Radiogeochemistry of Kamchatka soils

Background concentrations of Th and U in volcanic soils (Andosols) of Kamchatka are much lower than their clarkes in continental soils. The dose rate of gamma radiation above the soil surface (10–11.5 µR/h in the south and 8–9.5 m]R/h in the north of Kamchatka Peninsula) is lower than the natural level of this index for the mountainous areas in the boreal zone of Russia. The natural radiogeochemical background of Kamchatka soils is controlled by the petrochemical composition of volcanic ash composing the mineral basis of Kamchatka soils. It is higher in the southern soil province, where soils develop from acidic ashes, in comparison with the northern province, with a predominance of soils developing from ashes of basic and intermediate composition. This agrees with Th and U clarkes for the corresponding types of volcanic rocks and explains the natural origin of the elevated radiogeochemical background in the southern part of Kamchatka as compared with its northern part. The soils of the northern province developing from relatively fresh volcanic ashes show a lower Th/U ratio as compared to the soils of southern Kamchatka because of higher uranium content in the newly deposited ashes.