Geomorphological and Geoarchaeological Evidence of the Medieval Deluge in the Tagliamento River (NE Italy)

Between the second part of the sixth century and the seventh century, many regions of Europe have been characterized by dramatic changes in the hydrographic setting, probably related to a strong cooling phase. In northern Italy, the chronicle of a huge flood event referred by the Lombard historian Paul the Deacon to the autumn of 589 AD has achieved a major importance and induced many researchers to attribute to this “deluge” episode many of the floods occurred during early Middle Age. In this paper, we consider the alluvial system of Tagliamento, which is one of the main rivers fed by south-eastern Alps and experienced a strong avulsion phase between the sixth and eleventh centuries. In that period, the river activated up to three branches and the hydrographical changes strongly influenced the human activity. This work critically reanalyses both published data and new stratigraphic and archaeologic evidence in order to assess and quantify the times and modes of this instability phase. The data suggest the occurrence of an extreme flood event at the end of the sixth century, which was also responsible for the burial of the ancient city of Concordia Sagittaria. The geochronological constraints suggest the possibility that this catastrophic episode occurred in 589 AD, thus confirming the Medieval Chronicle. Anyhow, other alluvial events occurred in the distal plain of Tagliamento River slightly before and after that moment.