ALBERT

Description: Climatically formed alluvial river-terrace sequences offer an exceptional opportunity to study valley-width evolution under similar discharge and lithologic conditions. To investigate additional parameters controlling valley width, we globally compiled alluvial-terrace sequences that have been associated with late Quaternary climate changes. All terrace cross-sections that are accepted to our compilation (1) include both valley sides, (2) show absolute values of distance and height, as well as profile location, and, (3) display a minimum of three terrace levels out of which at least one is preserved as a paired terrace. The terrace width and height measurements are summarized in this dataset. The data are presented as Excel and ASCII tables.

Description: Examining the links and potential feedbacks between tectonics and climate requires understanding the processes and variables controlling erosion. At the orogen scale, tectonics and climate are thought to be linked through the influence of mountain elevation on orographic precipitation and glaciation; the only documented erosional processes capable of balancing rapid rock-uplift rates are glacial erosion or coupled river incision and landsliding. Our 20 new 10Be derived catchment-averaged denudation rates from the Western Southern Alps of New Zealand generally range between 0.6 and 9 mm/yr, within the same order of magnitude as fault-throw rates, exhumation rates, and erosion rates estimated from suspended sediment yields and landslide inventories. Combining our data with previously published 10Be denudation rates, we find that the proportion of catchment area in the 1,500–2,000 m elevation window is the variable that best explains denudation rate variability and the disparity between rock-uplift rates and denudation rates. This correlation indicates that enhanced erosion likely occurs at 1,500–2,000 m above sea level, where periglacial and paraglacial processes have been proposed to be most active. We find that these temperature-controlled erosional processes, which are also elevation-dependent, can play a greater role in modulating erosion during interglacials than precipitation or glaciation. Our data suggest that temperature-controlled peri- and paraglacial erosion could be efficient enough to balance some of the fastest rock-uplift rates on Earth. Hence, temperature-controlled erosion could contribute to limiting orogen elevations and modulating the erosion rates dictated by rock-uplift, playing an essential role in linking tectonics and climate.

Description: The width of fluvial valley floors is a key parameter to quantifying the morphology of mountain regions. Valley floor width is relevant to diverse fields including sedimentology, fluvial geomorphology, and archaeology. The width of valleys has been argued to depend on climatic and tectonic conditions, on the hydraulics and hydrology of the river channel that forms the valley, and on sediment supply from valley walls. Here, we derive a physically based model that can be used to predict valley width and test it against three different datasets. The model applies to valleys that are carved by a river migrating laterally across the valley floor. We conceptualize river migration as a Poisson process, in which the river changes its direction stochastically at a mean rate determined by hydraulic boundary conditions. This approach yields a characteristic timescale for the river to cross the valley floor from one wall to the other. The valley width can then be determined by integrating the speed of migration over this timescale. For a laterally unconfined river that is not uplifting, the model predicts that the channel-belt width scales with river flow depth. Channel-belt width corresponds to the maximum width of a fluvial valley. We expand the model to include the effects of uplift and lateral sediment supply from valley walls. Both of these effects lead to a decrease in valley width in comparison to the maximum width. We identify a dimensionless number, termed the mobility–uplift number, which is the ratio between the lateral mobility of the river channel and uplift rate. The model predicts two limits: at high values of the mobility–uplift number, the valley evolves to the channel-belt width, whereas it corresponds to the channel width at low values. Between these limits, valley width is linked to the mobility–uplift number by a logarithmic function. As a consequence of the model, valley width increases with increasing drainage area, with a scaling exponent that typically has a value between 0.4 and 0.5, but can also be lower or higher. We compare the model to three independent datasets of valleys in experimental and natural uplifting landscapes and show that it closely predicts the first-order relationship between valley width and the mobility–uplift number.