A criteria-based methodology for determining the mechanism of transverse drainage development, with application to the southwestern United States
The study of how rivers cross obstructing mountains, once popular in the early twenti- eth century, has seen a dramatic resurgence in the last decade. Since Hutton's scholarly introduction to a possible cause for trans- verse drainage, however, no single study has compiled all of the various criteria that can be used to discriminate among the four pos- sible mechanisms of antecedence, superimpo- sition, overfl ow, and piracy. This paper pres- ents the fi rst such compilation and related methodology to apply these criteria both in tabular and graphical formats, as well as an online interactive tool in the data repository. Combining nominal and ordinal data sources, this methodology generates an objective, reproducible assessment for the mechanism most likely to have established the trans- verse drainage at fi ordinal levels of con- fi dence. When applied to southwestern U.S. sites, randomly selected through an objec- tive spatial procedure, four general observa- tions emerged on the relationship between the development of transverse drainage and landscape evolution. (1) Streams persisting through lengthy periods of extension develop antecedent canyons. (2) In order to reestab- lish through-fl owing channels, streams over- fl ow closed basins as active extension wanes. (3) Following a drop in base level related to the newly developed trunk channels, streams tributary to the trunk channels incise into basin-fi ll deposits—sometimes leading to the development of superimposed drainages. (4) Tributaries eroding headward, in response to the integration of two or more closed basins, can capture and redirect drainage; this permits transverse drainage through both piracy and superimposition upstream of the capture event. Because extant criteria use nominal and ordinal data almost entirely, considerable potential exists to refi ne this approach through future strategies that incorporate interval data. Future use of a criteria-based method has the potential to inform on prior geomorphic studies by pro- viding a new perspective with which to study how basins evolve in active tectonic regions, the analysis of related basin sedimentation, the hydrological and biological aspects of drainage evolution, and transverse drainage found in Martian crater fi elds.