Aspect-dependent bedrock weathering, cliff retreat, and cliff morphology in a hyperarid environment

Abstract

Deciphering aspect-related hillslope asymmetry can enhance our understanding of the influence of climate on Earth’s surface morphology and the linkage between topographic morphology and erosion processes. Although hillslope asymmetry is documented worldwide, the role of microclimatic factors in the evolution of dryland cliffs has received little attention. Here, we address this gap by quantifying aspect-dependent bedrock weathering, slope-rill morphology, and sub-cliff clast transport rates in the hyperarid Negev desert, Israel, based on light detection and ranging (LiDAR)-derived topography, clast-size measurements, and cosmogenic 10Be concentrations. Cliff retreat rates were evaluated using extrapolated profiles from dated talus flatirons and 10Be measurements from the cliff face and sub-cliff sediments. We document systematic, aspect-dependent patterns of south-facing slopes being less steep and finer-grained relative to east- and north-facing aspects. In addition, cliff retreat and clast transport rates on slopes of the south-facing aspect are faster compared to the other aspects. Our data demonstrate that bedrock weathering of the cliff face and the corresponding grain size of cliff-derived clasts delivered to the slopes constitute a first-order control on cliff retreat and sediment transport rates. We demonstrate that the morphology of the cliff and the pattern of bedrock weathering co-vary with the solar radiation flux and hence that cliff evolution in hyperarid regions is modulated by aspect-dependent solar radiation. These results help to better understand interactions between climate and dryland surface processes.

Impacts of Rainstorm Intensity and Temporal Pattern on Caprock Cliff Persistence and Hillslope Morphology in Drylands

“…In each simulation, we also determine the median size fraction of the cliff‐derived debris (hereafter cliff‐derived grain size, or CGS), assuming that the masses of all other size fractions are normally distributed around it using a coefficient of variation of 0.8 as found by field observations (Duller et al., 2010; Whittaker et al., 2010). In all of our simulations, CGS ranges between 0.01 and 1 m which is in agreement with clast measurements in the Negev (Shmilovitz et al., 2020, 2022) and other published values from the literature (Verdian et al., 2021). For tuning the fragmentation module to arid environments rate, we calibrate ΔF against surface clast measurements from dated arid alluvial surfaces (Figure S2 in Supporting Information S1).…”

“…In each of the experiments, we set a constant rate for lateral cliff retreat, ω h , of 10 mm between the simulated storms, which is similar to published rates in drylands considering storm return period of 50–100 years (Duszyński et al., 2019; Shmilovitz et al., 2022). In each simulation, we also determine the median size fraction of the cliff‐derived debris (hereafter cliff‐derived grain size, or CGS), assuming that the masses of all other size fractions are normally distributed around it using a coefficient of variation of 0.8 as found by field observations (Duller et al., 2010; Whittaker et al., 2010).…”

“…Changes in the CGS represent diverse scenarios in which the cliff breaks either into large fragments or small clasts, due to the potential influence of lithology, weathering process, and caprock fracturing pattern. The values of CGS (representing the median grain size) range between 10 and 1,000 mm and cover a wide range of published values of cliff-derived sediment grain size (Neely & DiBiase, 2020;Shmilovitz et al, 2022;Verdian et al, 2021). To examine the sensitivity to changes in the magnitude of rainstorms, we multiply the 10-min intensity bins of the base-storm by a RIF ranging between 0.5 and 1.5 (Figure 3a).…”

The Impact of Extreme Rainstorms on Escarpment Morphology in Arid Areas: Insights From the Central Negev Desert

“…In addition, we measured the b‐axis size distribution of cliff‐derived clasts at 10‐cm intervals along two ∼20‐m long transects parallel to the cliff and spaced 0.5 m apart at each of the SWS and NES sites (Wolman, 1954). In each of the transects, we randomly collected and measured ∼200 clasts (Neely & DiBiase, 2020; Shmilovitz et al., 2020, 2022; Verdian et al., 2021).…”

“…In each of the transects, we randomly collected and measured ∼200 clasts (Neely & DiBiase, 2020;Shmilovitz et al, 2020Shmilovitz et al, , 2022Verdian et al, 2021).…”