This paper documents the various factors contributing to the evolution of landforms in the Kosi River valley, Ukhaldhunga area of the Kumaun Himalaya, Uttarakhand. The area falls in the major tectonic boundary between the Lesser Himalaya and the sub-Himalaya. Passing through the Parewa-Ukhaldhunga-Dabara area, this tectonic contact is known as the Main Boundary Thrust (MBT), which is characterized by presence of varied landforms. Study of the development of geomorphology, particularly those evolved in the MBT zone, suggests that the morphological features are intimately associated with the tectonic activities related to the movement of rocks along the MBT and the surface processes such as fluvial and mass movement. The various landforms observed in the MBT zone include strath terraces, fill terraces, paleochannels and V-shaped valley that pertain to fluvial genesis; gravity induced landforms such as landslide debris and colluvial fans; and tectonic landforms such as linear fault traces, swerving/swing of river course and linear depressions. Signature of recent tectonic activity along the MBT is observed between Dabara and Khakrakot. The activity is evident in the form of 8-km-long active fault trace trending NW-SE. Normal fault related landforms are observed in the hanging wall block of the MBT. Neotectonic strath terraces and fill terraces are well developed in the MBT zone. Multiple events of recurrence of landslides are evident from exposed section of landslide debris fans. The bedrocks are highly sheared, suggesting successive tectonic movements along the MBT. As a consequence, tectonic wedges have developed in the bedrocks. These wedges have facilitated for the recurrence of a number of landslides. The anthropogenic activities have also aggravated the slope stability. Truncation of older debris fan surfaces by an erosional/fault scarp is observed and the scarp separates the older fans from the youngest debris fan deposit. The scarp runs parallel to the MBT and Kosi River. Swerving of the Kosi River is as a result of the tectonic forcing along active lineaments/faults. The trend of lineaments of the maximum and high density is NE-SW, which is transverse to the trend of the NW-SE trending Himalayan fold-thrust belt.

本文记录了促成北阿坎德邦库玛恩•喜马拉雅山Ukhaldhunga地区科希河谷地貌演变的各种因素。该地区位于小喜马拉雅山与喜马拉雅山次大陆之间的主要构造边界内。穿过帕雷瓦-乌克哈德洪加-达巴拉地区，这种构造接触被称为主边界冲断层（MBT），其特征是存在多种地形。对地貌学发展的研究，特别是在MBT带中演化的地貌学研究表明，地貌特征与与岩石沿MBT的运动以及地表过程（如河流运动和质量运动）有关的构造活动密切相关。在MBT区域观察到的各种地形包括：阶地阶地，填充阶地，与河流成因有关的古河道和V型谷; 重力引起的地貌，例如滑坡碎屑和冲积扇；构造地貌，例如线性断层迹线，河道的倾斜/摆动和线性凹陷。在达巴拉（Dabara）和哈克拉科特（Khakrakot）之间观察到了沿MBT最近构造活动的特征。该活动以趋势为NW-SE的8公里长活动断层痕迹的形式体现出来。在MBT的悬挂墙块中观察到与正常断层有关的地貌。MBT地区的新构造地层阶地和填充阶地非常发达。从滑坡碎屑扇暴露的部分可以明显看出滑坡复发的多种事件。基岩被高度剪切，表明沿MBT的连续构造运动。结果，在基岩中形成了构造楔。这些楔形物促进了许多滑坡的发生。人为活动也加剧了边坡的稳定性。观察到较旧的碎屑风扇表面被侵蚀/断层的断头截断，并且该刮屑将较旧的风扇与最小的碎屑风扇沉积物分开。陡坡与MBT和Kosi河平行。科西河的枯竭是沿活跃的构造/断层的构造强迫的结果。最大和高密度的线性趋势是NE-SW，与NW-SE趋势喜马拉雅褶皱-冲断带的趋势成横向。观察到较旧的碎屑风扇表面被侵蚀/断层的断头截断，并且该刮屑将较旧的风扇与最小的碎屑风扇沉积物分开。陡坡与MBT和Kosi河平行。科西河的枯竭是由于沿构造活动/断层的构造强迫作用的结果。最大和高密度的线性趋势是NE-SW，与NW-SE趋势喜马拉雅褶皱-冲断带的趋势成横向。观察到较旧的碎屑风扇表面被侵蚀/断层的断头截断，并且该刮屑将较旧的风扇与最小的碎屑风扇沉积物分开。陡坡与MBT和Kosi河平行。科西河的枯竭是由于沿构造活动/断层的构造强迫作用的结果。最大和高密度的线性趋势是NE-SW，与NW-SE趋势喜马拉雅褶皱-冲断带的趋势成横向。