Landslides- I

Landslides- I

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logo By Afroz Ahmad Shah

Natural disasters like earthquakes, tsunamis, landslides, wildfires, cyclones, droughts, floods etc. continuously pose constant threats to our young, 10,000-years-old, civilization. The devastations of Sumatra and Thai coasts in 2004, of Kashmir and New Orleans in 2005, of southwest Java in 2006, of Sumatra again in 2007, western Sichuan and Myanmar in 2008, of Haiti in 2010, Japan, New Zealand and Turkey in 2011, brought about colossal damage in terms of death and destruction. The Hurricane Katrina and Rita, floods in Pakistan, forest fires in Russia, drought in East Africa, and numerous landslides and mudflow; for example a large-scale landslides which struck the Philippines in 2006, hitting the Albay province on 2nd December and the Leyte Island on 17th February. These resulted in huge loss of life and property. It is estimated that these hazards have increased recently, in the decade from 1976 to 1985, close to one billion people were affected by disasters and this number had more than doubled in the decade from 1996 to 2005, in which nearly two and a half billion people were affected. In the last decade about 3 billion people were affected and it killed around 750,000 people and cost around US$ 600 billion.

To cope with the natural disasters it is required to understand the science behind these events and plan a comprehensive program to educate the masses. It is important to put more emphasis on pre-disaster planning, rather than on post-disaster reaction. There are ample evidences to demonstrate that lack of scientific awareness has proved fatal in most of the natural disasters we have witnessed so far in the past. For example, the earthquakes in New Orleans and Port au Prince, which had long been recognised as a catastrophe waiting to happen, but somehow even that awareness did not produce the desired effect! Similarly, there are several places in the world, for example South East Asia, where knowledge about earthquakes, tsunamis, cyclones, floods etc. is still in its infancy. This has caused colossal loss to life and property. For example in Kashmir and Aceh, the tragic examples, in which basic scientific ignorance and the inability to translate the acquired knowledge into timely planned action clearly shows the challenges earth science faces today.

In my previous articles I have mentioned about earthquakes, tsunamis and volcanoes, here I will introduce another kind of natural disaster known as landslide.

Landslide is the movement of a mass of rock or debris down a slope. The dimensions of a landslide may be very small or huge, and its movement can be sluggish or very swift. There are various reasons for such movements; for example precipitation (rainfall), topography, geology (rock and soil types) and human activities, can all trigger landslides. Anything affecting slope conditions can cause slope failure, potentially in an area, which is prone to landslides. This includes human induced slope failures, especially during construction, mining etc. Earthquakes are one of the main causes, which trigger landslides and volcanic eruptions also contribute to these movements. One of recent examples of an earthquake induced landslides occurred in Muzaffarabad Pakistan, when a 7.6 magnitude earthquake struck this region in 2005 (Figure). It is estimated that more than 87,300 people lost their lives and several millions were rendered homeless. This has affected an area of more than 30,000 Kilometre square and triggered thousands of landslides. This risk has potentially increased because of post-seismic landslides and avalanches. Such a risk remains high during wet seasons and particularly in places like Muzaffarabad, Balakot, Garhi and Dopatta. There are several rivers, which are dammed. This could also cause hazard, if not managed properly. Generally, during an earthquake such a situation can occur, if a fault crosses a river. Artificial lakes/dams and/or waterfalls can form during such a process. This happened during the Kashmir earthquake and was seen in many other places. Any future town planning must take care of these risks, which are extremely important to save lives and property.

 

Afroz Ahmad Shah is a research fellow at Earth Observatory of Singapore, Nanyang Technological University, Singapore.

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