Browsing by Author "Raukas, Anto"

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    Hazardous radioactivity levels and heavy mineral concentrations in beach sediments of Lake Peipsi, northeastern Estonia
    (Instytut Geologii UAM, 2018-04) Järvelill, Johanna-Iisebel; Koch, Rein; Raukas, Anto; Vaasma, Tiit
    The present study discusses results of heavy mineral analyses and radioactivity of beach sediments of Lake Peipsi. Such analyses are commonly done globally, but had not yet been conducted for the fourth largest lake in Europe. The average heavy mineral content in Lake Peipsi beach sediments along the northern and western coast is higher than usual for Estonian coastal and Quaternary sediments. Concomitantly, elevated radioactivity levels have been measured in sev- eral places, with the highest concentrations observed at Alajõe (1885.5 Bq/kg), which is over five times more than the recommended limit. The aim of the present study is to find sites with higher radioactivity levels, because the northern coast of Lake Peipsi is a well-known recreational area.
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    Quaternary deposits and weathered bedrock material as a source of dangerous radon emissions in Estonia
    (Instytut Geologii UAM, 2015-06) Petersell, Valter; Jüriado, Krista; Raukas, Anto; Shtokalenko, Mihkel; Täht-Kok, Krista
    The risk of dangerous radon emissions in Estonia is high, being among the highest in Europe. In almost 33 per cent of Estonian land area, the content of radon in soil-contained air exceeds the safe limit for unrestricted construction (50 kBq/m 3 ). In such high radon-risk areas the concentration of radon in soil-contained air ranges from 50 to 400 kBq/m 3 , in a few cases reaching up to 2,100 kBq/m 3 exceeding the permitted level for residential areas. The situation is particu -larly serious in the northernmost part of the country, where uranium-rich graptolite argillite (Dictyonema shale) and the Obolus phosphorite are close to ground surface and their particles are constituent parts of Quaternary deposits. Radon emissions from bedrock have been investigated in detail, but to date Quaternary strata as a source of radon emissions are poorly studied. According to our measurements the highest concentrations of radon are related to tills containing clasts and fines of graptolite argillite and phosphorite. Glacial deposits include also granitoidal material, containing U, Th and K, which have been transported by glaciers from the outcrop areas of crystalline basement rocks in Finland and the Gulf of Finland. Due to weathering, outwash and repeated redeposition other genetic types are poorer in radioac -tive elements and they are weaker sources of radon.
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    The Kaali crater field and other geosites of Saaremaa Island (Estonia): the perspectives for a geopark
    (Bogucki Wydawnictwo Naukowe, 2010-03) Raukas, Anto; Stankowski, Wojciech
    The Island of Saaremaa in Estonia offers highly spectacular geological features that belong to the most interesting in the Baltic Sea area. A unique geological monument on the island is the Kaali meteorite–crater field, formed by nine meteorite impacts. There are also attractive coastal cliffs, huge erratics, alvars (limestone areas covered by a very thin soil) and well-developed glacial and marine landforms. Limestone cliffs and shingle beaches abound with Silurian fossils and offer great opportunities to fossil collectors. The island is a prospective geopark. During the past few years, the geology of the island has become an intensely studied object of Estonian and Polish geologists.