Disproportionate and chronic sediment delivery from a fluvially‐controlled, deep‐seated landslide in Aotearoa New Zealand

Past research has highlighted the importance of sediment delivery from multiple-occurrence regional landslide events triggered by storms or earthquakes. Herein, we examine a more persistent source sediment, that large, slow-moving in soft-rock hill country Aotearoa New Zealand. We map and monitor 80-ha Rangitikei Landslide 2015 to 2019 using time-lapse photography, ground surveys, photogrammetry, piezometers. show can be divided into several zones with distinctive movement patterns, but all respond river erosion. The fastest zone moves than 10 m per year flow-like fashion, while other move 0.01 via slow sliding. Movement occurs round, is two three times faster winter spring. While rainfall associated groundwater change are commonly attributed our data flow correlates closely weekly seasonal variability toe. This suggests fluvial erosion play an important role dynamics highly coupled landslides. estimate annual yield River at least 40 000 tonnes, this first quantification active Aotearoa. volume implies 7% total catchment suspended derived 0.03% contributing area, demonstrating disproportionate effect (and likely other) deep-seated landslide(s) as catchment. Sediment continuous episodic supply triggering events, delivering mostly fine-grained it potentially large impact on water quality.