Geology topics

John Sykes

Publications and source records attributed to John Sykes.

3 recordsLinked to original sources

USGS2026

Revisiting avalanche destructive scale and associated mass estimates

Avalanche destructive (D) size classifications are essential for forecasting, communication, and risk management, yet size estimation remains one of the more subjective elements of avalanche assessment. Practitioners typically rely on visual impressions of destructive potential, path length, and estimated mass and volume. Recent work indicates that size is often underestimated even by experienced observers, especially when based on photographs or distant observations. Although mass is central to defining destructive size, the empirical foundations of mass–size relationships have rarely been revisited, and expert variability in size assignment could be decreased if more consistent operational tools were available. We evaluated whether a simple, practitioner-focused calculation tool using slab dimensions, snow density, and snow water equivalent can provide reliable mass estimates that correspond meaningfully with existing destructive size classes. Using this tool, we estimated avalanche mass and compared the results to observer-assigned D sizes. We also simulated mass outputs using a dense flow avalanche simulation module and compared observer estimates and simple-tool outputs to recent volume-based methods for D-size classification. Across 143 well-documented dry snow avalanches from multiple avalanche climates, the size estimation tool tends to classify avalanches larger than field-based observers. We found a mean bias of 0.47 D-size units and a typical (mean absolute) disagreement of 0.56. Our results show that 95% of events landed within one whole D-class of each other and 71% within a half-class. Agreement between the simple tool mass estimates and dense flow avalanche simulations was generally strong, though discrepancies emerged in cases with substantial entrainment or complex terrain. We compared the size tool to the simulation module with entrainment (n=4) and without entrainment (n=8). With entrainment, the two methods estimate the same D-size class in 4 of 4 comparable events and 7 of 8 events without entrainment. Also, the simulation module estimates larger sizes than the observer in 7 of 8 cases without entrainment and all 4 cases with entrainment. These findings support that development of practical, mass-based tools could improve D-size consistency and emphasize the value of revisiting historical mass–size relationships. The accompanying application offers practitioners an accessible and operationally useful resource for improving D-size estimation from field observations.

Conference Paper↗

USGS2026

Applying automated avalanche terrain mapping to wildlife ecology: A case study of Dall's sheep in southcentral Alaska

Avalanche hazard has been studied extensively in the context of human risk, but its role in alpine wildlife ecology remains poorly understood. Long-term telemetry studies have revealed that avalanches are an important source of mortality for some mountain ungulates. Investigating the processes underlying these events is challenging because avalanche activity and snowpack conditions are rarely monitored across the spatial and temporal extent of wildlife studies. Recent advances in automated avalanche terrain mapping provide a new opportunity to address this knowledge gap by quantifying wildlife exposure to modeled avalanche terrain across large landscapes. We demonstrate this application using Dall's sheep (Ovis dalli dalli) in southcentral Alaska, where a 12-year study identified avalanches as the leading known cause of adult mortality. We used GPS locations from 134 adult Dall's sheep (385 sheep-years) collected between 2012 and 2024 across Chugach State Park and the Talkeetna Mountains, Alaska, USA. We characterized seasonal patterns of terrain exposure using the Automated Avalanche Terrain Exposure Scale and complementary metrics representing potential release areas, runout terrain, slope, and aspect. Guided by previous studies of Dall's sheep habitat selection, we developed a priori ecological expectations for seasonal exposure and used descriptive summaries of GPS locations to examine patterns of sheep use. Sheep locations occurred almost exclusively within avalanche terrain throughout the year, with Complex terrain accounting for 61–67% of locations across seasons. Winter and spring locations occurred on slightly steeper slopes while simultaneously having lower potential release area values and lower-value runout terrain than summer and autumn locations. Use of south-facing terrain increased from 64% of locations in summer to 70% in autumn and winter and 83% in spring—coinciding with the highest seasonal concentration of avalanche mortality. These descriptive patterns illustrate how complementary avalanche-terrain metrics can reveal patterns of wildlife exposure that would not be apparent from slope angle and aspect alone. Integrating automated avalanche terrain mapping with wildlife telemetry provides a new approach for identifying patterns of terrain exposure to guide further investigation into factors influencing wildlife avalanche risk.

Alaska↗

USGS2023

Spatial extent of forested avalanche terrain impacted by wildfire across the Sawtooth National Forest

Forest structure is a major driver of mountain snowpacks and avalanche occurrence. Healthy forests can reduce the incidence of dangerous slab avalanches, slow avalanches when in motion, shorten their runout distances, and act as a safety buffer for backcountry users, infrastructure, and transportation corridors. Since 1984, wildfire area in the seasonal snow zone of the western United States has increased by 70% throughout the seasonal snow zone, creating significant changes to avalanche prone mountains and their connected communities. A major unknown is the impact a reduction of forested area due to forest fires will have on avalanche occurrence. We hypothesize increased potential for avalanching in forested areas impacted by wildfire. Reduced tree cover may make previously heavily forested terrain more susceptible to avalanching. Increases in the size of avalanche start zones, paths, and runouts due to forest fires may increase the destructive size of avalanches and create cascading ecological effects within the adjacent forested terrain. Forest fires may therefore increase the likelihood of avalanche release, resulting in further loss of tree cover and increased avalanche area as well as decreased protection for human infrastructure. In this study, we quantify avalanche area changes before and after the Ross Fork wildfire (2022) in Sawtooth National Forest, Idaho, USA. We utilized satellite imagery, a digital elevation model and historical fire spatial data to quantify and characterize avalanche area changes within the fire perimeter using the Auto-ATES workflow (Sykes et al., 2022). We found decreases in forest coverage that contributed to widespread increases in potential avalanche release areas, avalanche tracks, and potential runout zones throughout the study area as well as the creation of new potential avalanche release areas and a substantial decrease in non-avalanche connected terrain within the fire perimeter. These preliminary findings help inform avalanche and snow safety professionals as well as land managers working in wildfire-prone forested areas about potential post-wildfire changes in avalanche terrain.

Idaho↗