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- Title
Rock Surface Freeze-Thaw and Thermal Stress Assessment in two Extreme Mountain Massifs: Bucegi and Măcin Mts.
- Authors
Vespremeanu-Stroe, Alfred; Vasile, Mirela
- Abstract
This work addresses the thermal behavior of the rock surface in two mountain sites with different, rather extreme climatic conditions. As thermal weathering is one of the highly potential driving factors in mountain morphodynamics, the evaluation of the processes involved is utterly important. Freeze-thaw cycles (F-TC) typology and development and the thermal stress experienced during the maximum insolation interval (INSIT) were considered. The study results show a more than double effective action of freezing processes in alpine relief modeling than in low-altitude massifs taking into account the large number of the freeze-thaw cycles (86), the high proportion of effective F-TC and the intensity of the annual cycle (6-7 m frost depth) comparing to low altitude Macin Mountains, where the freeze-thaw interval is significantly shorter (43 cycles) and frost depth only reaches 0.7-1 m during winter freezing. In attempting to determine the degree of frost effectiveness, a theoretical threshold of the diurnal freezing index of 12 °Ch was set, indicating that autumn (pre-siberian F-TC) is the least effective season for both locations, while postsiberian F-TC (mid-late spring in alpine area; late winter - early spring in low-altitude massifs) records the highest frequency and intensity of diurnal freeze-thaw cycles (the spring summarizes 60% in the Bucegi and 80% in the Macin from the over-year effective F-TC). The seasonal differences of freeze-thaw distribution, derived from temperature regime, are strengthen by a close correspondence to the precipitation regime especially in the alpine area, where the mean daily precipitation are double during spring F-TC season than during autumn. Rock thermal stress induced by summer solar radiation is 22% smaller at 2500 m level than at 330 m level, while the maximum thermal amplitudes are relatively similar, indicating a high sensitivity to thermal stress of the high-altitude outcrops during clear days. If the high-altitude Bucegi Mts. show lower values of the mean daily amplitudes (16.7 °C) than recorded in Macin (21.2 °C), and half diurnal maxima values, this occurs due to high nebulosity and low mean air temperature values. Sudden cooling triggered by cold winds, rainfalls or temporary cloud cover, typical in high mountain areas, could become favourable elements in rock thermal stress generation. Consequently, insolation induced thermal stress is the secondary process in thermal weathering of alpine relief, but it shows a greater potential than frost processes in low altitude environments.
- Subjects
MACIN Mountains (Romania); ROMANIA; THERMAL stresses; CLIMATE extremes; METEOROLOGICAL precipitation; SOLAR radiation
- Publication
Revista de Geomorfologie, 2010, Vol 12, p33
- ISSN
1453-5068
- Publication type
Article