Triggers of present-day rockfalls in the zone of sporadic permafrost in non-glaciated mountain region: the case study of Turnia Kurczaba (the Tatra Mts., Poland)

Abstract

In recent decades there has been growing evidence of the impact of ongoing climate warming on the frequency of rockfalls. However, these are not adequately documented, especially in non-glaciated, high mountain regions of middle latitude. This study comprehensively documents the Turnia Kurczaba rockfall, one of the most significant rockfalls recorded in recent decades in the Tatra Mountains. The precise projections of the volumes and distribution of rock losses and deposits, the determination of the trajectories, modes and speeds of movement of rock material, as well as information on the geological, morphological, and meteorological conditions behind the Turnia Kurczaba rockfall form a unique dataset. The data documents a spectacular episode in the contemporary development of a complex slope system in the Tatras in an all-encompassing way and can be used to validate and calibrate existing models and improve numerical simulations of other rockfalls, both for hazard and risk assessment and slope evolution studies. Moreover, in the context of archival data, they demonstrate that in the Tatra sporadic permafrost zone, only relatively small rockfalls have been recorded in recent decades. Their cause was not the degradation of permafrost but freeze-thaw processes with the co-participation of rainwater and meltwater. The largest of these occur within densely fractured cataclysites, mylonites, and fault breccias. The impact of rockfalls on the morphodynamics of talus slopes is uneven in the storied arranged rock-talus slope systems. Even colluviums belonging to the same slope system can differ in their development rate and regime, and different thermal and wetness drivers can control their evolution.