RESUMEN
Rivers form channel belts that encompass the area of the river channel and its associated levees, bars, splays and overbank landforms. The channel belt is critical for understanding the physical river evolution through time, predicting river behavior and management of freshwater resources. To date, there is no global-scale, quantitative study of the extent of river channel belts. Here we show, based on a pattern recognition algorithm, the global surface area of channel belts at an approximate 1 km resolution is 30.5 × 105 km2, seven times larger than the extent of river channels. We find 52% of river channels associated with the channel belts have a multi-threaded planform with the remaining 48% being single-threaded by surface area. The global channel belt (GCB) datasets provide new methods for high-resolution global scale landform classifications and for incorporating the channel belt into flood mitigation, freshwater budgets, ecosystem accounting and biogeochemical analyses.
RESUMEN
The deposition of a classic turbidite by a surge-type turbidity current, as envisaged by conceptual models, is widely considered a discrete event of continuous sediment accumulation at a falling rate by the gradually waning density flow. Here, we demonstrate, on the basis of a high-resolution advanced numerical CFD (computational fluid dynamics) simulation and rock-record examples, that the depositional event in reality involves many brief episodes of nondeposition. The reason is inherent hydraulic fluctuations of turbidity current energy driven by interfacial Kelvin-Helmholtz waves. The experimental turbidity current, with realistic grain-size composition of a natural turbidite, used only 26 to 33% of its in-place flow time for deposition, while the remaining time went to the numerous episodes of sediment bypass and transient erosion. The general stratigraphic notion of a gross incompleteness of sedimentary record may then extend down to the deposition time scale of a single turbidite.
