Toppling failures from alpine cliffs on ben Lomond,Tasmania |
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| Authors: | Nel Caine |
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| Abstract: | Large cliff failures involving forward toppling over a basal hinge have occurred on more than half of the plateau edge of Ben Lomond, northeastern Tasmania. This mode of failure, which is readily identified from the columnar structure of the dolerite involved, has affected up to 107 m3 of rock at a time and a total of more than 50 × 106 m3 in all the cases which can still be identified. It represents perhaps the most important form of cliff retreat, amounting to a rate of 0.2 mm yr?1 over the last 100,000 years. Topographic evidence and joint surveys suggest that two different mechanisms have produced the topples on Ben Lomond. One has involved failure in the sediments underlying the dolerite with consequent foundering and cambering of large sections of the plateau edge. This mechanism accounts for relatively few of the Ben Lomond topples, though it includes the largest individual cases. The second mechanism, dominant in most of the topples, involved slab failure in the cliffs. Both modes of failure have been facilitated by vertical weaknesses within the bedrock and both require an initially steep cliff profile. Because of the latter requirement, which is not met on the other mountains of northeastern Tasmania, large-scale topples are found only on Ben Lomond, and only there where glacial steepening of the cliff has been possible. Following the initial failure, topples of both types have migrated downslope by block sliding for distances up to 2 km. |
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| Keywords: | Topple Camber Slab failure Mountain walls Cliff development Tasmania |
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