A power-law relation of surface roughness and ages of alluvial fans in a hyperarid environment: A case study in the Dead Sea area

Abstract

Despite recent advances in mapping and dating alluvial fans, due to the availability of high-resolution remote sensing data and Quaternary dating techniques, quantifying surface features in remote sensing data remains a challenge. Surface roughness is a time-dependent feature under stable conditions, which indicates the relative age of alluvial fans in a hyperarid environment. Although surface roughness can be quantitatively inferred from remote sensing data, determining surface roughness in a uniform index remains a complex problem. Here, we used the normalized backscatter intensity (NBI) from high-resolution ALOS PALSAR data to quantify alluvial fan surface roughness, which is further used to quantitatively map alluvial fans. We established a robust power-law relation between the NBI value ( R) and the in-situ age ( T) as measured with independently dated alluvial fans. Based on the R-T relation, it can be further to apply the R measurement to T estimates as old as ∼540 ka with an average uncertainty of ∼25% on a regional scale. The NBI value, independent of atmospheric conditions and sensitive to surface roughness variability, is an effective criterion for quickly distinguishing alluvial fans and performing age estimation. We propose that insolation weathering is an important physical weathering pattern in the Dead Sea area, which mainly controls the surface roughness in this hyperarid region.