landslide classification
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Varnes LandslideClassification
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What is the purpose ofa classification?
To file material so it can be easily retrieved*
To organize thought To communicate*J.N. Hutchin so n, c. 2000
Our main need is for labels describing landslidetypes (typology)but the system must be flexible and adaptable tothe complexity of landslides
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Typological classificationDivide phenomena into repeatingpatterns (types) characterized by
several descriptors.
Requirements:
1) Comprehensive definition2) Type examples3) References
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Desirable qualities of atypological classification system:
1. Simple, not too many classes2. Respectful of previous usage
3. Flexible, with varying quality of data
4. Each class name to be supported by a
definition, examples and references
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What to do with complex types?Suggestion: leave the decision to the user.
Rock avalancheRock slide
Dr. Rick Guthrie
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Framework:
Pre-failure movementsPost-failure movements
Failureis the single most significantmovement episode.
Failureinvolves the first formation ofa rupture surface
It is up to the user to decide which.
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PrincipalmovementtypesCruden andVarnes, 1996
(dates back toBalzer, 1875)
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D.J. Varnes, 1978
33 types
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Landslide classification (Varnes, 1978 ) Co de: RAP ID , SLOW ( IN MOST CASES)
B E D R O C K DEBRIS (80% sand and finer)
FALLS ROCK F A L L D E B R I S F A L L E A R T H F A L L
TOPPLES B LOCK TOP P L E
FLEXURAL TOPPLE
- B LOCK TOP P L E
SLIDES ROCK SLUMP
ROCK SL I DE
DEB R I S SL I DE E A R T H S L U MP
EARTH SLIDE
SPREADS ROCK SPREAD - EARTH SPREAD
F L O WS R O C K C R E E P
SLOPE SAGGING
DEBR I S F L OW
DEBR I S
A V A L A N C H E
SOIL CREEP
SOLIFLUCTION
WET SAND AN D SI L T
F L OW
RA PI D E A R T H F L OW
LOE SS F L OW
D R Y S A N D F L O W
E A R T H F L O W
C O MP L E X ROCK A V A L A NCH E
EARTH SLUMP-EARTHFLOW
Ref.: Varn es, D.J., 1978. Slope movem ent types and processes. In Landslides, Analysis and Control. Special
Report 176, Transportation Research Board, Washington, pp. 11-33.
Varnes Classification Type Names
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Landslide velocity scale (Cruden and V arnes, 1996).
Velocity
class
Description Velocity
(mm/sec)
Typical
velocity
Human
response
7 Extremely Rapid N il
------------------------ 5x103 5 m/sec
6 Very Rapid N il
------------------------ 5x101 3 m/min
5 Rap id Evacuat ion
------------------------ 5x10 -1 1.8 m/hr
4 M oderate Evacuation
------------------------ 5x10-3
13 m/mo nth
3 Slow M aintenance
------------------------ 5x10-5
1.6 m/year
2 Very Slow M aintenance
------------------------ 5x10-7
16 mm /year
1 Extremely Slow N il
Ref.: Cruden, D.M. and Varnes, D.J., 1996. Landslide types and processes. In Landslides, Investigation and
Mitigation. Special Report 247, Transportat ion Research Board, Washington, pp. 36 -75.
Velocity scale
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- Rock- Debris(more than 20% coarse*)
- Earth(less than 20% coarse*)* Gravel clasts and larger
1. Difficult to evaluate2. Little relevance to slide behaviour3. Incompatible with established systems
Material categories:
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Suggested material classes
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Suggested material classes
Geotechnicalclasses- plastic
- granular
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Suggested material classes
Mixed materials- plastic- granular(Mixed grain sizes,
diluted by water)
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Clay, silt, sand, gravel, boulders
How to simplify?Suggestion: use dominant componentwith emphasis on mechanicalbehaviour.
Example:plastic clayey silt > claylow plasticity clayey silt > silt
Geotechnical materials:
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Supplementary terms, geomorphological
Do not use as primary names, because
there is insufficient correlation withlandslide behaviour.Example, Alluvial (could be gravel, silt, clay)
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Some additional movement types:- Rotational/ translational/ compound slide(Hut ch inson , 1988)
- Block topple/ flexural topple(Goodman and Bray, 1976)
- Flow slide (Terzagh i, Casag rande, Meyerhof ..)
- Slope deformation creep?
- Rock collapse? (croulement, felssturz)
- Debris flood (e.g. Au litzsk i, 1970)
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* Can be extremely rapid
Summary
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Rock, ice fall
Detachment, fal l , ro l l ing and bouncing o f roc k o r ice
fragments. May o ccur s ingly or in clus ters, but there is l i t t le
dynam ic interact ion between the most mobi le moving
fragments, which interact mainly with th e substrate (path).
Fragment deformation is un important, although fragments
can break dur ing impacts. Usual ly o f l imi ted volum e.
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Rock block
toppleChaco Canyon,
New Mexico
Forward rotat ion and over turn ing of roc k co lumns or
plates (one or many), separated by steeply-dipping
jo in ts . The rock is relat ively mass ive and ro tat ion oc-cu rs on wel l -def ined basal discon t inui t ies. Movement
may begin s low ly, bu t the last s tage of fai lure is
extremely rapid . Occurs at al l scales.
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Multiple block topple
Czech Republic
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Rock Flexural Topple
1980
1987
Bending and forw ard rotat ion of
a rock mass character ized by
very c losely-spaced, steeply
d ipp ing jo in ts or schis tose
part ings. The rock is relat ively
weak and fiss i le. There are nowel l-def ined basal dis continui t ies
that could al low for ro tat ion of
blocks around their bases. The
movement is general ly slow andtends to self-stabi l ize. However,
secondary rotat ional sl id ing may
develop in the hing e zone of the
topple. Occurs at large scale.
La Clapire, France
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Rock rotational slide (rock slump)Sl id ing o f a mass of w eak rock on a cyl ind r ical or el lipso idal
rup ture surface which is no t stru ctural ly-contro l led. Li t t le
internal deformation. A large main scarp and back -t i l ted
bench at the head. Usual ly s low to moderately s low.
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Rock translational (planar) slideSl id ing of a mass o f roc k on a planar rupture su rface. The
su rface may be s tepped forward. No internal deformation.
The sl ide head may be sepa-rating from stable rock along
a deep, vert ical tension c rack. Usual ly extremely rapid.
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Rock wedge slideSlid ing of a mass o f rock on a rupture surface formed of
two planes w ith downslope-or iented intersect ion. No
internal deformation . Usual ly extremely rapid .
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Rock compound slide
Scatter River, North-east British Columbia
(Hungr et al., 1984
Slid ing of a mass of roc k on a rupture sur face cons is t ing
of several planes, or a su rface of uneven curv ature, so that
mot ion is kinemat ical ly possib le only i f accompanied bysign i f icant internal distor t ion of the moving m ass. Horst-
and-graben features at the head and many secondary
shear su rfaces are typical . Parts o f the ruptu re sur face
may develop by shear ing through the rock. Slow o r rapid.
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Compound sliding
Internal deformationrequired
Graben
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Vaiont (1963)
A compound slide(Mencl, Hutchinson) non-circular
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Rock irregular slide (rock collapse)
view
section
randomjoints
Sl id ing o f a rock mass on an irregu lar rupture surface
cons ist ing of a number of random ly-or iented jo ints,
separated by segments of intact rock (rock bridges).Occurs in strong rocks wi th non-sys temat ic structure.
Fai lure mechanism is very complex and often di f ficul t to
descr ibe. May includ e elements o f toppl ing. Often very
sudden and extremely rapid.
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Clay, silt rotational slide (Soil slump)Slid ing o f a mass of (homogeneous and usu-ally cohesive)
so i l on a cyl ind r ical or ell ipsoidal rup ture su rface. Li t t le
internal deformat ion. Normally s low, bu t may be extremely
rapid in sensi t ive or co l laps ive soi ls.
rupture
surface
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Clay, silt planar slideSlid ing o f a block o f cohesive so i l on an incl ined planar
rup ture surface, form ed by a weak layer (usual ly pre-sheared).
The head o f the s l ide mass separates from stable soi l along a
deep tens ion c rack (no active wedge). May be slow or rap id.
Panama Canal
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Sand, Gravel,Debris slideSl iding o f a mass o f granu lar mater ial on a shal low, planar
su rface paral lel wi th the ground . Usual ly, the sl id ing massis a veneer of c ol luvium , weath-ered so i l , or py roc last ic
depos i ts rest ing on a stronger su bstrate. Many debr is
sl ides become f low -l ike after mov ing a short distance and
trans form into extremely rapid debr is ava-lanches.
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Sl id ing o f a mass of so i l on arupture sur face cons is t ing of
several planes, or a su rface of
uneven cu rvature, so that
mot ion is k inemat ica lly po ssib le
only i f accompanied by
sign i f icant internal distor t ion of
the moving mass. Horst-and-
graben features at the head and
many secondary shear surfacesare observed. The basal
segment of the rupture surface
often fol lows a weak ho r izon in
the soi l strat igraphy
Clay, siltcompound slide
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Rock slopespread
(or deformation?)Crest sagging in
s lopes formed from a
stro nger layer (caprock ) over weak rock.
Block s of the stronger
rock sp read and t i l t by
deformation of th e
under ly ing weak
mater ial, w ithout the
formation o f a def ined
rup ture surface.
Extremely s low.
Nemcok, 1982, Weak rocks
Initial stage, Mature stage, Final stage, Surficialmovements
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Sand, silt liquefaction spreadExtremely rapid lateral spreading o f a series of so i l block s,
f loat ing on a layer of saturated (loose) granu lar so i l , l iquefied
by earthquake shaking o r spon taneous l iquefact ion.
TurnagainHeights Slide,1964
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Sensitive clay spreadExtremely rapid lateral sp reading o f a series o f
coherent c lay b lock s, f loat ing on a layer of
remoulded sensit iv e clay.
St. Jude,Quebec, 2010
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Rock avalancheExtremely rapid, massive, f low -l ike mo t ion of
fragmented roc k from a large rock sl ide or rock fal l .
Frank Slide,1903
Inverse sorting
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Slow o r rapid f low -l ikemovement of loose dry,
moist o r saturated,
sor ted o r unsor ted
granu lar material,
w i thout excess pore-
pressure.
Dry (or non-liquefied)Sand, Silt, Gravel or
Debris Flow
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Very rapid to extremely rapid f low of sorted or unsortedsaturated granular mater ia l on m oderate slopes, involv ing
excess pore-pressu re or l iquefact ion of mater ial
or ig inat ing from the lands l ide source. Usual ly or ig inates
as a mult ip le retrog ressiv e fai lure. Often under water.
Sand, Sil t , Debris flow slid e:
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Very rapid to extremely rapid f low of
l iquef ied sensi t ive clay, due to remou lding
du ring a mu lt ip le retrogressive sl ide fai lure
at, or close to the orig inal water content .
(Photo: S.G. Evans)
Clay flow slide
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Debris flow:Very rapid to extr emely
rap id surg ing f low of
saturated non-plast ic
debr is in a steepchannel. Strong
entrainment of mater ial
and water from the f low
path . (Plastic i ty Index
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