The Pilato Lake has glacial origin, is located in the Sibillini Mountains, Central Italy and houses a particular endemism unique in the world: the small cruostaceous Chirocephalus marchesonii.
In the context of a research agreement with the Monti Sibillini National Park, ISPRA is carrying on some studies aimed to evaluate the effects of the 2016–2017 Central Italy earthquakes on the hydrogeological conditions controlling the lake’s evolution.
The study, started in July 2018, aims primarily at the reconstruction of the subsoil setting beneath the valley hosting the lake, both in terms of geological and hydrogeological boundaries. In order to define the conceptual model of groundwater circulation and, thus. to evaluate the emptying and recharge seasonal cycle of the lake, hydrogeological surveys and geophysical investigations were performed.
A drone photogrammetric survey allowed a preliminary reconstruction of the lake basin bathymetry that allowed, in turn, the calculation of the water basin volumes in the various observed periods, the estimate of evaporation from the lake surface and the comparison with the information relating to previous years compared to the present study.
The velocity profiles of the seismic surveys have estimated the maximum thickness of debris (detrital and glacial sediments on top of calcareous bedrock) equal to about 12-15 m. Further investigations through GPR will be addressed to the better definition of the geological boundaries.
The physical-chemical characteristics of the waters (T=12-13°C; pH=8-9; EC=60-125 µS/cm) are consistent with those of stagnant and slightly oxygenated waters. The low value of EC of the lake's waters is in accordance with the prevailing provenance of the lake's recharge by snow melting and precipitation.
The research program is still in progress and to date we can propose only preliminary remarks. The hydrogeological survey showed the absence of geomorphological evidence of earthquake ruptures: the crisis situation of the lake level in the summer of 2017 was probably due to the dry and warm meteo-climatic conditions of winter-spring 2016-2017.
The lake level from its maximum flooded quota in May-June 2018 (completion of snow melting) falls down rather rapidly to the elevation of the Fonte del Lago, which acts as an overflow, and then declines more slowly due to evaporation and infiltration through the soil of its bed down to the minimum levels which, in particularly arid years, lead to its drying out.