High‐resolution magnetic gradient and electrical resistivity tomography survey at the Plaka Petrified Forest Park in Lesvos Island, Greece

Abstract

Lesvos Island, in the North Aegean area of Greece, exposes large accumulations of fossilized tree trunks. They are collectively known as the Petrified Forest of Lesvos, a designated protected natural monument. The paper describes the results of a geophysical study that has been carried out in the area of Plaka on the western part of Lesvos in order to investigate the near‐surface geology and detect buried fossilized tree trunks.In situ and laboratory measurements of magnetic and electrical properties of the trunks have been conducted. Considering the magnetic susceptibility distribution and the contrast between the trunks and the surrounding material, magnetic gradient anomalies of negative signature were expected to reflect the existence of trunks. Electrical resistivity tomography has also been conducted in order to detect buried trunks, based on their resistivity contrast with the pyroclastic surrounding material.Flow paths of the pyroclastic material that can be related to the tectonic features at the time have been detected. In general, petrified trunks have been detected as high resistive bodies. In one case, where the trunk was buried very close to the surface, the resistivity was lower than the surrounding material.2D and 3D subsurface resistivity models of the surveyed area have been constructed, pointing out probable locations of buried petrified trunks. Excavations that followed the geophysical survey revealed petrified trunks in most of the cases although some of the excavated resistive targets proved to be surface fracture systems filled with resistive oxides.