DRAINAGE DIVIDE STRUCTURE: POTENTIAL TOOL AND VIABLE INFLUENCE ON THE EVOLUTION OF GLACIATED BASINS

Although the boundaries between glaciated drainage basins are consequent to the processes of erosion acting on adjacent valley floors and walls, the geometric properties of the ridges may be both diagnostic of and an influence on the dynamic evolution of alpine landscapes. In map view, networks of drainage divides are generally dendritic and appear to be the negative image of valley networks. In 3D, however, ridge profiles are distinct from the longitudinal profiles of valleys and offer two valuable insights. First, the geometry of ridge profiles in glaciated mountains appears distinguishable (steeper and rougher) from those in fluvial ones, thus potentially serving as a topographic measure of the effect of glaciation. Second, the character of glaciated ridge profiles may reflect specific denudation mechanisms. For example, spikier profiles may reflect aggressive competition of adjacent basins via headwall retreat and cirque formation. In contrast, where periglacial weathering controls mass wasting, smoother profiles might result, because weathering should be spatially independent of drainage network. Drainage divide networks may also influence basin evolution, given the potential stability of divide junctions. Triple junctions are fundamental traits of ridge networks that are coincident with the highest points of a landscape. A global survey of both glacial and fluvial areas reveals that over 90% of prominent peaks occur at divide junctions. Detailed surveys of positive relief distributions of ridge profiles also shows that the majority are associated with divide junctions. These findings imply that divide junctions, which are essentially mass clusters that fill space and elevate local base level, are mechanically more stable and erode more slowly that the ridges that feed into them. If true, divide junctions and associated peaks may be like hardened points that anchor drainage networks, limiting the degree of divide migration via processes such as headwall retreat. These findings suggest that drainage divides are an insightful textural element of landscapes that warrant further attention from both field and modeling based studies.