A GIS-based application to volume estimation and spatial distribution analysis of tephra fallout: the 122 BC Etna eruption case study

Abstract

In this work we show the use of a geo-spatial information system (GIS) for the volume estimation of fallout deposits and for the identification of syn- and post-eruptive depositional mechanisms. For the first time, we present thickness distribution maps, isopachs maps and fallout deposit volume for the single stratigraphic units (A-F) of the 122 BC Plinian eruption of Etna, the most powerful eruption of this volcano in historical times. Thickness data collected during the field survey were organised in a geo-referenced database and several interpolation algorithms were used to calculate the volumes of the six fallout layers of eruption (units A-F). Results have been compared with those obtained using the Pyle’s method that bases volume calculation on the exponential thickness-decay law of the deposits. Differences in 20 results of the two methods have been analyzed applying 2 and 3D geo-statistical analysis to thickness data and an “ideal” fallout deposit has been used as a reference. Our approach allowed both the identification of stratigraphic sections which deposits were affected by secondary erosional or accumulation phenomena, and the assessment of whether the secondary processes were caused by local morphologic conditions or variation in eruptive dynamics (e.g. rotation of the dispersal axis direction).