Geological Society of America

T16 Physical Experimentation and Modeling in Surface Processes

Monday, 26 October 2020
1:30 PM - 5:30 PM
Meeting Rooms

ASPECT-DEPENDENT ESCARPMENT RETREAT, SEDIMENT MOBILIZATION, AND SLOPE EVOLUTION UNDER HYPERARID CONDITIONS

Paper number: T16-12
Program: Technical Sessions
Time: 3:50 PM – 4:00 PM

Authors

Yuval Shmilovitz Presenting Author
The Hebrew University of Jerusalem, Jerusalem
Yehouda Enzel
The Hebrew University of Jerusalem, Jerusalem
Efrat Morin
The Hebrew University of Jerusalem, Jerusalem
Moshe Armon
The Hebrew University of Jerusalem, Jerusalem
Ari Matmon
The Hebrew University of Jerusalem, Jerusalem
Amit Mushkin
Geological Survey of Israel, Jerusalem
Itai Haviv
Ben-Gurion University, Beer Sheva

Abstract

Hillslope aspect has a prominent global influence on slope morphology. However, the relative role of micro-climatic factors in escarpment evolution and retreat pattern is still unknown. Here, we quantify aspect-dependent cliff retreat, clast transport rates, and slope and rill dynamics based on high-resolution (0.5 m²) LiDAR-derived topographic dataset, field observations, clast size measurements, and cosmogenic ¹⁰Be concentrations. Utilizing these datasets, we address the influence of aspect on cliff retreat and sediment transport and examine its long-term imprint on escarpment evolution.

Topographic analysis of escarpment and sub-cliff slopes in the hyperarid Negev (Israel) reveals a systematic decrease in cliff gradient between north- and south-facing slopes (mean gradient of 40 and 35, respectively) along with decreasing grain-size of the sediment derived from the cliffs. Coarser sediments characterize the north aspect and can explain its steeper rills. Escarpment retreat rates were evaluated using ¹⁰Be and extrapolated profiles of dated talus flatirons which are now disconnected from the active cliff. Our results highlight a systematic decrease in the long-term escarpment retreat from south-facing (80-90 m) to north-facing slopes (30-60 m). Furthermore, the transport rate of the clasts on the pediment is also aspect-dependent with southern clast transport rate ~5 times faster (0.05 - 0.25 cm year^-1). The clasts along these pediments are mobilized by sheetwash during rare transport events. Our results demonstrate that bedrock weathering of the cliff-face, and the related grain size distribution of the sediment delivered to the slopes, is a first-order factor controlling escarpment retreat rate and escarpment topography. The morphology of the escarpment covary with the solar radiation flux and the latter has a direct effect on the bedrock weathering pattern.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-357510

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