title: Landscape response to progressive tectonic and climatic forcing in NW Borneo: Implications for geological and geomorphic controls on flood hazard.
abstract: Empirical models have simulated the consequences of uplift and orographic-precipitation on the evolution of orogens whereas the effects of these forcings on ridgelines and consequent topography of natural landscapes remain equivocal. Here we demonstrate the feedback of a terrestrial landscape in NW Borneo subject to uplift and precipitation gradient owing to orographic effect, and leading to less-predictable flooding and irreversible damages to life and property. Disequilibrium in a large catchment recording the lowest rainfall rates in Borneo, and adjacent drainage basins as determined through χ, a proxy for steady-state channel elevation, is shown to result in dynamic migration of water divide from the windward-side of the orogen towards the leeward-side to attain equilibrium. Loss of drainage area in the leeward-side reduces erosion rates with progressive shortening resulting in an unstable landscape with tectonic uplift, gravity faults and debris flows.14C dating of exhumed cut-and-fill terraces reveal a Mid-Pleistocene age, suggesting tectonic events in the trend of exhumation rates (>7 mm a-1) estimated by thermochronology, and confirmed by morphotectonic and sedimentological analyses. Our study suggests that divide migration leads to lowered erosion rates, channel narrowing, and sediment accretion in intermontane basins on the leeward-side ultimately resulting in enhanced flooding.
authors.affiliation: Université Bretagne Sud, Laboratoire Géosciences Océan, UMR CNRS 6538, rue Yves, Mainguy, 56017, Vannes cedex, France. dmenier5@gmail.com.
authors.forename: David
authors.initials: D
authors.lastname: Menier
authors.affiliation: Université Bretagne Sud, Laboratoire Géosciences Océan, UMR CNRS 6538, rue Yves, Mainguy, 56017, Vannes cedex, France.
authors.forename: Manoj
authors.initials: M
authors.lastname: Mathew
authors.affiliation: Ecole Normale Supérieure UMR 8538 du CNRS, 24 rue Lhomond, 75231, Paris, Cedex 05, France.
authors.forename: Manuel
authors.initials: M
authors.lastname: Pubellier
authors.affiliation: Total E&P MENA Dubai, The H-Dubai Office Tower, 24th Floor, 1, Sheikh Zayed Road, P.O. Box, 116538, Dubai, United Arab Emirates.
authors.forename: François
authors.initials: F
authors.lastname: Sapin
authors.affiliation: Université de Caen. UMR 6143 M2C, Morphodynamique continentale et côtière 24, Rue des tilleuls, 14000, Caen cedex, France.
authors.forename: Bernard
authors.initials: B
authors.lastname: Delcaillau
authors.affiliation: Universiti Teknologi PETRONAS Faculty of Geosciences & Petroleum Engineering, Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia.
authors.forename: Numair
authors.initials: N
authors.lastname: Siddiqui
authors.affiliation: Periyar University Department of Geology, 636011, Salem, India.
authors.forename: Mu
authors.identifier: 0000-0002-4038-6978
authors.initials: M
authors.lastname: Ramkumar
authors.affiliation: University of Adelaide, Department of Earth Sciences, Adelaide, SA 5005, Australia.|China University of Geosciences, Beijing School of Earth Sciences and Resources 29 Xueyuan Road, Beijing, 100083, China.
authors.forename: M
authors.initials: M
authors.lastname: Santosh