Landslide inventory in northern Calabria, southern Italy A. CARRARA 1 Consiglio Nazionale delle Ricerche, Istituto di Ricerca per la Protezione Idrogeologica, 87030 Castiglione Scalo-Cosenza, Italy L. MERENDA J ABSTRACT were attempted. These studies have shown Mezzogiorno, 1968; Burton, 1970; Meli- the serious slope instability conditions of doro, 1971). In Calabria, the toe of the Italian boot, many regions and have given a general out- Because of its geological history, climatic landsliding and slope instability, produced line of the distribution of stable and unsta- conditions, and extensive human activity, by soft rocks, rapid tectonic uplift, earth- ble areas (Nicotera, 1959; Cassa per il Calabria is extremely susceptible to land- quakes, and seasonally heavy precipitation, constitute a major geologic hazard. For this reason a detailed inventory of landslide and accelerated erosion events has been in- itiated in northern Calabria. To carry out this project, a methodology for the collec- tion and mapping of slope instability phenomena has been established. The method is based on the use of a standardized form for the collection of field data. The data form and related map sym- bols reflect the purpose of the project, which is the collection of information that is as quantitative and objective as possible on a large number of slope instability phenomena by surveyors with varying de- grees of field and laboratory experience. The morphometric and typologic data gathered in this way constitute a convenient basis for statistical analysis of factors re- lated to the slope stability and for the prep- aration of landslide susceptibility maps. The maps also can be used readily for soil conservation measures. This inventory method has been tested in two sample areas and is at present being applied to an area of about 1,000 km2. INTRODUCTION In the past decade, regional slope stabil- ity studies have been undertaken by scientific institutions of various countries. In Czechoslovakia, for instance, detailed and general engineering-geological maps have been prepared for most of the country; these maps are based on a large number of field and laboratory data and show the locations of landslides and erosional phenomena and many of their features (Zaruba and Mencl, 1969; Demek, 1972; Rybar and others, 1965; Rybar, 1973). Similar investigations, which are providing basic information needed for land use plan- ning, have been initiated in California, par- ticularly in the more densely populated areas (Nilsen and Brabb, 1973). In Italy, mostly in the southern part of the country, investigations and inventories of landslides Figure 1. Geological sketch map of Calabria and location of study areas. Geological Society of America Bulletin, v. 87, p. 1153-1162, 9 figs., August 1976, Doc. no. 60809. 1153 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/87/8/1153/3444071/i0016-7606-87-8-1153.pdf by guest on 28 September 2021 Figure 2. Example of a damaged village (A) due to landslides (B) at the Calabna-Lucama border. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/87/8/1153/3444071/i0016-7606-87-8-1153.pdf by guest on 28 September 2021 LANDSLIDE INVENTORY IN ITALY 1155 sliding and slope instability. The Paleozoic terpretation (particularly for old, fossil, example, for a flysch sequence with alter- and Mesozoic metamorphic and igneous dormant, or exhausted landslides), training nating sandstone and marls, S-C will be en- rocks that underlie most of the territory ex- of the surveyors is needed as well as the tered. perienced intense folding, faulting, crush- standardization of the working criteria. Structural data (sec. 5) are reduced to es- ing, and dislocation during the Hercynian To achieve standardization and to in- sentials to avoid overly complex and time- and Alpine orogenies. These rocks and the itiate a quantitative investigation of slope consuming field investigations. The slope overlying poorly consolidated sedimentary instability phenomena, a field data form has morphology (sec. 8) is that preceding the sequences of Tertiary-Quaternary age (Fig. been prepared (Fig. 3A, B). The aim of this event. The terms "rectilinear," "concave," 1) are deeply dissected by a dense stream form is the collection of quantitative and and "convex" refer to a vertical (first col- network resulting from the rapid tectonic objective information on a large number of umn) and to a horizontal (second column) uplift of the region (about 1,000 m in the slope instability events by surveyors with profile of the hillslope. In the case of a land- past 1 m.y. [compare Ogniben, 1973]). A varying degrees of field and laboratory ex- slide that occurs on a previous landslide Mediterranean climate with abundant and perience. Therefore, geotechnical informa- zone or on terraced slope, the item seasonally intense rainfall has produced a tion was reduced to the minimum, and "nonuniform slope" will be checked. thick weathering mantle over most of the more space was given to morphometric lithologic units. In addition, Calabria is the data (Institute of British Geographers, Erosion site of frequent strong to catastrophic seis- 1971; Brunsden, 1973; Blong, 1973b). mic activity. All these factors, when as- The study and mapping of erosional sociated with extensive human activity (in- Form for Data Collection phenomena are carried out partly in the cluding systematic deforestation), have field and partly by means of air photo- played an important role in producing For each landslide or accelerated erosion graphs, which are particularly useful for steep, irregular, and highly unstable slopes. event (mapped on a scale of 1:10,000), the this kind of investigation. Sections 12 The costs of landslide damage are ex- form is compiled partly in the field and through 13 can be readily filled in the tremely high in Calabria; expenditures for partly in the laboratory (for more details, laboratory. road, railroad, aqueduct, and housing re- see Carrara and Merenda, 1974). Answers pairs have been estimated, for 1972 to 1973 are given by checking one or more boxes of Landslide alone, to be more than $200 million (com- each section and, where possible or neces- pare also Commissione Interministeriale sary, numbering them according to the The distinction between landslide and per lo Studio della Sistemazione Idraulica e order of importance (Fig. 3 shows a form landslide zone (sec. 18) arises from practi- della Difesa del Suolo, 1974). The human compiled for a landslide located in sample cal necessities; areas of small but wide- and social implications are even more seri- area 2). The form is divided into three main spread landslides affecting large parts of a ous; landsliding is forcing the abandonment parts plus a space for geographic location slope, together with unmappable and (or) of almost 100 villages with a total popula- and file data: (1) general ( sees. 3 through potential landslides and creep phenomena, tion of about 200,000, thus contributing to 10), to be compiled both for landslide and are classified as "landslide zones." The the further impoverishment of this already for erosion; (2) erosion (sees. 11 through landslide classification adopted is substan- poorly developed part of Italy (Fig. 2A, B). 17), reduced to essential information be- tially derived from that of Varnes (Eckel, Because of the urgent need for soil con- cause erosional phenomena are not the 1958), which at present is used by Czechos- servation measures, slope stabilization, and main purpose of the project; and (3) lovakian authors and by the International regional planning, a long-term project in- landslide (sees. 18 through 26), discussed in Geographical Union (Nemcok and others, volving a detailed inventory of landslide more detail because it is the main object of 1972). However, the present classification and erosional phenomena has been initiated the investigation. is considered to be more detailed and for a large part of northern Calabria. This flexible than that of Varnes. Two boxes are will be followed by a statistical analysis of General beside the terms "sliding," "fall," and the data collected for the preparation of "flow"; the first is for indicating the charac- landslide susceptibility maps. This part is filled out in the field using ter of the event in its initial evolutionary Taking into consideration the methodol- geological and topographic maps. Besides stage, the second for its present character. ogy and analytical techniques of various au- marking the presence and the thickness of For example, for the landslide M-8 (Fig. thors (Eckel, 1958; Jones and others, 1961; soil (sec. 3), the lithologic units are listed in 3B) the mass movement was initiated as Rybar and others, 1965; Desio, 1968; stratigraphic or tectonostratigraphic order sliding; at present the phenomenon pro- Brunsden, 1973; Nilsen and Brabb, 1973; (a,b,c) and the formations affected by the ceeds with similar characteristics. There- Blong, 1973b), we have worked out a event are checked. Where possible, the fore, the form has been compiled as in Fig- method for the collection and mapping of thickness and nature of the contact between ure 3B. If, instead, the landslide were now slope instability phenomena. This method, the lithologic units are marked (see also nearly stabilized with the depositional area which is briefly illustrated in this paper, has sketch of sec. 27). Geological maps are affected just by creep phenomena, the form been tested in two sample areas (Fig. 1; see available on a 1:25,000 scale for all of should be filled in as follows: sliding CDD also Carrara and Merenda, 1974) and at Calabria, and their formational symbols and creep •m. a present is being applied to an area of about (Sfe, P !-2) are used in the form. In section 4 Most of the morphometric data (sec. 21) 2 1,000 km . the geotechnical characteristics of the rocks are derived from Eckel (1958), Brunsden in the area of slope instability are given (1973), and Blong (1973a, 1973b).