RADON EMANATION FROM GIANT LANDSLIDES OF KOEFELS (TYROL, AUSTRIA) ANDLANGTANG-HIMAL (NEPAL)

The identification of extremely high indoor radon concentrations in th e village Umhausen (Tyrol, Austria) initiated a scientific program to get information about the source and distribution of this noble gas. T he high concentrations can not be related to U anomalies or large-scal e fault zones. The nearby giant landslide of Koefels, with its highly fractured and crushed orthogneisses, are the only possible source of r adon, despite the fact that the U and Ra content of the rocks is by no means exceptional. The reasons for the high emanation rates from the landslide are discussed and compared to results gained from a similar examination of the giant landslide of Langtang Himal (Nepal). The exce ptional geologic situation in both cases, as well as the spatial distr ibution of different concentration levels, indicate that both landslid es must be considered as the production sites of radon. Independent of the U and Ra contents of the rocks, the most important factors produc ing high emanation rates are the production of a high active surface a rea and circulation pathways for Rn-enriched soil air by brittle defor mation due to the impact of the landslidemass.