Coastal cliffs hazard Natural and human-induced hazards. Stefano FURLANI, Stefano DEVOTO Department of Mathematics and Geosciences

Transcription

1 Coastal cliffs hazard Natural and human-induced hazards Stefano FURLANI, Stefano DEVOTO Department of Mathematics and Geosciences

2 Program of the lecture Types of landslides Geohazards Accidents and perception of risks References

3 Type of landslides Landslide classification

4 Types of coastal landslides Source: Devoto, 2013

5 FALL DEBRIS FLOW TOPPLE TRANSLATIONAL SLIDE ROTATIONAL SLIDE EARTH FLOW ROCK SPREADING Landslide types SOIL SPREADING

6 Rock fall very common it usually involves small volumes of rock it is associated to cracks generated by structural setting and/or enlarged by the action of different processes such as marine, karst, etc very dangerous because this type of landslide causes casualties Photo: Rock falls

7 Rock topple Photo: Rock topple

8 Rock slide Photo: Rotational slide witnessed by rotated limestone block This type is characterized by the presence of a slip surface, which can be circular or not The theory of equilibrium limit was born for investigating coastal landslide located in the port of Gotheborg Rotational landslide usually involves huge volumes

9 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

10 Rock spreads Photo: Persistent crack generated by rock spreading phenomena they generate persistent cracks, that can assist geomorphologists to detect them rock spreads favour the occurence of other types of landslides such as rock falls and block slides

11 Rock spreads

12 Rock spreads Photo: Lowered blocks detached and moved by rock spreading phenomena

13 Flows not common as on mountains They involves quantities material usually small of They are associated mainly to clayey terrains They are triggered by intense rainfalls. For these reasons, they are more dangerous for human structures respect to tourists or visitors Earth slides/flows

14 Natural and humaninduced hazards Hazard and risks

15 Coastal instability and related risk issues In recent years the interest for coastal hazards has increased significantly due to extreme events - sometimes related to climate 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

16 Coastal instability and related risk issues Conversely respect to inland slopefailure processes, coastal small events are more dangerous respect to extensive landslide processes. The volume of fallen material that caused the example causuality was extremely small (2-3 m 3 ), witnessing that even small-sized landslide events can be extremely dangerous and should not be overlooked in the process of hazard assessment

17 Coastal instability and related risk issues Predisponing 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

18 Coastal instability and related risk issues Predisponing factors Joint system is a predisponing factor for some types of landslides (rock falls, topples and slides) Geomechanical surveys can assist geomorphologists for investigating sea cliff retreat Source: Furlani et al., 2011

19 Coastal instability and related risk issues Triggering factors In 1970 a 12 years old boy was killed by a rock fall on the NW coast of Malta, at Gnejina Bay and other injuries were reported more recently Sea action favoured erosion of weakened layers situated at the bottom of rocky cliff. The latter is made up of resistant limestone at the top and soft sandstone at the bottom

20 Coastal instability and related risk issues Triggering factors Coastal landslides can be caused or accelarated by earthquakes

21 Coastal instability and related risk issues Strategies Type of material and type of movement Different SPEED Different hazard (and vulnerability) for different landslide types!!

22 Coastal instability and related risk issues Strategies Landslide Inventory Map Susceptibilty Landslide Map Hazard Map (very difficoult)

23 Coastal instability and related risk issues Speed classes It is important to define for extensive landslide

24 Source: Devoto, 2013

25

26 It is important to define for extensive landslide

27 Coastal instability and related risk issues Landslide Inventory Map (LIM) LIM are produced by means of outputs of traditional activities such as geomorphological mapping and aerial photo interpretation Good quality is essential for further steps as susceptibilty map Source: Devoto et al., 2012

28 Coastal instability and related risk issues Landslide Inventory Map (LIM)

29 Coastal instability and related risk issues Landslide susceptibility Identification and classification of active mass movements within the area of interests Definition of factors contributing to slope instability and creation of related dataset Source: Piacentini et al., 2015

30 Coastal instability and related risk issues Landslide 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

31 Coastal instability and related risk issues Landslide susceptibility Source: Piacentini et al., 2015 Prediction rate curve of the predisposing factors

32 Coastal instability and related risk issues Landslide susceptibility A susceptibiltity map was produced at a regional scale and classify the coast into 5 classes: - Very low; -Low; - Medium; -High; -Very High Source: Piacentini et al., 2015

33 Coastal instability and related risk issues Landslide Hazard Technique Main Advantages Main Limits Interferometry Identify past deformations No information on planar components of displacements GPS Reliable Post-processing Tape extensometer Automatic fissurimeters Easy to be carried out and costeffective Possibility to correlate displacements and precipitation Measures only along some scanlines Installed only in secure areas, to avoid vandalism we have to insert time on susceptibility

34 Acquisition of necessary knowledge to define methods to analyse coastal geo-hazard Definition of field protocols which can be used in different coastal environments for investigation of coastal geo-hazard Production of thematic maps also taking into account issues related to climate change (sea-level change, more frequent extreme meteorological events) Source: Furlani et al., 2013

35 Accidents and perception of risk Accidents and suicides

36 Accidents and injuries from cliffs Cliff 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)

37 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

38 References Main references to scientific literature

39 References BIRD 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. And Shuster R.L. (Eds), Landslides: Investigations and Mitigation. National Research Council, Special Report 247, DEVOTO S., BIOLCHI S., BRUSCHI V., FURLANI S., MANTOVANI M., PIACENTINI D., PASUTO A. & SOLDATI M. (2012). Geomorphological map of the NW coast of the Island of Malta (Mediterranean Sea). Journal of Maps, 8:1, 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 cliff instability along the Slovenian coasts. In: Micallef A. (ed.), MCRR Conference Proceedings, Journal of Coastal Research, Special Issue, 61, FURLANI S., ANTONIOLI F., BIOLCHI S., GAMBIN T., GAUCI R., LO PRESTI V., ANZIDEI M., DEVOTO S., PALOMBO M. & SULLI A. (2013). Holocene sea level change in Malta. Quaternary International, 288, PIACENTINI D., DEVOTO S., MANTOVANI M., PASUTO A., PRAMPOLINI M. & SOLDATI M. (2015). Landslide susceptibility modeling assisted by Persistent Scatterers Interferometry (PSI): an example from the northwestern coast of Malta. Natural Hazards, 78, WILLIAMS M.J. & WILLIAMS A.T. (1988). The perception of, and adjustment to, rockfall hazards along the Glamorgan Heritage Coast, Wales. Ocean and Shoreline Management, 11,