Morphometric analysis of solifluction lobes and rock glaciers in the Swiss Alps

Solifluction lobes and rock glaciers show similar geometry with a wide range of sizes. Morphometric analysis classifies these lobate landforms in the eastern Swiss Alps into five subgroups. A bouldery rock glacier has an active layer composed of matrix-free boulders, whereas a pebbly rock glacier consists of matrix-supported debris derived from less resistant rocks. Both move by permafrost creep at 5-30 m depth, but the former tends to have a longer tread. A high solifluction lobe, having a riser 0.2-3 m high, originates mainly from annual gelifluction operating within the top 0.5 m of sediment, and its variation, a mudflow-affected high solifluction lobe, occurs where prolonged snowmelt triggers a rapid flow of the thawed surficial layer. A low solifluction lobe has a riser up to 0.2 m high and occurs where thin fine-grained debris responds mainly to diurnal frost creep. These lobes show, on the whole, positive relations between the tread length (L), width (W) and the riser height (H). However, a regression analysis separates the rock glaciers from the solifluction lobes by a distinct gap at W (or L) = 30 m and H = 3 m and provides different regression lines for the two populations. The morphometry primarily determined by the transport process is H, which approximates or slightly exceeds the maximum depth of movement. The depth of movement also affects the horizontal extent of a moving mass, which defines W. A lobe appears where horizontal homogeneity exceeds 3H, and advances with time until reaching a maximum L controlled by climatic or dynamic conditions. Lobe morphometry can be used as an environmental indicator. Copyright (c) 2005 John Wiley & Sons, Ltd.