| Research Abstract |
Serpentinitic mountains often show peculiar features in comparison with its adjoining non-serpentinitic mountains: Generally, large-scale serpentinitic mountains are higher in altitude, lower in drainage density, gentler and smoother in slope form, rounder in ridge form, and smaller and shallower in landslide dimension than the adjoining mountains. To explain these features of serpentinite, physical and mechanical properties of fresh and weathered serpentinite were examined in the field and in the laboratory, and morphometry was performed. The results of the measurements of rock properties show that fresh massive serpentinite is hard and impermeable rock, but if it is unloaded and weathered, the strength (positive resistance) decreases markedly, whereas the permeability (negative resistance) increases. Morphometry shows that relative height between serpentinitic mountain and its adjoining non-serpentinitic mountains is roughly in direct proportion to the area of serpentinitic mountain (A_s), and tend to show negative value for the small A_s less than about 10 km^2 and positive value for the large A_s more than about 10 km^2. The reason for this is probably due to the so-called snowman's effect on the denudational processes of serpentinite as follows. Denudational processes acting on the slope of serpentinitic mountains will be characterized mainly by creep and shallow landslide, and hence result in the gentler and smoother slopes. If the rates of these denudational processes are almost constant for every serpentinite body, serpentinite with small A_s form relatively lower mountain, whereas those with large A_s will form higher mountains than the adjoining mountains composed of the non-serpentinitic rocks of which the superficial part has not high permeability and much expandable clay minerals.
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