Glacially-induced scaling relations in mountain drainage basins

In glaciated British Columbia, Canada, Quaternary climate changes are responsible for profound spatial reorganization of earth surface processes. These changes have left a landscape characterized by topographic anisotropy associated with a hierarchy of glacial troughs. The evolution of formerly glaciated landscapes is examined by considering a set of scaling relations and assessing their departures from known unglaciated trends. Ultimately, the magnitude of these departures should provide a measure of the state of landscape recovery (transience) from glacial disturbance. The set of scaling dependences studied includes slope-area relations, for assessing geomorphic process domains; landslide magnitude-frequency (LMF) and yield-area relations, for evaluating landslide-driven sediment dynamics; and the spatial organization of channel-reach morphology. In addition, along channel long-profiles the scaling between drainage area and channel cross-sectional variates (downstream hydraulic geometry), coarse grain-size fraction, and stream power indices are examined. The methodological approach couples extensive field surveys, GIS-based topographic analysis, air photo interpretation, and multivariate statistical analysis. Slope-area analysis reveals generalized process-form disequilibrium with a mismatch between topographic signatures and currently active geomorphic process domains. At the landscape scale of "source" colluvial channels, the glacial/paraglacial signature commonly overrides that produced by contemporary debris flows. Along the axis of former ice flows, relict glacial cirques introduce a "hanging" fluvial domain at contributing areas as small as 8*10⁻² km² and produce complex channel long-profiles similar to those observed for rivers responding to tectonic forcing. The concept of process domains appears to hold; however, some major glacially-forced modifications in the alluvial-colluvial transition are observed and the definition of a depositional colluvial sub-domain is proposed. Direct spatial scale linkages and generalized departure from unglaciated scaling relations are observed at all levels of investigation. Glacial macro-forms, by imposing local channel gradient and degree of colluvial-alluvial coupling, dictate the spatial distribution of process domains, which in turn affect LMF relations, landslide yield, channel-reach morphology, downstream hydraulic geometry, and stream power. The combination of glacial and post-glacial fingerprints and the effects of ongoing earth surface processes generate a complex landscape whose glacial signatures may persist until the onset of the next ice age.