Large lateral spreading and transient uplift of gravitational grabens along the passive continental margin (Pampa de Salamanca, Argentine Patagonia)

Although large-scale landslides mostly occur in tectonically active orogens, they can also exceptionally develop in intracontinental settings and passive continental margins. This study investigates lateral spreading across more than 80 km of the Pampa de Salamanca coastal range in eastern Patagonia. The region is underlain by weakly consolidated Cenozoic sedimentary and volcaniclastic rocks and lies on a passive continental margin that has experienced rapid late Quaternary uplift, which is unusual for this type of tectonic setting. To analyze the origin and dynamics of large-scale lateral spreading, we integrated optical satellite imagery, TanDEM-X topographic data, field surveys, and interferometric (DInSAR) analysis. Spreading has produced a horst-and-graben morphology defined by synthetic, antithetic, and cross gravitational faults, with scarps exceeding 6 km in length. Grabens occur on both ridge tops and slopes, while lower slope sections often show transitions into rotational and translational slides. Although the lack of chronological markers hinders precise dating, geomorphological evidence reveals evolution throughout the Quaternary and ongoing deformation, evidenced by valley floor offsets and damming by antithetic scarps. DInSAR data from 2017 to 2021 reveal centimetre-scale cumulative horizontal and vertical displacements, with strong uplift (>10 cm) systematically concentrated in graben zones. This uplift peaked after an extreme rainfall event in March–April 2017, which brought over 150 % of the annual precipitation in ten days. We interpret this transient uplift as resulting from the preferential accumulation of water in graben depressions, which led to the wetting and expansion of clay-rich soils. Subsequently, water infiltration along gravitational faults and the upward expansion of clay layers might have further contributed to the uplift. We conclude that substantial Quaternary uplift and erosion of weak rocks in the Pampa de Salamanca range facilitated the development of a regional-scale lateral spreading terrain. Superimposed on deep-seated failure kinematics, uplift of near-surface layers from substantial water input can temporarily reverse the otherwise dominant subsidence of lateral spreading grabens.