Home – Home – Jornals – Earth’s Cryosphere 2024 number 4

In the context of modern climate change, permafrost degradation from the surface takes place in Western Siberia. This is manifested by an increase in temperature and a decrease in the area of distribution and thickness of frozen layers. To establish the rate of reduction in permafrost area, a cartographic model was created to predict the change in the position of its southern limit by the middle of the 21st century. Based on temperature, ice content, rock composition, and section structure data, permafrost areas were ranked concerning the thawing rate of the upper 10-m-thick permafrost layer. It was found that the expected change in the southern limit of permafrost in Western Siberia will be uneven and dependent on the local conditions related to the cryolithogenic foundation of the landscape.

This article discusses the results of retrospective verification of the strength prediction model for saturated rocks of southern Yakutia. The model was developed for the geotechnical conditions of the city of Neryungri. The input data for the model consisted of the decay rate coefficients of the harmonic field of a vertical magnetic dipole measured at a 1.125 MHz frequency using the geometric electromagnetic induction sounding method. The error of model predictions was close to the allowable error of ±20 % for average laboratory estimates of rock sample strength and ranged from ±16.8 to ±33.5 % for different site conditions with a probability of about 70 %. The total error of the model at this probability is 27.2 % with maximum outliers overestimating the laboratory strength of weak rocks by 120.5 % or underestimating the strength of strong rocks by 86.8 %. The model predictions were more accurate (errors of 22.8 and 21.9 %) for the rock masses composed predominantly of moderately strong (15-50 MPa) and strong (50-120 MPa) rocks. The statistical results indicate that the model is regionally representative and can be applied in the areas of warm and cold permafrost sedimentary rocks of southern Yakutia for rapid, cost-effective terrain evaluation by rock strength.

The purpose of this work was to specify the hydrogeological conditions in the poorly studied northeastern part of the Lena-Amga interfluve. We analyzed archival (1965-1995) and published data on subpermafrost waters and permafrost thickness in the Churapcha and Tattinsky districts of the Republic of Sakha (Yakutia), including new field studies (2009-2022). The research was based on the data from 19 groundwater exploration wells, 450 to 650 m in depth. It is shown that the Jurassic and Middle Cambrian aquifer complexes differ in piezometric pressures and chemical composition. Based on the new information, it is suggested that the boundary between these two aquifer complexes should be shifted northward by 50-80 km. A zone with distinct specific hydrogeological conditions confined to the Tatta-Tompo fault was identified. Presumably, the fault was formed under conditions of horizontal compression, which resulted in the compaction of the rocks and their reduced permeability along the fault, as well as in the increased freezing intensity in the strata with a low water content during periods of decreased global temperatures.

Natural gas hydrates exist in porous media under high pressure and low temperature conditions, including permafrost. The development of methods for calculating the phase equilibria in hydrate-bearing soils and sediments is of great interest. This includes the equilibrium content of nonclathrated water, as pore water in equilibrium with pore hydrate and under given thermobaric conditions. Nonclathrated water is similar to unfrozen water in frozen soil. The current study focuses on thermodynamic relationships for calculating nonclathrated water content in soil under certain thermobaric conditions based on experimental data of pore water activity and soil water content. It has been shown that at a constant temperature the nonclathrated water content decreases sharply according to a power law as gas pressure increases. The results of thermodynamic calculations are in agreement with direct measurements of nonclathrated water in soil systems using the contact method. Thus, at temperatures below 0°C, the nonclathrated water content decreases by more than two times in kaolinite clay and in sandy clayey soils with an increase in methane pressure from 2.3 to 11 MPa. The obtained relationships allow us to recalculate the nonclathrated water content after transition from one hydrate-forming gas to another, as well as calculate nonclathrated water content using the unfrozen water content curve at different temperatures. Developed thermodynamic approach can be applied to various hydrate-forming gases and their mixtures.

Climate change affects the parameters of snow cover, including the distribution of snow storage on plain territories under forests and in fields. A comparison of the average long-term maximum snow storage in forests and fields for different climatic periods is carried out. The average value of snow storage on fields for the current climatic period (1991-2020) increased by 4 % compared to the period 1966-1990; in forests, it decreased by 6 %. Average snow storage in forests and fields in 2001-2010 amounted to 127 and 123 mm; in 2011-2020, it decreased to 121 and 120 mm, respectively. The ratio of snow storage in forests to its value in fields - the snow accumulation coefficient - for 1966-1990, 1981-2010, and 1991-2020 has been constantly decreasing and amounted to 1.16, 1.08 and 1.05, respectively. Maps of the distribution of snow storage and the coefficient of snow accumulation within plain territories of Russia for different climatic periods have been constructed. The tendency of leveling the maximum snow storage in forests and fields under the modern climate (1991-2020) has been confirmed.

The main stages in the development of geocryology in the XX-XXI centuries are highlighted. The major research achievements are presented in the fields of permafrost science, permafrost engineering, historical geocryology and regional geocryology. The most important results of research at the Melnikov Permafrost Institute of the Siberian Branch of the Russian Academy of Sciences are described.