The influence of nivation and cryofraction on periglacial relief formation on Velebit Mt. (Croatia)

The peak areas of the Velebit mountain range display an interesting periglacial geomorphology. The appearance of forms is the result of the interdependent geological, geomorphologic, climatic, vegetational and pedological characteristics of the area. The structural and lithological properties of the rock complex, and the inclination of the slope, play a significant role in periglacial relief modelling. Climatic elements are also important, as they influence the intensity and duration of the processes. Low temperatures and relatively high precipitation during the last ice age (Würm III), served to intensify the activity of periglacial processes and relief modelling of the entire Velebit area. Nivation and cryofraction are the predominant periglacial processes which are represented by snow avalanches and stone streams. Air temperatures and soil temperatures (at 30, 60, 90 cm depth) were measured, presented and reviewed, together with other attributes and the slope inclination of the area. The interactions between ground temperature, snow cover and wind patterns play important roles in frost action. In addition to slope inclination, the penetration of warm winds (jugo) and warming of snow on the NE slopes are also important factors in destabilizing the snow cover and triggering avalanches. Snow avalanches are most intensive on slopes with declinations from 35° up to 50°, especially on the parts without vegetation cover.