Native civilizations, as that of the ancient Greeks, are directly connected to the geological and the physicogeographical regime of the regional area in which they have been developed, and mainly to its geoenvironmental evolution since the last glacial period (18,000 BP). Volcanoes, earthquakes and mineral resources, as building materials, the underground water and the various minerals, consist the so called geological regime. Soil, climate, relief, shorelines and coastal areas belong to the physicogeographical regime of an area. The regional territory, where the prehistorical and historical ancient Hellenic civilization has been developed is the Hellenic Peninsula, Aegean Sea and the coasts of Minor Asia, from the geotectonic point of view, composing the Hellenic Arc which is characterized by intense tectonic, seismic and volcanic activity. The main factor contributing to the evolution of the Hellenic civilization is the climate and its fluctuations, mainly during the last 18,000 years, and most essentially the impact of these changes in the displacement of the shorelines and the coastal areas in general. It is widely known that climate changes periodically and that the main reasons for this periodicity are astronomical (Milankowitch theory). Thus, during Quaternary, several successive glacial and interglacial periods have been observed due to the increasing and decreasing of the solar radiation that earth receives. The last glacial period ends approximately 18,000 years BP, since, for the same astronomical reasons, earth's mean temperature abruptly increased. Due to this increase, huge volume of glaciers started to melt resulting to the release of large water quantities, which until that time were trapped within the glaciers, resulting in the gradual rise of the global sea level that, around 18,000 years BP, was about 125 m. lower than today. This rise caused successively transgression of all areas that nowadays constitutes the seafloor of Aegean Sea until a depth around 125 m. This transgression happened within a few thousands of years, namely between 18,000 and 6,000 years BP approximately. Therefore, prehistoric man who inhabited the area of the Aegean Sea, though until 18,000 years BP was living for tens of thousands of years in a geoenvironment unfavourable but more or less stable, following 18,000 BP and due to the increase of the mean temperature of the earth's atmosphere, he witnessed cosmogony changes. These especially concern the change of the coastal scene, since year after year, slowly but steadily, coastal areas are being submerged, featuring high mean velocities that under certain conditions should exceed 5 m per year. Together with these shoreline displacements if one takes also into account seismicity, volcanic activity and the related phenomena (tsunamis, abrupt uplift or subsidence of the coastal areas caused by earthquakes, landslides, rockfalls, etc.), the physicogeological scenery should have been a nightmare. The third generation of the Gods must have been originated during this period. This generation is the result of the union of Gaia (Earth), the Big Mother of all, and Ouranos (Heaven), namely Titans, Ekatoncheires, Cyclops and Giants, who might represent the destructive natural powers that terrify man and move the earth under his feet. What else than volcanoes might Giants represent, when, according to the Hellenic Mythology ".... they (the giants) breathed fire from their mouth ...." "...they were crying out wildly....", "they were shooting rocks and blazing trees in the sky "! ? Yet, Paleolithic and Mesolithic man needs to create more gods who will protect him from all these natural disasters. So, he originates the fourth generation that comes out of the union of the Titan Kronos and the Titanide Rhea. In this generation belong some of the great gods, such as Hera, Demeter, Estia, Hades, Poseidon and Zeus. The favorable climate ensures the basic nutrition species that man needs, either he is a food collector or he is a food producer, and especially without any particular effort. This means that it allows prehistoric man to have enough free time. Especially after his inhabitance in towns, he may be continuously mobile in the open space and he may communicate with other men having free time as well. In order to attitude within his small society, he has to learn to discuss, to argue, to oppose, to agree or to disagree with his co-speakers. Yet, all these constitute the basic substantial features of Democracy. All these physicogeographical and geological changes of the mythological and the prehistorical, in general, era, that have determined directly or indirectly all partial settings and the evolution of the civilization itself, should be promoted in such a way that the relationship between physicogeographical environment and civilization should be primarily introduced.
The Hydrothermal Vent Field at the Eastern Edge of the Hellenic Volcanic Arc: The Avyssos Caldera (Nisyros)
