Radon (Rn), a natural colorless, odorless, noble radioactive gas, with a half-life of 3.8 days, is an important source of natural ionizing radiation. It originates from the initial concentrations of uranium and its transmuted daughters in rocks, soil, and finally, waters and tends to be concentrated in closed spaces such as underground mines. The concentration of radon in mines contributes significantly to the increase in the dose of ionizing radiation received by humans visiting, accessing, working in these areas. The comparison of radon concentration in active and inactive mining sites, its effect on human health, and the different concentrations’ upper limits, applicable by state, are discussed in this paper.

The Samaria Gorge is a dominant geomorphological and geological structure on Crete Island and it is one of the national parks established in Greece. Due to the complex tectonics and the stratigraphic ambiguities imprinted in the geological formations of the area, a comprehensive review of the geological models referring to the geological evolution of the area is essential in order to clarify its geomorphological evolution. In particular, the study area is geologically structured by the Gigilos formation, the Plattenkalk series and the Trypali unit. Regarding lithology, the Gigilos formation predominantly includes phyllites and slates, while the Plattenkalk series and the Trypali unit are mainly structured by metacarbonate rocks; the Plattenkalk series metacarbonate rocks include cherts, while the corresponding ones of the Trypali unit do not. Furthermore, the wider region was subjected to compressional tectonics, resulting in folding occurrences and intense faulting, accompanied by high dip angles of the formations, causing similar differentiations in the relief. Significant lithological differentiations are documented among them, which are further analyzed in relation to stratigraphy, the tectonics, and the erosion rate that changes, due to differentiations of the lithological composition. In addition, the existing hydrological conditions are decisive for further geomorphological evolution.