Coastal cliffs hazard - η-Τάξη ΕΚΠΑ · Coastal cliffs hazard Natural and human-induced...
Transcript of Coastal cliffs hazard - η-Τάξη ΕΚΠΑ · Coastal cliffs hazard Natural and human-induced...
Coastal cliffs hazardNatural and human-induced hazards
Stefano FURLANI, Stefano DEVOTO
Department of Mathematics and Geosciences
Program of the lecture
Types of landslides
Geohazards
Accidents and perception of risks
References
Type of landslidesLandslide classification
Types of coastal landslides
Source: Devoto, 2013
FALL
TOPPLE
ROTATIONAL SLIDE
DEBRIS FLOW
TRANSLATIONAL SLIDE
SOIL SPREADING
ROCK SPREADING
EARTH FLOW
Landslide types
Rock fall
very common
it usually involvessmall volumes ofrock
it is associated tocracks generated bystructural settingand/or enlarged bythe action ofdifferent processessuch as marine,karst, etc
very dangerousbecause this type oflandslide causescasualties Photo: Rock falls
Rock topple
Photo: Rock topple
Rock slide
This type ischaracterized by thepresence of a slipsurface, which canbe circular or not
The theory ofequilibrium limit wasborn for investigatingcoastal landslidelocated in the port ofGotheborg
Rotational landslideusually involves hugevolumes
Photo: Rotational slide witnessed by rotated limestone block
Rock spreads
this type of landslide involves clayey terrains capped by resistant materials
they are extensive and are characterized by slow speeds
Photo: View of a extensive rock spread, which evolves into a block slide
Rock spreads
they generate persistent cracks, that can assist geomorphologists to detectthem
rock spreads favour the occurence of other types of landslides such as rockfalls and block slides
Photo: Persistent crack generated by rock spreading phenomena
Rock spreads
Rock spreads
Photo: Lowered blocks detached and moved by rock spreading phenomena
Flows
Earth slides/flows not common as onmountains
They usuallyinvolves smallquantities ofmaterial
They are associatedmainly to clayeyterrains
They are triggeredby intense rainfalls.For these reasons,they are moredangerous forhuman structuresrespect to tourists orvisitors
Natural and human-induced hazardsHazard and risks
Coastal instability and related risk issues In recent years the interest for coastal hazards has increasedsignificantly due to extreme events - sometimes related toclimate change – which often induce high risk situations
Recent tragedies occurred in Italy at the Island of Ventotene(20 April 2010) and near Brindisi (21 October 2010): three persons were killed due to coastal landslides
Coastal instability and related risk issues
Conversely respectto inland slope-failure processes,coastal small eventsare more dangerousrespect to extensivelandslide processes.
The volume of fallenmaterial that causedthe examplecausuality wasextremely small (2-3m3), witnessing thateven small-sizedlandslide events canbe extremelydangerous andshould not beoverlooked in theprocess of hazardassessment
Coastal instability and related risk issuesPredisponing factors
The profiles of marine cliffs are the result of the interplay of different factors, such as:
•Geology
•Climate
•wave and tidal regime
•vegetation
•nearshore water depth, type and amount of beach material
•topography of the cliff-top area
•Rslc
The profile of cliff is crucial for the occurence of landslide
Vertical cliff favour rock falls, whereas low-lying coast are not affected by landslide
Coastal instability and related risk issuesPredisponing factors
Joint system is apredisponing factorfor some types oflandslides (rock falls,topples and slides)
Geomechanicalsurveys can assistgeomorphologists forinvestigating sea cliffretreat
Source: Furlani et al., 2011
Sea action favoured erosion of weakened layers situated at the bottom of rocky cliff. Thelatter is made up of resistant limestone at the top and soft sandstone at the bottom
In 1970 a 12 years oldboy was killed by arock fall on the NWcoast of Malta, atGnejina Bay and otherinjuries were reportedmore recently
Coastal instability and related risk issuesTriggering factors
Coastal landslides can be caused or accelarated by earthquakes
Coastal instability and related risk issuesTriggering factors
Different hazard (and vulnerability)for different landslide types!!
Different SPEED
Type of material and type of movement
Coastal instability and related risk issuesStrategies
Hazard Map (very difficoult)
Landslide Inventory Map
Susceptibilty Landslide Map
Coastal instability and related risk issuesStrategies
It is important to define for extensive landslide
Coastal instability and related risk issuesSpeed classes
Source: Devoto, 2013
It is important to define for extensive landslide
Coastal instability and related risk issues
Landslide InventoryMap(LIM)
LIM are producedby means of outputsof traditionalactivities such asgeomorphologicalmapping and aerialphoto interpretation
Good quality isessential for furthersteps as susceptibiltymap
Source: Devoto et al., 2012
Coastal instability and related risk issuesLandslide InventoryMap (LIM)
Coastal instability and related risk issuesLandslide susceptibility
Identification andclassification of active massmovements within the area ofinterests
Definition of factorscontributing to slopeinstability and creation ofrelated dataset
Source: Piacentini et al., 2015
Coastal instability and related risk issuesLandslide susceptibility
We used predisponing factors such as
slope angle
curvature
distance from coastline
distance from scarp
distance from faults
distance from joints
Topographic Position Index
Source: Piacentini et al., 2015
Coastal instability and related risk issuesLandslide susceptibility
Prediction rate curve of the predisposing factors
Source: Piacentini et al., 2015
Coastal instability and related risk issuesLandslide susceptibility
A susceptibiltity map wasproduced at a regionalscale and classify the coastinto 5 classes:
- Very low;
-Low;
- Medium;
-High;
-Very High
Source: Piacentini et al., 2015
Technique Main Advantages Main Limits
Interferometry Identify pastdeformations
No information on planar components of displacements
GPS Reliable Post-processing
Tape extensometer
Easy to be carriedout and cost-effective
Measures only along some scanlines
Automaticfissurimeters
Possibility to correlate displacements and precipitation
Installed only in secure areas, toavoid vandalism
Coastal instability and related risk issuesLandslide Hazard
we have to insert time on susceptibility
Source: Furlani et al., 2013
Acquisition of necessary knowledge to define methods to analysecoastal geo-hazard
Definition of field protocols which can be used in different coastalenvironments for investigation of coastal geo-hazard
Production of thematic maps also taking into account issues related toclimate change (sea-level change, more frequent extrememeteorological events)
Accidents and perception of riskAccidents and suicides
Accidents and injuries from cliffsCliff instability may be the scene of accidentes or deaths of people
People have been killed or injured because of activities carried out on the cliffs, such as climbing, walking
There are also injuries and deaths regarding suicides or attempted suicides by jumping from high cliff tops, in particular in romantic and easy to reach contexts (e.g. the Rilke path at Duino, Trieste -Italy, Beachy Head, Sussex - England)
The perception of risks
As noted by Williams and Williams (1988), the perception of risks changes between social groups and individuals
People living along the coasts are more aware of cliff hazard than occasional tourists because of their own experience
As noted by Bird (2016), geologists, as well as botanists, ecologists, etc, face the problem of relating geological research and training with cliff hazard
ReferencesMain references to scientific literature
ReferencesBIRD E. (2016). Coastal Cliffs: Morphology and Management. Springer, pp.92.
CRUDEN D.M. & VARNES D.J. (1996). Landslide Types and Processes. In: Turner A.K. AndShuster R.L. (Eds), Landslides: Investigations and Mitigation. National Research Council,Special Report 247, 36-75.
DEVOTO S., BIOLCHI S., BRUSCHI V., FURLANI S., MANTOVANI M., PIACENTINI D., PASUTOA. & SOLDATI M. (2012). Geomorphological map of the NW coast of the Island of Malta(Mediterranean Sea). Journal of Maps, 8:1, 33-40.
DEVOTO S. (2013). Geomorphological map of the NW coast of the Island of Malta(Mediterranean Sea). Unpublished PhD thesis, University of Modena and Reggio Emilia.
FURLANI S., DEVOTO S., BIOLCHI S. & CUCCHI F. (2011). Factors triggering sea cliffinstability along the Slovenian coasts. In: Micallef A. (ed.), MCRR3-2010 ConferenceProceedings, Journal of Coastal Research, Special Issue, 61, 387-393.
FURLANI S., ANTONIOLI F., BIOLCHI S., GAMBIN T., GAUCI R., LO PRESTI V., ANZIDEIM., DEVOTO S., PALOMBO M. & SULLI A. (2013). Holocene sea level change in Malta.Quaternary International, 288, 146-157.
PIACENTINI D., DEVOTO S., MANTOVANI M., PASUTO A., PRAMPOLINI M. & SOLDATIM. (2015). Landslide susceptibility modeling assisted by Persistent ScatterersInterferometry (PSI): an example from the northwestern coast of Malta. NaturalHazards, 78, 681-697.
WILLIAMS M.J. & WILLIAMS A.T. (1988). The perception of, and adjustment to,rockfall hazards along the Glamorgan Heritage Coast, Wales. Ocean and ShorelineManagement, 11, 319-338.