The three-dimensional structure of the Colli Albani volcano
In this paper we describe the structural architecture of the Colli Albani from the sedimentary cover to the upper mantle. The regional stratigraphy, deep wells and sedimentary xenoliths embedded in the pyroclastic deposits have been considered in order to constrain the composition and structure of the sedimentary substratum, whereas the lithospheric structure of the volcano has been investigated using seismic tomography and receiver function analyses. The main features at depth are a sub-horizontal Moho located at 20–24 km and a low velocity in the uppermost mantle. The Moho separates two anisotropic regions, one located in the uppermost mantle and a second in the lower crust. The anisotropic fabric can be interpreted as being due to a sub-vertical flux in the mantle coherent with the magma uprise from a mantle source. Seismological analyses do not discriminate velocity reductions ascribable to melt in the shallow crust. An intrusive body, which up-domed the limestone layer, is present beneath the central part of the volcano at depths greater than 5 km. These data are in agreement with the position of the magma chamber deduced by the presence of thermo-metamorphic xenoliths related to dolostone and limestone protolithes, which represent the lowermost portion of the Mesozoic–Cenozoic sedimentary sequence.
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The Colli Albani volcano (also Alban Hills volcano) is the large quiescent volcanic field that dominates the Roman skyline. The Colli Albani is one of the most explosive mafic calderas in the world, associated with intermediate to large volume ignimbrites. At present it shows signs of unrest, including periodic seismic swarms, ground uplift and intense diffuse degassing, which are the main short-term hazards. New studies have discovered deposits related to previously unknown pre-Holocene and Holocene volcanic and phreatic activity. In the fourth Century B.C.E. Roman engineers excavated a tunnel through the Albano maar crater wall to keep the lake from breaching the rim and flooding the surrounding countryside, events that had previously destroyed this region several times.
The Colli Albani Volcano contains 21 scientific contributions on stratigraphy, volcanotectonics, geochronology, petrography and geochemistry, hydrogeology, volcanic hazards, geophysics and archaeology, and a new 1:50 000 scale geological map of the volcano. The proximity to Rome and the interconnection between volcanic and human history also make this volcano of interest for both specialists and non-specialists.