Mineral permafrost mounds (lithalsas) have been studied in the Sentsa River valley (East Sayan Mountains, western Buryatia). This is the first detailed study of permafrost in the area based on analysis of cryostructures and distribution of stable isotopes in lithalsa intrusive-segregation ice. The lithalsas predominantly have reticulate or lenticular cryostructures and ice contents over 50-60 %. The lateral and vertical δ¹⁸O and δ²H patterns suggest cascade growth with the large lithalsa formed before the small one. Lithalsas can nucleate and grow during progressive lake shallowing. They feed mainly from ground water during freezing of wet frost-susceptible finegrained soil, or less often, from meteoric or lake water. Lithalsas grow quite rapidly, at tens of centimeters per year, and can reach more than 5 meters high in 50-100 years.

Data was submitted and proofread by Yurij K Vasil'chuk and Lyubov Bludushkina at the faculty of Geography, department of Geochemistry of Landscapes and Geography of Soils, Lomonosov Moscow State University.