Suppl. Geogr. Fis. Dinam. Qua!. III, T. 2 (1997), 105-121, 16 figg. FOURTH INTERNATIONAL CONFERENCE ON GEOMORPHOLOGY - Italy 1997 Guide for the excurSlon FUNDAMENTS FOR A GEOMORPHOLOGICAL OVERVIEW ON ROMA AND ITS SURROUNDINGS P. BELLOTTI C), C. CAPUTO C), S. CICCACCI C), D. DE fuTA (2), S. DONATI (), P. FREDI C), R. FUNICIELLO (), G.B. LA MONICA C), B. LANDINI C), F. MARRA (), S. MILLI (\ M. PAROTTO () & F. PUGLIESE C) Eds.: C. CAPUTO INTRODUCTION a kind of umbilical cord between the «Mater Roma» and (C. Caputo) the Mediterranean Sea coasts along which the mighty Ro­ man Empire rapidly developed and spread out. In this synthetic guide the main aspects which distin­ The Monti Sabatini alkaline-potassic volcanic district guish the landscape of the area around Roma are descri­ had a prevailingly explosive activity from a great number of bed; it gives an easy geological and morphological descrip­ emission centres; they are mainly concentrated in the ea­ tion of the EternaI City and its surroundings, which can be stern sector and around the large depression holding the visited during a short field trip. Lago di Bracciano and erupted a remarkable volume of vol­ The first of these aspects is represented by the landsca­ canic products. Especially the emplacement of pyroclastic pe of the four large Quaternary volcanic complexes of La­ flows can be considered the main responsible of the gene­ tium. It is mainly on the products of two of these volcanic rally flat morphology of the Campagna Romana (or Agro complexes that Roma is built: they are the Monti Sabatini, Romano). This area is 2,000 km2 large and is bordered by to the NW, and the Colli Albani to the SE of the city. Ro­ the Monti Sabatini, the Colli Albani, and the south-western ma and its morphological features, strictly connected with carbonate reliefs of the Latium pre-Apennines and is passed the Quaternary volcanic activity and the human presence through by the lower course of the Fiume Tevere which, af­ since antique times, is the second outstanding landscape. ter having crossed Roma, flows into the Tyrrhenian Sea. Finally the third important landscape of the area around The expansion of Roma has been with no doubt linked Roma is that of the flat region extending from the city to to the many historical events which followed one another the Tyrrhenian Sea and forming, on the whole, the delta of during more than 2,000 years. Nevertheless, many diffe­ the Fiume Tevere which had a prominent role in the hi­ rent factors controlled the development of Roma; among story of Roma. Actually its waters have always represented them the natural ones surely had a very important role. For instance, the unbalanced expansion of the city astride the Fiume Tevere, can be explained on morphological basis. (l) Dipartimento di Scienze della Terra, Università degli Studi «La Sapien­ In fact, on the hydrographical right side of the river the hi­ za», Roma, Italy. gher ridge of the Vatican hills acted like a blockage. On (2) Dipartimento di Scienze Geologiche, Università degli Studi Roma Tre, Roma, Italv. the contrary, the smoother Seven Hills and the infra-hill (3) Dipartz~11ento di Geologia e Geofisica, Università degli Studi di Bari, Italy. areas, ~n the river left sides, represented a more suitable Work financially supported by: Ministero dell'Università e della Ricerca pIace where a more harmonious expansion could take pIa­ Scientzfica e Tecnologica, Consiglio Nazionale delle Ricerche, Università de­ ce. Moreover, especially the expansion of Roma has been gli Studi di Roma «La Sapienza» (Pro! E. Lupia Palmieri). The relative ex­ conditioned by the existence of numerous creeks and mar­ cursion has been patronized by the Regione Lazio and the Comune di Roma shes; however also the geological arrangement was impor­ and financially supported by: Università degli Studi di Roma «La Sapien­ za», Consiglio Nazionale delle Ricerche, Ministero dell'Università e della tant, as it determined which areas were more or less prone Ricerca Scientifica e Teconologica. • to sliding. 105 If the above mentioned conditions have controlled the (Ostia Antica), burial areas (Necropoli di Porto on the Iso­ development of Roma «town of the living», the same must la Sacra) or simply roads (Via Severiana). Also different te­ be said for the «necropolis», generally placed along the stimonies come from the Classics. Among these worth of main consular roads and, according to Roman laws, outsi­ being mentioned is PLINIO IL GIOVANE (Pliny the Youn­ de the town walls. The most renowned sepulchral area is, ger; I-II cento A.D.); he frequently provides accounts of perhaps, the Appian way (the famous Via Appia, «Regina different natural phenomena with the utmost sciemific Viarum» of the Romans) which winds, starting about 3 km exactitude. from Porta San Sebastiano (to the South of Roma) on The accretion of the Fiume Tevere delta lasted for a an important lava flow connected with the Colli Albani long time, but during the past 50 years changes imo an op­ activity. posite trend were observed and erosion processes affected After Christianity gained the upper hand over pagani­ the delta. This obviously caused serious troubles to the sm, other burial areas arose: the catacombs. One example coastal centres and specifically to Lido di Ostia, an area may be the Catacombs of Priscilla, near the Via Salaria, which is by now integraI part of Roma. As a consequence which develop in hypogaea, cubicula and galleries of diffe­ extensive defences had to be built. rent length within the pyroc1astic products of the Monti In view of the above comments, the main morphologi­ Sabatini volcanic complex. cal characteristics of a vo1canic complex (Monti Sabatini), Both the Sabatini and the Colli Albani vo1canic com­ the City of Roma, and the Tevere delta with its shore will plexes have conditioned in time the flowing of the Fiume be described in following pages. Tevere which, with its solid supply, was gradually building up its delta through different stages: from a wide lagoon to a more and more well-marked delta body. During histori­ THE MONTI SABATINI VOLCANIC COMPLEX cal times the Tevere delta was affected by continuous ­ (P. Fredi, S. Ciccacci & D. De Rita) although at changeable rates - accretion; many archaeologi­ cal witnesses testify to the great importance of this area in The Monti Sabatini vo1canic district is located in the Roman life. And these same witnesses offer a valuable northern-central Latium, about 20 km to the North-West aid for the study of the evolution itself; they are towns of Roma and it is bordered to the North by the Vico volca- FIG. 1 - Roma and its surroun­ dings. At the cemre of the picture is the meandering course of the Fiume Tevere, which, after ha­ ving crossed the City of Roma, flows imo the Tyrrhenian Sea th­ rough its typical delta. On the ri­ ght side oE the river, part of the Monti Sabatini volcanic complex with the Lago di Bracciano and the smaller Lago di Martignano. On the river left side the volcanic edifice of Colli Albani with the Albano and Nemi crater lakes (LANDSAT 4,1983). 106 no, to the West by the Monti della Tolfa, to the South by Graben-like structure; it was characterized by differentiate the Tevere lower valley and to the East by the Monte So­ chemism and is not considered part of the «Provincia Ro­ ratte-Monti Cornicolani structure. This volcanic district, mana» but of the acidic «Tuscan volcanic Province» (LAU­ together with the other Latian volcanic districts, Monti RO & NEGRETTI, 1969). Vulsini and Vico (to the NW of Monti Sabatini) and Colli In the eastern sector of the Sabatini district, the first Albani (to the SE of Roma), is part of the «Provincia Ro­ volcanic activity began at the margin of the Monte Soratte­ mana», a K-alkaline volcanic province, which developed Monti Cornicolani structure. At present the most ancient mainly during the Pleistocene and that has been active up eruptive centre is not morphologically recognizable, but it to recent times. This volcanic province originated in an should have developed about 0.60 Ma ago, between the area characterized by the presence of a series of buried me­ small towns of Morlupo and Castelnuovo di Porto. The so-cenozoic structurai highs and Iows elongated with an products of this centre Iay directly on the Plio-Pleistocene Apennine (NW-SE) direction. Such a trend is connected sediments; they consist of a trachytic lava flow followed by to a Plio-Pleistocene tectonic phase which affected the a thick sequence of fall and surge Ievels. The activity ended whole centraI Tyrrhenian area. with the emplacement of a hydromagmatic pyroclastic flow The structurai setting of the area where the Sabatini which testifies for magma/water interactions. volcanic complex developed can be sketched as a Iarge During the Iast stage of Morlupo-Castelnuovo di Porto Graben-like structure Iimited to the West by the Monti activity volcanism started aiso in the westward area, where della Tolfa structurai high and to the East by the Monte the Sacrofano centre developed. This centre is one of the Soratte-Monti Cornicolani sedimentary structure; in the major volcanic features of the Sabatini district because centraI-eastern sector of the main Graben there are secon­ of its long period of activity which Iasted from 0.55 Ma dary structurai highs such as the Cesano-Baccano one (fig. ago untii about 0.30 Ma ago, when the caldera collapse 2). The areaI distribution of the Plio-Pleistocene marine se­ occurred. diments shows that this structurai setting was already exi­ In its first stage Sacrofano activity was mainly vulcanian stent before the volcanism started.