Catena 104 (2013) 219–232

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Review

Landslide process and impacts: A proposed classification method

Yashar Alimohammadlou a,⁎, Asadallah Najafi b, Ali Yalcin c

a Department of Civil Engineering, Zanjan Branch, Islamic Azad University, Zanjan, Iranb Department of Industrial Engineering, Zanjan Branch, Islamic Azad University, Zanjan, Iranc Department of Geological Engineering, Aksaray University, 68100 Aksaray, Turkey

⁎ Corresponding author. Tel./fax: +98 241 4260063.E-mail address: y.alimohammadlou@azu.ac.ir (Y. Ali

0341-8162/$ – see front matter © 2012 Elsevier B.V. Allhttp://dx.doi.org/10.1016/j.catena.2012.11.013

a b s t r a c t

a r t i c l e i n f o

Article history:Received 6 July 2012Received in revised form 28 November 2012Accepted 29 November 2012

Keywords:Landslide hazardsEnvironmentProcessClassificationLosses

Various impacts of landslides have increased in past decades due to the rapid growth of urbanization in thedeveloping world. Landslide effects have damaged many aspects of human life and the natural environment,and many difficulties remain for accurate assessments and evaluations. Many investigations by landslide re-searchers have attempted to achieve a comprehensive view of landslide consequences, however, the lack of fur-ther systematic studies have resulted in a limited view. Hence, this study considers an alternative classificationtheory concerning significant concepts of landslide hazard and risk through the presentation of numerous casestudies. This classificationmethod categorizes landslide impacts into twomain groups as general and particular,and discusses them in an environmental and socio-economic framework. The findings illustrate that the rate ofphysical or socio-economic losses critically impact populated regions and civilization centers. This paper at-tempts to describe a systematic organizational approach in framing landslide impacts in order to more reliablydescribe and integrate analysis and mitigation measures.

© 2012 Elsevier B.V. All rights reserved.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2192. Materials and methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220

2.1. General classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2212.1.1. Natural environment impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2212.1.2. Socio-economic impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223

2.2. Particular classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2232.2.1. Public and private losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2232.2.2. Direct and indirect impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223

3. Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2243.1. Natural environmental impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224

3.1.1. Morphologic/topographic impact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2243.1.2. Forest and land cover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2253.1.3. Streams and water sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227

3.2. Socio-economic impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2273.2.1. Economic impact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2273.2.2. Human impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228

4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231

mohammadlou).

rights reserved.

1. Introduction

Natural disasters are the complex of detrimental events that occurcompletely beyond the people's control, and are often indirectly madeworse by human interventions. Some hazards are known to be more

220 Y. Alimohammadlou et al. / Catena 104 (2013) 219–232

prevalent such as droughts, windstorms, floods, earthquakes, volcano,and extreme temperature; however, landslides are the 7th largest killeramong natural disasters (Herath and Wang, 2009), and contributes toabout 17% of mortalities (Kjekstad and Highland, 2009). Generally,movement of large volumes of soil or rock from high altitude to low-lying ground along slopes is a permanent factor of Earth's topographicchanges and its current shape. However, this event occurring in vulner-able regions and civilization centers involves serious damages to variousaspects of human life. Yalcin (2011) has discovered that, the economiclosses and casualties due to landslides are greater than generally recog-nized, and they cause a yearly loss of property larger than from anyother natural disaster in some countries such as Turkey. In the UnitedStates, landslides cause an estimated between one and 3.6 billion dollars(converted to 2010 dollars) in economic losses and about 25–50 peopleare killed each year (Highland et al., 1998), thus it is one of themost cost-ly disasters worldwide. Similarly, Japanese annual losses are reported tobe between 4 and 6 billion US$ (Herath and Wang, 2009). Li and Wang(1992) reported that, the most disastrous landslides have claimed asmany as 100,000 lives.

Various studies have been reviewed as to different aspects of landslidescience such as; causes and their effect priority (Cascini et al., 2011;Zezere et al., 1999), respective parameters assigning slope sensitiv-ity (Gullà et al., 2008), development of warning systems (Dai et al.,2002), providing landslide susceptibility mapping for use in urbandevelopment programs (Goetz et al., 2011; Wang et al., 2009), mit-igation measures against probable reactivated landslides (Kwonget al., 2004), and finally case studies in numerous areas and theirfailure scenarios (Anbarasu et al., 2010; Tang et al., 2011). Investiga-tion of landslide impacts and losses will determine the importanceof each mentioned aspect to achieve more accurate results and toaid in the prevention of greater damages.

According to Schuster and Highland (2004), landslide damagesto natural environments can be divided into two categories. Thefirst one is the impacts on total environment which includes effectson people, homes and possessions, farms and livestock, industrialestablishments and other structures, and lifelines. The second cate-gory for natural environment effects are morphological changes,land covers (forest or grassland), and native wildlife on the Earthor in rivers. It must also be noted that, landslides have numerous

Table 1

7

6

5

4

3

2

1

Extremely fast

Very fast

5 x 103 5 m/s

3 m/min

1.8 m/hr

13 m/month

1.6 m/year

16 mm/year

5 x 101

5 x 10−1

5 x 10−3

5 x 10−5

5 x 10−7

Fast

Moderate

Slow

Very slow

Extremely slow

Speed class Description Velocity(mm/s)

Typ.velocity

Probable destructivesignificance

Disaster of major violence, buildings destroyed by impact of displaced material, many deaths, escape unlikely

Some lives lost; velocity too great to permit all persons to escape

Escape evacuation possible; structures, possessions and equipment destroyed

Some temporary and insensitive structures can be temporarily maintained

Remedial construction can be undertaken during movement; insensitive structures can be maintained with frequent maintenance work if total movement is not large during a particular acceleration phase

Some permanent structures undamaged by movement

Imperceptible without instruments, construction possible with precautions

Classification of velocity of movement according to Cruden and Varnes (1996) andAustralian Geomechanics Society (2002).

impacts which this paper will try to classify and review. Some ofthese concepts include the social and economic losses, effects on in-frastructure development, natural dam constructions, insurance is-sues and real estate costs, streams and water quality, tsunami andcoastal damages, and income sources for economies particularlythe tourism sector.

The study of risks incurred by landslides cause a profound focuson risk management. It means that, investigation of landslide riskwill determine sufficient measures in different regions for improve-ment in hazard recognition, prediction, mitigation measures, warn-ing systems, hazard mapping and assessments, and emergencypreparedness response and recovery (Herath and Wang, 2009). Onthe other hand, development of landslide studies in countries withhigh frequency of occurrence and attaining a reliable frameworkwill be useful for other regions. Consequently, the developing coun-tries will be able to adopt powerful economic policies in order tosupport mitigation strategies against this hazard.

Also, this paper will describe remarkable aspects of landslide im-pacts and present a comprehensive framework in order to classifydifferent concepts. The emphasis will be on important principles ofclassification and identification of landslide hazard on the built andnatural environment. Another key point in this paper is discussionabout causes and parameters which intensify landslide effects or in-crease frequency of occurrence. This concept is essential for preven-tion activities and for the promotion of mitigation measures.

2. Materials and methods

Landslides are one of the most widespread disasters that cause se-rious losses to various aspects of life. The term “Landslide” includes alltypes of mass movement down a slope which can consist of soil, rock,debris, organic matter, artificial fill, or a combination of these. Thedownward or outward movements have been classified in differentgroups based on the velocity of motion (mm/year to tens of m/s),the water content of the materials, for example, and other character-istics. Varnes (1978) has presented a comprehensive categorization oflandslide process that includes falling, toppling, sliding, spreading,and flowing, all of which constitute conditions of causal effects andslope characteristics.

Generally, slope stability is related to balance between the stimulat-ing factors (that increased shear stress) and the parameters that supplythe soil mass resistance against sliding. Accordingly, Terzaghi (1950)has illuminated the landslide occurrence dependent on the distinctionbetween internal changes within a slope; for example, factors that in-duce shear strength reduction, and external causes, which give rise toan increased shear stress. Therefore, attention on type and magnitudeof the various effective factors and slope characteristics is one of thebasic and essential fields of landslide study. It is necessary to notethat both subaerial and submarine mass movements are mostly trig-gered by precipitation (rainfall and snowmelt), seismic activity,human interventions, volcanism, weathering, seepages and springs,and river erosion. Any one of these items will determine differenttypes of landslides (based on Varnes (1978) classification) by a com-bination of geological and geotechnical properties of soil, constituentmaterials of slope (the materials will slip), velocity of mass move-ments, and volume of sliding area.

There is no single factor that can accurately characterize landslidehazard estimation; a collection of parameters should be analyzed inter-actively. This matter explains the mutual effect of factors on each otherand their joint impacts on the sliding process. Several studies havepresented different classification systems (e.g. Crozier, 1986; Terzaghi,1950; Zogning, et al., 2007). These methods have placed sliding factorsin various groups and have analyzed themajor factors of each one basedon their role in sliding process and the accompanying triggering factors.The key aspect of this discussion is themodification of triggering factorsby human activities and resultant interferences with nature. According

221Y. Alimohammadlou et al. / Catena 104 (2013) 219–232

to Zezere et al. (1999), the causes of more than 20% of landslides arehuman interventions. With regard to civilization and urbanization ex-pansion, human activities in reforming andmodifying the environmentwill increase in order to enable more utilization of facilities. These casesgenerally encompass themeasures such as excavation on slope body ortoe, overloading by installation of residential infrastructure such aspipes, dynamic impaction to obtain appropriate subgrade for variousstructures, construction of hydraulic structures on rivers, deforestationand land-use change for purposes of acquiring more territory, theconstructing or redirecting of irrigation and water transition channels,and air pollution due to industrialization. The mentioned human mod-ificationswill cause some natural occurrences whichmay inflict seriousdamages. The most crucial aspects commonly start out as the distur-bance of slope balance and slope sliding, seismic stimulations andearthquakes' damages which are enlarged by interventions, drawdownof reservoirs due to immediate inundation or intense rainfall, waterleakage and heavy rainstorms due to climatic regime changes, and tsu-nami. These occurrences may result in the increase of velocity and vol-ume of landslides and an increase of landslide intensity of these twoparameters (Glade et al., 2005). The increased hazard due to rise inmass movement velocity is discussed in Table 1.

The increase in human interventions on nature and environmentmultiplies the effect of triggering factors. Therefore, the multiplicityand intensity of landslide occurrence will rise respectively and leadto an increase in the human and environmental loss rates. The effectswhich result in an enhancement of frequency and the resultant in-crease in damages and casualties are interconnected and character-ized by the following cycle (Fig. 1).

Undoubtedly the most effective factor of landslide initiation is rain-fall; hence the high landslide risk area is a subset of the regions that re-ceive intense precipitation. Furthermore, anthropomorphic activities arean additional influence on this triggering factor. The changing patternsof rural poverty, overpopulation and uncontrolled urbanization, particu-larly in less-developed countries, result in settlement on hillsides and onthe banks of ravines, which may not be suitable for housing or othermodifications (Bommer and Rodriguez, 2002). Hazard evaluation ofnew residential areas and the land-use change associated with forestswhich may include domestic animal overgrazing and increased irriga-tion may intensify the erosion caused by rainfall, thus increasing thefrequency of landslide occurrence. Another problem that may appearas a result of populationmigration is the increasing construction activitythat commonly occurs (residential and common-use infrastructure) andas a result, the hazard from landslides may increase. With regard to re-quirements of water and the effects of drought in recent decades, oneof the significant matters is the rainfall regime change due to cloudseeding, for example, whichmay lead to increasing precipitation. Unfor-tunately, the cloud-seeding approach is exclusively focused on regional

Human intervention and nature

Landslide occurrence

and intensity

Losses and damages

Fig. 1. Relationship between human intervention and losses.

water shortage; however, it may be the cause of irreparable damages inlandslide-prone areas, based on the inattention to systematic studiesthat includes landslide hazard evaluation. Another remarkable causewhich changes precipitation regime in some world-wide regions is theincrease in rapid industrialization. This results in potential changes inweather patterns may be a factor in overall climate change and conse-quently cause changing rainfall patterns by which an increase in suchmay cause a greater landslide frequency and/or intensity.

With regard to the necessity of water-distribution systems and in-dustrial waste water treatment, another factor of anthropomorphicactivities is the construction or redirecting of pipes and channels. Theleakage of such systems particularly sewer systems, in addition to thesaturation of soils, may intensify the effects on clay layers which havelow soil shear resistance (Preuth et al., 2010). Another prevalent effectis the road construction and landscapemodification that result in weak-ening of support conditions that result in slope failure. The cut operationin a part of a slope will create fissures and cracks by weakening, unset-tling, and shifting soil conditions on the upper portion. The discontinu-ities will provide suitable conditions for precipitation penetration andmaterial displacement in earthquake-induced landslides. One of theother problems that will be caused by the development of the transpor-tation system (roads and railways) is the dynamic effect of trains andheavy trucks in a landslide-prone area. The vibration and shakingstimulations generated by several vehicles traffic may be one of thesignificant causes for triggering landslides. These factors frequentlychange a slope to a marginally stable state and exacerbate conditionsfor triggering factors. Compaction and blasting activities can alsocause vibration and shaking, in a similar way as seismic impacts. Inaddition to mentioned items, there are other factors in the field ofhuman intervention that increase the influence of triggering factors,and consequently increase the rate of landslide occurrence. As isshown in the cycle above, the impacts of human activities will indi-rectly increase losses and landslide effects on the natural environ-ment and human life.

In this study, as is presented in Fig. 2, the proposed classificationconsisted of two main sections. The first section is General classificationwhich is divided two subsets as natural environmental and socio-economic impacts. The second section is presented as Particularclassification with two separate subsets. The Public and Privatelosses in one hand and the Direct and indirect impacts on theother hand have constituted this section. As can be seen in Fig. 2, dif-ferent parts of each section are described in following flowchartwith some criteria and examples.

2.1. General classification

In most places of the world, landslides and soil mass move-ments are a significant cause for the loss of human life, destructionof residential or industrial developments, and lifelines such as high-way, railroad, and other lifeline systems. The various aspects oflandslide impacts and their resultant injuries have been consideredby several scholars (Atta-ur-Rahman et al., 2011; Larsen, 2008;Smyth and Royle, 2000), however, in order to achieve the systematicanalysis of landslide effects, the said aspects are described in twocategories:

a. Natural environment impacts.b. Socio-economic impacts.

2.1.1. Natural environment impactsOne of the most important parts of landslide impacts is the natu-

ral environment damages that are often the first effect of damaginglandslides. The natural environment impacts include various itemswhich Schuster (2001) has considered and are classified into fourcategories: (1) the morphology of both subaerial and submarinesurfaces of the Earth, (2) the natural forests and grasslands that

Public and Private losses

Direct and Indirect losses

Damages to physical health

Adjacent region’s destruction

Personal possessions of inhabitants

Damage to mental health

Private losses

Public losses

Monitoring of movement

Losses of tax revenues

Highways/roads and accessorystructures

Traffic delays and disruption

Direct losses

Deaths and injuries

Residential or industrial constructions

Infrastructure

Natural environment

Indirect losses

Reduced real estate values

Loss of tax revenues

Industrial, agricultural, and forestproductivity and tourist revenues

Loss of human or animal productivity

Natural environment impacts

The intensity of the phenomenon, in relationto its disturbing effect on nature

Streams and Water Sources

Forest and Land cover

Native Fauna on Earth andin oceans or streams

The function of the forest or of theendangered animal and vegetal species

The sensitivity and rareness of this specie

1. Degradation and mass wasting2. Natural landslide dams3. Landslide-generated tsunamis

Morphologic/Topographic

Housing sectorPublic buildingsLivelihood and earningsInfrastructure

Economic Impacts

Human Impacts

Socio-economic impacts

Human healthRelative’s mortalityFamily economic

Criteria in Natural components

Criteria in Social components

The intensity of the phenomenon

The sensitivity of the population

The capacity of understanding phenomenon

Proposedclassification in landslide losses

GeneralClassification

ParticularClassification

Fig. 2. Flowchart describing the proposed classification designed for landslide losses.

222 Y. Alimohammadlou et al. / Catena 104 (2013) 219–232

cover much of the Earth's surface, (3) quality of streams and otherbodies of water, and (4) the habitats of native fauna, both on theEarth's surface and in its streams and oceans.

Indeed, the landslide event and mass movement hazard accompanythe constantly-changing morphology of the Earth's surface. The key con-cept of this argument is that, degradation and mass wasting occurring in

Table 2

No. of events Total affected (number of people)

Africa 22 19,740Ave. per event 897Americas 139 4,667,943Ave. per event 33,582Asia 220 5,055,856Ave. per event 22,981Europe 75 41,536Ave. per event 554Oceania 15 11,015Ave. per event 734

Total number of people reported affected, by continent and by avalanches and landslides(1993–2002).

223Y. Alimohammadlou et al. / Catena 104 (2013) 219–232

valleys and low-lying ground sometimes intensify the consequences ofevents such as flood and tsunami. Natural landslide dams are formed bythe tremendous amount of rock fall, soil, and debris that often fall orslide into rivers and streams, blocking their flow, and inmany cases caus-ingwater to form a lake above the blockage. These natural landslide damsmay persist for periods from several minutes to millennia (Costa andSchuster, 1988). Natural erosion that leads to the water breaching thedam, can cause sudden, catastrophic flooding to areas below the initialdam. Another relevant consequence due to landslides is the tsunami phe-nomenon. Landslide-generated tsunamis occur in water bodies aroundthe world (Locat and Lee, 2002) and affect or remove the environmental(forests or farmlands) and structural (residential or industrial) regionsfrom the shoreline by the action of the high waves.

The second concept of natural environment impacts is related tothe denudation of different kinds of vegetation (especially as the ir-reparable mode in rare kinds), grasslands, farmlands, and scenicparks. According to Geertsema et al. (2009), this is common inmany parts of the world, but particularly in tropical areas as a resultof the combination of intense rainfall and earthquake shaking. Thelandslide impacts on water resources and flow and loss of springsdue to rock fall often result in negative socio-economic effects andare in the third concept of Schuster (in press)'s categorization.The fourth section includes the landslide impacts on the habitat ofnative animals and fish which live in rivers and springs. The de-struction of terrestrial and aquatic fauna will create problems forthe food resources of inhabitants.

It is necessary to note, that the damages to natural environment aredifficult to evaluate in monetary terms and have no merchant value,therefore Castelli et al. (2002) have presented these three ideas to de-termine the landslide effects on natural components:

a. The intensity of the phenomenon, in relation to its disturbing effecton nature.

b. The function of the forest or of the endangered animal and vegetalspecies.

c. The sensitivity and rareness of these species.

2.1.2. Socio-economic impactsThe second group of landslide consequences constitutes physical

losses and social impacts. The concept of physical impact includeseffects on human health (wounds or deaths) and its possession. Inother words, the physical impacts could be categorized in two parts as(1) economic impacts and (2) human impacts. The economic losses in-clude all repair and replacement activities of structures in the landslideregion. Therefore, the remedial costs will closely relate to the type andquality of the materials. Generally, Atta-ur-Rahman et al. (2011) haveclassified the landslide economic impacts into four groups: (1) damagesto housing sector, (2) damages to public buildings, (3) damages to var-ious sectors of livelihood and earnings (such as forests, farmlands andtourist sectors), and (4) extent of damage to infrastructure (roads and

railways, bridges, irrigation channels, and electricity networks). Anoth-er relevant aspect of socio-economic losses is the human impacts. Alldamages by landslides and their aftermaths which include injuriesand/or mortality, constitute this group. These impacts indirectly in-fluence the section of economic, social, and national development.Table 2 shows the average rate of impacts to humans due to landslide(Herath and Wang, 2009).

One of the interesting concepts in the identification of landslideeffects is the social impacts on people suffering from damages. Thelosses of human health, relative's mortality, homes and habitat, familyeconomic, and economic situation in the region (particularly earningsources in tourist areas) have deep psychological consequenceswhich may lead to mental health issues. The study of social impactsis a hidden aspect of landslide impacts and there are several reasonsto investigate theme. Kjekstad and Highland (2009) have consideredsome aspects as: viable recovery and resettlements of the damagedregions, measures to reduce social vulnerability, necessity of invest-ments for landslide risk mitigation and reduction, and insurance is-sues for mentioned risk. The rate of social impacts is different invarious cases and generally is described by three criteria (Castelli etal., 2002):

a. The intensity of the phenomenon (as described before based ontype, volume, and velocity of landslide).

b. The sensitivity of the population (the varied social (cultural) factorsand economic circumstances can explain the risk tolerance diversity(Winter and Bromhead, 2012)).

c. The capacity of understanding phenomenon and tomove away fromexposed zone (awareness of inhabitants about landslidemanner andits probable risks candecrease the social impacts (Atta-ur-Rahmanetal., 2011)).

2.2. Particular classification

As discussed above, various types of landslide impacts were cate-gorized in different groups by a General classification. However,identifying the numerous destinations for damages as well as the es-timation costs to loss categories will be one of the activities consid-ered, in order to implement required investments and preventivemeasures. To achieve a denotative investigation and analysis of thelandslide effects, the classification of such should be based on thesetwo groups:

A. Public and private losses.B. Direct and indirect impacts.

2.2.1. Public and private lossesAs the first step of impact categorization, the losses are divided into

two designations, which are private and public losses. The private con-cept includes the damages to physical and mental health or to personalpossessions of inhabitants and adjacent regions. It is necessary to notethat, the private losses are inmany cases far less than the public impacts.Accordingly, the public impacts are the damages that affect communitiesand governments. These cases are presented as: case–study recognition,monitoring of landslide movement in specified regions, and damageson highways/roads and accessory structures such as sidewalks andstorm drains, redirecting of rivers and water or waste channels for pre-vention of side erosion, losses of tax revenues, reduction of transmissioncapabilities of lifelines, reduction of productivity of government forests,traffic delays and disruption, and evacuation of residents and tourists.Susceptibility mapping may occur later as a measure to reduce thelosses from future occurrences.

2.2.2. Direct and indirect impactsLandslide impacts are classified as to whether they cause direct or

indirect consequences. The direct impacts include the damages to infra-structure (inclination and cracks), heterogeneous change to residential

224 Y. Alimohammadlou et al. / Catena 104 (2013) 219–232

or industrial constructions, excessive damage or destruction of hydrau-lic structures on rivers, and effects on the population such as deaths andinjuries. The direct consequences can also relate to the natural environ-ment, which include the destruction of forests, animals and their habi-tats, and springs and water resources. These direct effects influencethe region immediately after landslide occurrence while, the indirectimpacts may appear over a longer period of time. Unfortunately, theassessments of landslide indirect consequences are severely difficultto assess, because theymay encompass the larger area beyond the land-slide zone. In general, Kjekstad and Highland (2009) have discussed thedifferent aspects of this argument as: (1) loss of industrial, agricultural,and forest productivity and tourist revenues as a result of damage toland or facilities or interruption of transportation systems, (2) reducedreal estate values in areas threatened by landslides, (3) loss of tax reve-nues on properties devalued as the result of landslides, (4) measuresthat are required to be taken, to prevent ormitigate additional landslidedamage, (5) adverse effects on water quality in streams and irrigationfacilities outside the landslide, (6) loss of human or animal productivitybecause of injury, death, or psychological trauma, and (7) secondaryphysical effects, such as landslide-caused flooding, for which lossesare both direct and indirect. Sidle and Ochiai (2006) attempted to con-trast direct costs with total costs, shown in Table 3. They have alsoreported average annual costs of landslides in various nations.

3. Results and discussion

3.1. Natural environmental impacts

3.1.1. Morphologic/topographic impactOne of the main effects of landslide is the morphological or topo-

graphical change, for both subaerial and submarine cases. In otherwords, the changing of Earth's surface will be constantly associatedwith displacing large volume of soil which often changes the region'slandscape. To illustrate this argument and describe the importance ofthis matter, some crucial cases are considered in this section.

The M=7.6 Kashmir earthquake on 8 October 2005 in northernPakistan (Fig. 3) dislodged landslides which transformed about80 million m3 of soil mass into a debris avalanche (Owen et al.,2007). Similarly, on September 21, 1999, the Chi-Chi earthquakewith a magnitude of 7.3 induced extensive landslides in central re-gion of Taiwan which devastated an area of more than 8000 ha (Linet al., 2008). In another case, on April 20, 2000, the Yigong Landslideoccurred at Zamulong Ditch, Yigong, and Pomi, Tibet due to seismicshaking and it involved the collapse of 30 million m3 of rock mass

Table 3

country Average annualdirect costs (USD)

Average annualtotal costs (USD)

Comments

Canada $70 million A more recent estimate oftotal costs is up to $1.4billion annually

Japan $1.5 billion $4 billionKorea $60 million – Based on poor recordsItaly – $2.6–5 billion Rough estimateSweden $10–20 millionSpain $0.2 billionFormer USSR $0.5 billionChina $0.5 billion – Costs based on valuations

in 1989India $1.3 billionNepal $19.6 million – Includes flood damage, but

likely incompleteNew Zealand – 26.3 million 90% of costs are sustained

in rural areas

Estimated average annual costs (USD) of landsides in various nations.

(Huang, 2008). Knapen et al. (2005) have studied 98 recent land-slides in the Mount Elgon area in Uganda and have reported thatthe transformed soil volume is about 11 million m3 in an area ofapproximately 154 km2 caused by landslides. Most of the massivelandslides which caused large topographic effects, have been trig-gered by sever seismic shaking in earthquake-prone areas. This as-sertion has been described by Plafker et al. (1969) in a historiclandslide analysis. The 1964 Alaska Landslide was triggered by theM=9.2 earthquake which has had significant morphological impacton an area of about 260,000 km2. In 1938, Harrison and Falcon pub-lished a paper in which they described one of the huge prehistoriclandslides that occurred at the Simareh in southwest Iran (Fig. 4).This event encompassed an area of 166 km2 and displaced a volumeof 24–32 km3 and is one of the world's largest subaerial landslides(Shoaei and Ghayoumian, 2000).

Another influential factor in Earth's changing morphology is sub-marine landslides. The mechanism and changes of landslide bothabove and beneath the surface of the sea have numerous similarities;however, a high volume of transported matter is the most egregiousdifference between these. In submarine landslides, great masses ofthe soil displace from shallower to deeper areas of the sea floor.One of these cases which, has recently been discovered by Vannesteet al. (2006), is the Hinlopen Slide which took place along a glaciatedmargin in the Arctic Ocean. This landslide has a volume of about1350 km3 (Locat and Lee, 2009). One of the world's largest knownsubmarine slides is the Storegga Slide which has a displaced volumein excess of 3000 km3 and a run-out of the mass of about 300 km(Marui and Nadim, 2009). Following this event, a destructive tsunamidecimated the coasts of Norway, Scotland and the Faeroe Islands.Consequently, the environmental and built-environment damagesto coastline zones will be one of the submarine landslide's effects.On July 9, 1958, a tremendous earthquake (M 7.9–8.3) induced rockand ice slides in Gilbert Inlet (Lituya Bay), a large inlet on the north-east of the Alaska Gulf. The giant waves with a maximum height ofabout 150 m were created by these slides that resulted in a tsunamiin the mentioned shore. According to Fritz et al. (2001), the inunda-tion has been estimated as large as 5 mi2 of land with a run-up heightof 524 m, the largest in recorded history (Fig. 5).

Another significant change in landslide morphologic impacts isthe creation of natural landslide dams which block the flow of nearbyrivers. In addition to blocking rivers and streams, landslide dams mayimpound large quantities of water that accumulate behind the slide,causing flooding in the upstream area. The formation of natural tem-porary dams ranges from rock avalanches in steep-walled, narrowvalleys to sensitive-clay failures in flat river lowlands (Costa andSchuster, 1988). In a comprehensive study of 390 natural dams,Schuster (1993) found that more than 90% of the causative landslideswere triggered by either rainstorms/snowmelt or earthquakes. Ac-cordingly, more than 85% of landslide dams fail within one year ofemplacement (Costa and Schuster, 1988). The damages and topo-graphical changes in the affected region, take on special importanceas to their investigation. Fracture of natural dams may result inrapid flooding causing loss of life, farmland, and downstream struc-tures (Duman, 2009). Gasiev (1984) identified the Lake Sarez on theBartang (Murgab) River in the Pamir Mountains of Tajikistan as thelargest natural landslide dam on Earth (Fig. 6). This dam was formeddue to the Usoi Landslide (estimated 2–4∗109 m3), which was trig-gered by a 1911 earthquake. The lake that was impounded upstreamfrom the landslide is 500–700 m in height. The lake on the Indus Riverin Baltistan of Pakistan which formed by the Rondu Mendi Landslidewith a height exceeding 950 m is accepted as the world's deepest lakeimpounded by a landslide dams (Hewitt, 1998). In 1929, exceptionalrainstorms triggered a landslide in the Pontide Mountains at Turkeyand formed a temporary lake on the Solakli River. Breaching of this land-slide dam created the largest flood in Turkey and caused the loss of 148lives, 18 bridges and 2539 houses (Pamir, 1930). It must also be noted

Fig. 3. The Hattian Bala debris avalanche and the two lakes impounded by the landslide debris in the Karli and Tang valleys, Pakistan. http://landslide.usgs.gov/learning/photos/images/international/2005_pakistan_kashmir_earthquake_landslides/pakistan2005.jpg)Photograph from DigitalGlobe Quickbird II Natural Color, October 27, 2005.

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that the landslide-dammed lakes occasionally result in positive en-vironmental impacts. In this case, the Tortum Landslide located90 km to the north of Erzurum in Turkey occurred as a rock slideon Tortum River and formed the largest landslide-dammed lakeof Turkey with 538 million m3 of water and a maximum height of270 m (Fig. 7). According to Duman (2009), the positive impactsof this lake include the semi-mild micro-climate area in the gener-ally terrestrial climatic region, tourism development, hydropower

Fig. 4. Photo of Simareh LandsliGraphics by David Petley, Durha

generation, and the creation of the appropriate conditions for fish-ery and greenhouse agriculture.

3.1.2. Forest and land coverAs noted before, landslide may be associated with denuding large

tracks of forest and the destruction of vegetation cover of thousandsof square kilometers which result in an accelerated erosion rate andlarger landslides. This process is common in many parts of the world,

de in Iran, by Google Earth.m University, United Kingdom.

Fig. 5. A few weeks after the 1958 tsunami, Lituya Bay. The areas of destroyed forest along the shorelines are clearly recognizable as the light areas rimming the bay.Photo by U.S. Geological Survey.

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particularly in tropical regions as a result of the intense precipitationand seismic shaking. In February 2006, a devastating rock slide and de-bris avalanche occurred in Guinsaugon of Leyte Island located in thePhilippines where there is high rainfall and tectonically active charac-teristics (Kjekstad and Highland, 2009). The mentioned landslides(Fig. 10) involved a total volume of 15 million m3 and destroyedpaddy fields and heavily forested areas (Evans et al., 2007). Similarly,on December 4, 2007, a 3 million m3 of rock slide caused a tsunami in

Fig. 6. Satellite photograph of the UPhotograph by Dr. E. DiBiagio, Norw

Chehalis Lake near Vancouver, Canada. The waves removed treesfrom the shoreline resulting in several hectares of destroyed forest(Geertsema et al., 2009). The intense rainfall and earthquake atReventador Volcano in Ecuador and the Paez region in Colombia trig-gered debris flows and denuded land covers. Schuster et al. (1996)reported that the Reventador Landslide in 1987 removed the sub-tropical jungle from more than 75% of southwestern slopes. Else-where, Figueroa et al. (1987) have estimated that about 230 km2 of

soi Dam in eastern Tajikistan.egian Geotechnical Institute, Oslo, Norway.

Fig. 7. The Tortum Landslide from main scarp to toe and landslide-dammed lake.

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natural forests were destroyed in the area. Similarly, the 1994 PaezLandslide denuded 250 km2 of soil and vegetation (Martinez et al.,1995). In another case in 1960, the large earthquake in Chile trig-gered a landslide that destroyed more than 250 km2 of forest lands(Geertsema et al., 2009). In addition to loss of vegetation in some re-gions, soil denuded down to bedrock can cause bare tracks of land toexist for hundreds of years. Consequently, there is no soil for newplantsto grow on and the process of soil creation will take many years.

3.1.3. Streams and water sourcesRivers and springs located downslopes and in valleys are an effective

factor of internal erosion and slip process acceleration. Landslides, partic-ularly debris and mud flow, transport sediment in water channels andblock the flow of streams so that the flow of water downstream will beaffected. In other words, demolition of springs' structure and preventionofwater leaving on one hand, and sediment accumulation in rivers chan-nel on the other hand, are two effects of landslides. In a remarkable studyon 19 debris flows in the Van Duzen River basin (northern California),Kelsey (1978) reported the annual yield of sediment to the river in-creased from 2200 m3 to 41,000 m3 per event. Similarly, in November2000 Typhoon Xangsane triggered large-scale debris flows in Chonhoarea of Taipei County, northern Taiwan. The landslides destroyedstreams and rivers by moving within channels which eroded about122,720 m3 of material, and deposited sediment of 105,970 m3 (Chenet al., 2006). One of the cases that illuminates mutual impacts and dam-ages of springs and landslides is the Lanta Khola slideswhich occurred onthe North Sikkim Highway (NSH) in Sikkim State in India. According toSengupta et al. (2010) the lower part of the slide is characterized by anumber of anastomosing streams. In another situation, The Xiao-LinLandslide, in Jishian, Kaohsiung County, in southern Taiwan destroyedthe Lushan tourist region. This landslide which was triggered by Ty-phoon Morakot in August 2009, harmed hot-spring areas, thus affectingcommercial incomes (Lee and Chi, 2011). Furthermore, sediment move-ment in river channels by debris flow or avalanches may negatively af-fect water resources for local people.

3.2. Socio-economic impacts

As mentioned in previous literatures, the development of humancivilization and relevant activities (as transportation systems, land-usechange to housing or agricultural fields, mining, tourism, and climatic

regime changing) have increased the incidence of hazard events andhence significant growth in socio-economic risks. It is clear that the ex-tensive interference of natural conditions and the disturbance of thebalance will cause more damage to human life. This argument is inten-sified in developing regions. In 1992, Anderson considered three rea-sons which make metropolitan areas more vulnerable to disasters:

a. the concentration of people and activities in defined and limitedspace.

b. the sheer numbers of people and activities.c. The proximity to human-made hazards.

Therefore, this section will discuss some remarkable cases in twogroups showing the economic and human aspects of impacts moreclearly.

3.2.1. Economic impactOne of the most important private-property impacts of landslides is

the damage to the housing sector. These types of impacts are usuallydisclosed as total collapse, partial collapse, and cracks or sinking whichhave different rates in several parts of civilization such as urban areas,urban fringe, and rural regions. In a study of theMurree Landslide locat-ed in the Himalaya Mountains in Pakistan, Khan (2001) has describedthat among the total of 182 affected households, 38.5% belonged to thecity, and 44.5% were living in the rural regions. This analysis describesthat the important part of damages has occurred in population centersparticularly unstable residential areas in villages. Another relevant caseis a large-scale debris flow in Taipei County, northern Taiwan in Novem-ber 2000. Chen et al. (2006) reported that the landslide covered the en-tire area of Chonho Village, destroyed around thirty houses, and left thevillage isolated for approximately 30 h. In June 2005, The Laguna BeachLandslide occurred due to heavy rainfall in southern California, USA(Fig. 8). This landslide severely destroyed 19 homes and caused theevacuation of 345 (Highland, 2005).

Similarly, in the community of La Conchita in Ventura County,California (Fig. 9), 13 houses were destroyed, 23 houses were ren-dered uninhabitable, and 10 people were killed by a landslide onJanuary 10, 2005 due to intensive rainfall (Jibson, 2006). Elsewhere,Knapen et al. (2005) have investigated the landslide in November1997 at night in Bududa/Bushika region of Uganda and have reportedthat 31%, 339,330 m3 of slope material slid down slowly, destroying97 houses and displacing about 700 people. In cases where the

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hazard threatens urban and developed areas, the state buildings willbe included as a part of damages hence the rate of public losseswill increase. In a study lasting for three decades on landslides ofCameroon, Zogning et al. (2007) disclosed that more than 700 build-ings including residential houses, churches, schools, and administra-tive establishments were totally or partially destroyed and thisdisaster rendered more than 2500 people homeless and displacedthousands to new localities. It must also be noted that the publiccosts are not limited to the losses on buildings after the hazard oc-currence. In a review study about landslides of Hong Kong, Kwonget al. (2004) identified that since 1976, the Hong Kong Special Ad-ministrative Region (HKSR) has spent over HK$ 3.6 billion on studiesand upgrading works on both public and private man-made slopesand retaining walls.

One of the aspects of landslide impacts that are inflicting greatpublic losses to governments is the landslide occurrence in touristregions. Gran Canaria located in Spain is a tourist area that is visitedby about 3 million tourists each year. Longpré et al. (2008) have an-alyzed the El Risco Landslide effects on this region and consideredthat the road GC-200 has been destroyed by numerous landslidesand damaged the tourism sector. In addition to road structure,power lines which are in landslide-prone areas have been destroyeddue to their location on landslide deposits. The tourist rate increasein these areas will result in an increase in service activities, publicand private incomes, and hence the migration of people to tourist re-gions in order to work and increase their incomes. It is necessary tonote that the landslide hazards in these regions are more highlightedthan uninhabited lands due to economical and human effects. In astudy of Lushan Landslide, Lee and Chi (2011) have described enor-mous losses to restaurants, hotels, and other recreational establish-ments. Lushan is a popular hot-spring mountain resort in centralTaiwan, having a history of over 60 years of commercial operations(Lee and Chi, 2011).

Slope failure in transportation corridors (roads and railways) oftenis caused by lack of government standards and regulations; however,damages in some counties are a result of the lack of urban planning.Unplanned urban growth on landslide-prone areas which is created

Fig. 8. Photo of the Laguna Beach, CPhotos by Jim Bowers, USGS.

by the increase in population and extensive migration will increaseloss rates. Another aspect of damages is destruction of infrastructurewhich has been expanded along with human necessities. The Ministryof Water, Lands and Environment (2003) of Uganda has reported thatthe economic costs of the bridges and road repair after the 1997heavy rains amounted to 1,273,000 US$ for Mbale District.

Blockage of roads and railways for hours or several dayswill result indirect and indirect impacts. For instance, onMay 12, 2008, a devastatingearthquake with a magnitude 8.0 Ms caused landslides atWenchuan inSichuan Province in China. These landslides blocked the main roads toWenchuan, Beichuan andMaoxian andhampered the search and rescueteams from entering the epicentral area (Yin et al., 2010). Similarly, de-bris flow on August 18, 2004 at Glen Ogle on the A85 road in Scotland,UK, blocked the road. About 20 vehicles were trapped between thetwo flows, and the 57 occupants were airlifted to safety (Winter andBromhead, 2012).

3.2.2. Human impactsAs noted before, one of the main landslide effects is physical and

mental injuries. On October 8, 2005, the Kashmir earthquake inducedseveral landslides in northern Pakistan and caused fatalities. It hasbeen identified as deadliest disaster in south Asia's recent history,with >86,000 fatalities, >69,000 people injured, >32,000 buildingsdestroyed, and 4 million people left homeless (Owen et al., 2007).In another study, Zogning et al. (2007) have considered a number ofCameroon catastrophic mass movements within the last three de-cades. It has reported that from 1987, about thirty known landslidehave resulted in the loss of some 128 human lives (Zogning et al.,2007). In a study of landslides of Mount Elgon of Uganda, Knapen etal. (2005) have investigated that in 1933, 1964 and 1970 respectively,25, 18 and over 50 people were killed by landslides. Elsewhere,Knapen et al. (2005) have reported that in 1997, at least 48 peoplewere killed, the crops and dwellings of 885 families disappeared fromthe map, and 5600 people became homeless. Similarly, In August2009, Typhoon Morakot induced the Xiao-Lin Landslide, in Jishian,Kaohsiung County, in southern Taiwan, which buried more than 300people at once (Lee and Chi, 2011). In February 17, 2006, the Leyte

alifornia Landslide, June 2005.

Fig. 9. The La Conchita Landslide, Ventura County, California.Photo by Mark Reid, U.S. Geological Survey.

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Landslide (Fig. 10) destroyed the town of Guinsaugon and buried over1100 people who were directly in the path of landslide (Evans et al.,2007).

As noted above, the Wenchuan earthquake induced more than56,000 landslides (Fig. 11) in steep mountainous terrain covering anarea of about 41,750 km2 (Dai et al., 2011). According to Yin et al.(2009), the landslides directly caused more than 20,000 fatalities.Similarly, on October 7, 1985, a rock-block slide in Barrio Mameyes(Fig. 12), located on the northwest side of Ponce, in Puerto Rico, killedan estimated 129 people (Jibson, 1989). In another case, thousands oflandslides on steep slopes of Caracas, Venezuela that were triggeredby heavy rainfall in December 1999, resulted in an estimated deathtoll of 15,000 people (Larsen and Wieczorek, 2006). In addition tolandslides, the storm caused numerous debris flows that seriouslydamaged the state of Vargas.

It is clear from earlier discussion that the landslide-generated nat-ural environment impacts such as morphological change, streammodification, and native fauna and flora losses are a part of naturalprocesses; however, mitigation of landslide hazard can be enhancedby studying landslide effective factors in each region. The results ofthis study indicate that most of the landslides which caused forestsand land cover denudation have commonly occurred in rainy areaswith excessive precipitation and the effects can be controlled by anadequate drainage system or other engineering approaches. The cur-rent study found that the remarkable part of landslide losses is socialand economic impacts which include populated areas, particularlyrural regions; these losses are very closely-related to natural environ-ment impacts. One unanticipated finding is that in some reactivatedlandslide cases which have retaining structures to prevent futurelosses, the subsequent occurrences still had damaging effects oninhabitants. This argument has important implications for develop-ing mitigation planning in landslide-prone areas. It is interesting to

note that breaching of natural dams due to water flow can seriouslydestroy structures and agricultural lands in plains areas as well as inmountainous regions. Consequently, construction in riverbeds andfloodplains may have more dangerous consequences. The study showsthat considerable numbers of landslide have occurred in tourist areas.Uncontrolled increase in population in order to generate more incomeor tourist attractions caused unplanned development, and increasedthe hazard from landslides. These findings further support the idea ofcycles noted in a previous section (Fig. 1) and further verify the inter-connection of human activities and the resultantmultiplication of dam-aging effects. Unplanned developments of the tourist sector in theseregions have increased landslide risk; furthermore the human and eco-nomic damages will be several times higher, when the effect of multi-plicity is taken into account.

4. Conclusion

Considering the fact that landslide occurrence and differenttypes of mass movements have become more and more frequent,and human impacts on the environment have increased during re-cent decades, the objective of this study was to illuminate a compre-hensive system for the classification of landslide impacts. This workserved to encompass all aspects of damages in two classificationcategories noted as general and particular. Therefore, it will be a sys-tematic and reliable method to achieve a logical view of loss assessment.

In the course of this study, the discussion encompasses numerouscases of landslide investigation and the determination of that their im-pacts, have not received adequate attention. It is clear from the analysisthat, the rate of physical or socio-economic losses have increased overtime in populated regions, however, the environmental impacts aremore intense in natural lands. It must also be noted that, the further

Fig. 10. The Leyte Landslide of Philippines, in February 2006.Photo by http://www.nat-hazards-earth-syst-sci.net, presented by: USGS.

Fig. 11. Photo of the town of Qushan, Beichuan County, China destroyed by the 2008 Wenchuan debris flow.Photo by Dave Wald, U.S. Geological Survey.

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Fig. 12. The Mameyes, Puerto Rico Landslide, 1985.Photograph by Randall Jibson, U.S. Geological Survey.

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research andmeasures should be emphasized for the following aspects inorder to more accurately analyze and mitigate damages:

• Evaluating and estimating of damages in susceptible regions and regu-lating development investments.

• Developing suitable frameworks for the countries that are proactive inlandslide investigation and using the knowledge and lessons that maybe applicable in other regions.

• Risk assessment in tourist or high traffic regions and mitigation mea-sures to prevent further damages.

• Promoting awareness of people who are inhabitants in landslidedamage-prone areas and presenting free education about landslide-prevention methods.

• Modifying the human interventions which may increase landslide fre-quency or intensity.

Acknowledgment

The author profoundly thanks Ms. Lynn Highland who spentmuch of her valuable time and efforts for careful review and excel-lent editing. I gratefully acknowledge Dr. Mahtab Motavaselian forproviding original research material. Thanks to Mr. Shanebandi andMr. Farzad Rezaie and other anonymous persons for their importantcomments. In addition, I also thank to those who gave permission touse their previously published text, photographs and graphics espe-cially the U.S. Geological Survey.

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