landslide

What is a landslide?

The term landslide is used to denote the movement of mass rock, debris or earth down a slope (Cruden, 1991). Many other scientists consider landslides as "a sudden, short-lived geomorphic events that involved the rapid-to-slow descent of soil or rock in slopping terrain".

Landslides become a hazard since they cause the damage or lost of natural landscape, human living, and infrastructure. It has become one of the world's major disasters for the past few year in many countries. Globally, landslides cause approximately 1000 deaths a year with property damage of about US$4 billion (ISU, 1993).

Factors of landslides

Although gravity acting on an over steepened slope is the primary reason for a landslide, there are other contributing factors:
   - Erosion by rivers, glaciers, or ocean waves create oversteepened slopes
   - Rock and soil slopes are weakened through saturation by snowmelt or heavy rains
   - Earthquakes create stresses the make weak slopes fail

- Earthquakes of magnitude 4.0 and greater have been known to trigger landslides
- Volcanic eruptions produce loose ash deposits, heavy rain, and debris flows
- Excess weight from accumulation of rain or snow, tick[illing of rocj or ore, from waste piles, or from man-made strctures may stress weak slope to failure and other structures

Research on landslides

Forecasting the probability of occurence of a landslides is a somewhat difficult task because enormous of data with high accuracy are required to predict the spatial and temporal occurence of a landslide. Many methods and techniques have been proposed to evaluate the lanslide hazards and produce maps portraying spatial distribution. On a regional scale the temporal dimension of landsliding is essetially a function of the triggering mechanims which ars climatic ot geodynamic in nature. In spite of the investigation at local and regional scale on these mechanimss, the timing of such triggers cannot readily be linked to a model of spatial instability which is essentially based upon the geomorphological and geological feature of a region. Hence, most of the current hazard maps aim to predict where failures are most likely occure without any clear indicaton of when they are likely take place (Carrara, 1996).

One of the earliest forms of research on landslide was landslide inventory. Inthis stage the distribution and the style of landslide are desribed in detail. The result of this study was normally a detail description of each landslide with the single map. A slope instability map is normally created as the next study to improve the understanding in slope instability. This map represents a particular form of terrain analysis map.To investigate the landslides in relation with their probability of occurences, the hazard zonation or hazard susceptibility map must be established in different scales. The prediction of the potential landslide hazard for areas not concurrently subject to landsliding is based on the assumtion that hazardous phenomena the have occurred in the past can provide useful information for prediction of future occurences (van Westen, 1996). When people are going to consider the hazard affecting human life having economic effects or causing environment change, the use the term "risk" and "vulnerability".
The flowchart belowing shows the recent trend of landslide prediction.

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