The large and destructive 1669 AD Etna eruption: reconstruction of the lava flow field evolution and effusion rate trend.

Abstract

The 1669 AD flank eruption was the most destructive event on Etna volcano in historical times (~700 BC) and provided, because of the presence of numerous quarries and subsurface data, the opportunity for a unique case study in which we directly measured the thickness of the lava field. Moreover, analysis of historical documents allowed reconstruction of the temporal evolution of the lava field and estimation of the average effusion rate. One hundred and thirty eight thickness measurements, acquired from field surveys and subsurface data, allowed us to divide the lava field into twelve zones of homogenous mean thickness and to calculate a total lava volume of (607 ± 105) × 106 m3, corresponding to an average effusion rate of 58 ± 10 m3/s. This new volume differs by −24% up to +64%, from previously published values. The temporal evolution of the cumulative volume and average effusion rate were reconstructed for the first fourteen days, from field data and analysis of historical records. A short initial phase was characterized by a rapid increase in effusion rate, which reached a peak of ~640 m3/s after three days. This was followed by a longer phase in which the flow rate decreased. The first fourteen days were crucial for the development of the lava field, and in this time it covered 72% of its final area and produced most of the damage. Thereafter, the growth of a complex lava tube network promoted lava field lengthening to the city of Catania, 17 km away from the vent. Effusion rate trends like those of the 1669 eruption can be adopted for future investigations aimed at assessing the effects of similar events on Etna’s most highly urbanized area and at other effusive basaltic volcanoes.