Rock walls distribution and Holocene evolution in a mid-latitude mountain range (the Romanian Carpathians)

Rock walls in high mountain areas are the expression of long-term slopes response (10(3)-10(5) years) to tectonics, weathering and denudation and a major source of sediment and hazard. Controls of mountain rock walls (RW) distribution and the response to post-glacial evolution are rarely discussed in the literature at the scale of mountain ranges. Using a database of 791 RW mapped in the Romanian Carpathians, we present their distribution and morphometry in respect to lithological classes, structural features and topography and relate their exposure to post-Younger Dryas (Holocene) rock slope failure chronology. Statistical analysis results show the high significance of structural and tectonic control on RW distribution, which prevails in sedimentary units where it imposed the predominance of West and North orientations and led to the formation of RW with dimensions up to a degree higher compared to other lithologies. Morphometric data indicate that metamorphic and igneous RW (linked to a great extent to glacial valleys and cirques headwalls) are usually restricted to the highest sectors of the mountain slopes, being characterized by reduced relative heights, asymmetrically distributed, common on the North-exposed slopes and extremely rare on the South. Based on 38 in-situ produced Be-10 surface exposure ages obtained on meter-sized boulders from the Southern and Eastern Carpathians, we hypothesise that metamorphic and igneous RW in the formerly glaciated Carpathian valleys were significantly shaped during Early Holocene (before 9 ka) by rock slope failures events that followed the deglaciation of the highest cirques and by intense RW permafrost degradation, which also affected some of the highest sedimentary units. We associate the long-term imprints of frost weathering to the significant North/South RW and rock glaciers distribution asymmetry, also identified in other mid-latitude mountain sites with similar topographic constraints.

Automated summary

Rock walls in high mountain areas are the result of long-term slopes response to tectonics, weathering, and denudation. This study focuses on the distribution and morphometry of rock walls in the Romanian Carpathians and reveals the significant influence of structural control on their distribution. Metamorphic and igneous rock walls are found in the highest sectors of the mountain slopes, most likely shaped during Early Holocene by rock slope failure events and permafrost degradation.