1Among the numerous environmental indicators of climatic variation, several geomorphological processes (and their related deposits and landforms) are of primary importance. Glacial landforms, stratified slope deposits and alluvial deposits, amply present in the Central Italian peri-Adriatic region, are some of these fundamental elements.
2Inactive glacial landforms, represented by cirques and moraines, are still preserved in the higher portions of the Umbro-Marchean Appenines (Sibillini Mts.). Glacial cirques are visible along a band running north-south for over 30 km; the southern portion is 2-3 km wide while the central and northern ones are 10-12 km wide. Two different generations of cirques were identified; the older and wider one is attributed to the middle-final Pleistocene cold phase, while the less extensive younger generation, superimposed on the older one, was emplaced during the Late Pleistocene. Glacial moraines, with a minimum elevation of 1170 m a.s.l. and related to the younger phase, sometimes cover residual limbs of older deposits or are interbedded with them, as observed in other areas of the central-northern Apennines (F. DRAMIS et al., 1980; P.R. FEDERICI, 1979; E. JAURAND, 1992, 1994; C. BISCI et al., 1999; B. GENTILI, 2002). The contemporary periglacial morphogenesis of the surrounding areas, regularized the middle-low portions of the slopes, emplacing thick and wide stratified slope deposits; two main generations of these deposits (Middle Pleistocene and Late Pleistocene, respectively) were recognized. The younger generation is the most widespread in the study area; sometimes rare and limited limbs of cemented gravels, connected with a generation older than both, are present (F. DRAMIS et al., 1980; F. DRAMIS, 1983).
3The occurrence of periglacial climatic conditions produced a strong and systematic conditioning of the hydrographic system evolution. Generalized areal erosion of the relief summits and prevalent sedimentation along the valley floors in the middle-upper portions of river catchments were the results. Afterwards, the temperate phase that followed, with a generalized and marked uplift during the Middle and Upper Pleistocene (P. AMBROSETTI et al., 1981), favored the rapid incision of alluvial deposits and of the bedrock itself, forming terraces or completely erasing the original material. Consequently, sedimentation migrated valleywards down to the river mouths, along the coasts and to the Adriatic Sea.
4To such processes, the genesis of three different orders of fluvial terraces has been referred. Their elevation, with respect to the present valley floor, is generally comprised between 80 and 200 m for the 1st order (Middle Pleistocene), 40 and 80 m for the 2nd order (end of Middle Pleistocene), and 15 and 30 m for the 3rdorder (Upper Pleistocene –M. COLTORTI et al., 1991). The deposits are mainly made up of calcareous gravels, whose texture ranges from a few to tens of centimeters. Pebbles are well rounded, and sometimes also silty and sandy lens and levels are present. The genesis of the recent alluvial plain of Holocene age (4th order), which is 4-6 m above the river bed, is related to degradation processes as a result of intense anthropization of the slopes and subordinately to possible climatic fluctuations. Within these deposits, higher pebble heterometry and significant increase of silty-sandy classes together with a major sandstone component in correspondence with the piedmont-hilly belt were observed. Significant thicknesses of fine materials, deposited by historical flooding are often visible on top of the sequence (E. BIONDI and M. COLTORTI, 1982; B. GENTILI and G. PAMBIANCHI, 1987; M. BUCCOLINI et al., 1989).
5The present study aims to indicate possible geomorphological indicators of climatic variations, in particular those of the Late Holocene, in the form of minor landforms whose activation and evolution is closely connected to superficial and ground circulation of large quantities of water. It shows and analyzes several indicators from three different sample areas, which are very representative of the same number of physiographic units of the Central Adriatic Region in Italy (Fig. 1): debris flow phenomena and flooding processes in the Sibillini Mountains (central Apennine range); fast erosion processes ("calanchi" and related landforms) and landslides on Mount Ascensione in the peri-Adriatic sector; historical variations of the shoreline close to the Chienti river mouth. Morphochronological andmorphoclimatic data and interpretations related to these three categories of elements, except those referring to "calanchi", are for the first time clearly described in detail in this paper.
6The Sibillini massif was made up by the merging of the southern portions of the Umbro-Marchean and Marchean ridges (Fig. 1). Altitudes range between almost 350 m (the lowest valley floors) and the 2476 m a.s.l. of Mt. Vettore, with many reliefs exceeding 2000 m a.s.l.. The landscape is characterized by deep and narrow valleys interrupted by wide watersheds with ridges and edges; it shows values higher than 1000 m and slope angles of over 60 % with frequent subvertical walls.
Figure 1 - Geological and geomorphological sketch of central-southern Marches.
1: main fluvial and coastal deposits (middle Pleistocene-Holocene). 2: gravels and conglomerates (early Pleistocene-middle Pleistocene). 3: pelites and sands with intercalating arenaceous (a) and conglomeratic (b) bodies (Pliocene-Pleistocene). 4: turbidites (Messinian). 5: turbidites (Tortonian-early Messinian). 6: marly terrains (Oligocene-middle Tortonian). 7: marly limestones (Aptian p.p.-Priabonian). 8: limestones (late Trias). 9: faults and fractures. 10: Sibillini thrust. 11: cross section (A-A'). 12: limit of study area.
7The bedrock is made up of the "Successione umbro-marchigiana" (Upper Trias - Aquitanian p.p.) and of limestone at the base (Calcare massiccio), overlain with stratified cherty micritic limestone, marly limestone and marls. This sequence continues with thick calcareous (Maiolica) and marly-calcareous (group of "Scaglia" formations) units, represented by intercalated layers of marly clays and marly limestone of the "Marne a Fucoidi" formation (E. CENTAMORE and G. DEIANA, 1986).
8The structural setting is characterized by east-verging folds whose eastern sides are truncated by thrusts. The most important is the "Sibillini thrust" that caused the overlying of calcareous units on more ductile Miocene lithotypes of the piedmontane belt. These structures were formed during a compressive tectonic phase between the Upper Messinian and Lower Pliocene. Normal faults (with NNW-SSE and ENE-WSW directions) related to a Quaternary extensional phase, markedly dissected the previous structures; the most important faults, trending NNW-SSE, formed blocks at different heights and an intra-mountain depression along the Apennine ridge, from the end of the Lower Pleistocene on. Some of these depressions give a clear indication of recent activity, as witnessed by the frequent seismicity of the area (F. CALAMITA and G. DEIANA, 1988).
9Superficial deposits of different genesis hide wide portions of bedrock. Among them, thick slope deposits (stratified or massive), moraines, fluvial-torrential deposits and landslides are particularly important for the aim of the present study (Fig. 2).
Figure 2 - Map of main geomorphological features of Sibillini Mountains.
1: main alluvial fans of Late Pleistocene-Holocene. 2: recent or active debris flow of Holocene time. 3: main slope deposits of Middle Pleistocene-Holocene. 4: old debris flow of Late Pleistocene. 5): lacial cirques of Late Pleistocene. 6: main morains of Middle Pleistocene-Late Pleistocene.
10Together with the litho-technical characteristics, morphogenetic control is also connected with the hydrogeological properties of the bedrock, that drive runoff or infiltration and the deep circulation of meteoric water. Circulation along fractures and channels characterizes calcareous and marly-calcareous bedrock. The high permeability (mean effective infiltration of about 550 mm/y, where the mean rainfall is 1000-1100 mm/y) is mainly connected to tectonic open fractures, strata surfaces and subordinately to karstic phenomena. Sometimes, where the marly levels are prevalent with respect to fracturing, permeability may become extremely low. Marked differences are also observed in the velocity of water circulation inside the permeable bedrock; depending on the different kind of permeability and the hydraulic gradient, this velocity ranges from one centimeter/day to hundreds of meters/day up to more than one kilometer/day (C. BONI et al., 1986).
11Circulation by porosity characterizes continental cover. Great differences are due to the different cementation of materials but mostly to their sedimentological and stratigraphic characteristics. In particular, silty-clayey levels, intercalated with gravels in stratified slope deposits (Photo 1), generate high potentiometric levels with associated artesian aquifers located within the deposit or at the bedrock-cover contact.
Photo 1 - Typical example of stratified slope-waste deposit in the Sibillini area.
12The main landforms connected with materials coming from isolated alluvial fans or debris flow deposits were examined. The former are located at the confluence of the channels of the minor hydrographic network, along the higher order axes, while the latter occur at the same location (Fig. 2) when characterized by a high topographic gradient. In this case they could have reshaped the original fluvial-torrential or fluvial-glacial incisions and formed flat orsmoothly U-shaped small valleys (Photo 2). The alluvial fans are made up of medium-coarse gravels, poorly reworked and only little stratified and sorted. Their emplacement is related to intense runoff, as shown by gullies located upward or by the shallow and poorly ranked hydrographic network.
Photo 2 - Flat valley due to debris-flow at Vallestretta.
13Debris flows, whose deposits show neither stratification nor sorting (and texture ranging from clays to pebbles with rare scattered blocks), developed at the expense of thick detritic cover, mobilizing most superficial levels (up to 2 m in thickness). These are extremely rapid movements of viscous-plastic fluids, with variable density from 1.8 to 2.6 t/m3 and a solid fraction representing 70-90% of the total weight (J.E. COSTA, 1984). According to T. TAKAHASHI (1991), they are generated by a consistent presence of water inside the detritic mass or by superficial runoff when the thickness value of mobilized material (d) is not too low with respect to flow height (h), i.e. d>0.7 h. U. MAIONE (1998) considered those situations characterized by intermediate processes to be very common and defined them as "immature debris flows".
14Starting from the geomorphological analysis of more recent and well recognized debris flow deposits in the Sibillini Mts area (Castelsantangelo sul Nera and Ussita in 1906; Nocelleto and Rapegna in 1946 – Photo 3; Visso in 1959), through oral testimony and archive data, detailed geomorphological surveys and in-depth historical investigations were carried out. These allowed us to recognize many events (Fig. 2) and to establish two main kinematic phases. The first stage eroded the detritic cover along the medium-low sectors of slopes, causing planar slides over surfaces parallel to the slope and/or piping phenomena (Photo 4).
Photo 3 - Evidence of flooding at Rapegna during recent times.
Photo 4 - Piping phenomenon within debris flow deposit at Calcara.
15Both processes are related to high hydrostatic pressure connected to the above-mentioned hydrogeological setting. During the second stage, which mainly occurred along the valley floors, a convergent effect in the mobilizing of materials exercised by debris flows on previous mechanisms was observed. Analogous, though much less intense, action seems to have been carried out also by alluvial fans.
16The shape of small valleys, modeled by processes, is systematically characterized by a regular longitudinal profile (average slope 10-15 % and more) and by a transversal one with sharp breaks linking the surface of the (U-shaped) deposit to the steep slopes sideways (no deposit is present in between). Moreover, the total absence of any hydrographic network and sporadic vegetation are evident on the deposit.
17The possible chronological collocation of most ancient deposits, attributed to the end of the Upper Pleistocene-Lower Holocene, was established on the basis of a correlation with alluvial, glacial and periglacial landforms. A very significant example can be observed at Foce, where a flat or smoothly U-shaped small valley, with a mean slope of about 13 %, 200 m wide and 2.8 km long, connects the overhanging glacial valley, characterized by moraines of the last generation, with the source area of the Aso river (F. DRAMIS et al., 1980; E. JAURAND, 1992). The connection between valley-floors and slopes is constituted, on both sides, by concave surfaces related to huge and widespread slope deposits (maximum thickness of 10 m), which clearly overlay debris flow deposits in their lower portions. Another old debris flow deposit is that identified at Castro (Photo 5); its distal portion, deeply incised by fluvial erosion, shows a progressive change along two natural sections from a mixed (debris flow – fluvial) to a clear fluvial deposit. Lateral sides, particularly that on the hydrographic right, can be topographically related with limited limbs of flattened surfaces valley-ward, attributed to the third order terrace (end of Late Pleistocene – G. CILLA et al., 1996). Also in this case, the process has probably been fed by more recent moraines. However, only rare and limited remnants of these deposits have been recognized; corresponding glacial cirques are, instead, clearly evident (Photo 4).
Photo 5 - Detail of debris flow deposit at Castro.
18Many phenomena can be attributed, on the basis of historical investigations, to the medieval and post-medieval periods. Historical sources, directly or indirectly, witness to the recurrence of such processes starting from the XIIth century; this was due to the need to adapt villages and the elevation of the road network to higher topographic levels as a result of flood events. In any case, the main intense and destructive events occurred during a period that encompasses the XVth to XIXth centuries (1494, beginning of the XVIIth century, 1667, 1670, 1807, and 1858). The same sources repeatedly evidence the execution of hydraulic remedial works starting from the second half of the XVth century (A. FABBI, 1965; R. FALCONI, 1986; M. BUCCOLINI et al., 1989; B. GENTILI, 2002). The debris flow chronology is supported also by comparison of old morphologies and those related to landforms of the XXth century. In fact, the old ones are characterized by: borders slightly smoothed by deposition of thin colluvial deposits, local and weak incision of deposit; well-developed vegetation cover, presence or remnants of medieval and post-medieval handmade articles.
19The activation of the oldest phenomena was related to the Late Pleistocene-Early Holocene deglaciation; the consequent large amount of water along the slopes favored activation of gravitational processes. As far as the phenomena of the early Middle Ages are concerned, the main cause can be attributed to intense agricultural practices and to the development of forestry, even though evidence of rainfall increase, compared to the previous dry period, is available (M. PINNA, 1984). In fact, the continual human presence, induced by these agricultural practices on the slopes, favored high-scale debris production; this is the primary condition for debris flow activation.
20During the following period, until the mid-XIXth century, mass movements were related to climate worsening and consequent rainfall increase, which started in the mid-XVIth century and continued for about three centuries (M. PINNA, 1984). Snowfalls, in particular, seem to have been extremely favorable to the piezometric level increase. Such climatic conditions, even though modest with respect to the cold climate of the Pleistocene, can be expected to have produced important morphogenetic effects, since they worked in an environment where agriculture had destabilized vast portions of the landscape. This phenomenon, which reached its maximum in the mid-XVIth century, favored cultivation up to 1500 m, after a huge-scale elimination of the vegetation cover. In addition, the progressive abandonment of cultivated areas (starting from the most elevated zones) subsequent to climatic worsening (A. FABBI, 1965), and the subsequent high degree of hydraulic “disorder” on the slopes, certainly contributed to the activation of debris flow processes.
21From the beginning of the XIXth century up to the middle of the XXth century, the agricultural practices, which were restarted in the same areas as those cultivated during the Middle Ages and Renaissance, destabilized the slopes. This happened because defense works in these areas were either absent or inefficient. These defense works, when present, became useful (due to the improvement of techniques or to their wider utilization) only during the last twenty years of the above-mentioned period. It was mainly this renewed setting of the rural landscape that drove the XXth century processes.
22Mount Ascensione, the highest relief (1110 m a.s.l.) of the peri-Adriatic belt, is located in the southern Marches (Fig. 1), inside a portion of a large sedimentary basin where, from the end of Early Pliocene to the end of Early Pleistocene, terrigenous sediments, in tectonic contact or transgressive on the Laga Formation (Messinian turbidites) were deposited. The Mt. Ascensione relief (Photo 6-a) is a huge conglomeratic body intercalated with clays of the Pliocene-Pleistocene sedimentary sequence, which crop out on the southwestern and southern slopes. On the eastern slope, the sequence continues with a thick and widespread pelitic unit, with the Castignano and Colle Cilestrino sandy-conglomeratic levels intercalated at different heights (E. CENTOMORE and G. DEIANA, 1986).
Photo 6 - a) Panoramic view (from south) of Mount Ascensione (for description see the text); b) detail of glacis deposit remnants
23The structural setting of the study area is characterized by an ENE verging monocline, 15-20°dip. This structure is also affected by several joint systems and dip-slip faults mainly trending NW-SE, NE-SW, N-S and E-W (B. GENTILI et al., 1995).
24Fundamental geomorphological elements in the Mt. Ascensione area are constituted by stratified slope and glacis deposits which were later affected by fast erosion processes ("calanchi") and mass movements (Photo 6-a and 6-b). The glacis represents a beautiful example of such a landform, almost unique along the peri-Adriatic belt of central Italy. Its original extension was over 10 km2 while the maximum thickness of the corresponding deposit possibly exceeded 30 meters. Fragments of charcoal found at different heights inside the deposits and dated with the C-14 technique (Beta Analytic Inc., Miami, Florida, U.S.A.) allowed us to estimate for this deposit an age comprised between 41.640 y ±1260 B.P. and 22.680 y ± 170 B.P (B. GENTILI et al., 1998). This detritic cover, mostly overlying the pelitic bedrock and currently reduced to small remnants along watersheds, is made up of polygenic and heterometric pebbly-sandy deposits, produced by the erosion of conglomeratic-sandy-pelitic bedrock. The degree of cementation is not very high even though in some places deposits are well cemented.
25The Mount Ascensione morphostructure, totally regularized by slope and glacis deposits at the end of the Pleistocene, was partially remodeled by Holocene dynamics, which were particularly intense along the southern and eastern sectors. Such a stratigraphic setting favored the genesis of huge aquifers in correspondence with the thickest detritic bodies.
26Three main erosive phases have been identified (B. GENTILI et al., 2002). The first phase, favored by the biostasy conditions, probably at the end of the Pleistocene but likely at the beginning of Holocene, and by a long-lasting tectonic uplift, caused a hydrographic network deepening that, on reaching the bedrock, interrupted the glacis deposit continuity. This new geomorphological setting activated a second erosive phase, characterized by huge and frequent mass movements. These affected the detritic cover (until their total erosion over vast portions of the watersheds, or until they arrived at the more resistant bedrock levels. At the same time, spectacular "calanchi" morphologies set in. In a third phase, which is still active, mass movement spread down to the bedrock, and the "calanchi" evolution is related with it. Geomorphological surveys have been supported by historical investigation, whose sources (P.C. CARLINI DE CAROLIS, 1792; N. GALIÈ and G. VECCHIONI, 1999) provided some interesting data about the main landslides of the last millennium (Fig. 3).
27The southern slope of Castignano, an old village founded at the beginning of the Middle Ages, was affected several times during the centuries by landslide phenomena; these processes led people to move to the northern sectors. From historical chronicles, the oldest mass movement appears to be that of 1204, which affected the head of a stream close to the village, modeled on the southern border of a sandstone plate overlying the pelitic bedrock. Its activation has been attributed to rapid and deep stream incision, as a consequence of intense deforestation during the previous two centuries. Landslide reactivation, with mountainward withdrawal of the landslide crew and consequent northward movement of the city walls, has been observed: in 1335; between 1450 and 1500 when the phenomena were almost continuous; and again in 1574, 1605, 1634, 1717, 1772, and 1777. The last damage to the town dates back to 1927; after that, a high check wall, which is still standing, was built. At Ripaberarda, an ancient village of the IVth-Vth century B.C.E. (Before Common Era) built over the sandy glacis deposits of Mount Ascensione and with a fortress dating from 1298 C.E. (Common Era), a landslide destroyed a portion of the castle and the church inside the city walls at the beginning of the XVIth century. The same sources report a considerable downcutting of the Macchia stream inside the clayey bedrock before the event. A bell tower of 1518 is today tilted westward because of a mass movement connected with the "calanchi" withdrawal on the hydrographic left of the above-mentioned stream.
Figure 3 - Mount Ascensione area.
1: location of main "calanchi". 2: dated landslides.
28During the XVIth century, landslide phenomena destroyed the old village of Capradosso, built on continental cover. Rebuilt in 1735, it is still inhabited and free of significant movement. The castle of Porchiano, built before 1237, and located on stratified second-generation slope deposits, collapsed together with several houses at the end of the XVIIth century. In this case as well, the reason was the erosion caused by the Chiaro Morto stream and to the withdrawal of “calanchi” heads on the hydrographic left. Remnants of the old village are located above a limited detritic plate (about 30 m thick); its borders and middle zone show fissures and fractures, of clear gravitational origin, that are roughly parallel to the slope and present also within the clayey bedrock beneath (photo 7).
Photo 7 - Porchiano: gravitational fractures and fissures within glacis deposit.
29At Rotella, an old center built over a third order alluvial terrace, the church of S. Maria (built in 1430) partially collapsed together with a portion of the village, because of erosion caused by the Oste stream at the base of the fluvial scarp. Castel di Croce, a XVIth century village constructed around a castle, actually shows a reduction in size with respect to the past, due to chronologically uncertain mass movements. The Poggio Canoso castle of the XIVth-XVth centuries was inhabited for a relatively short period and abandoned due to landslides. Both villages are located on arenaceous-conglomeratic levels covering clayey bedrock. The regular stratigraphic and structural setting of the study area, the geomorphological context and historical information allow us to classify many mass movements as translational slides and minor falls. The latter affected more or less large portions of more resistant units (arenaceous or arenaceous-conglomeratic or alluvial and/or glacis conglomerates). These landslide bodies subsequently evolved into flows which filled small secondary valleys. Only crews or scarps, but not deposits, are left from such movements; dismantled by fluvial-torrential processes, they increased fluvial solid transport of the Tronto and, subordinately, the Tesino river. The main predisposing activation and control factors of the above mass movements are connected to: (1) the recurrent stratigraphic and hydrogeological setting, characterized by the overlaying of tough units (aquifers) and clays (aquicludes) and associated with significant piezometric levels; (2) tectonic fracturing (only on arenaceous bedrock); (3) a rapid and marked deepening of the hydrographic network connected with runoff over steep slopes, that generated high relief and the exposure of stratigraphic discontinuities; (4) poor geotechnical characteristics of the clayey bedrock, increased by intense softening (B. GENTILI et al., 1995). This fact is connected with groundwater and the high thermal excursion of southward slopes affected by landslides. In addition, an important role could have been played by the frequent seismicity of the area, even though sure data about the magnitude are not available. Locally, practices connected with the anthropization of the area may have played a significant role, mainly increasing the erosive processes of the hydrographic network.
30A correct chronology of the above-mentioned different erosive phases proves to be uncertain and problematic. On the basis of geomorphological evaluations, the first phase could probably be referred (as mentioned before) to the Early Holocene. The second, whose beginning is uncertain, shows intense morphodynamic action during the post-medieval period, between the XVth and the XVIIIth centuries. Therefore, it eems correct to associate the mass movements, taking into account their activation factors, to increase of precipitations (rainfalls and snowfalls) or to prevailing snowfalls, particularly favorable to rises in piezometric levels and connected to the above-mentioned climatic worsening (M. PINNA, 1984).
31The mouth of the Chienti river, with its typical delta shape and moderate convexity toward the sea, is mainly made up of polygenic gravels (with sandy matrix) where calcareous and marly calcareous pebbles, coming from the Umbro-Mrchean Succession, are abundant. The mouth represents the end of a 91-km-long river course (average slope 1.2 %) while its catchment (area = 1250 km2; hmax = 2102 m; have = 508 m) extends up to the northern slope of the Sibillini Mountains. As well as having the main catchments of the Marches region, the river Chienti transversally crosses the territory from WSW to ENE, cutting both the formations ofthe Umbro-Marchean Apennines and the arenaceous and clayey turbidites of the piedemontane and hilly belt (Fig. 1). Five reservoirs, built between 1954 and 1967, interrupt the main river courses or tributaries; other important works along the river beds consist in check dams, groynes and banks built during the first half of the XXth century.
32As far as the Marches Region is concerned, several studies, through absolute dating, or directly or indirectly by historical chronicles, testify to a coastal morphology characterized by active cliffs and bays (corresponding to the river mouths) starting in the Early Holocene (U. GORI, 1988) and continuing up to pre-Roman times (G. SPERANZA, 1934; M.L. DE LUCA, 1939; S. ZAVATTI and P. MORLACCO, 1971). On the contrary during the following periods, throughout the post-medieval period and up until the first half of the XXth century, geomorphological analyses show a coastal dynamics regime characterized by sedimentation processes. Moreover these are responsible for the genesis of the delta and low pebbly-sandy beaches with a width ranging from a few tenths of a meter up to over 1000 m (D. ALBANI, 1933; M. BULI, 1944; B. GENTILI and G. PAMBIANCHI, 1987; U. GORI, 1988; R. BEVILACQUA, 1994; M. CORTOLTI at al., 1995; C. BISCI et al., 1995; M. COLTORTI, 1997; D. ARINGOLI et al., 2003).
33From when they started in 1850, remarkable shoreline withdrawals have been recorded in several parts of Italy. The same phenomenon has been observed in the Marches region, even though the clearest evidence is that of the first decades of the XXth century (D. ALBANI, 1933; M. BULI, 1944). Because of the applied implications of shoreline variations, the topic has been analyzed in detail for more recent periods but only in areas close to the Marchean river mouths. As far as the last 100 years are concerned, several geomorphological analyses, based on comparison between topographic maps and aerial photographs of different periods, have confirmed a general shoreline withdrawal even near river mouths characterized by more complex dynamics. Different withdrawal values noted between 1892 and 1956 (1892-1933, 1933-1944, 1944-1956), followed by a phase of advancement up to 1967, then by a marked withdrawal up to 1975 and then by substantial stability up to 1986 have been identified. During this period, the average withdrawal rate for eleven rivers is estimated to be 1.86 m/y (2.58 m/y for the Chienti river), with a maximum of 5 m/y for the Tronto river (M. BUCCOLINI and B. GENTILI, 1986; B. GENTILI,and G. PAMBIANCHI, 1987; C. BISCI et al., 1992; M. CORTOLTI et al., 1995).
34Among the several Marchean river mouths analyzed, that of the Chienti and the corresponding northward shoreline portion, where the city of Porto Civitanova is located, was investigated. That choice was conditioned by vast availability of data (maps from different periods up to the XVIth century) and to reliable historical sources dating back to the Roman age, though not always in agreement with each other (R. ALMAGIÀ, 1960; M. ORTOLANI and N. ALFIERI, 1967; V. GALIÈ, 1988).
35On the basis of the data collected (Fig. 4-a), shoreline variations north of the river mouth were elaborated. A substantial stability between the IIIrd and Vth century B.C.E. was detected, followed by a nearly constant and relatively fast (0.5-0.6 m/y) period of advance of about a thousand years. Between 1500 and 1810 C.E. the advance is less clear, despite the occurrence of numerous and intense floods, such as those reported between 1574 and 1590 (six events) and again in 1607 and 1616. It is more marked during the following period (1810-1935 with an average rate of 3.2 m/y). The period from 1935 to the present day is characterized by a significant delta withdrawal (about 3.5 m/y), that has led to the present configuration of the river mouth.
Figure 4 - Shoreline variation.
a: near Chienti river mouth from Roman times up to present-day. b: at Porto Civitanova from 1705 up to present-day.
37Figure 4-b represents shoreline variations recorded during the last three centuries in the built-up area of Porto Civitanova. They were defined on the basis of the above-mentioned historical sources as well as of reliable data, which derive from the planning, execution and management of structural and infrastructural works connected with modern urban area development during this period. A progressive shoreline advance characterized the period 1705-1935 (about 1.1 m/y). Much more evident is the following increase (2.8 m/y between 1935 and the present day) but this morphodynamic evolution is not very significant because it has been clearly influenced by the harbor construction which was begun in 1932 and completed in 1938. The climatic interpretation of the river mouth withdrawal-advance processes represents the subject of the following conclusions.
38Twenty years of research on the geomorphological evolution of the Marchean rivers and their corresponding mouths, allows us to consider in detail the morphodynamic evolution of the Chienti river mouth, which is very representative of the whole coastal system of the Italian Adriatic Region. Taking into account that the shape of the river mouth, which derives from the interaction between slope, and fluvial and coastal dynamics, represents the "memory" of complex environmental transformations triggered by natural or anthropic processes within river catchments, an attempt can be made to correlate the data presented in this paper, even though they are related to various geomorphological units.
39The data collected have allowed us to confirm the conflicting effects produced by human impact on fluvial transport during the last 4000 years in the Marches region (D. ALBANI, 1933; M. BULI, 1944; D.G. LOLLINI, 1976) as well as in other Mediterranean areas (C. VITA FINZI, 1969; C. DELANO-SMITH, 1979). An important role was played by post-medieval agricultural practices on the slopes, whose consequent erosive processes produced a significant increase in fluvial solid transport. On the contrary, the effective and widespread agricultural and forest remedial works, starting from the second half of the XIXth century, and the construction of dams and check dams along river beds limited or slowed down the transport of debris toward the coastal system.
40The recent morphodynamic evolution of the hydrographic networks, as a consequence of quarrying activity along river beds, already significant during the first decades of the XXth century but intensively practiced from 1960 to 1975, has been associated with the generalized advance of the period 1956-1967. This was caused by erosive phenomena activated downstream during the initial phase of quarrying. This phase was significant around 1930 but became more intense around 1950, mostly near river mouths. These processes ended rapidly when river deepening, overcame alluvial deposits and reached clayey bedrock (M. BUCCOLINI and B. GENTILI, 1986; B. GENTILI and G. PAMBIANCHI, 1987).
41In any case, because of the complex and problematic interpretation of the processes, climatic factors should also be taken into account. In fact, even though relationships between the coastal setting of the XVIth-XIXth centuries (characterized by substantial stability) and rainfall increase during that period (testified to by the geomorphological indicators of two previous sample areas and by certain historical sources) have not been detected, we also relate the morphodynamic evolution of the Chienti river mouth to cold-humid climatic conditions, delayed in time because of the considerable distance between the source area and the river mouth.
42The notable shoreline advancement from 1810 to 1935 can only be explained by the arrival at the river mouth of a great quantity of material with a texture which favored sedimentation. The originof the polygenic gravels constituting the delta must therefore be associated with the progressive erosion of deposits, overloading middle and high portions of the rivers. This was the result of intense fluvial-torrential and/or mass transportation processes activated in mountainous and hilly areas by the significant rainfall increase of the "Little Ice Age" (M. PINNA, 1984).
Acknowledgements: Research supported by the following research project: MIUR-PRIN 2004, "The influence of climatic variations and/or of land use changes on erosion processes in Mediterranean environment" (Coordinator: G. RODOLFI), sub-project "Impact of rural landscape transformations on slope degradation processes during Holocene and its consequences on the fluvial-coastal system (Adriatic sector of central Italy)" (Local Coordinator: B. GENTILI).