some activities in the mountains probably cause too much environmental damage - in the highland areas fruit farming appears to me to be causing extreme levels of degradation for example, and the construction of "hot spring resorts" is often insensitive and poorly planned - but most mountain communities should be helped to change their way of life, not to be forced into relocating.

So here is my suggested manifesto for reducing (but not eliminating) the risk from landslides in Taiwan:

• Develop and implement a comprehensive national plan for managing slopes, covering design standards, training, land use management, emergency response, etc. This effectively mirrors the very successful slope management programme developed in Hong Kong and, more recently, in Malaysia.
  
• Develop a comprehensive research programme to understand the natural processes occurring in the mountain areas of Taiwan. The National Environmental Monitoring Center being proposed by National Taiwan University seems to me to be an essential element of this that could also provide world class science outputs. Operate in the network in a manner similar to GEONET in New Zealand, having both science and public understanding ofd science benefits, Ensure that the outcomes of the research are fed back into the planning and management process.
• Undertake a properly coordinated and sensitive programme to evaluate the safety of all upland communities. Where risk is found to be high, identify the best mechanism to bring this to a tolerable level, through combination of well-designed engineering works, education programmes, warning systems and, in extremis, relocation to nearby safe sites. This will need to be accompanied by a programme to determine the level of tolerable risk in this environment, and to ensure that there is an understanding that the aim is not to elimate risk, but rather to manage it.
  
• Constitute a national disaster management agency to coordinate disaster risk reduction and disaster response.

Templates for all of the above exist in other countries. To achieve this will take considerable political will, and both resource and time. However, management of risk is achievable without forced relocations or catastrophic environmental damage.

A first decent view of the Shiaolin (Hsiao-Lin) Landslide

First, apologies if my posts are a little sporadic (and if I am not replying to your emails). I am currently on leave in the Swiss Alps. However, I will continue to make short posts over the next fortnight, especially in light of the Taiwan landslides.

Thanks again to Tsou Ching-Ying of Kyoto University for bringing to my attention a Youtube video of the Shiaolin site. This is of course the village that was most seriously impacted by Typhoon Morakot. The video appears to have been shot from a UAV. The quality is a little marginal, but you will get a very clear impression of the landslide if you view it below:



If you cannot view it above it should be visible here.

This is not really a mudslide as the media have described it. It is a little hard to characterise from this view, but it looks to be a large-scale, catastrophic rock slope failure that has transitioned into a debris flow. It appears to have had a long runout - I guess it is unsurprising that the loss of life was so high.

Typhoon Morakot mudslides: Before and after photos of Shiaolin (Hsiao-lin) village in Taiwan

Thanks to Tsou Ching-ying from Kyoto University for providing this pair of images, showing the impact of the mudslides on Shiaolin village in Taiwan as a result of Typhoon Morakot.

Before (from an online album here):

After (from an online album here):

Taiwan mudslides - a very lucky escape for most

(AFP image)

This morning various news agencies are reporting the very good news that four days after Typhoon Morakot 726 survivors have been found from the villages destroyed by the mudslides. This does not mean that the mudslides had no victims - the Taiwan police are saying that it is difficult to know how many people were buried.

A strange update on the Nachterstedt landslide

A strange update has appeared in the "The Local" regarding the Nachterstedt landslide. This reports that "Scientists at the Collm Observatory at Leipzig University registered an underground movement in the area measuring 1.0 on the Richter Scale, just six minutes before the first call to the emergency services on July 18. An earthquake can be ruled out, the scientists told Der Spiegel magazine, but they suggested it would be feasible that an old mining tunnel collapsed, causing the landslide. "

For info a magnitude 1.0 earthquake is the equivalent of about 30 kg of TNT. I cannot understand why the scientists believe that this was a tunnel collapsing. To me it is far more likely that the signal was the landslide itself occurring. I must admit that I cannot understand why the collapse of an underground mine working would cause this catastrophic slide anyway.

On another matter, the paper also reports that a further collapse is considered likely:
"Surveyors have been pulled back out of the Auf der Halde community, where the ground has sunk by a further 0.4 millimetres and is expected to also collapse. Preparations are now being made for emergency measures to be taken should the remaining houses also fall into the Concordia Lake, which was created by flooding an old open-pit mine."

Landslides from the Fiordland earthquake, New Zealand

GNS Science in New Zealand have released details of the mapped landslide distribution from the Fiordland earthquake on 15th July. As I noted a day later, the number of landslides appears to be surprisingly low:

The earthquake produced only 187 landslides, most of which were shallow and comparatively small. The area affected by landslides was 5600 square kilometres. Comparison with the graph below (see my original posting) suggests that this is at the bottom end of the expected number for a Magnitude 7.8 earthquake.

According to Graham Hancox the reasons for this lower than expected level of landslides are thought to be:

1. The ground motions were smaller than would normally be expected for a magnitude 7.8 earthquake;

2. The dominant fault rupture motion was away from land;

3. Lower than average rainfall occurred in the two months prior to the 2009 quake.

The map suggests that there is a very strong relationship between the ground motion and the occurrence of landslides, with most of the mass movements being concentrated in the vicinity of the epicentre. This is consistent with, for example, the Chi-Chi earthquake in Taiwan.

Another catastrophic landslide - this time in China

As soon as I had posted the round-up of catastrophic landslides below another one appeared on the newswires, this time in Mainland China. Xinhua is reporting that Typhoon Marakot has triggered a landslide in Pengxi Township, Taishun County in Zhejiang Province, burying half a dozen apartment blocks:

"A massive landslide occurred in an eastern Chinese town Monday night, causing six or seven apartment buildings to collapse and burying an unknown number of residents, local authorities said Tuesday. The accident took place at about 10:30 p.m. in Pengxi Township, Taishun County of Wenzhou City in Zhejiang Province, when the unexpected landslide soon destroyed the 4-story apartment buildings at the foot of a mountain, rescuers said. Rescuers have pulled six people alive from the debris, but one of them is in critical condition. It is not immediately known how many people were buried, rescuers said, adding that it is very difficult for them to carry out search operation due to a huge amount of mud and rock. The landslide was triggered by continuous torrential rain brought by Typhoon Morakot, which has left six people dead and three others missing on the Chinese mainland after a powerful landing in east China Sunday. "