Humans are altering Earth's surface at unprecedented scales due to rapid urban expansion. Here we investigate the long-term geomorphic consequences of large-scale anthropogenic landscape modification, focusing on a recent mountain excavation and city construction project in the Loess Plateau region of China. In this project, tens of square kilometers of urban region were newly constructed by mountain top removal and valley filling, significantly altering the region's topography. We applied a Landscape evolution model (LEM) to simulate future natural landscape dynamics, including the erosional stability, soil thickness, and landslide potential over the next one hundred years following this landscape alteration. Moreover, we evaluate the short-term impacts on the stage water height and infiltration, which is related to potential flooding risk during heavy rainfall events. Our results reveal that the altered landscape exhibits significant susceptibility to soil erosion, redistribution of soil thickness, and increased landslide potential, particularly along the margins of the newly constructed zones and at the outlet of the Yanhe River tributary. Perturbations in infiltration rates and runoff behavior are also observed during the rainy season. This study underscores the scientific potential of LEMs as predictive tools for understanding the long-term behavior of engineered loess terrains-environments that are highly sensitive to anthropogenic modification and hydrological variability. By capturing the coupled feedback between erosion, infiltration, and slope instability, the modeling framework offers a robust basis for forecasting geohazards in the context of rapid urban expansion. These findings not only support proactive hazard mitigation and infrastructure planning but also contribute to advancing theoretical frameworks in anthropogenic geomorphology. Continuous monitoring, integrated with model-driven land-use planning, will be essential for achieving resilient and sustainable development in highly engineered and geomorphically dynamic landscapes.