L'intermittenza delle sorgenti del Torbidone nella Piana di Norcia: analisi delle fonti storiche a partire dal XIV secolo

Abstract

In the Norcia plain (Umbria, Central Italy) the springs of Torbidone are characterized by a peculiar behavior, i.e. the periodical appearing and vanishing for years. The reasons of this peculiarity are not yet well defined.In the popular opinion, the springs has a periodicity of 7 years, at least until 1859 afterward the Norcia earthquake that was described in detail by Father Angelo Secchi, when started a more detailed collection of hydrologic data.Many authors described the prodigious of this springs and their periodically appearance. The first citations was in the half of XIV century by Fazio degli Uberti, that in his Dittamondo wrote about the seven years periodicity of the springs.Hereafter, many authors deal with this argument, whether by a scientific or juridical point of view.In recent time, some established a correlation between the seismicity of this part of the Central Apennine and these extraordinary springs; without a doubt, they re-appeared after the extremely intense seismic period that shaked this area in the August - October 2016. In fact, after these events the springs resurfaced again with a very high flow rate of about 1,500 l/s draining the Sibillini Mounts reservoir feed by the Castelluccio Plain hydrogeologic system.The springs disappeared after the 1979 Valnerina earthquake, evoking the correlation between the water flow and seismicity. To limit the increased water volume has been necessary to reshape the original fluvial bed reworked, over the time, by agriculture.This event highlight how the anthropization processes often forget the occurrence of natural events, even if they have short return times or a regular periodic.It is so necessary to understand that the historical research on the original bibliographic sources is essential to reconstruct in the right way the natural events effect, above all for those having a recurrent character.