**2. Study area**

The Abruzzi region is located in the central eastern part of the Italian peninsula along the Central Apennines (Fig. 1). The regional physiographic and morphostructural setting of Abruzzo is defined by three main orographic and morphostructural domains: the Apennine Chain, Piedmont area and the Coastal Plain (D'Alessandro et al. 2003b).

Fig. 1. Location map (a) and main physiographic domains of the Abruzzo region (b).

The hydrography of the region is characterised by three main types of rivers and hydrographic basins, mostly perpendicular to the coast: 1) rivers rising from the inner part of the chain and cutting it transversally, flowing through the piedmont area to the coast; 2) rivers rising from the front of the chain, incising the piedmont down to the coast; 3) rivers

Geomorphological effects of heavy rainfall were analysed through a field surveys, aerial photo analysis and inventories and technical reports, mapping the distribution of the

This work allowed us to highlight that these types of methods, investigations and data are basic in applied studies for the stabilisation and management of slopes and minor or major drainage basins, and for general land management. Only a high level of knowledge of geomorphological instability, connected to drainage, geological-geomorphological and morphostructural features and to meteorological events - particularly when joined to

Finally, these types of studies are basic and complementary to recent methods of the investigation and mapping of land sensitivity to such geomorphological processes as landslides, soil erosion and desertification, etc. They allow us to define the future scenarios which sustainable land planning and management should be based on - by taking into account the specific destination of different areas and contributing to the identification of proper sites for quarries, dumps and purification plants, or else proper areas for industry, urban expansion, thereby generally supporting the process of creating an urban plan.

The Abruzzi region is located in the central eastern part of the Italian peninsula along the Central Apennines (Fig. 1). The regional physiographic and morphostructural setting of Abruzzo is defined by three main orographic and morphostructural domains: the Apennine

Fig. 1. Location map (a) and main physiographic domains of the Abruzzo region (b).

The hydrography of the region is characterised by three main types of rivers and hydrographic basins, mostly perpendicular to the coast: 1) rivers rising from the inner part of the chain and cutting it transversally, flowing through the piedmont area to the coast; 2) rivers rising from the front of the chain, incising the piedmont down to the coast; 3) rivers

geotechnical data - allows effective stabilisation and management plans.

Chain, Piedmont area and the Coastal Plain (D'Alessandro et al. 2003b).

landslides, soil erosion and flooding.

**2. Study area** 

rising within the piedmont area and rapidly reaching the coast. A fourth, secondary type but very important in heavy rainfall events - is given by small catchments flowing on the coastal slopes directly to the coastal plain.

The relief of the Apennine Chain is made up of carbonate ridges (NW-SE, NNW-SSE, N-S) separated by parallel valleys carved in terrigenous foredeep deposits or filled up with continental ones and by wide intermontane basins partially filled with Quaternary continental deposits. To the east, the relief abruptly slopes down into the piedmont area, where a hilly landscape is carved by cataclinal valleys (SW-NE) on arenaceous-pelitic thrusted and faulted successions and on a gently NE-dipping homocline of clay, sand and conglomerate deposits. Along the valleys and close to the coast, alluvial plains with fluvial and alluvial fan deposits join a narrow coastal plain.

The lithologies of the Abruzzo area are made up of different units, mostly of sedimentary origin. In the recent official Geological map of Italy (CARG Project, Geological Survey of Italy, ISPRA, 2011) the lithological units are referable to pre-orogenic units (mostly marine Meso-Cenozoic carbonate rocks), syn-orogenic units (mostly Neogene arenaceous and pelitic rocks), and post-orogenic units (marine Plio-Pleistocene clay-sand-conglomerate rocks and Quaternary clastic continental deposits). These can be grouped in a limited number of units (Fig. 2). These units are mantled, particularly in piedmont slopes and valleys, by eluvial and colluvial, cover up to several meters thick.

The structural setting of the chain area is defined by thrust ridges and faulted homocline ridges separated by tectonic valleys and basins. Main regional fault systems affect the chain area: Mio-Pliocene NW-SE to N-S low angle thrust faults, Pliocene NW-SE to NNW-SSE high angle normal faults, Quaternary (in some cases still active) NW-SE and SW-NE high angle normal faults. The piedmont area is defined in the inner part by thrust reliefs which are affected by regional NNW-SSE Pliocene thrusts and by minor high angle normal faults and, in the outer part, by a wide homocline slightly NE-dipping which is affected by minor high angle normal faults.

The geomorphological processes affecting the whole Abruzzo region are mainly fluvial slope processes and mass wasting. In the coastal areas, marine and aeolian processes are also very important, while in mountain areas karst landforms are present and the landform remnants of ancient Pleistocene glacial processes are preserved. These processes are frequently activated by the heavy rainfall events that affect the region. Fluvial processes affect the main rivers, alternating between channel incisions and flooding. The slope processes that are due to running water mostly affect the clayey and arenaceous-pelitic hills of piedmont and the coastal areas, generating outstanding landforms such as badlands (or "calanchi") and minor landforms, such as rills, gullies and mudflows (which are very common all over the hill slopes).

Mass wasting processes have induced the formation of a huge number of landslides and mass movement in the Abruzzi region, mostly affecting the hilly piedmont area as well as the chain area and - locally - the coastal one (Fig. 2; D'Alessandro et al., 2003a, 2007).

This geological and geomorphological setting is the result of a complex geological and morphostructural evolution due to the Neogene compressional deformation of different Meso-Cenozoic paleogeographic domains and Neogene foredeep domains (that formed a NE-verging thrust belt) and to Quaternary extensional tectonics and uplift (that formed

Geomorphological Instability Triggered

et al., 2008; D'Alessandro et al., 2008).

analysis and inventories and technical reports.

**4. Heavy rainfall events** 

almost 72 h.

Popoli; Fig. 4a).

**4.1 2003 event (23-25 January)** 

(D'ALESSANDRO et al., 2004).

daily rainfall, monthly rainfall and previous monthly rainfall.

**3. Methods** 

by Heavy Rainfall: Examples in the Abruzzi Region (Central Italy) 49

of Quaternary continental deposits (slope, fluvial, lacustrine and coastal deposits) (Demangeot, 1965; Bigi et al., 1996; Miccadei et al., 1999; D'Agostino et al., 2001; D'Alessandro et al., 2003b; Pizzi, 2003; Farabollini et al., 2004; Miccadei et al., 2004; Ascione

This work is based on the analysis of the meteorological aspects and geomorphological effects of heavy rainfall occurring during the three events affecting the piedmont and coastal area of the Abruzzi region: 1) on 23-25 January 2003 (in the whole region), 2) on 6-7 October 2007 (in a small part of the hilly and coastal Teramo area), and 3) on 1-2 March 2011 (in the hilly and coastal Teramo and Pescara area). The analysis was performed by means of the statistical processing of precipitation data and by means of field surveys, aerial photo

The meteorological aspects were studied processing a >40 pluviometric station database provided by Servizio Idrografico e Mareografico (Direzione Protezione Civile e Ambiente, Regione Abruzzo), including daily and monthly historical data (30-70 years) and 5-15 min pluviometric registrations for at least six days around the main events. The data processing enabled the analysis and comparison of hourly rainfall intensity, event cumulative rainfall,

The geomorphological effects of these heavy rainfall events were analysed through field surveys, aerial photo analysis, and inventories and technical reports, and they enabled the mapping of landslides, soil erosion and flooding. The percentage and areal distribution of these effects was also analysed for the different events and so also concerned the affected

The 2003 heavy rainfall event affected almost the entire region - but mostly the central and south-eastern part (Chieti and Pescara province and part of L'Aquila and Teramo) - for

The monthly rainfall analysis shows January 2003 values very much higher than the average historical values, ranging from 50 mm to 150 mm (Fig. 3a), which in some cases is up to 3 times. Several values are >250 mm and some are > 300 mm, up to a maximum recorded value of 388 mm (Salle station; Fig. 3a). These values are close or in some cases higher than the previous historical January maximum values (Fig. 3a). Moreover, the rainfall occurred after a December which had already been very rainy, with a two month precipitation value up to 60% or even 80% of the average annual precipitation

The daily rainfall is high but less than it was for the 2007 and 2011 events. The higher values - up to > 120 mm - are recorded along the front of the chain, in the Maiella area (Salle,

lithologies, providing a contribution for the definition of the controlling factors' role.

Fig. 2. Geological scheme of the Abruzzo Region (modified from Vezzani and Ghisetti, 1998; ISPRA, 2011); the red dots indicate the location of landslides (modified from Progetto IFFI, D'Alessandro et al., 2007). The black boxes indicate the approximate distribution of heavy rainfall events and related geomorphological effects: a dash-dot line for the 2003 event; a continuous line for the 2007 event; a dashed line for the 2011 event.

faulted homocline ridges, tectonic basins and homocline reliefs) (Cipollari et al., 1997; Lavecchia et al., 2004; Parotto and Praturlon., 2004; Patacca and Scandone, 2007; Cosentino et al., 2010). In the chain as a whole, the morphogenetic processes began during the last phases of thrust belt emplacement in the Early Pliocene. However, the most important morphogenetic impulses are due to the regional uplift processes and the development of extensional tectonics. After the Apennine area emerged, the activity of morphosculptural processes in the continental environment began in a variable relationship with morphostructural processes. This process, together with the morphostructural action of the extensional tectonics, has controlled the geomorphological evolution of the ridge, basin and valley of the chain and in the piedmont relief of the major fluvial valleys systems and the coastal plain. These processes also induced the mantling of slopes and valleys with a cover of Quaternary continental deposits (slope, fluvial, lacustrine and coastal deposits) (Demangeot, 1965; Bigi et al., 1996; Miccadei et al., 1999; D'Agostino et al., 2001; D'Alessandro et al., 2003b; Pizzi, 2003; Farabollini et al., 2004; Miccadei et al., 2004; Ascione et al., 2008; D'Alessandro et al., 2008).
