The Albano Maar Lake High resolution bathymetry and dissolved CO2 budget (Colli Albani District, Italy): constrains to hazard evaluation

The Albano Lake is the deepest volcanic lake in Italy and fills the youngest maar of the quiescent Colli Albani volcano. The lake has undergone dramatic level changes and overflows about ~5800 yrs B.P. and likely in 398 b.C., when Romans excavated a tunnel drain through the maar wall. Hazardous lake rollovers and CO2 release are still possible because the Albano volcano still shows active ground deformation, gas emissions and periodic seismic swarms. On November 2005, the first very high resolution bathymetric survey of the Albano Lake was performed. Here we show results provided by a Digital Elevation Model and 2-D and 3-D images of the crater lake floor which is made by coalescent and partly overlapping craters. Submerged shorelines have been identified at various depths and indicate the occurrence of lake level changes. The current lake volume is ~447.5 x 106 m3 and its critical value for outflow is ~895.7 x 106 m3. The total quantity of dissolved CO2 has been estimated to 6846 tons by chemical analyses of samples collected on May 2006. A decrease of one order of magnitude of the CO2 dissolved in the lake water below - 120 m, observed from December 1997 to May 2006 (from 4187 to 465 tons respectively), has been attributed to lake water overturn.