Short communication Flank eruptions of Mt Etna during the Greek–Roman and Early Medieval periods: New data from 226 Ra– 230 Th dating and archaeomagnetism Stefano Branca a, ⁎, Michel Condomines b , Jean-Claude Tanguy c a Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo, Piazza Roma 2, 95125 Catania, Italy b Géosciences Montpellier, Université de Montpellier and CNRS, Place Eugène Bataillon, 34095 Montpellier Cedex 5, France c Institut de Physique du Globe de Paris, 94107 Saint-Maur des Fossés Cedex, France abstract article info Article history: Received 10 June 2015 Accepted 2 September 2015 Available online 11 September 2015 Keywords: Etna volcano 226 Ra– 230 Th dating Archaeomagnetic dating Flank eruption In this paper, we present new data from 226 Ra– 230 Th dating and archaeomagnetism with the aim of improving the knowledge of the flank eruptions that occurred at Mt Etna during the Greek–Roman and Early Medieval periods, as defined in the new geological map of the volcano. The combination of the two dating techniques demonstrates that three major flank eruptions occurred on the lower north and west flanks during Greek–Roman epochs, producing large scoria cones and extensive lava flows. In particular, the Mt Ruvolo and Mt Minardo events highly impacted the territory of the west flank, notably by damming the Simeto River. The new data of the Millicucco and Due Monti lava flows, on the lower north–east flank, indicate a younger age than their stratigraphic ages quoted in the 2011 geo- logical map, since they occurred around 700 and 500 AD, respectively. None of the large flank eruptions occurring on the lower slopes of Etna during the Early Medieval age are reported in the historical sources. Overall, our paper shows that a comprehensive assessment of eruptions at Mount Etna in the last three millennia can only be achieved through a multidisciplinary approach. © 2015 Elsevier B.V. All rights reserved. 1. Introduction The eruptive activity of Mount Etna (Italy) during historical time is one of the most studied and best documented for a volcano worldwide, starting from the early geological investigations performed by Sartorius von Waltershausen (1843–1861) between 1836 and 1843. Recently, improvements in the knowledge of the eruptive activity related to the flank eruptions of the past 2400 years have been made through cross- correlation between geological and stratigraphic data (Branca et al., 2011) and age determinations of the lava flows (Tanguy et al., 2007, 2012). During the drafting of the new geological map of Etna volcano at 1:50,000 scale, several Holocene tephra marker beds were used to better constrain the age of the lava flows erupted during the Mongibello activity (b 15 ka, for details see Branca et al., 2011). Concerning the his- torical period, the pyroclastic fallout deposit of the 122 BC plinian erup- tion (FS tephra layer of Coltelli et al., 1998) is a marker bed used to constrain the stratigraphic age of recent lava flows. The 122 BC pyroclas- tic deposit shows a southeast dispersion, so that its stratigraphic rela- tionships with the lava fields in this area of Etna are well defined. Moving away from the area of dispersion, there is a progressive increase in the uncertainties of the stratigraphic position of lava flows due to the discontinuity of outcrop and\or absence of the 122 BC deposit. In this paper, we present new age determinations obtained with the 226 Ra– 230 Th and archaeomagnetic techniques of several large lava flow fields characterized by uncertain stratigraphic relationships with the Holocene tephra marker beds (Fig. 1). We show that most of these flows belong to the Greek and Roman epochs or Early Medieval age, thus allowing a re-evaluation of historical flank eruptions of Mt Etna be- fore 1000 AD. This is therefore an important contribution to the strati- graphic reconstruction defined in the 2011 geological map. 2. Principles of archeomagnetic and 226 Ra– 230 Th dating Archeomagnetic dating was performed through the large sample method already discussed in Tanguy et al. (2003, 2007). However, this method only gives reliable ages for samples of the last 2400 years. This is important because the direction of the geomagnetic field (DGF) during its secular variation (SV) makes several loops that intersect as shown in Fig. 2 (for instance the DGF was the same around 1650 and 750 AD, and again during the Greek epoch), leading to an increasing number of ambiguities on ages when going back further into the past. For a few lavas of which paleoDGFs (pDGFs) lead to several possible magnetic ages or undetermined prehistoric ages, the problem can be solved by using the 226 Ra– 230 Th dating method (Condomines et al., 1995, 2005). This method, though less precise (ages determined within centuries) than archaeomagnetism (ages within decades), gives independent results Journal of Volcanology and Geothermal Research 304 (2015) 265–271 ⁎ Corresponding author. Tel.: +39 0957165820; fax: +39 095435801. E-mail address: stefano.branca@ingv.it (S. Branca). http://dx.doi.org/10.1016/j.jvolgeores.2015.09.002 0377-0273/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Volcanology and Geothermal Research journal homepage: www.elsevier.com/locate/jvolgeores