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Landslide & Slope Instability Geohazards: Diagnostic Characteristics

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Landslide & Slope Instability Geohazards: Causes & Triggers

 

 

 

Landslide & Slope Instability Geohazards: Landslide Classification

Many systems have been proposed for the classification of landslides, however, the most commonly adopted systems are those of Varnes (1978) and Hutchinson (1988). In 1991 a European classification was developed from the EPOCH (1991-1993) project (The Temporal Occurrence and Forecasting of Landslides in the European Community, Contract no. 90 0025). The EPOCH classification was simple and suitable for European conditions. Dikau et al (1996) produced a classification of landslide mechanisms, compatible with Hutchinson (1988) and EPOCH (1993).

The International Geotechnical Societies' UNESCO Working Party on World Landslide Inventory ( WP/ WLI) was formed for the International decade for Natural Disaster Reduction (1990 to 2000). The WP/ WLI (1990) report "A Suggested Method for Reporting a Landslide" uses Varnes' (1978) classification and reports that it is the most widely used. The World Road Association ( PIARC) report "Landslides: Techniques for Evaluating Hazard" (Escario et al., 1997) also presents a classification based on Varnes.

The landslide classification based on Varnes' (1978) system has two terms: the first term describes the material type and the second term describes the type of movement. The material types used  by the various schemes are Rock, Earth, Soil, Mud and Debris, being classified as follows:

Rock: is “a hard or firm mass that was intact and in its natural place before the initiation of movement”.

Soil: is “an aggregate of solid particles, generally of minerals and rocks, that either was transported or was formed by the weathering of rock in place. Gases or liquids filling the pores of the soil form part of the soil”.

Earth: “describes material in which 80% or more of the particles are smaller than 2mm, the upper limit of sand sized particles”.

Mud: “describes material in which 80% or more of the particles are smaller than 0.06mm, the upper limit of silt sized particles”.

Debris: “contains a significant proportion of coarse material; 20% to 80% of the particles are larger than 2mm, and the remainder are less than 2mm”.

The terms used should describe the displaced material in the landslide before it was displaced.

The types of movement describe how the landslide movement is distributed through the displaced mass.

The five kinematically distinct types of movement are described in the sequence fall, topple, slide, spread and flow.

Combining the two terms gives classifications such as Rock fall, Rock topple, Debris slide, Debris flow, Earth slide, Earth spread etc.

 

 

Landslide & Slope Instability Geohazards: Activity States and Styles

Classification of the states of activity of landslides used in the Multilingual Landslide Glossary: (1) active; (2) suspended; (3) re-activated; (5) dormant; (6) abandoned; (7) stabilized; (8) relict. State (4) inactive is divided into states (5)–(8). See below for explanation of states. After WP/WLI (1993).

(Image Source: Cooper, R.G. (2007) Mass Movements in Great Britain, Geological Conservation Review Series, No. 33, Joint Nature Conservation Committee, Peterborough, 348 pp.)

Active: An active landslide is currently moving. In the example shown erosion at the toe causes a block to topple.

Suspended: A suspended landslide has moved within the last 12 months, but is not active at present. In the example shown local cracking can be seen in the crown of the topple.

Reactivated: A reactivated landslide is an active landslide which has been inactive. In the example shown another block topples and disturbs the previously displaced material.

Inactive: An inactive landslide has not moved within the last 12 months and can be divided into 4 states: Dormant, Abandoned, Stabilised and Relict.

Dormant: A dormant landslide is an inactive landslide which can be reactivated by its original causes or other causes. In the example shown the displaced mass begins to regain its tree cover and scarps are modified by weathering.

Abandoned: An abandoned landslide is an inactive landslide which is no longer affected by its original causes. In the example shown the fluvial deposition has protected the toe of the slope, the scarp begins to regain its tree cover.

Stabilised: A stabilised landslide is an inactive landslide which has been protected from its original causes by remedial measures. In the example shown a retaining wall protects the toe of the slope.

Relict: A relict landslide is an inactive landslide which developed under climatic or geomorphological conditions considerably different from those at present. In the example shown uniform tree cover has been established.

Distribution of the activity of landslides: (1) advancing; (2) retrogressive; (3) enlarging; (4) diminishing; (5) confined; (6) moving; (7) widening. See below for explanation of terms. After WP/WLI (1993).

(Image Source: Cooper, R.G. (2007) Mass Movements in Great Britain, Geological Conservation Review Series, No. 33, Joint Nature Conservation Committee, Peterborough, 348 pp.)

Advancing: In an advancing landslide the rupture surface is extending in the direction of movement.

Retrogressive: In a retrogressive landslide the rupture surface is extending in the direction opposite to the movement of the displaced material.

Enlarging: in an enlarging landslide the rupture surface of the landslide is extending in two or more directions.

Diminishing: In a diminishing landslide the volume of displaced material is decreasing.

Confined: In a confined landslide there is a scarp but no rupture surface visible at the foot of the displaced mass.

Moving: In a moving landslide the displaced material continues to move without any visible change in the rupture surface and the volume of the displaced material.

Widening: In a widening landslide the rupture surface is extending into one or both flanks of the landslide.

Styles of landslide activity: (1) complex; (2) composite; (3) successive; (4) single; (5) multiple. See below for explanation of terms. After WP/WLI (1993).

(Image Source: Cooper, R.G. (2007) Mass Movements in Great Britain, Geological Conservation Review Series, No. 33, Joint Nature Conservation Committee, Peterborough, 348 pp.)

Complex: A complex landslide exhibits at least two types of movement (falling, toppling, sliding, spreading and flowing) in sequence. In the example shown a gneiss and a pegmatite vein toppled with valley incision. Alluvial deposits fill the valley bottom. After weathering had weakened the toppled material some of the displaced mass slid further downslope.

Composite: A composite landslide exhibits at least two types of movement simultaneously in different parts of the displacing mass. In the example shown the limestones have slid on the underlying shales causing toppling below the toe of the slide rupture surface.

Successive: A successive landslide is the same type as a nearby, earlier landslide, but does not share displaced material or rupture surface with it. In the example shown the later slide AB is the same type as CD but does not share displaced material or a rupture surface with it.

Single: A single landslide is a single movement of displaced material.

Multiple: A multiple landslide shows repeated development of the same type of movement.

Landslide & Slope Instability Geohazards: Velocity Classification

The figure below shows the velocity scale proposed by Cruden & Varnes (1996) which rationalises previous scales. The term “creep” has been omitted due to the many definitions and interpretations in the literature.

(Image Source: Landslide Risk Management Concepts and Guidelines, Australian Geomechanics Society, Sub-Committee on Landslide Risk Management http://www.australiangeomechanics.org/LRM.pdf)

 

Landslide & Slope Instability Geohazards: Classification Schemes

Hutchinson, J. N. 1988. General Report: Morphological and geotechnical parameters of landslides in relation to geology and hydrogeology. Proceedings, Fifth International Symposium on Landslides (Ed: Bonnard, C.), 1, 3-35. Rotterdam: Balkema

Varnes, D. J. 1978. Slope movement types and processes. In: Special Report 176: Landslides: Analysis and Control (Eds: Schuster, R. L. & Krizek, R. J.). Transportation and Road Research Board, National Academy of Science, Washington D. C., 11-33.

EPOCH. 1993. The temporal occurrence and forecasting of landslides in the European community (Ed: Flageollet, J. C.). Contract No. 90 0025, 3 Volumes.

Dikau, R., Brunsden, D., Schrott, L. & M.-L. Ibsen (Eds.) 1996. Landslide Recognition. Identification, Movement and Causes. Wiley & Sons, Chichester.

 

Landslide & Slope Instability Geohazards: Types

| Rock Fall | Rock Topple | Rock Slide | Block Slide | Rock Flow | Rock Avalanche | Sturzstrom | Debris Fall | Debris Topple | Debris Slide | Block Slide | Debris Spread | Debris Flow | Soil Fall | Soil Topple | Soil Slide | Slab Slide | Soil Spread | Soil Flow |

There are five kinematically distinct types of landslide identified by Varnes (1978):

a) Falls: A fall starts with the detachment of soil or rock from a steep slope along a surface on which little or no shear displacement takes place. The material then descends largely by falling, bouncing or rolling.

 
b)
Topples: A topple is the forward rotation, out of the slope, of a mass of soil and rock about a point or axis below the centre of gravity of the displaced mass.

 
c)
Slides: A slide is the downslope movement of a soil or rock mass occurring dominantly on the surface of rupture or relatively thin zones of intense shear strain.

 
d)
Flows: A flow is a spatially continuous movement in which shear surfaces are short lived, closely spaced and usually not preserved after the event. The distribution of velocities in the displacing mass resembles that in a viscous fluid.


e)
Spreads: A spread is an extension of a cohesive soil or rock mass combined with a general subsidence of the fractured mass of cohesive material into softer underlying material. The rupture surface is not a surface of intense shear. Spreads may result from liquefaction or flow (and extrusion) of the softer material.

However, Varnes (1978) also presented a sixth mode of movement, Complex Failures. These are failures in which one of the five types of movement is followed by another type (or even types). For such cases the name of the initial type of movement should be followed by an "en dash" and then the next type of movement: e.g. rock fall-debris flow ( WP/ WLI, 1990).

Types of landslides: (1) a fall; (2) a topple; (3) a slide; (4) a spread; (5) a flow. After WP/WLI (1993):

(Image Source: Cooper, R.G. (2007) Mass Movements in Great Britain, Geological Conservation Review Series, No. 33, Joint Nature Conservation Committee, Peterborough, 348 pp.)

The EPOCH (1993) project (The Temporal Occurrence and Forecasting of Landslides in the European Community) produced a European classification based on Varnes (1978).

This section has been subdivided on the basis of the EPOCH Classification System - Please Select a Button For Further Information:

Movement Rock Debris Soil
Fall Rock Fall Debris Fall Soil Fall
Topple Rock Topple Debris Topple Soil Topple
Slide Rotational Rock Slide Debris Slide Soil Slide
Slide Translational Block Slide Block Slide Slab Slide
Spread Rock Spread Debris Spread Soil Spread
Flow Rock Flow

Rock Avalanche

Sturzstrom

Debris Flow Soil Flow

| Rock Fall | Rock Topple | Rock Slide | Block Slide | Rock Flow | Rock Avalanche | Sturzstrom | Debris Fall | Debris Topple | Debris Slide | Block Slide | Debris Spread | Debris Flow | Soil Fall | Soil Topple | Soil Slide | Slab Slide | Soil Spread | Soil Flow |

 

 

Index | Diagnostic Characteristics | Geographic Occurrence | Investigation & Mitigation | Key Contacts & Expert AdvicePhoto Gallery  | Essential References & Further Reading | Definitions & Glossary |


Engineering Group Working Party on Geological Hazards