Three-dimensional reconstruction of the main unconformities of the Colli Albani stratigraphy and deposit volume calculations
G. Diano, A. Bonamico, G. Giordano, 2010. "Three-dimensional reconstruction of the main unconformities of the Colli Albani stratigraphy and deposit volume calculations", The Colli Albani Volcano, R. Funiciello, G. Giordano
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The quiescent Colli Albani volcano is composed of overlapping edifices, with each showing changes in volcanic style over the 600-ka history of the volcanic field. The edifices and changes in eruption style through time are indicated in the field by the major unconformities, which have been identified from surface geology and borehole stratigraphies. This reconstruction of the major unconformities allows for three-dimensional geometric reconstruction of the relevant rock packages, computation of the deposit volumes, and evaluation of syn-volcanic tectonic or volcano-tectonic activity. Furthermore, some rock packages, such as the Pisolitic Tuffs, the Tufo Lionato and the Albano maar deposits, are characterized by relatively low permeability, and are therefore essential for modelling of the hydrogeological circulation and flow of volcanic gases. The reconstructions of the isopachs of the three main caldera-forming ignimbrites erupted between 460 and 355 ka have allowed the calculation of their minimum preserved extracaldera volumes at 59 km3 (Pozzolane Rosse), 20 km3 (Pozzolane Nere) and 30 km3 (Villa Senni Fm.) respectively. The total volume of volcanic deposits erupted after the last caldera collapse (<355 ka) is calculated as 34.7 km3. The preserved deposits of the most recent Albano polygenetic maar have been calculated to be 0.9 km3.
The total minimum deposit volume of the Colli Albani volcano is 208.1 km3. This volume does not include the intracaldera ignimbrite volumes which may add some 80 km3 to the total volume.
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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.