My Overview of Landslides: Literature Review

 Landslides

Natural hazards like landslides, avalanches, floods and debris flows can result in a lot of property damage and human losses in mountainous regions. Landslides are among the most hazardous natural disasters and during the years, landslide hazard and risk have been attempted to be assessed and its spatial distribution to be portrayed (Metternicht et al., 2005). This geological phenomenon includes a wide range of ground movement and generally defined as a down slope movement of a mass of soil and rock material (Cruden, 1991).

Landslides are very common geological slope failure phenomenon in some countries like Brazil, Peru, Iran and Malaysia. Generally, lots of their areas have been subjected to slope failure under the effect of numerous factors, and triggered by events such as extreme rainfall or earthquake or both.

Landslides Descriptions

There are a number of definitions of landslide, range from geomorphic features and processes it encompasses. Derek H.C. (2005) wrote that the term landslide is sometimes felt to be inadequate because many types of slope movement do not involve sliding. The geomorphologist term mass wasting is little improvement. Cruden (1991) has suggested a simple definition of landslide ‘the movement of mass of rock, debris, or earth down a slope’. Sharpe (1938) begins to define landslide as ‘the perceptible downward sliding or falling of a relatively dry mass of earth, rock or mixture of two’. J. Suhaimi (2006): Sharpe (1938) it was explained further by Terzaghi (1943) ‘landslide is rapid displacement of rock, residual soil or sediments adjoining a slope and center of gravity of moving the mass advances in a downward and outward direction’. While Varnes (1978) defines landslides as ‘downward and outward movement of slope forming materials composed of natural rock, soils, artificial fills or combinations of these materials’. Hutchinson (1978) explain landslide as ‘relatives rapid down slopes movement of soils and rock, which take place characteristically on or more, discrete bounding slip surfaces which define the moving mass’. However ‘the movement of rocks, debris or earth flowing down a slope’ by Cruden (1991) is the most widely used (J. Suhaimi, 2006; Fell, 2000).

 Landslides Classification

The commonly used type of landslides was proposed by Varnes (1978), that category the landslide into five (5): falls, topples, slides, lateral spread and flows. Then has been updated and partly revised by Cruden & Varnes (1996) with another category, which are composites (combination of types).

Type of Movement		Type of Material
		Bedrock	Engineering Soil
			Predominantly coarse	Predominantly fine
Falls		Rock fall	Debris fall	Earth fall
Topples		Rock Topple	Debris Topple	Earth Topple
Slide	Rotational	Rock Slide	Debris Slide	Earth Slide
	Translational
Lateral Spreads		Rock Spread	Debris Spread
Flows		Rock Flow (deep Creep)	Debris Flow (Soil Creep)	Earth Flow (Soil Creep)
Composites (combination of two or more principle type of movement)

Table 1 Category of Landslide

The cause of landslide as listed below (H.R. Thomas, 2002):

a)      Overloading slope;

b)      Increase fill on slope without adequate drainage;

c)      Remove vegetation;

d)     Increase the slope rate;

e)      Increase the slope length by cutting at the bottom of slopes;

f)       Changing surface drainage route; and

g)      Changing in subsurface drainage route.

No.	The Causes
1	Overloading slope (weight of building or road)
2	Increase fill on slope without adequate drainage
3	Remove vegetation
4	Increase the slope rate
5	Increase the slope length by cutting at the bottom of slope
6	Changing surface drainage route
7	Changing in subsurface drainage route

Table 2 The Causes of Landslide

Landslide did not occur due to a single factor, Cruden & Varnes (1996) explains, landslide can triggered by rainfall, earthquakes, volcanic activities, changes in groundwater, disturbances and change of slope profile by construction activities or combination of these factors. This explanation is supported by N.W. Chan (1997, 1998, 1999), Main Rindam (1996) and Crozier (1986), landslide did not a happened naturally but it was a result of human actions. W. Mokhtar (2006) stressed that, main factor that caused slope failure or landslides at numbers site in hillside development in Malaysia are rainfall and storm water activities. 

Prevention of Landslide

Prevention rather than remediation is desirable where slope failure is likely to be rapid and there is a high risk of damage and injuries. These failures flow slides, earthquake-induced slides, and rock slides. Potential landslides due to these causes can be reduced in a cost-effective way by taking several actions:

a)      Identifying landslide risk through hazard mapping and past experience, then implement a plan of hazard reduction on a prioritized basis.

b)      Periodic inspections of facilities that are vulnerable to landslides to observer any early signs of distress and, if appropriates, take preventive action to avert a landslide.

c)      Maintaining and improving drainage measures in area vulnerable to landslide.

d)     Protecting lifeline facilities, buildings and other place of public access from earthquake-induced landslides.