Identification of rock and fracture kinematics in high Alpine rockwalls under the influence of altitude
- 1Chair of Geomorphology, University of Bayreuth, Bayreuth, 95447, Germany
- 2Derpartment of Physical Geography, Utrecht University, Utrecht, 3584 CB, Netherlands
- 3Chair of Landslide Research, Technical University of Munich, Munich, Germany
Abstract. Alpine environments are characterized by fractured rock. Fractures propagate by weathering processes in a subcritical way, and prepare and trigger rock slope failures. In this study, I investigated (1) the influence of thermal changes on rock kinematics on intact rock samples from the Hungerli Valley, Swiss Alps. To (2) quantify thermal and ice induced rock and fracture kinematics and (3) identify differences of their spatial occurrence, I instrumented crackmeters at intact and fractured rock at four rockwalls reaching from 2585 to 2935 m. My laboratory data shows that thermal expansion follows three phases of rock kinematics: (1) cooling phase, (2) transition phase and (3) warming phase, which result in a hysteresis effect. The cooling phase is characterized by rock contraction, while all samples experienced rock expansion in the warming phase. During the transition phase, rock temperatures differ between rock surface and rock depth, which results in a differentiated response. The dummy crackmeters in the field reflect temperature phases observed in the laboratory and data suggest a block size dependency of the transition phase. In fractured rock, fractures open during cooling and reversely close during warming on daily and annual scale. The dipping of the shear plane controls if fracture aperture decreases with time or increases due to thermal induced block crawling. On seasonal scale, slow ice segregation induced fracture opening can occur within lithology-dependent frost cracking windows. Snow cover controls the magnitude and the number of daily temperature changes, reduces the magnitude of annual cooling but increases the length of the cooling period and, therefore, the potential occurrence of ice segregation. The effects of snow cover increases with altitude due to longer snow duration. Climate change induced warming will shift annual thermal stresses at lower altitudes, however, a shortening of the snow period can increase ground cooling and thermal stress at higher altitudes but also can reduce the length of the ice segregation period. In conclusion, climate change will affect and change rock and fracture kinematics and, therefore, rockfall patterns in Alpine environments.
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