Description: The urban area of Avigliano is widely affected by a conspicuous proneness to landslides which results in heavy damage to buildings and facilities. Some ancient, recent and current mass movements can be recognized which undergo periodica1 total or partial reactivation due mainly to the unstabilizing influence of repeated rainfalls. Landslides are also caused by earthquakes and by unwary human activities. This paper aims at ascertaining the true incidence of rainfall on the landslides occurring in the urban area of Avigliano, by means of rigorous hydrological and statistica1 methods. Five major landslides were selected based on the following criteria: good knowledge of the corresponding geometrical, geomorphological and evolutionary features, availability of an accurate database on landsliding, triggering causes, reactivations occurred in the last decades following heavy rains, availability of hydrological, geognostic, aerial photography and historical data. The role played by rainfalls in the reactivation of the investigated landslides was studied by applying hydrological and statistical empirical models previously used and checked by the authors. The probability grades of the daily cumulative amounts of rain were also determined broadening the concept of rainfall threshold. These grades may also account for hazard thresholds beyond which landslides may be individully reactivated.

Description: Published

Description: 23-30

Description: N/A or not JCR

Description: open

Description: Slope instability phenomena are widespread in the geological context of Southern Apennines. The paper reports the slope instability features characterized the medium valley of the Basento River, which is crossed by a major road/railroad stretch linking Potenza to Metaponto and which is not infrequently affected by instability phenomena. The attention is focused on one of the most significant landslides periodically reactivated by rainfalls which badly damaged the important railway line.

Description: Published

Description: Maratea (PZ), Italy

Description: open

Description: A long and intense international research activity has by now confirmed the basic role of atmospheric precipitations on the dynamics of landslides. This paper is within the framework of such an activity and describes how solid and liquid meteoric precipitations really affect landslides. A detailed study of the empirical hydrological methods aimed at the determination of exceptional meteoric events to be correlated with landslide is performed. Finally, based on the analysis of real cases occurred in the Mediterranean environment, the opportunities offered by such an approach are discussed.

Description: Published

Description: 42-49

Description: N/A or not JCR

Description: open

Description: The Vadoncello landslide was mobilized in December 1993 and is still active. It involves highly tectonized soils and is the reactivation of a landslide dragged by a larger landslide at the toe of the slope soon after the 1980 Irpinia (Southern Italy) earthquake. Investigations and monitoring of the Vadoncello landslide were carried out, between 1994 and 1996, within an EC funded research project. The slope has been found to be formed of chaotic successions of soil and rock strata which have been grouped into soil complexes. The soil mechanical properties are shown to be very poor, the deep soils being prone to large plastic straining even due to relatively small loading changes. The soil displacements show that a shallow fast rotational sliding has occurred at the top of the slope and a shallow earthflow has developed downslope, both lying above deeper soils involved in a mechanism of slow and long-lasting irrecoverable movements. These slow deep movements are considered to be consequent to the plastic flow of the clayey soils. They can be activated by the effects of seasonal rainfall, of low-medium intensity seismic events and by the effects of the morphological changes resulting from the slow movements themselves. The landslide reactivation in 1993 is seen to have been the combination effect of a low return-period rainfall event and the slow movements active at depth in the slope.

Description: Published

Description: 165-185

Description: JCR Journal

Description: open

Description: South-Eastern Calabria is among the areas in Southern Italy which are hardest hit by heavy and relentless rainfalls able to induce geomorphological phenomena sometimes resulting in widespread damage. The Catastrophic Geomorphological Events which have occurred over a time period of 67 years across an area of about 700 Km2 are characterised with a view to correlating major phenomena, such as landslides and flooding, with heavy rains and anthropic expansion. Igneous, metamorphic and sedimentary rocks outcrop and slope stability phenomena affecting the area vary in density and frequency accordingly. Induced phenomena are divided in landslides, floods and “secondary floods”. The analysis of historical precipitation series highlighted the space and time distribution of rainfalls, determining their exceptionality as return period of daily cumulative rainfall of different duration, with respect to the various disastrous phenomena triggered. The aim of this study is to predict different scenarios characterised by various severity levels related to rainfall return periods.

Description: Published

Description: Maratea (PZ), Italy

Description: open

Description: Damaging Hydro-geologic Events (DHEs), de- fined as landslides and floods caused by heavy or prolonged rainfall, represent an important source of economic damages. We propose an approach to classify DHEs, considering 1) meteorological antecedent conditions, 2) the season during which the event occurs, 3) the return period of maximum daily rainfall triggering the event, 4) geographic sectors hit, 5) types of triggered damaging phenomena; and 6) induced damage. We applied this approach to a case study of time series of DHEs that occurred over 85 years in Calabria (southern Italy). We analysed 13 DHEs that, between 1921 and 2005, triggered landslides, floods and secondary floods, causing severe damage and tens of causalities all over the Calabria region. During the analysed events, 64% of Calabria’s municipalities suffered many types of damage. The most relevant rain phenomena and the largest damages were caused by the persistent effects of perturbations on Calabria, which were preceded by the appearance of low-pressure fields in two different areas located westwards. We sorted the events into three types based on geographic damage distribution and types of triggered phenomena and induced damage. The first two types are characterised by similar severity levels, while the third shows the highest severity, in terms of both damage and victims. Independent of the type of event, the S-SE and E sectors of the region are the most frequently affected by DHEs. As regards human life, floods are the most dangerous type of phenomenon, causing the highest number of fatalities. Our analysis indicates a decreasing frequency of DHEs during the study period, and an absence of the most severe type for more than 50 years. The number of victims is also decreasing over time.

Description: Published

Description: 105-118

Description: JCR Journal

Description: open

Description: The aim of this work is to highlight the influence exerted by meteoric events on landslide triggering. Taking into account the main geomorphological and hydrogeological features at the mass movements, simple hydrological/statistical methods are suggested. Cumulative daily rainfalls over 1 to 180 days are studied to determine probability distribution functions. Hence the critica1 rainfall period is determined for a specific landslide and the return period of the hydrological event associated with the landslide is quantified.

Description: Published

Description: Rio de Janeiro (Brasil)

Description: open

Description: In the course of time the ancient Agrigento - a superb Greek city - and later urban settlements have been expanding unti1 these days over a vast area - the one described in this study. This is un area of extreme archeological interest which is characterized by the presence of a regressive type of Pliopleistocenic succession, essentially consisting of clay, sand and calcarenite. From below upwards, one can distinguish a basement from the Miocene and Pliocene epoch followed, in transgressionm by the Trubi Formation and, further up, by the Mt. Narbone and Agrigento formations. Closing the lithostratigraphic succession, the terraced marine deposits of the Sicilian and Thyrrenian, and current debris, alluvial and coastal deposits can be observed. In the San Leone river valley, a series of morphostructural evidences suggest that here geomorphologic dynamics is very likely controlled by ~Canberry and Valley building~ type phenomena due to complete erosion of the calcarenite plaque. Among the most outstanding evidences are: a marked westward and eastward rotation of the structural axes, on the right and left side of the torrent respectively, the presence of remoulded clay stripes and levels, also at considerable depth, and sub-horizontal discontinuities. The calcarenites are marked by a thick mesh of cracks made more pronounced by erosion and dissolution processes. Eventually, this kind of dynamics results into the separation and i subsequent detachment and collapse of calcarenite blocks from the top of the huge plaque upon which the Greek city's famous Temples were built. Some remarkable mass movements that occurred during this last century should be viewed in the light of the complex dynamics just described. Especially important are three landslides: two of them inside the area of today's Agrigento, in 1944 and 1966 respectively, and one that occurred in 1976 along the eastem side of the Hill of Temples. The 1976 slide was caused by a remobilization that followed heavy rainfall: this conclusion was reached at the end of un empirical hydrological-statistica1 study based upon un origina1 method [15]. Daily cumulated rains (1 to. 180 days) were studied to cover the whole century, and this approach enables the recurrence interval of each rainfall event associated to the three investigated landslides to be determined. The results of the hydrological-statistica1 analysis were fully confirmed in the case of the 1976 slide, where it was found that rains are the main causative agent: these results were obtained by means of the physical and hydrological characterization of the soils in the landslide body and some simple calculations concerning the flow of infiltration water.

Description: Published

Description: 359-373

Description: N/A or not JCR

Description: open

Description: The literature contains many examples, which demonstrates the importance of climatic conditions, particularly of rainfall but also temperature, on landslide activation. Normally landslides occur during specific hydrologic conditions; the relative importance of each factor will however vary with the landslide type. Heavy rains are one of the main natural factors producing landslides as they may cause pore pressure to increase on slopes or can create adverse seepage conditions, modify the slope's geometry as a result of erosion and originate swelling and softening processes in clay soils. According to their different behaviour, it is necessary to distinguish shallow or deep-seated landslides, first-time or reactivated landslides, the nature of landslide body (terrain or rock) as well as the hydrogeological nature of soils. Shallow landslides in soils and weathered rocks are often generated on steep slopes during the most intense part of a storm (lasting from minutes to several hours). The higher permeability of the outermost portion of the slope, compared to the bedrock below, allows for the creation of a temporary perched water-table, inducing the progressive increase of pore-water pressure. On the other hand, deep-seated landslides can be mobilised as a consequence of moderate intensity rainfalls lasting several days, owing to the longer recharging time required for ground-water level to rise and cause a significant build up in pore-water pressure. Pioneer studies, concerning landslides triggered by rainfalls, go back to '30s. Were selected 138 papers and key information was collected in a database. Nearly 82 % of all records are local investigations carried out in 23 countries. Italy provides the largest sample as for author’s nationality and widespread proneness to landslides; followed by United States (15 %), Hong Kong (8 %), Japan and United Kingdom. Two main approaches have been used to investigate rainfall-induced landslides: -empirical or semi-empirical relationships, using statistical correlation and forecasting techniques; -deterministic modelling of groundwater recharge and pore-water pressure changes. Studies concerning the first type of approach have reached interesting results about combination of antecedent rainfall and rainstorms intensity able to trigger widespread soilslip activation in specific geological, morphological and climatic settings. Relationships between rainfall intensities and duration associated with shallow landslides and debris flows activation has also been found and they are often used for warning purposes. For the activation of widespread mass movements, some authors underline the role of an effective rainfall period ended by a pronounced increased of rainfall intensity; in this situations hazard precursors may be considered as a combination of cumulate rainfall and rainfall intensity. The second approach requires the development of a clear picture of the modes of water flow on and below the ground surface: where groundwater flow is concerned, attention is focused on both the saturated and the unsaturated zones and complete hydrological models of slopes must be defined. The present paper is a critical overview of recent international research activity on this subject. Methods and experiences are compared and classified. Some author's direct experiences are utilised for these purposes.

Description: Published

Description: Roma

Description: open

Description: Rainfall is the most common cause of landslides. The cost of Rainfall Triggered Landslides (RTL) is not well documented and often unobtainable. In areas where they do not pose a threat to life, great damage is caused to farmland and communication infrastructures and pasture bio-mass production is heavily reduced (Table 1). In Japan more than 10,000 RTL are reported every year which claim the lives of some 400 persons (Fukuoka, 1980); A single event has killed 100 persons and inflicted property damages estimated at 300 billion yen Shimizu (1988). Given the importance of the topic, some 138 papers dealing with RTL were selected and key information was collected in a database. Nearly 82 % of all records are local investigations carried out in 23 countries. Italy provides the largest sample as for authors' nationality and widespread proneness to landslides; followed by United States (15 %), Hong Kong (8 %), Japan and United Kingdom. About 21 % of all selected papers are methodological research or syntheses and comparisons of different methodologies. Investigations refer to widespread landsliding (69 % of AD) (that is the Available Data number for each database field), the remainder corresponds to single or few landslides. A landslide classification proposed by Hutchinsons (1995) and based on the maximum depth of failure (Vm), is adopted in this work. About 40 % of AD are intermediate or deep-seated landslides (Vm 〉 10 m), that include all reactivations, the rest are shallow or superficial landslides, generally first-time movements. The most frequent types are: flows, translational and rotational slides, slips, avalanches and creep, decreasing order (Cruden & Varnes 1996) with soil or debris generally constituting the landslide bodies. Daily (54 % of AD), hourly (28 %), monthly (15 %) and yearly (4 %) rainfalls are used as input. Roughly 49 % consider cumulative rainfall (a rain water height obtained adding regularly monitored rainfall) of different duration. The prevalent approach is empirical, statistical or hydrological-qualitative; one out of four is partially physical and often uses numerical modelling. About 10 % combine rainfall effect characterisation with geotechnical stability analysis. The results of research in progress have been summarised.

Description: Published

Description: 1219-1226

Description: 4.4. Scenari e mitigazione del rischio ambientale

Description: open