05 landslides
TRANSCRIPT
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Landslides
Dr. Jos Cepeda, DIC MSc PhD
Natural Hazards division
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Why are landslides important?
Area exposed: 3.7 million km2
Exposed population: 300 million (4-5% of world population)
High risk zones:820 000 km2
66 million people
Source: Global landslide hotspots (Nadim et al., 2006)
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What is a landslide?
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Basic definitions
Landslide: the movement of
a mass of rock, debris, or
earth (soil) down a slope
Materials:
Rock Soil
Earth: D80< 2 mm
Debris
Santa Ana volcano, El Salvador
October 2005
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Basic definitionsTypes of movement
Fall Topple
Slide Flow
Spread
Cruden & Varnes (1996)
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Naming conventions
Naming and classification conventions based
on JTC-1, Joint Technical Committee of the: ISSMGE International Society of Soil Mechanics and
Geotechnical Engineering, ISRM International Society of Rock Mechanics, and
IAEG International Association of Engineering Geologists
References: Cruden & Varnes (1996); Fell et al. (2008)
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Basic definitions
Type of
movement
Material Fall Topple Slide Spread Flow
Rock Rock fallRock
toppleRock slide
Rock flow
(rock avalanche)
Soil Soil slideSoil
spreadSoil flow
Earth Earth slide Earth flow
DebrisDebris
slideDebris flow
Landslide types based on material andmovement (most common are named)
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Main features of a landslide
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Landslide = unstable slope
Numerical measure of thestability of a slope:
Factor of Safety (FS)
resisting actions ()FS =
driving actions ()FS > 1: slope is stable (no
landslide)FS 1: slope is unstable (a
landslide occurs)
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How can a landslide be initiated?
Reducing resistingactions () Increasing drivingactions ()
For example, landslidescan be triggered by:
adding weight or load(fill)
steepening slope (cut
and fill) building with loosematerial (fil)
adding water
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What happens after a landslide is
initiated?
Characteristics of landslide
propagation:
Maximum distance (runout
distance)
Thickness or depth
Velocity
Landslide intensity (potentialfor destructiveness) is directly
related to propagation
characteristics.
www.usgs.gov
Casita landslide (Nicaragua, 1998):2500 people killed 6 km away fromrelease area
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Landslide intensity
The spatial distribution of:
velocity of sliding
coupled with slide
volume, or
kinetic energy of the
landslide, or
total displacement.
H High
M Medium
L Low
Intensity
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Vulnerability
Li et al. (2010)
R = resistance ofexposedelements
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Landslide hazard and risk
assessment
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Hazard and risk
Landslide Hazard = Susceptibility factors x Triggering factors
Landslide Risk = H. V. (E) . U
H = Landslide Hazard(temporal probability oflandslide occurrence)
V = Vulnerability of element(s)at risk, (E=Exposure ofelement(s) at risk)
U = Utility (or value) ofelement(s) at risk
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Susceptibility factors
Slope (+): steeper slopes, higher susceptibility.
Geology (-): lower resistance of geological materials,higher susceptibility.
Ground water (+): higher moisture and water
pressures, higher susceptibility
Others
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Basic definitions
Landslide susceptibil ity:
A quantitative or qualitative
assessment of the classification,volume (or area), and spatial
distribution of landslides in an area.
A choice of quantitative measure:
Factor of Safety(FS).San Salvador volcano,
El Salvador, October 2008
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Triggering factors
Precipitation
Earthquake
Anthropic
Others
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Triggering factors: precipitation
Rainfall threshold
Boundary curve or surface
separating triggering and non-
triggering rainfall events.
Global catalogue of thresholds:
http://rainfallthresholds.irpi.cnr.it/
Global gridded precipitation data:
http://gpcc.dwd.de/Duration (h)
Intensity
(mm/h)+
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http://rainfallthresholds.irpi.cnr.it/http://gpcc.dwd.de/http://gpcc.dwd.de/http://gpcc.dwd.de/http://rainfallthresholds.irpi.cnr.it/ -
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Importance of rainfall-induced
landslides
Significant in total number
of landslides:
~ 80%
Numerous transform indebris flows:
~ 90%
Debris flows: Long runout distances: several
kilometres
High velocities: > 18 km/h, but
often > 100 km/h
www.unicaen.fr
www.usgs.gov
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Triggering factors: earthquake
Earthquake action
Keefer (1984) & Rodriguez et al. (1999)
Landslidesoccur onsusceptibleareas
No landslide
Global map of earthquake accelerations:http://www.seismo.ethz.ch/static/GSHAP/
http://www.seismo.ethz.ch/static/GSHAP/http://www.seismo.ethz.ch/static/GSHAP/ -
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Susceptibility and hazard
assessment
Freeware GIS platform: ILWIShttp://52north.org/communities/ilwis
Deterministic method:ftp://ftp.itc.nl/pub/ilwis/pdf/appch06.pdf
Statistic method:
ftp://ftp.itc.nl/pub/ilwis/pdf/appch05.pdf
Including earthquake effect:ftp://ftp.itc.nl/pub/ilwis/pdf/appch07.pdf
http://52north.org/communities/ilwisftp://ftp.itc.nl/pub/ilwis/pdf/appch06.pdfftp://ftp.itc.nl/pub/ilwis/pdf/appch05.pdfftp://ftp.itc.nl/pub/ilwis/pdf/appch07.pdfftp://ftp.itc.nl/pub/ilwis/pdf/appch07.pdfftp://ftp.itc.nl/pub/ilwis/pdf/appch05.pdfftp://ftp.itc.nl/pub/ilwis/pdf/appch06.pdfhttp://52north.org/communities/ilwis -
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Susceptibility and hazard
assessment
Working scale is important.
Quality of theme maps used as input data.
Statistical methods require reliable inventories in the
study area.
Global inventories of landslides: DesInventar: http://gar-isdr.desinventar.net/DesInventar/
NASA:http://trmm.gsfc.nasa.gov/publications_dir/landslide_catalog_2003_2007_2008_2009.xls
http://gar-isdr.desinventar.net/DesInventar/http://trmm.gsfc.nasa.gov/publications_dir/landslide_catalog_2003_2007_2008_2009.xlshttp://trmm.gsfc.nasa.gov/publications_dir/landslide_catalog_2003_2007_2008_2009.xlshttp://trmm.gsfc.nasa.gov/publications_dir/landslide_catalog_2003_2007_2008_2009.xlshttp://trmm.gsfc.nasa.gov/publications_dir/landslide_catalog_2003_2007_2008_2009.xlshttp://gar-isdr.desinventar.net/DesInventar/ -
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Risk assessment
Van Westen et al. (2006)
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Risk assessment
Most problematic aspects
Van Westen et al. (2006)
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Risk assessmentSensitivity of results to numerical models:same case, but two different results
Van Westen et al. (2006)
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Risk assessment
Van Westen et al. (2006)
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Landslide risk assessment: overview
NGI (2009)
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Landslide risk assessment: example
Cepeda et al. (2010)Landslide risk in Indonesiahttp://www.preventionweb.net/english/hyogo/gar/2011/en/bgdocs/Cepeda_et_al._2010.pdf
http://www.preventionweb.net/english/hyogo/gar/2011/en/bgdocs/Cepeda_et_al._2010.pdfhttp://www.preventionweb.net/english/hyogo/gar/2011/en/bgdocs/Cepeda_et_al._2010.pdfhttp://www.preventionweb.net/english/hyogo/gar/2011/en/bgdocs/Cepeda_et_al._2010.pdfhttp://www.preventionweb.net/english/hyogo/gar/2011/en/bgdocs/Cepeda_et_al._2010.pdf -
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Landslide risk reduction
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Landslide risk reduction- some relevant aspects
When preventing landslide initiation (or reducingmobilisation) is feasible:
Slope stabilisation measures (increasing Factor of Safety to
a minimum level, usually specified by building codes or
country/regional guidelines. Example: see section 7.4 in
http://www.wsdot.wa.gov/publications/manuals/fulltext/M46-03/Chapter7.pdf)
When preventing landslide is not feasible:
Deviate landslide path or trajectory away from exposedelements
Timely evacuation of exposed population (need for an Early
Warning System, EWS)
Landslide Early Warning Systems
http://www.wsdot.wa.gov/publications/manuals/fulltext/M46-03/Chapter7.pdfhttp://www.wsdot.wa.gov/publications/manuals/fulltext/M46-03/Chapter7.pdfhttp://www.wsdot.wa.gov/publications/manuals/fulltext/M46-03/Chapter7.pdfhttp://www.wsdot.wa.gov/publications/manuals/fulltext/M46-03/Chapter7.pdf -
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Landslide Early Warning Systems
(EWS) some aspects for precipitation-induced landslides Monitoring system:
Variables directly related to landslide initiation (mobilisation):
stresses and displacements
Indirect variables: meteorological elements (precipitation,
temperature, etc.)
Threshold model: Physically-based: feasible when spatial (and time) variability
of mechanical & hydraulic properties can be established
Empirical: non physically-derived functions of direct or
indirect variables
Usual practical approach at regional scale: empirical
thresholds based on precipitation
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Types of thresholds
Cepeda & Devoli (2008)
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Early-warning systems
Identifying release zones (susceptibility mapping) Identifying propagation zones (landslide intensity
maps)
Monitoring triggering factors (e.g., precipitation)
Precipitation thresholds
Identification of evacuation routes
System for making decisions and communications
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Landslides and
multi/cascading hazards
E t lti l / di h d
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Exposure to multiple/cascading hazards
Earthquake Volcanic eruptionsRainfall-triggered
landslides
San Salvador,El Salvador
X X X
San Vicente,
El SalvadorX X
San Cristbal and
Casita,
Nicaragua
X X X
Concepcin,
NicaraguaX X
Mt. Soufriere Hills,
Montserrat X X
Mt. Pinatubo,
PhilippinesX X
Example of multihazards :San
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Example of multihazards :San
Salvador, El Salvador
~1 km grid
~15 km window
Volcanic eruption& earthquake
(1917)~ 50 killed
Ethq.-triggeredlandslide(2001)
600+ killed
Rainfall-triggereddebris flows(1954 and1982)~300 killed
5.4 Msearthquake(1986)~1500 killed
6.3 Msearthquake(1965)~120 killed
Example of cascading hazards:
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Example of cascading hazards:
San Vicente, El Salvador
13 Feb. 20016.2 Mw earthquake
Blanco et al (2002)
Blanco et al (2002)
Earthquake-triggeredrockfalls andlandslides
(unknown numbercasualties)
La Prensa Grfica (2001)
Collapse ofnon-engineered
structures due toearthquake shaking
(300+ killed)15 Sept. 2001111 mm rainfall
in 24 hours
USGS (2001)
Rainfall-trigggereddebris flow
(4 killed)
All the events produceddamage and casualties
Debris flows also in: 1774, 1912, 1934, 1936, 1995Earthquakes also in: 1719, 1854, 1860, 1872, 1899, 1936, 1999
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Thank you for your attention!
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References
Cepeda & Devoli (2008) http://meetings.copernicus.org/www.cosis.net/abstracts/EGU2008/03879/EGU2008-A-03879.pdf
Cepeda et al. (2010) http://www.preventionweb.net/english/hyogo/gar/2011/en/bgdocs/Cepeda_et_al._2010.pdf
Cruden & Varnes (1996) http://pubsindex.trb.org/view/462501
Fell et al. (2008) http://dx.doi.org/10.1016/j.enggeo.2008.03.009
Keefer (1984) http://bulletin.geoscienceworld.org/cgi/content/abstract/95/4/406
Li et al. (2010) http://dx.doi.org/10.1007/s10346-009-0190-3
Nadim et al. (2006) http://dx.doi.org/10.1007/s10346-006-0036-1
NGI (2009) Report 20071600-1.
Rodriguez et al. (1999) http://dx.doi.org/10.1016/S0267-7261(99)00012-3
Van Westen et al. (2006) http://dx.doi.org/10.1007/s10064-005-0023-0
http://meetings.copernicus.org/www.cosis.net/abstracts/EGU2008/03879/EGU2008-A-03879.pdfhttp://www.preventionweb.net/english/hyogo/gar/2011/en/bgdocs/Cepeda_et_al._2010.pdfhttp://pubsindex.trb.org/view/462501http://dx.doi.org/10.1016/j.enggeo.2008.03.009http://bulletin.geoscienceworld.org/cgi/content/abstract/95/4/406http://dx.doi.org/10.1007/s10346-009-0190-3http://dx.doi.org/10.1007/s10346-006-0036-1http://dx.doi.org/10.1016/S0267-7261(99)00012-3http://dx.doi.org/10.1007/s10064-005-0023-0http://dx.doi.org/10.1007/s10064-005-0023-0http://dx.doi.org/10.1016/S0267-7261(99)00012-3http://dx.doi.org/10.1007/s10346-006-0036-1http://dx.doi.org/10.1007/s10346-009-0190-3http://bulletin.geoscienceworld.org/cgi/content/abstract/95/4/406http://dx.doi.org/10.1016/j.enggeo.2008.03.009http://pubsindex.trb.org/view/462501http://www.preventionweb.net/english/hyogo/gar/2011/en/bgdocs/Cepeda_et_al._2010.pdfhttp://meetings.copernicus.org/www.cosis.net/abstracts/EGU2008/03879/EGU2008-A-03879.pdf