Holocene alteration of glacial sediments as a possible mechanism for slope instability in central Vermont

Presenter's Name(s)

Genevieve Foran

Abstract

In May 2019, the Cotton Brook landslide in Waterbury, Vermont, displaced over 200,000 m³ of sediment, representing the largest landslide in the state’s recent history. The site remains active, offering a critical case study for examining the geochemical and geomorphological controls on landslide initiation. This study identifies key factors contributing to slope failure by analyzing the mineralogical composition of surficial sediments, assessing geochemical weathering processes, and evaluating sediment characteristics that influence slope instability. Particle size distribution analysis, combined with X-ray diffraction and fluorescence, reveals interstratified illite-chlorite rich clay strata and well-defined alternating fine sand and silty clay layers. The mineralogical composition of the clay layers corresponds to temperate to polar weathering regimes, suggesting that Holocene alterations to glacial sediments may contribute to the formation of preferential slippage planes. The presence of clay deposits outside the bounds of former glacial lakes also indicates a possible higher extent of lake level than previously measured. These findings provide insight into landslide susceptibility in glaciated landscapes, with potential applications for hazard assessment and sediment management in Vermont and similar geological settings. Understanding these processes is particularly relevant for mitigating risks to infrastructure and managing sediment transport into the Waterbury Reservoir, where ongoing slope failure continues to drive sediment accumulation.

Primary Faculty Mentor Name

Nicolas Perdrial

Status

Undergraduate

Student College

College of Arts and Sciences

Program/Major

Geography

Primary Research Category

Physical Science

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Holocene alteration of glacial sediments as a possible mechanism for slope instability in central Vermont

In May 2019, the Cotton Brook landslide in Waterbury, Vermont, displaced over 200,000 m³ of sediment, representing the largest landslide in the state’s recent history. The site remains active, offering a critical case study for examining the geochemical and geomorphological controls on landslide initiation. This study identifies key factors contributing to slope failure by analyzing the mineralogical composition of surficial sediments, assessing geochemical weathering processes, and evaluating sediment characteristics that influence slope instability. Particle size distribution analysis, combined with X-ray diffraction and fluorescence, reveals interstratified illite-chlorite rich clay strata and well-defined alternating fine sand and silty clay layers. The mineralogical composition of the clay layers corresponds to temperate to polar weathering regimes, suggesting that Holocene alterations to glacial sediments may contribute to the formation of preferential slippage planes. The presence of clay deposits outside the bounds of former glacial lakes also indicates a possible higher extent of lake level than previously measured. These findings provide insight into landslide susceptibility in glaciated landscapes, with potential applications for hazard assessment and sediment management in Vermont and similar geological settings. Understanding these processes is particularly relevant for mitigating risks to infrastructure and managing sediment transport into the Waterbury Reservoir, where ongoing slope failure continues to drive sediment accumulation.