| The Wei River Basin is a first-order tributary of the Yellow River Basin,involving three major geomorphic units: the Loess Plateau,the Wei River Graben,and the Qinling Mountains.Slot canyons are one of the most important types of fluvial landforms in this region.However,due to their extremely small width-to-depth ratio and the fact that valley slopes are much greater than valley bottoms,as well as the widespread occurrence of gourd-shaped and rockshelter/rock-house landforms,the observation conditions are very complex,and both DEM data structure and resolution do not meet the requirements.Therefore,the genesis of slot canyons in the Wei River Basin remains at the qualitative research stage,and there is still considerable controversy over the genesis type.This study investigated the main river valleys in the area,identified eight typical slot canyons,overcame difficulties such as narrowness and weak GNSS signals,combined Sf M-MVS photogrammetry and lidar technology to conduct 3D reconstruction and genetic analysis,and obtained the following understanding:1)Eight typical slot canyons were obtained with relatively complete point cloud datasets,which can well characterize the complex 3D features of the valleys.The overall resolution of the generated 3D model ranges from 5cm to 50 cm,and the local resolution can reach the millimeter level,which can be used to identify and extract multi-scale geomorphic features of the valleys.2)Micro-landforms such as potholes,threshold,erosion trough,and scouring grooves,as well as geological features of bedrock such as bedding,joints,and fractures,can all be extracted through the 3D model.The results show that micro-landforms formed by water erosion further expand into slot canyons under the control of rock structural construction.These valleys are either located near small watershed divides or at cracks formed by new tectonic uplift,or in bedrock river sections where joints are developed.3)The newly slot canyons in Weihe Basin were identified and defined as four types: ?Slot canyons developed in red eolian sandstone that is not controlled by structures,such as Maoxiang and Tongchuan,which are the products of erosion by flowing water.These slot canyons lack vertical joints and dissolution,and cannot develop into Danxia landforms composed of networked lanes and valleys and peak clusters.?Loess-type slot canyons,which are widespread in loess plateaus and hillsides,such as the Muyugou valley in Bailuyuan,formed by rapid water erosion during flood season under the conditions of loess subsidence and vertical joints.?Slot canyons controlled by structure,such as Shiguxia in Linyou,Xiangshitan in Qianxian,and Yeyu River in Kouzhen,where Shiguxia and Xiangshitan are mainly controlled by conjugate shear joints produced by old structures,while Yeyu River is based on the old tectonic foundation,forming a newly generated Guanshan-Kouzhen active fault,controlling the development of the landform ? Gneissic granite type slot canyons,such as Fengyu and Tianziyu.These valleys are developed in gneissic granite at the northern foot of the Qinling Mountains.Due to the relatively uniform lithology and developed unloading joints,they quickly erode and retreat into shallow dish-shaped and U-shaped forms after the pot holes penetrate.In summary,3D point cloud detection technology is reliable in the study of slot canyons;the four typical slot canyons in the Wei River Basin exhibit obvious diversity,and this geomorphic differentiation evolution is mainly controlled by the lithology,structure,and rainfall of different blocks.The newly identified landscape resources can help promote rural revitalization and sustainable development. |
