Examining the influence of disequilibrium landscape on millennial-scale erosion rates in the San Bernardino Mountains, California, USA

Publication Date

1-1-2024

Document Type

Article

Publication Title

Bulletin of the Geological Society of America

Volume

136

Issue

3-4

DOI

10.1130/B36734.1

First Page

1526

Last Page

1540

Abstract

Temporal and spatial variations of tec-tonic rock uplift are generally thought to be the main controls on long-term erosion rates in various landscapes. However, rivers con-tinuously lengthen and capture drainages in strike-slip fault systems due to ongoing motion across the fault, which can induce changes in landscape forms, drainage net-works, and local erosion rates. Located along the restraining bend of the San An-dreas Fault, the San Bernardino Mountains provide a suitable location for assessing the influence of topographic disequilibrium from perturbations by tectonic forcing and channel reorganization on measured erosion rates. In this study, we measured 17 new ba-sin-averaged erosion rates using cosmogenic 10Be in river sands (hereafter, 10Be-derived erosion rates) and compiled 31 10Be-derived erosion rates from previous work. We quan-tify the degree of topographic disequilibrium using topographic analysis by examining hillslope and channel decoupling, the areal extent of pre-uplift surface, and drainage di-vide asymmetry across various landscapes. Similar to previous work, we find that erosion rates generally increase from north to south across the San Bernardino Mountains, reflecting a southward increase in tectonic activity. However, a comparison between 10Be-derived erosion rates and various topo-graphic metrics in the southern San Ber-nardino Mountains suggests that the pres-ence of transient landscape features such as relict topography and drainage-divide mi-gration may explain local variations in 10Be-derived erosion rates. Our work shows that coupled analysis of erosion rates and topo-graphic metrics provides tools for assessing the influence of tectonic uplift and channel reorganization on landscape evolution and 10Be-derived erosion rates in an evolving strike-slip restraining bend.

Funding Number

EAR-1945431

Funding Sponsor

University of Vermont

Department

Geology

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