Extreme CO2 evasion from channel deposits produced by devastating failure of landslide induced dam in eastern Taiwan

Rock weathering is crucial for regulating carbon transformation across the Earth's spheres. While silicate weathering is considered kinetically limited, pyrite-driven carbonate weathering and rock-bound organic carbon oxidation are supply limited. As the control of supply limitation depends on reactant mobility, availability, and reactivity, weathering intensity can vary dynamically from the reactant generation to exhaustion at outcrop to catchment scales. How these contrasting weathering regimes operate in terrains with steep topography and deeply incised rivers remains largely unconstrained. The failure of a landslide-induced dam in the Matai’an river in the Central Range of eastern Taiwan delivered approximately 50 million cubic meters of sediments along the river bank (~17 km between landslide dam and lower reach) on September 23, 2025. By combining the dam residue, the total amount of landslide deposits was estimated to be 320 million cubic meters. Such an enormous quantity of materials (primarily composed of schists and marbles) freshly produced by mass wasting and fluvial processes on a monthly scale could be reactive for CO₂ production, thereby providing an unparalleled opportunity to constrain the fluxes and governing processes of carbon cycling at the incipient stage of major landscape change in orogenic belts.

To investigate how extreme and what mechanism CO₂ evasion is manifested by material supply, direct measurements of CO₂ gas flux were conducted using a modified closed chamber method. Our measurements for more than 100 sites yielded gas accumulation at a rate spanning from 0.4 to 60 g-C/m2/d with a median value of 16 g-C/m2/d. The fluxes were not correlated with sediment temperature, sediment depth, or distance to the active channel, a pattern in contrast to the temperature-dependent flux for sedimentary rock setting. This range ranks among the highest ever reported for weathering processes in mountainous catchments. Analyses of carbon isotopic compositions further revealed that the collected CO₂ was predominantly sourced by pyrite-driven carbonate dissolution, with minor contributions from rock-bound and soil organic carbon. By integrating the surface area of sediment coverage along the river, the enormous generating capacity of reactive materials from the landslide renders the CO₂ emissions exceeding the baseline level inferred from prior riverine chemistry by at least an order of magnitude. Our results demonstrate that the transient and extremely hazardous landscape change in active orogenic belts jumpstarts carbon evasion through rapid weathering of bank sediments at a pace that can substantially alter the catchment-scale carbon budget.