Speaker
Dr
Jacek Szczygieł
(Department of Fundamental Geology, Faculty of Earth Sciences, University of Silesia)
Description
In the extensive parts of the Niedźwiedzia Cave in Kletno discovered in 2011-2013, several dozen broken and fallen stalagmites, stalactites and flowstones have been documented, the largest of which are nearly 0.6 m in diameter and ~ 2 m in height. Damaged speleothems can be observed in the whole cave, as well as collapses of thickness up to several meters. In order to decipher the causes of these damages, the structural plan of the cave with particular reference to faults and map of damages were prepared. Samples of damaged speleothems were collected to determine the time interval in which the deformation took place by dating the youngest layer of the broken speleothem and the oldest layer of regrown one. In total 16 samples were taken from 8 sites.
Miscellaneous possible causes may result in macroscopically similar deformations: ice creeping, freezing, compaction or liquefaction of clastic deposits underlying speleothems, seismic activity, or just gravity movements. However, the amount and size of the speleothems deformation in the Nieźwiedzia Cave and their superposition within clastic, auto- and allochthonous sediments suggests strong linkage of deformations with the phenomena affecting the entire cave, i.e. tremor or gravitational collapse of the cave. Creeping ice and the accompanying frost should also be considered.
The Sudetes seismic activity, combined with faults documented in the cave of possible Alpine origin, as well as the time intervals when the damage occurred, lead us to propose the seismic hypothesis as the primary genetic factor. The seismic hypothesis is supported by the oldest deformations, which occurred around 320-310 ka, i.e. in the warm Pleistocene period (MIS 9). The most intense deformations in the cave, including the massive collapse in the Mastodont Chamber, occurred between ~ 170-155 ka, i.e. the cold Pleistocene phase (MIS 6). However, the mere fact of the speleothems growth at this period suggests that there should not be massive amounts of ice inside the cave.
Assuming the hypothesis that local earthquakes led to speleothems and passages deformation in the Niedźwiedzia Cave at least a few different source areas could be considered. According to the interpretation of structural data from the cave, first ground shaking seismic zone could be indicated to the west, to be linked with a fault zone limiting the Upper Nysa Kłodzka Graben. Another active zone may be considered in the north, the one associated with the eastern termination of the Hronov-Pořiči fault zone. At the same time, a strong tremor within the Sudetic Marginal Fault located about 20 km towards NE cannot be unequivocally discarded, since this is one of the most important tectonic lines in this part of Central Europe nowadays, noteworthy with documented neotectonic activity.
The work is a result of a research project no. DEC-2017/01/X/ST10/00375 financed from the funds of the Polish National Science Center. The work was partially financed from the bilateral cooperation project between ING PAN and IG CAS MOBILITY PAN-17-22.
Primary author
Dr
Jacek Szczygieł
(Department of Fundamental Geology, Faculty of Earth Sciences, University of Silesia)
Co-authors
Dr
Artur Sobczyk
(Institute of Geological Sciences, University of Wrocław)
Prof.
Helena Hercman
(Institute of Geological Sciences, Polish Academy of Sciences)
Prof.
Michał Gąsiorowski
(Institute of Geological Sciences, Polish Academy of Sciences)
