production by reconstructing paleolandscapes using tephrochronology and lidar: Waipaoa River, New Zealand

Abstract Hillslope response to climate-driven fluvial incision controls sediment export and relief genera-tion in most mountainous settings. Following the shift to a warmer, wetter climate after the Last Glacial Maximum (LGM) (18 ka), the Waipaoa River (New Zealand) rapidly incised up to 120 meters, leaving perched, low-relief hillslopes unadjusted to that base level fall. In the Mangataikapua—a 16.5 km2 tributary principally composed of weak melange—pervasive post-LGM landslides responded to>50 m of fluvial inci-sion by sculpting and denuding>99 % of the catchment. By reconstructing LGM and younger paleosurfaces from tephra identified by electron microprobe analysis (EMPA) and lidar-derived surface roughness, we esti-mate the volume, timing, and distribution of hillslope destabilization in the Mangataikapua and the relative contribution of landslide-prone terrain to post-LGM landscape evolution. We calculate volume change between four paleosurfaces constrained by tephra age (Rerewhakaaitu, 17.5 ka; Rotoma, 9.4 ka; Whakatane, 5.5 ka; and Waimihia, 3.4 ka). From the paleosurface reconstructions, we calculate the total post-LGM hill-slope sediment contribution from the Mangataikapua catchment to be 0.56 0.06 (s.d.) km3, which equates to a subcatchment averaged erosion rate of 1.6 mm yr21. This is double the previous hillslope volume when normalized by study area, demonstrating that landslide-prone catchments disproportionately contrib-ute to the terrestrial post-LGM sediment budget. Finally, we observe particularly rapid post-Waimihia ero-sion rates, likely impacted by human settlement. 1