Abstract. Dobšiná Ice Cave has attracted the attention of many researchers since its discovery more than 150 years ago. Although the cave is located outside the high-mountain area, it hosts one of the largest blocks of underground perennial ice. The topographic mapping of this unique UNESCO Natural Heritage site has led to several historical surveys. In the last decades of rapid climate change, this natural formation has been subject to rapid changes that are dynamically affecting the shape of the ice body. Not only increased precipitation, the rise in year-round surface temperatures, but also the gravity cause significant shape changes in the ice filling. This paper describes modern technological tools to comprehensively survey and evaluate interannual changes in both the floor and wall of the underground ice block. Technologies such as digital photogrammetry, in conjunction with precise digital tacheometry, make it possible to detect ice accumulation and loss, including the effect of sublimation due to airflow, as well as sliding movements of the ice block to the lower part of the cave. In the last two years, geophysical methods (microgravimetry and ground penetrating radar) have been added to determine the thickness of the floor ice in the upper parts of the cave due to the complexity of the measurements. The paper not only highlights the current technological possibilities but also points out the limitations of these technologies and then sets out solutions with a proposal of technological procedures for obtaining accurate geodetic and geophysical data.
Combination of microgravity and GPR method constrains each other and help to detect subsurface cavities in a very effective way. Several examples are presented, some of the data-set were acquired during common summer schools between Kiel University and Comenius University in Bratislava.
Several surface geophysical methods were used to study the displays of undermined spaces in their physical fields and to try to distinguish undermined from non-undermined parts of underground mining area. The studied area of the Čáry lignite mine in the Western Slovakia represents an actively subsided place with high risk to the population. Despite very low radioactivity and relatively high gas permeability of building geological formations, the results of soil radon emanometry show the possibility of radon gas accumulation inside the undermined spaces, but their permanent subsidence causes loosing of overlying material and escape of radon gas. The boundaries (edges) of undermined and sunken areas were identified as the only places with increased values of 222Rn activity, probably due to the presence of vertical supporting mine walls allowing radon gas accumulation and upward movement. Thus, the soil radon emanometry clearly indicates the borders between undermined or sunken and non-undermined parts.
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