In Italy rapid landslides are the most frequently occurring natural disasters and, after earthquakes, cause the highest number of victims. 
In this contribution we attempt to prove that there exist a tight connection between the presence of a specific soil type, namely andic soils, and the occurrence of the main catastrophic mudflows and debris flows occurred in Italy in the last decades. 
The study was performed by means of an integrated pedological and hydrological analysis on the detachment crowns of some of the most important catastrophic mudflows and debris flows occurred in Italy in the last decades and involving/evolving surface soils.
The results at both regional (Campania) and National (Italy) scale clearly show that despite the large variability of the environmental settings of the studied sites there are indeed some striking homogeneous soil features in the detachment crowns including (i) soil morphology, (ii) andic features ranging from high to moderate, (iii) high water retention throughout a large range of pressure heads. Results seem to reveal clear cause-effect evidences between andic soils and the investigated catastrophic mudflows/debrisflows; this must be related to the unique physical properties of these soils inducing high landslide vulnerability

A. Basile

AGRILLO, ANTONIETTA

DE MASCELLIS, ROBERTO

G. Mele

IAMARINO, MICHELA

LANGELLA, GIULIANO

MILETI, FLORINDO ANTONIO

MINIERI, LUCIANA

MORETTI, PIERPAOLO

TERRIBILE, FABIO

VINGIANI, SIMONA

English

Archivio della ricerca - Università degli studi di Napoli Federico II

© 2010 19th World Congress of Soil Science, Soil Solutions for a Changing World 1 – 6 August 2010, Brisbane, Australia.  Published on DVD. 1 Andic soils and catastrophic mudflows in Italy: Morphological and hydropedological evidences   Fabio Terribile A,  Michela Iamarino A, Antonella Agrillo A, Angelo BasileB, Roberto De MascellisB, Giuliano LangellaB, Giacomo MeleB, Antonio Mileti A, Luciana Minieri A, Pierpaolo Moretti A, Simona Vingiani A   AUniversità di Napoli Federico II, DISSPAPA, Portici Napoli, Italy; Email; fabio.terribile@unina.it BCNR ISAFOM Ercolano, Napoli, Italy, Email a.basile@isafom.cnr,it   Abstract  In Italy rapid landslides are the most frequently occurring natural disasters and, after earthquakes, cause the highest number of victims. In this contribution we attempt to prove that there exists a tight connection between the presence of a specific soil type, namely andic soils, and the occurrence of the main catastrophic mudflows and debris flows occurred in Italy in the last decades. The study was performed by means of an integrated pedological and hydrological analysis on the detachment crowns of some of the most important catastrophic mudflows and debris flows that occurred in Italy in the last decades and involving/evolving surface soils. The results at both regional (Campania) and National (Italy) scale clearly show that despite the large variability of the environmental settings of the studied sites there are indeed some striking homogeneous soil features in the detachment crowns including (i) soil morphology, (ii) andic features ranging from high to moderate, (iii) high water retention throughout a large range of pressure heads. Results seem to reveal clear cause-effect evidences between andic soils and the investigated catastrophic mudflows/debrisflows; this must be related to the unique physical properties of these soils inducing high landslide vulnerability.  Key Words Landslide, hydropedology, andic soils  Introduction Due to its relief and its lithological and structural characteristics, Italy is a country where landslides are the most frequently occurring natural disasters and are the cause, after earthquakes, of the highest number of victims. The national landlslide inventory database (IFFI) surveyed 482,272 landslides covering an area of almost 20,500 km2, which is equivalent to 6.8% of Italy. In such scenario rapid mudflows (and debrisflows) are among the major catastrophic types of landslides occurring in Italy especially in terms of victims and damages. Mudflow is a very rapid to extremely rapid flow (i.e. velocity 0.05–5 m s-1) of saturated plastic materials having a high water content (e.g. Hungr et al., 2001). Fast mudflow landslides are grave dangers to people and infrastructures as they can potentially activate large amounts of materials across extended distances in very short time periods. In this contribution we attempt to demonstrate that there is tight connection between the presence of a specific soil type, namely andic soils, and the occurrence of the main catastrophic mudflows and debrisflows occurred in Italy in the last decades and involving/evolving surface soils. In order to perform such study we performed an integrated pedological and hydrological analysis on the detachment crowns of some of the most important catastrophic mudflows and debrisflow occurred in Italy in the last decades and involving/evolving surface soils. We investigated the following landslide sites: Sarno (1998), Salerno (1954), Platì (1951), Versilia (1996) and Albaredo (1987, 2002). A more detailed hydro-pedological study was also performed, using a 2D Richard’s based water balance simulation model, in order to address two critical issues for Campanian flow slides susceptibility, namely (i) the presence of discontinuities along the slope (e.g. roads, cliffs, etc.) (ii) the relationship with slope aspect. It must be emphasised that, a part from the sites of Campania (Sarno and Salerno), no andic soil are reported in the available soil maps referring to the other Italian sites.  Methods The point based and land based integrated analysis carried out in this study focus on the only catastrophic landslides producing fast mudflows (Table 1). We selected landslides that caused human victims and have suitable technical documentation in the published literature. Landslides occurring before 1841 were not been considered. More than 20 soil profiles from 19 detachment crowns were described and analysed in the field. Only the six most representative sites are given in this contribution attempting to cover a large range of landscapes in terms of geology, geomorphology and latitude. The upper parts of slopes where detachment occurs are generally extremely steep (more than 50-60°). The profiles have been described using the FAO system (1990). Undisturbed soil samples for hydrological analysis were collected from the main horizons © 2010 19th World Congress of Soil Science, Soil Solutions for a Changing World 1 – 6 August 2010, Brisbane, Australia.  Published on DVD. 2 with steel cylinders of about 100 and 200 cm3. Bulk soil samples were also collected from all soil horizons.  After air drying, samples were sieved to less than 2 mm and analysed according to USDA (1996) methods: pH in H2O, organic matter by the Walkley-Black method, Al, Fe and Si in the amorphous oxides/hydroxides and in the organic matter were selectively extracted with ammonium oxalate (Feo, Alo, Sio) treatment at pH=3 (Schwertmann, 1964) and with sodium pyrophospate (Fep, Alp, Sip) (Bascomb,1968), respectively, and their content levels were determined by ICP-AES. Values of Al and Fe extracted with ammonium oxalate were used to calculate the andic property index Alo+0.5Feo. Allophane and imogolite quantities were estimated using the Parfitt (1990) method, based on selective extractions.  On undisturbed soil samples the saturated hydraulic conductivity was measured applying the constant head method (Klute and Dirksen, 1986). Following an evaporation process, the method of Wind for determining water retention and hydraulic conductivity was applied (Tamari et al., 1993) on larger samples (200 cm3). The soil water retention curves (θ(h)) of smaller samples (100 cm3) were determined through use of the tension table (Dane and Hopmans, 2002). The water retention and hydraulic conductivity experimental data were parameterised according to the Mualem-van Genuchten relationship (van Genuchten, 1980).  Constitutive hydraulic functions where applied in a 2D simulation model (Hydrus 2D, Simunek et al., 1999). This model enable us to simulate the soil water balance of slope assuming a defined length and soil depth, and an infinite width. Runs were performed on the same soil simulating the water balance in presence and absence of roads or cliffs. This was obtained changing the boundary conditions: (i) free drainage in case of pedo-continuity and (ii) a seepage face in case of pedo-discontinuity due to roads or cliffs. Runs were also performed to compare soil water balance on two soils on North and South slope (Basile et al., 2003).   Results  The main features of the investigated sites where the catastrophic landslides occurred are given in Table 1. Almost all the sites refer to very steep mountain environments having different aspects and geologies. All sites have a forest land use, generally chestnut. The landslides have generally occurred in a very large number and with different rainfall intensity. The number of victims and damages are typically related to the presence of urban settings along the flows rather than to the landslide magnitude.  Table 1. Main features of landslides and detachment crowns (det.=detachment; (l)= data obtained from literature). Location Date (l) Landslide type (l) Elevation range of det. crown (m asl)  Slope range of det. crowns Main aspect Main land use Main bedrock  Number of land-slides (l) Rain peak (l) Vic-tims (l) Albaredo (Lombardia) 16/11/02 Soil slip-debris flows 1000-1100  41°-50° W Grassland with chestnut Metamorphic rocks 50 230mm /60h 0 Versilia (Toscana) 19/6/96 Soil slip-debris flows 300-900 31°-45° NE Chestnut forest Metamorphic arenaceous rocks & Phyllitic schist 647 400mm /6h 14 Salerno (Campania) 26/10/54 Soil slip-mud flows 200-800 40°-50° N Chestnut forest Limestone NA 504mm /24h > 300 Sarno  (Campania) 5/5/98 Soil slip-debris/earth flow  700-950 33°-55° SW Chestnut forest Limestone 100 173mm /48h 159 Platì (Calabria) 16/10/51 Soil slip-debris flows 700-1100 40°-50° SE Mixed forest (Chestnut - Oak) Metamorphic rocks NA 1495mm /72h    19 Giffone (Calabria) 29/6/05 Soil slip 500-1000 38-45° NW Chestnut forest Granite NA NA NA The most important morphological and chemical features of these soils are given in table 2. All soils are rather deep, they frequently have some kind of vertical discontinuities (e.g. buried soils) and have a dominant sandy loam texture. The soil structure of surface horizons is always granular with a rather high organic C content. pH ranges from acid to neutral, and most importantly all soils show striking andic features ranging from high (Alo+0,5Feo>2%) to moderate ((Alo+0,5Feo:1-2%). The andic features range from silandic in southern sites to aluandic in Northern sites but some of these andic soils do not fulfil WRB requirements for Andosols.  In fig. 1 some water retention curves referring to the most important soil horizons of the investigated sites are reported. The curves show a striking homogeneous behaviour with a very high water retention over all pressure heads but especially near saturation. In fact water content at saturation is comprised between a minimum of 0.52 cm3 cm-3 till a maximum of 0.78 cm3 cm-3. Moreover, these are very permeable soils according to their very high saturated hydraulic conductivity (data not shown). © 2010 19th World Congress of Soil Science, Soil Solutions for a Changing World 1 – 6 August 2010, Brisbane, Australia.  Published on DVD. 3 0.00.10.20.30.40.50.60.70.80.1 1.0 10.0 100.0 1000.0 10000.0suction, h (cm)volumetric water contentLombardia M27 Bw ToscanaM24 Bw1(mina)ToscanaM24 Bw1 ToscanaM23 Bw1Platì A 15-25 Platì P1 Bw1 50-60Quindici P1 A/C1 0-52 Quindici P1 A/C2 52-85Quindici P2 2C 85-100 Quindici P2 3Bw 100-125Giffoni L155 Giffoni L156Giffoni L139 Giffoni L168Sarno 2A/Bb Sarno 2B/Cb Figure 1. Water retention curves of representative soil horizons of the investigated sites. At more local scale, discontinuities in the soil cover (i.e. abrupt slope change, road cut) were also modelled and the resulting effects were shown in Fig.2 where the time evolution of soil water storage in the profile (2 m) is reported, both for pedo-continuity (P-C) and pedo-discontinuity (P-DC) simulations. The results refer to the same vertical section located at 100 m from the up slope position. The increase in water storage due to the boundary effects ranges from 30% in the rainy days till 45% in the dryer period. This increases the soil weight and reduces the effective stress inside the soil: therefore, the P-DC condition will increase the risk of instability of the pyroclastic slope cover. Table 2. Most important features (FAO, 1990) of the soils in the detachment crowns of the investigated landslides. Abbr.S: sandy; Si: silty; L:loam; G: granular, SB subangular blocky, m: medium, c: coarse,wd :weakly developed; md: moderately developed; sd: strongly developed Profile Horizon Boundaries (cm) Texture Structure Carbonates pH (H O) Organic C (g kg-1) Alo+0,5Feo (%) Alp/Alo A 0 - 20 SL G m, wd none 7,3 98,5 4,99 0,25 Bw 20 - 38 SL SB m, wd none 7,5 10,7 2,46 0,05 Bc 38 - 71 LS SB c, wd none  4,2 5,68 0,00 C 71 - 100     none 7,5       Sarno-P1 (Campania) 2A/Bwb 100 - 140 SL SB c, wd none  10,5 2,05 0,06 A 0 - 9 SL G c, sd none 7,3 58,0 4,47 0,04 Bw1 9 - 28 SiL SB m, sd none 7,4 24,3 4,95 0,03 Bw2 28 - 48 SiL SB m, md none 7,6 15,60 5,47 0,02 Salerno -M25 (Campania) Bw3 48 - 70 SiL SB m, md none 7,8 9,60 3,49 0,05 OA  0-2 S G c, sd none 4,1 178,80 0,24 1,00 Bw1  2-65 SL SB c, md none 4,8 12,92 0,50 1,00 Versilia  M24 (Toscana) Bw2  65-150 SL SB m, md none 4,6 9,55 1,03 0,64 A  0-40 S SB m, md none 5,1 32,00 1,35 0,73 Albaredo-M27_3 (Lombardia) Bw 40-110 SL SB m,  md none 5,3 11,03 1,82 0,19 A 0-45 L G c, md none 5,1   1,35 1,08 Bw1 45-90 CL SB m, md none 5,1 24,97 1,53 0,48 Bw2 90-120     none 5,2 18,90 1,26 0,54 Platì (Calabria) BC > 120       6,0 19,80 0,85 0,39 A1 0-15 SL G m, sd none 5,1 51,40 1,53 <0,5 A2 15-30 SL SB m, md none 5,0 49,41 2,26 <0,5 Bw1 30-50 SL SB m, md none 5,3 30,95 2,37 <0,5 Bw2 50-80 SL SB m, md none 5,6 25,65 1,60   2Ab 80-110 SL SB m, md none 5,5 30,11 2,24   3Bw1 110-150 SL SB c, md none 5,6 16,98 1,83   Giffone (Calabria) 3Bw2 150-200 SL SB c, md none 6,0 1,76 0,72   © 2010 19th World Congress of Soil Science, Soil Solutions for a Changing World 1 – 6 August 2010, Brisbane, Australia.  Published on DVD. 4 010203040506070800 20 40 60 80 100 120 140Time (doy)water storage (cm)pedo-discontinuity (P-DC)pedo-continuity (P-C) Figure 2. Effects of pedo-continuity (undisturbed slope) and pedo-discontinuity (seepage face) on soil water storage.  Conclusions The study of soils in the detachment crown of the investigated catastrophic landslides in Italy clearly shows that despite the large differences in geological and climatic settings soils are rather similar and show similar morphology and both andic features and high water retention features. Overall the results at the Italian scale seem to reveal an evident cause-effect between andic soils and the investigated catastrophic mudflows/debrisflow. This is important considering that non-andic non-sliding soils are very much reported in the available soil maps of the investigated landscapes. We believe that andic soils, because of the unique physical properties (hydrological properties, high susceptibility to liquefaction, etc.) induce high landslide vulnerability. We also believe that hydropedology should be added to classical approaches to ameliorate the understanding and the risk assessment of these complex phenomena. These findings are of primary importance and prove the need of using soil information for classifying zones of different landslide hazard risk (landslide hazard assessment).  We also believe that our findings are important also in stimulating similar studies in other areas of the world, especially but not exclusively volcanic, where this type of landslides occur.  References Bascomb CL (1968) Distribution of pyrophosphate-extractable iron and organic carbon in soils of various groups. Journal of Soil Science 19, 251-268 Basile A, Mele G, Terribile F (2003) Soil hydraulic behaviour of a selected benchmark soil involved in the landslide of Sarno 1998. Geoderma 117, 331-346. Dane JH, Hopmans JW (2002) Soil Water Retention and Storage - Introduction. In ‘Methods of 555 Soil Analysis. Part 4. Physical Methods’ (Eds. Dane JH, Topp GC), pp. 671-674. Soil Science Society of 556 America Book Series No. 5. FAO (1990) Guidelines for Soil Description. 97 pp. FAO, Rome, Italy. Hungr O, Evans SG, Bovis MJ, Hutchinson JN (2001) A Review of the Clas-sification of Landslides of the Flow Type. Environmental & Engineering Geoscience 7, 221-238. Klute A, Dirksen C (1986) Hydraulic conductivity and diffusivity: Laboratory methods. In ‘Methods of soil analysis, Part 1, Physical and Mineralogical Methods’ pp. 687-734. 2nd ed. Agronomy 9 (2). American Society of Agronomy. Madison, Wisconsin. Parfitt RL (1990). Allophane in New Zealand - a review. Aust, J, Soil Res. 28, 343-360. Simunek J, Sejna M, van Genuchten MTh (1999) The HYDRUS-2D Software Package for Simulating the Two-Dimensional Movement of Water, Heat, and Multiple Solute in Variably-Saturated Media. Ver. 2.0. U.S. Salinity Laboratory, ARS, USDA, Riverside, CA, USA, pp 228. Schwertmann U (1964) Differenzierung der Eisenoxide des Bodens durch Extraktion mit Ammoniumoxalat-Lo¨ sung. Zeitschrift Pflanzenerna ¨ hr. Dungung Bodenkunde 105, 194-202. Tamari S, Brukler L, Halbertsman J, Chadoeuf J (1993). A simple method for determining soil hydraulic properties in the laboratory. Soil Science Society American Journal 57, 642-651.  van Genuchten, M. Th., 1980. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Sci. Soc. Am. J. 44, 892-898. 

Andic soils and catastrophic mudflows in Italy: morphological and hydropedological evidences

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Andic soils and catastrophic mudflows in Italy: morphological and hydropedological evidences

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