Search

Many characteristics of the natural environment where Rome has developed for the last 3000 years have played a major positive role in promoting the excellence of Rome as a political, economic and administrative power, the so-called Caput Mundi of the ancient world. Aside from anthropological and ethnological factors, the positive geological and geomorphological setting of the future site of Rome favoured the settlement of several archaic villages along the left bank of the Tiber River since the beginning of the third millennium B.P. The sites were strategically located, being characterized by proximity to the river, over isolated tufaceous cliffs dominating the alluvial plain, the abundance of spring water and the wide availability of stones and natural building material that promoted a quick technological development of building and infrastuctural services to the growing town. The main natural factors playing a strategic role in the development of the long-lived city of Rome have been: - The geomorphology of the distal volcanic plateau - Tiber river network and the related alluvial deposits - The surface geology and its natural materials - The hydrogeology and microclimatic constraints

According to the historical sources, the Colosseum suffered several types of damage related to earthquakes. In particular, the damage is mostly concentrated in the southern portion of the amphitheater where the study of the geological features shows the presence of a Holocene alluvial valley, a situation that is potentially responsible for significant amplification of ground motion during earthquakes. A detailed reconstruction of the subsurface geology in the area of the Colosseum was performed with the purpose of verifyipg whether the heterogeneity of the damage observed could be associated with the variability of the geological conditions of the site where the monument was built.

Some deep wells (1400–3000 m) have been drilled into the volcanic system of the Sabatini Mts., north of Rome, in search of high enthalpy geothermal fluids. Baccano caldera has formed over a carbonate structural high with a Quaternary volcanic cover, on the inside of a large graben that developed from the Upper Miocene and is characterized by a strong positive thermal anomaly. A spatially irregular Neogenic neoautochthon cycle, an allochthonous flysch complex (‘Sicilidi’ s.l.) and a Meso-Cenozoic ‘basal’ carbonate sequence were recognized in the sediments crossed by these wells below the volcanic cover. The observed structural setting can be correlated to that of analogous outcropping structures (Mt. Soratte) and shows a tensional tectonic phase overlying an older, mainly compressional phase. The stratigraphic and mineralogic analyses revealed important differences in the Trias, which is mainly calcareous in the western sector of the area and anhydritic in the eastern: the two facies at present seem to be tectonically brought closer to one another. The isotopic analyses all show values comparable to those of the sedimentary carbonate host rocks, suggesting limited circulation of the hydrothermal fluids. 18 O/ 16 O analyses on specimens in the most restrictive locations next to interfaces show a relatively larger extent of isotopic exchange with aqueous fluids. Fluid circulation, which is mainly extinct, seems to belong to a closed system. Two types of circulation have been recognized: the first of these is connected to the stratigraphic discontinuities (especially at the contact between the allochthonous flysch complex and the basal carbonate sequence) and is characterized by mainly K-feldspar and Sulphide-Sulphate mineralizations; the second circulation is tied to the fracture systems and is particularly widespread in the pyroclastic cover where it appears in the form of sulphate- and carbonate-rich dykes. This system seems to have undergone a mixing with surface waters.

The characteristics of wind erosion as the dominant process involved in eroding crater ejecta deposits on Mars are studied. Present-day crater formation in mid to high latitudes involves impact into some thickness of aeolian debris, while impact in the equatorial zone is more likely to involve target materials consisting of coarse-grained aeolian lag deposits or even bedrock. Latitudinal variation dominates differences in ejecta emplacement mechanisms and probably differences in patterns of wind erosion of ejecta and surrounding intercrater materials. Escarpments develop as the deposits are eroded back toward crater rims. Erosion only takes places at escarpment edges where surface roughness may be low enough to allow particle entrainment. Preferential preservation of ejecta emplaced in thick debris may occur. An empirical model developed for wind erosion of ejecta deposits in nonmantled areas suggests that removal of ejecta materials on the average is exceedingly slow. Results suggest high differential aeolian erosion rates that are a function of both grain sizes and large-scale surface roughness.

New results for the Colli Albani volcano (Roma, Italy) surveyed for the Geological Map of Italy at 1:50,000 scale (CARG Project), integrated with previous data, provide insights on caldera evolution. The Colli Albani, a quiescent volcano, became active at ∼600 ka. Eruptive compositions are consistently mafic ( 50 km 3 deposits), forming the Villa Senni Eruption Unit ignimbrites at ca. 355 ka, two edifices were built within the caldera: (1) The horseshoe-shaped Tuscolano-Artemisio (TA) composite edifice (or lithosome) consists of coalescing, peri-caldera, fissure-related scoriae cones interbedded with lava flows; the fissure system forms two segments controlled by regional fractures; (2) The steep-sided Faete stratovolcano (949 m a.s.l.) filled the caldera. The TA and Faete lithosomes partly interfinger and were emplaced at ∼350–260 ka. Their products indicate reduced eruption rates relative to the VL period and a change to effusive and mildly explosive eruptions. The most recent and still active phase of phreatomagmatic activity formed overlapping maars and tuff cones along the western and northern slopes of the volcano, collectively named Via dei Laghi composite lithosome. The Colli Albani caldera is poly-phase: (1) a piecemeal caldera is associated with large volume ignimbrites of the VL edifice; the present shape of the caldera is related to the Villa Senni eruption; 2) the TA composite edifice, erupted from peripheral-caldera fissures, is unrelated to explosive phases of caldera collapse: the TA final products cover a morphologically stable caldera wall. The peripheral fractures feeding the TA composite edifice are interpreted as volcano-tectonic structures activated during the late stage downsag of the caldera. Reduced eruption rates during the TA and the Faete stages (10 −1 km 3 /1 ka respect to >10 0 km 3 /1 ka for the VL edifice) suggest a reduced recharge of the magma chamber that may have induced prolonged deflation and downsagging of the caldera floor and the opening of outward dipping peripheral fractures. By this interpretation, the TA edifice represents the surface expression of ring dykes at depth. The absence of similar fissure-structures along the western caldera rim may relate to the deep geometry of the ring-faults dipping inward in those areas and therefore not favourably oriented for magma intrusion during a period of general subsidence. By contrast, the following and still active phreatomagmatic phase, that has emplaced the Via dei Laghi composite edifice, is located right on the western side of the caldera, and may therefore relate to resurgent conditions. Classical petrological and PERs (Pearce Elements Ratios) analyses indicate that lavas are co-genetic and show a differentiation trend up through stratigraphy driven by

[1] A century after the catastrophic event, the sources of the 1908 Messina, Southern Italy, earthquake and tsunami, which caused at least 60,000 deaths, remain uncertain. Through a simple backward ray-tracing method, we convert the tsunami travel-time data reported in a 100-years-old paper into distances and find that the sources of the earthquake and tsunami are different. Overturning a long-held assumption, reconsideration of the available tsunami, bathymetric, seismic, and seismological data indicates that the tsunami was generated by an underwater landslide.

ARTICLE I NFO The depositional and erosional history of the Lapis Tiburtinus endogenic travertine located circa 25 km to the east of Rome, Central Italy, near the Colli Albani quiescent volcano, is interpreted through three-dimensional stratigraphy and uranium-series geochronology. Analyses of large exposures located in active quarries and of cores obtained from 114 industrial wells reveal that the travertine deposit is about 20 km 2 wide and 60 m thick on average. The travertine thickness is over 85 m toward its western N-S-elongated side, where thermal springs and large sinkholes occur aligned over a seismically-active N-striking fault. The travertine age was calculated using the U/Th isochron method. Results constrain the onset and conclusion of travertine deposition at about 115 and 30 ka, respectively. The three-dimensional study of the travertine shows that this deposit is characterized by a succession of depositional benches grown in an aggradational fashion. The benches are separated by five main erosional surfaces, which are associated with paleosols, conglomerates, and karstic features. This evidence shows that the travertine evolution was mostly controlled by water table fluctuations. Chronological correlations between travertine evolution and paleoclimate indicators suggest that the travertine deposition was partly modulated by climate conditions. Other influencing factors may have been fault-related deformation and volcanic events.

Integrated petrological and structural investigations of eclogites from the eclogite zone of the Voltri Massif (Ligurian Alps) have been used to reconstruct a complete Alpine P-T deformation path from burial by subduction to subsequent exhumation. The early metamorphic evolution of the eclogites has been unravelled by correlating garnet zonation trends with the chemical variations in inclusions found in the different garnet domains. Garnet in massive eclogites displays typical growth zoning, whereas garnet in foliated eclogites shows rim-ward resorption, likely related to re-equilibration during retrogressive evolution. Garnet inclusions are distinctly different from core to rim, consisting primarily of Ca-, Na/Ca-amphibole, epidote, paragonite and talc in garnet cores and of clinopyroxene ± talc in the outer garnet domains. Quantitative thermobarometry on the inclusion assemblages in the garnet cores defines an initial greenschist-to-amphibolite facies metamorphic stage (M1 stage) at c. 450-500 °C and 5-8 kbar. Coexistence of omphacite + talc + katophorite inclusion assemblage in the outer garnet domains indicate c. 550 °C and 20 kbar, conditions which were considered as minimum P-T estimates for the M2 eclogitic stage. The early phase of retrograde reactions is polyphase and equilibrated under epidote-blueschist facies (M3 stage), characterized by the development of composite reaction textures (garnet necklaces and fluid-assisted Na-amphibole-bearing symplectites) produced at the expense of the primary M2 garnet-clinopyroxene assemblage. The blueschist retrogression is contemporaneous with the development of a penetrative deformation (D3) that resulted in a non-coaxial fabric, with dominant top-to-the-N sense of shear during rock exhumation. All of that is overprinted by a texturally teamphibolite/greenschist facies assemblages (M4 & M5 stages), which are not associated with a penetrative structural fabric. The combined P-T deformation data are consistent with an overall counter-clockwise path, from the greenschist/ amphibolite, through the eclogite, the blueschist to the greenschist facies. These new results provide insights into the dynamic evolution of the Tertiary oceanic subduction processes leading to the building up of the Alpine orogen and the mechanisms involved in the exhumation of its high-pressure roots. © 2005 Blackwell Publishing Ltd.