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.
Highlights
The continued, yet variable rates of interactions between tectonic and climatic forcing result in diversity of landscape evolution
Our study shows that in intermontane basins affected by tectonic and climatic forcing, the response of the landscape can act as a driving mechanism for flooding despite low rates of rainfall in the orogen interior
We propose that recent and/or active tectonics persisted in NW Borneo and that the magnitude of uplift in this region was considerably high in order to maintain a young topography
Summary
The continued, yet variable rates of interactions between tectonic and climatic forcing result in diversity of landscape evolution. In a natural landscape, subject to tectonic uplift and climatic perturbations, the feedback of ridgelines and subsequent rain-shadowed topography remains less-understood. These natural processes, often aggravated by anthropogenic intervention can result in catastrophic geohazards such as flooding, causing irreversible damages. Other explanations for the cause of recent tectonics onshore and offshore NW Borneo include subduction in the NW Borneo Trough until the Late Neogene or present-day[18, 19], regional compression[16, 20, 21], or extension[22], ongoing convergence of blocks or plates, inheritance from former subduction or far-field stresses[17, 23, 24], and possible large-scale mantle processes. Flooding has been globally attributed to excessive amounts of rainfall among other lesser contributing factors (e.g., ground cover, tidal influences, flat topography of coastal zones, ruptured dams etc.), the geologic and geomorphic evolution of a landscape as a principal contributing element to flooding in areas receiving low annual precipitation has received less attention
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