Carbon dioxide (CO2) is one of the key components in hydrogeochemistry of karst systems, which largely controls the process of dissolution and precipitation of calcium carbonate. The concentration of carbon dioxide in the atmosphere karst caves ranges typically from 0.1 to 1.0% (which is 1-2 orders higher than the values for open atmosphere - 0.03-0.04%), more rarely reaches 2.8%. Currently, carbon dioxide of soil and atmospheric origin is considered as the main source of CO2 in most of karst systems, and its concentrations in the caves mainly related to the intensity of the ventilation. The purpose of this work that was carried out in May 2016 is further study of the problems related to CO2 in the air of New Athos cave. The areal mapping of CO2 distribution in the halls of the cave indicates change from 0.04-0.08% in the southern halls to 0.16-0.18% in the Apsny hall. The high correlation of CO2 with equivalent equilibrium volume activity of radon was revealed, that indicates the general character of the behavior of both gases in atmosphere of the cave. The resulting distribution is well explained by the feature of air-exchange in the halls with the surface. Stationary observations using data loggers in the Apsny hall showed that the most significant factor influencing the concentration of CO2, is air leaks through the transport tunnel at its forced ventilation and opening of paddle doors for passage of groups. So it was possible to preliminary evaluate the influence of the pressure factor on the dynamics of CO2. Calculation of potential CO2 concentrations in equilibrium of which the composition of the cave water seepage was formed, provides estimations in range 0,9-2,75% (that approximately reflects the concentration in the upper part of the vadose zone, where the composition of these waters was formed). The calculation of the equilibrium concentrations of Ca2+ for observed CO2 partial pressures in the cave atmosphere showed avalability of conditions favorable for calcite crystallization. Morphological study of the sample of modern calcite from the Apsny hall showed that the growth occurs under conditions of high supersaturation with fast degassing of CO2 from water seepage. In the context of the observations we can assume that a technological transformation of the ventilation in the cave after tunnel construction has increased the rate of calcite precipitation (since decreased pCO2 in the atmosphere). However, this calcite, due to the predominance of non-equilibrium crystal forms, does not look aesthetically pleasing. For understanding of the processes related to the carbon dioxide balance in the cave,it is necessary to conduct focused research and continuous monitoring.

Part 1. Analysis of current state of mudflow processes in the Kozydon and Zemegondon river basins on the territory of the year-round tourist and recreational complex “Mamison” According to the Federal target program of development of resorts of the North Caucasus within the next 10 years in the Republic of the North Ossetia-Alania it is supposed to create year-round tourist and recreational complex “Mamison”. Dangerous glacial processes: avalanches, landslips, landslides, etc. are characteristic for the territory of the complex “Mamison”. These mudflow processes are of serious danger for the objects of the future resort “Mamison”. As a result of realized field surveys and decoding of satellite images of various periods the maps of M:10000 scale of the mudflow basin limits, their centers and the database of morphometric characteristics of mudflow basins were created. As a result of investigation 14 mudflows near Kozydon river and 10 mudflows near Zemegondon river were discovered. The rate of possible maximum volume of mudflows in Kozydon river basin is about 75000 m³. The rate of possible maximum volume of mudflows Zemigondon river basin is 65000 m3. The mudflows in the investigated area take place with more frequency than once in a decade. In the mudflow sediments the size of large fragments does not exceed 25–50 centimeters, some fragments amount to 0.5–2.5 meters in diameter. The mentioned current intensification of mudflow processes in the Kozydon and Zemegondon river basins is connected with defrosting of loose and frozen rocks and possibly with natural phenomena in the break zones. It may be supposed that intensification of mudflows will take place in other areas as well. In this connection, it is necessary to provide monitoring. Therefore, to avoid negative consequences on this territory in future it is recommended to distribute recreational objects of the complex “Mamison” on the basis of considered recommendations that provide full anti-mudflow security. The climate and water balance of the territory also contribute to mudflow formation. Average-annual temperature of the region is +8°С with the minimum average-monthly temperature for 6 snowy months is -5.5°С, maximum average-monthly temperature in July- August is +14.2°С, with 250–300 sunny days a year. Averageannual amount of precipitation is 650–700 mm, 25% of which are in the winter period. There were no floods of catastrophic level in Mamisondon river. Average-monthly water flow rates change from 1 m3/sec. in winter months and to 15 m3/sec — in summer. In the floods period with extreme precipitation water flow rates in Mamisondon river may intermittently exceed 100 m3/sec.