The role of rock mass strength in landscape development based on the rating of natural rock masses in the Bükk Mts., Hungary

Studying the relationship between geological conditions and the geomorphology of a landscape has always been in the focus of geomorphology research. The relationship between structural and morphological elements can be analysed on the basis of a morphotectonic approach in which the role of rock strength is clear in slope conditions and thus in the morphology of an area. The strength of natural rock masses, however, cannot be modelled simply by the laboratory measurements of rock strength. The complex approach of rock mass strength is reflected in the development of various rock mass rating methods.

The authors evaluate the strength of natural rock masses in the Bükk Mountains in Northern Hungary based on the rock mass rating of more than a hundred outcrops scattered across the mountains. Some widespread rock mass rating methods are compared and the rock mass strength values of similar and also of different rock types are analysed. The results reveal that rock type has smaller influence on the strength of rock masses than parting conditions. Therefore, the role of parting surfaces needs to be analysed in detail, especially in areas with strong deformation features. On the edge of tectonic blocks where the deformation of rock masses is strongest, sinigficant fault planes with slickensides, folded structures and thrusts with shear zones compose the dense parting surfaces with so strong compression that massive limestone rock masses have smaller rock mass strength values than porous but much less deformed rhyolitic tuff rock masses.

Based on the results, the role of rock mass strength is assessed in the development and orientation of landforms in certain study areas in the mountains. Moreover, the relationship between rock mass strength and valley density is also studied. Finally, we take a look at the relationship between rock mass strength and the dominant deformation elements of the rocks of the mountains to see what tectonic geomorphological implications can be found.

Based on the rock mass rating methods, some recommendations can be given in relation to slope stability in terms of construction geological applications.