Landslides are the result of the interplay of two types of factors: predisposing factors (slope angle, soil type, vegetation cover, etc.) which put slopes in a range of situations ranging from completely stable to marginally stable; and triggering factors (rainfall, earthquake, etc.) that are responsible for the onset of the slope failure. Both types of factors determine the probability of occurrence of a landslide.
More than 90% of roadside landslide disasters in Japan were caused by heavy rain and only two percent by earthquake. Japan is exposed to heavy rainfall in the rainy season from June to July and in the typhoon season from September to October. Japan is prone to earthquakes as it is located on active tectonic plates.
Most of the landslides recorded in Laos were caused by high wet season groundwater and perched water levels in soils and weathered rock masses exposed to steep roadside cuts. Slope failures were often observed to originate from the upper portions of cut slopes where weaker material predominates in the weathering profile.
The intensive unscientific cutting of hills in India for new roads and for widening existing roads using heavy machinery had added to geological disturbances, resulting in the greater instability of hills and more slope failures. Every year the triggering of landslides occurs frequently in different locations, as a result of monsoon rains. Quarrying and the careless disposal of surplus materials were other sources of roadside landslides.
The main causes of landslides in Nepal were steep slopes, combined with loose material and excessive rainfall during monsoons. Activities such as severe cutting into hillsides, disturbing natural drainage systems, and inappropriate land use contributed to landslide risk.
Inappropriate land use in Thailand increased the risk of landslide. Farmers practiced slash and burn methods for farming on slopes without proper understanding of slope degradation and the potential for slope destabilization. In addition, slopes had been covered with inappropriate types of vegetation such as banana, bamboo, etc. The shallow root systems of these plants do not contribute much to soil stability.
In the Philippines, a study of the Baguio area determined that it is subject to many factors favoring the occurrence of landslides: the mostly mountainous terrain; a humid climate with frequently occurring typhoons and associated heavy rainfall; earthquakes; deforestation caused by logging, mining, industrial development, agriculture; etc.
In general, roadside landslides are more common in places where there is sloping terrain with unstable conditions. Landslides may cause a large number of deaths if there are houses or settlements in steep terrain and the population density is relatively high.
More than 90% of roadside landslide disasters in Japan were caused by heavy rain and only two percent by earthquake. Japan is exposed to heavy rainfall in the rainy season from June to July and in the typhoon season from September to October. Japan is prone to earthquakes as it is located on active tectonic plates.
Most of the landslides recorded in Laos were caused by high wet season groundwater and perched water levels in soils and weathered rock masses exposed to steep roadside cuts. Slope failures were often observed to originate from the upper portions of cut slopes where weaker material predominates in the weathering profile.
The intensive unscientific cutting of hills in India for new roads and for widening existing roads using heavy machinery had added to geological disturbances, resulting in the greater instability of hills and more slope failures. Every year the triggering of landslides occurs frequently in different locations, as a result of monsoon rains. Quarrying and the careless disposal of surplus materials were other sources of roadside landslides.
The main causes of landslides in Nepal were steep slopes, combined with loose material and excessive rainfall during monsoons. Activities such as severe cutting into hillsides, disturbing natural drainage systems, and inappropriate land use contributed to landslide risk.
Inappropriate land use in Thailand increased the risk of landslide. Farmers practiced slash and burn methods for farming on slopes without proper understanding of slope degradation and the potential for slope destabilization. In addition, slopes had been covered with inappropriate types of vegetation such as banana, bamboo, etc. The shallow root systems of these plants do not contribute much to soil stability.
In the Philippines, a study of the Baguio area determined that it is subject to many factors favoring the occurrence of landslides: the mostly mountainous terrain; a humid climate with frequently occurring typhoons and associated heavy rainfall; earthquakes; deforestation caused by logging, mining, industrial development, agriculture; etc.
In general, roadside landslides are more common in places where there is sloping terrain with unstable conditions. Landslides may cause a large number of deaths if there are houses or settlements in steep terrain and the population density is relatively high.
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