36 Advances in understanding landslides and other mass movements

In this session we want to highlight advances in understanding mass movements, including studies focused on description, mapping, monitoring, triggering mechanisms, mitigation, modeling, and evaluating susceptibility.

Wednesday, 11 March 2026
8:30 AM - 10:30 AM
RCC, 105

Geological and Geotechnical Evaluation of Slope Stability in the Spruce Mountain Landslide Area, Northeastern Nevada

Paper number: 36-6
Program: Technical Sessions
Time: 9:50 AM – 10:05 AM

Authors

Abstract

The Spruce Mountain area (SMA) in Elko County, Nevada is characterized by steep slopes, complex lithology, and extensive faulting which creates conditions favorable for landslides, mostly large rock avalanches (LRA). A key problem with LRAs involves identifying the geological and geomorphological factors that control slope instability and determining the landslide mechanisms. By combining field observations, geological and geomorphological mapping, remote sensing data, and slope stability modeling, our study provides a comprehensive understanding of the processes governing both ancient and modern mass movements. Morphostructural analysis of the SMA identified potential source zones for the mass movement and confirmed the estimated movement velocity of up to 3 ms⁻¹ which indicates an extremely rapid rock avalanche event. For slope stability analysis in OPTUM G2 software, the main parameters of the geological model were determined including the thickness and distribution of lithological units, the orientation of faults, and slope geometry. In the calculations, the focus was placed on the upper part of the slope section, identified through structural-morphometric modeling as the principal source area of the LRA at Spruce Mountain. The geological model includes two stratified rock units: undifferentiated fractured dolomites (O3-D1) and limestones of Pogonip Group (O1-O2). The results of the Strength Reduction Method (SRM) and Limit Analysis (LA) indicate that the slope is close to its limit state; the computed factor of safety ranged between 0.73 (lower bound) and 1.449 (upper bound). The LA yielded a gravity multiplier of approximately 1.565, which is consistent with the SRM upper bound. The overall slope stability is controlled by the contrasting mechanical behavior of dolomites and limestones. Dolomites, characterized by higher cohesion and friction angle, exhibit relatively stable behavior. In contrast, limestones show significantly lower resistance, as evidenced by higher strain concentrations and displacement vectors directed downslope even at relatively low gravity multipliers (1.4–1.6). The modeling results strongly suggest that limestone layers in the upper part of the slope were the most unstable part of the slope and likely served as the source of massive rockfall and rock avalanche accumulations observed in the SMA. The combination of weaker mechanical parameters, structural complexity, and gravitational loading provides a consistent explanation for the origin and evolution of large-scale slope failures in this geological setting.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1

doi: 10.1130/abs/2026SE-411827

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