Denudational processes and landform of serpentinite

蛇纹岩山与其毗邻的非蛇纹岩山相比，往往表现出特有的特点：大型蛇纹岩山一般海拔较高，排水密度较低，坡形较平缓，脊形较圆，滑坡尺度较毗邻山较小、较浅。为了解释蛇纹岩的这些特征，我们在野外和实验室对新鲜和风化的蛇纹岩进行了物理和力学性质的研究，并进行了形态测定。岩石性质测量结果表明，新鲜块状蛇纹岩为坚硬不透水岩石，但经卸荷风化后，其强度（正阻力）显著降低，渗透率（负阻力）显著增加。形态测量表明，蛇纹岩山与相邻的非蛇纹岩山的相对高度与蛇纹岩山的面积（A_s）大致成正比，小于10 km^2的小A_s呈负值，大于10 km^2的大A_s呈正值。其原因可能是由于所谓的雪人对蛇纹岩剥蚀过程的影响如下。蛇纹岩山的剥蚀作用以蠕变和浅层滑坡为主要特征，使其坡度平缓、光滑。如果每个蛇纹岩体的剥蚀速率几乎是恒定的，则小α -s的蛇纹岩形成相对较低的山，而大α -s的蛇纹岩形成的山比相邻的由非蛇纹岩组成的山高，后者的表面渗透性不高，粘土矿物易膨胀。

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.