A century of urban landslides: the legacy and consequences of altering riverbank landscapes

Urban landslides are a deadly and costly hazard. Human actions, such as altering the grade, composition, and vegetation-cover of hillslopes, can increase the threat of mass movements. Here, we use an interdisciplinary approach to examine the spatial distribution, timing, and cause of landslides affecting a state highway and adjacent buildings along the top of a steep, urban riverbank in the mid-latitude, humid-temperate state of Vermont. Using over 100 years of mapping, photographs, and written records, we demonstrate that most mass movements in our field area occurred on slopes over-steepened by the addition of uncompacted artificial fill – added without engineering considerations. Emplaced atop glacial and post-glacial sediment with low hydraulic conductivity, the fill, having little to no cohesion, expanded buildable areas, but the new infrastructure sat on unstable ground. Over the following decades, repeated failures, (n=20), mostly shallow translational landslides in fill material along with several deeper-seated rotational slides, sent buildings, trees, and segments of road into the river below. Solutions include incentivizing the removal of structures built on fill and limiting further filling activities through changes in zoning regulations and more effective enforcement of existing municipal codes. The approach we use provides a framework for similar geographic settings and can inform urban planning and risk assessment. Thematic collection: This article is part of the Engineering Geology and Hydrogeology of the Anthropocene collection available at: https://www.lyellcollection.org/topic/collections/engineering-geology-and-hydrogeology-of-the-anthropocene Supplementary material: https://doi.org/10.6084/m9.figshare.c.7103608