Contribution
Landform transitions in a fluviokarst landscape
Phillips, Jonathan D.
Zeitschrift für Geomorphologie Volume 61 Issue 2 (2017), p. 109 - 122
publié: Aug 1, 2017
manuscrit accepté: May 16, 2017
manuscrit reçu: Feb 7, 2017
ArtNo. ESP022006102001, Prix: 29.00 €
Abstract
Abstract Flow diversions and landform transitions between channelized surface (fluvial) and concentrated subsurface (karst conduit) flows may be common in fluviokarst landscapes. Identifying landforms associated with fluvial-to-karst or karst-to-fluvial transitions shows this to be the case at three study sites in the Inner Bluegrass karst region of Kentucky. Forms representing the capture or diversion of stream flow to subsurface conduits include sinking streams, dry karst valleys, paleovalleys resulting from karst stream piracy, and alluvial collapse dolines. Features indicating karst-to-fluvial transitions include stream incision into dry karst valleys, doline breaching by surface runoff or stream incision, and formation of karst pocket valleys and karst windows. Many smaller transitional landforms also exist (e.g., stream swallets). The three study sites have about three larger transitional landform features per km2, with karst-to-fluvial features slightly more common. Dissolution in bedrock-controlled stream channels leading to karst piracy is the most common cause of fluvial to karst transitions, while general stream incision driven by Kentucky River downcutting is the main driver of karst-to-fluvial shifts. The landform transitions are examined via a network model based on hydrological probability and flow partitioning. The model is dynamically unstable. Instability indicates that local changes and disturbances that modify moisture fluxes, local relief, conduit or surface channel conveyance capacity, or hydraulic slopes are likely to persist and grow, resulting in hydrogeomorphic transitions. Evolution of the Kentucky fluviokarst is best understood as mutual reinforcement, whereby fluvial dissection can be intensified and accelerated by the presence of karst features, and karstification is enhanced by stream incision.
Mots-clefs
Fluviokarst • geomorphic transitions • hydrological probability • flow partitioning • mutual reinforcement