Abstract
AbstractGlobal measurements of incision rate typically show a negative scaling with the timescale over which they were averaged, a phenomenon referred to as the “Sadler effect.” This time dependency is thought to result from hiatus periods between incision phases, which leads to a power law scaling of incision rate with timescale. Alternatively, the “Sadler effect” has been argued to be a consequence of the mobility of the modern river bed, where the timescale dependency of incision rates arises from a bias due to the choice of the reference system. In this case, incision rates should be independent of the timescale, provided that the correct reference system is chosen. It is unclear which model best explains the “Sadler effect,” and, if a timescale dependency exists, which mathematical formulation can be used to describe it. Here, we present a compilation of 581 bedrock incision rates from 34 studies, averaged over timescales ranging from single floods to millions of years. We constrain the functional relationship between incision rate and timescale and show that time‐independent incision rate is inconsistent with the global data. Using a power law dependence, a single constant power is inconsistent with the distribution of observed exponents. Therefore, the scaling exponent is site dependent. Consequently, incision rates measured over contrasting timescales cannot be meaningfully compared between different field sites without properly considering the “Sadler effect.” We explore the controls on the variable exponents and propose an empirical equation to correct observed incision rates for their timescale dependency.
Highlights
Fluvial incision into bedrock can occur rapidly, with meters of incision during a single flood event, but more commonly it is a slow process that unfolds over geological timescales of thousands and millions of years
We explore the controls on the variable exponents and propose an empirical equation to correct observed incision rates for their timescale dependency
Measured incision rates I span 8 orders of magnitude, ranging from 0 to 8.8 × 105 mm yr−1 (Figure 3b), the majority of the rates are between 10−2 and 102 mm yr−1
Summary
Fluvial incision into bedrock can occur rapidly, with meters of incision during a single flood event, but more commonly it is a slow process that unfolds over geological timescales of thousands and millions of years. Process‐based models, such as the stream power model for erosion, have been used to infer signals of rock uplift (e.g., DiBiase et al, 2010; Wobus et al, 2006), climate (e.g., Ferrier et al, 2013), and lithology (Duvall et al, 2004). For these purposes, field data are required that often include measurements of fluvial incision rates. Like other process rates such as subsidence, uplift, and sediment accumulation, channel incision rates are dependent on the timescale of NATIV AND TUROWSKI
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