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On May 31, 2019, a landslide near Waterbury in central Vermont removed >200,000 m3 of glacial lake deposits from a hillside in the Mt. Mansfield State Forest and transported the material across Cotton Brook, creating a dam near its toe. In the months following the slide, the brook breached the toe, removing ≥54, 000 m3 of sediment and transporting it ~1.3 km downstream into the Waterbury reservoir where it formed a large sedimentary delta. The delta grew 243% by Fall, 2020 until it began to erode into the reservoir in 2021. A collaborative team from the Vermont Geological Survey, the Vermont Agency of Transportation, Norwich University, and the University of Vermont team began a yearly monitoring of these events in 2019 using field-based mapping of bedrock and surficial geology, photogrammetry using annual drone surveys, and two LiDAR data sets. The first LiDAR data set was collected in 2014 prior to the slide by the Vermont Center for Geographic Information and the second after the slide in 2021 by the U.S. Army Corp of Engineers. Time-lapse spatial differencing allowed us to (1) quantify changes in surface topography over time, (2) calculate sediment budgets from source (landslide) to sink (delta), and (3) determine how mechanisms of mass wasting changed over time. Through this study we have also documented the following: (a) a second slip event in 2020 that removed ~25, 000 m3 of additional material from the hillside and contributed to growth of the Waterbury reservoir delta, (b) bedrock basins defined by the intersection of bedrock foliation and orthogonal fracture sets that appear to control slip location and geometry, (c) bedrock structures that influence the subsurface hydrology of the slip, which is expressed by oxidized groundwater seeps and a preferential deepening of rills into gullies on one side, and (d) how horizontal variations in the type and thickness of glacial lake sediments influenced mass-wasting mechanisms, including catastrophic failure of the hillside, the slumping of landslide sidewalls, the formation of crescent-shaped earth fractures, channeling around slumps, and the removal of material in deepening gullies. This study shows how a large landslide evolves from a major failure phase through later erosional and colluvial adjustments and supplies sediment at an episodic rate to the surface water system.
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Alpine hillslope failure in the western US: insights from the Chaos Canyon landslide, Rocky Mountain National Park, USA
The Chaos Canyon landslide, which collapsed on the afternoon of 28 June 2022 in Rocky Mountain National Park, presents an opportunity to evaluate instabilities within alpine regions faced with a warming and dynamic climate. Video documentation of the landslide was captured by several eyewitnesses and motivated a rapid field campaign. Initial estimates put the failure area at 66 630 m2, with an average elevation of 3555 m above sea level. We undertook an investigation of previous movement of this landslide, measured the volume of material involved, evaluated the potential presence of interstitial ice and snow within the failed deposit, and examined potential climatological impacts on the collapse of the slope. Satellite radar and optical measurements were used to calculate deformation of the landslide in the 5 years leading up to collapse. From 2017 to 2019, the landslide moved ∼5 m yr−1, accelerating to 17 m yr−1 in 2019. Movement took place through both internal deformation and basal sliding. Climate analysis reveals that the collapse took place during peak snowmelt, and 2022 followed 10 years of higher than average positive degree day sums. We also made use of slope stability modeling to test what factors controlled the stability of the area. Models indicate that even a small increase in the water table reduces the factor of safety to <1, leading to failure. We posit that a combination of permafrost thaw from increasing average temperatures, progressive weakening of the basal shear zone from several years of movement, and an increase in pore-fluid pressure from snowmelt led to the 28 June collapse. Material volumes were estimated using structure from motion (SfM) models incorporating photographs from two field expeditions on 8 July 2022 – 10 d after the slide. Detailed mapping and SfM models indicate that ∼1 258 000 ± 150 000 m3 of material was deposited at the slide toe and ∼1 340 000 ± 133 000 m3 of material was evacuated from the source area. The Chaos Canyon landslide may be representative of future dynamic alpine topography, wherein slope failures become more common in a warming climate.
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- PAR ID:
- 10508673
- Publisher / Repository:
- Copernicus
- Date Published:
- Journal Name:
- Earth Surface Dynamics
- Volume:
- 11
- Issue:
- 6
- ISSN:
- 2196-632X
- Page Range / eLocation ID:
- 1251 to 1274
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/esurf-11-1251-2023
