Hydrogeology of the Colli Albani volcano
This study, based on numerous investigations previously conducted by the Authors, was carried out for different purposes, in the field of water resource management. The hydrogeological setting of the Colli Albani Volcano was defined by using a large stratigraphic database, the data of which were processed with GIS and numerical aquifer modelling methodologies. The process made it possible to reconstruct the fundamental geological surfaces and, from them, the local hydrogeological complexes. The complexes were then associated with permeability values obtained from in-hole hydraulic tests. After numerous surveys, detailed piezometric maps were built. The maps describe the morphology of the top of the saturated zone referred to the basal groundwater system. Based on the geometry obtained, the ‘Colli Albani’ Hydrogeological Unit has been subdivided into hydrogeological basins.
In the Colli Albani area, streams (particularly in their terminal section) are in close relationships with groundwater. Under natural conditions, these relationships control the flow of groundwater towards the catchment area. At present, however, lowering of saturation levels is causing a sharp decrease in stream-bed discharge and often a reversal of the directions of groundwater flow. Water budgets were computed for the overall hydrogeological system and for each hydrogeological basin. The computations considered not only the natural parameters of outflows and inflows to and from the hydrogeological system, but also human activities having a major impact on aquifer recharge. So far, water withdrawal from the two basins has exceeded the availability of and strongly depleted the local renewable water resources. The paper also presents maps describing the physico-chemical characteristics of groundwater in the study area and isopleths of their electrical conductivity and temperature values.
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The Colli Albani Volcano
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.