Rock avalanche morphology and new results from the Tschirgant deposit in Tyrol
Rock avalanche morphology reflects internal emplacement processes and external influences, such as runout path topography and sedimentary fill. Additionally, preparatory conditions at the source slope dictate, for example, the sequence of material spreading (stratigraphy), or the maximum clast size that any given unit can possibly exhibit in the final deposit. A wealth of descriptive, investigative, and experimental studies has shown that there are intrinsic behavioural patterns of granular materials in motion that express themselves in particular depositional morphologies. Most rock avalanche deposits are described as complex, but then the question arises what is typical or universal? This question will be addressed and exemplified at the Tschirgant rock avalanche in Tyrol, Austria, which did produce a complex deposit 200-250 x 106 m3 in volume and 9.8 km2 in area. The landslide resulted from deep-seated failure of an intensely deformed carbonate rock mass on the southeast face of a 2,370-m-high ridge. The rock mass rapidly fragmented as it moved towards the floor of the Inn River valley. Part of the debris collided with and moved around an opposing bedrock ridge and flowed into the Oetz valley, reaching up to 6.3 km from source. Some parts spread freely, but most suffered some topographic interference, or were affected by the large volume of mobilized sedimentary gravels and sands found beneath and within rock avalanche. Some morphological signatures are related to differences in mechanical behaviour of the involved lithologies, while others reflect particular emplacement modes of the same lithology. And finally, variations in internal fabric can be closely correlated with surface features, and both are linked to topographic interference.
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Rock avalanche morphology and new results from the Tschirgant deposit in Tyrol
Abstract
Rock avalanche morphology reflects internal emplacement processes and external influences, such as runout path topography and sedimentary fill. Additionally, preparatory conditions at the source slope dictate, for example, the sequence of material spreading (stratigraphy), or the maximum clast size that any given unit can possibly exhibit in the final deposit. A wealth of descriptive, investigative, and experimental studies has shown that there are intrinsic behavioural patterns of granular materials in motion that express themselves in particular depositional morphologies. Most rock avalanche deposits are described as complex, but then the question arises what is typical or universal? This question will be addressed and exemplified at the Tschirgant rock avalanche in Tyrol, Austria, which did produce a complex deposit 200-250 x 106 m3 in volume and 9.8 km2 in area. The landslide resulted from deep-seated failure of an intensely deformed carbonate rock mass on the southeast face of a 2,370-m-high ridge. The rock mass rapidly fragmented as it moved towards the floor of the Inn River valley. Part of the debris collided with and moved around an opposing bedrock ridge and flowed into the Oetz valley, reaching up to 6.3 km from source. Some parts spread freely, but most suffered some topographic interference, or were affected by the large volume of mobilized sedimentary gravels and sands found beneath and within rock avalanche. Some morphological signatures are related to differences in mechanical behaviour of the involved lithologies, while others reflect particular emplacement modes of the same lithology. And finally, variations in internal fabric can be closely correlated with surface features, and both are linked to topographic interference.
