The substrate of the Rodafnidia Quaternary deposits consists of ignimbrite, the product of pyroclastic pumice flow released during the volcanic activity of the Early Miocene (23-16 My). The hill is bordered to the north by a small stream and to the west by a larger stream, which is fed by the hot springs of Lisvori. The two streams meet northwest of the hill and flow into the Kalloni Gulf, east of the Polichnitos salt pans. In the southern and western sides of the hill, a small gorge has been shaped on the ignimbrite floor, due to tectonics and the flow of the stream. The terrain there is steep and rocky. The northern side of the hill presents a smooth relief with low inclination.
The Palaeolithic hominins lived around an alluvial plain. Across this plain a drainage system for the basin was established. During the lowering of the sea level, the river channels caused deep erosion and pebbles were deposited in their beds (high energy). On the contrary, during the rising of the sea level, fine clastic material was deposited as the area was transformed into a floodplain. By the end of the Middle Pleistocene, due to the tectonic regime, a network of normal and strike-slip faults resulted in rotational movement of blocks. The Rodafnidia hill was created due to the uplift and rotation of such a fault block, which was uplifted to the SE and subsided to the NW. On the south side of the hill, the tertiary sediments have been eroded and the ignimbrite substrate of the archaeological site is visible, while on the north “subsided” side tertiary deposits have been preserved, including the Middle Pleistocene layers with the Palaeolithic artefacts.
Geological analyses and the study of the stratigraphic sequence in Rodafnidia allow the reconstruction of an extensive hydrological network of larger and smaller rivers and streams flowing through this area. During glacial periods, when arid conditions prevailed and the sea level dropped, coarse-grained sediments were deposited into this system, deeply incising the palaeo-riverbeds. During the interglacials, on the contrary, the climate was warmer but wetter, and with the rising sea level the area was flooded and covered with fine-grained sediments, progressively transforming into an alluvial plain. The identification of these successive units, coarse-grained sediments during glacials and fine-grained sediments during interglacials, within the sequence enables the correlation of stratified archaeological finds with their palaeoenvironments, following the succession of the climatic cycles (glacials-interglacials).
Various strands of the research project reveal that southwestern Lesbos not only provided a crossing for the dispersing hominins of the Lower Palaeolithic across the heart of Eurasia but also an area for settlement. The remarkable archaeological visibility here is largely the result of consistent preference by the Acheulean hominins for physiogeographic characteristics such as: the volcanic landscape, which is dotted with hot springs and volcanic rocks; the complex topography with steep rocky formations and higher observation points; and the extensive hydrological network and variable water-fed habitats opening to the impressive Kalloni Basin and Vatera.
During the Middle Pleistocene (780-125 thousand years Before Present), and during the Quaternary period in general, the palaeogeography of Lesbos and the entire Aegean region was subject to alterations due to complex geological processes. Tectonic and volcanic activity along with the effects of eustatic change, leading to gradual but continuous sea-level changes, cause ongoing landscape transformation.
For long periods during the glacials of the Quaternary, the coastal areas of the Aegean expanded as sea levels dropped. Islands were then connected to each other or to the adjacent coasts. During the glacial lowstands, Lesbos was connected to the western coast of Asia Minor by land bridges, now submerged, allowing terrestrial species such as reptiles and mammals, including primates and hominins, to disperse and occupy the island. The latter is confirmed by the fossil remains of terrestrial vertebrate fauna, purely continental, found at the Vatera sites and dated to the beginning of the Pleistocene. This palaeontological assemblage includes among other species the primate Paradolichopithecus arvernensis, the canid Nyctereutes megamastoides, the rhinoceros Stephanorhinus cf. etruscus, the giraffe Palaeotragus cf. inexpectatus and the giant turtle Geochelone atlas. The relatively smooth seabed of the Mytilene strait seems to be the most likely passage; a 50m sea-level drop would connect the island with Anatolia and turn it into a western extension of the Asian coastline.
During periods of lower sea level the two large basins of the island, the Gulf of Kalloni and the Gulf of Gera, were disconnected from the sea. Palaeogeographic evidence suggests that throughout the Middle Pleistocene the gulfs were transformed into huge lakes of brackish and progressively fresh water, attracting animals and hominins. In addition, southwestern Lesbos is covered to a significant degree by volcanic rocks such as ignimbrites, basalts, dacites, andesites, and other rock types such as cherts. The latter are secondary products of geothermal origin, resulting from the Early Miocene volcanism and were abundant in the vicinity of Lisvori-Rodafnidia. Both types of rock were used by Middle Pleistocene hominins for stone tool knapping. To judge from other eastern African and western Asian records, coterminous with the Lisvori-Rodafnidia record, the volcanic landscape of this part of the island presented a familiar setting for the hominins to adapt to and live in.