Geology topics

Erika Hart Birkeland

Publications and source records attributed to Erika Hart Birkeland.

2 recordsLinked to original sources

USGS2026

Stability changes after weak layer collapse: Insights from an unexpected dataset

While conducting avalanche mitigation or traveling through the backcountry, avalanche professionals sometimes experience a "whumpf": a collapse-mode crack accompanied by surface cracking that does not produce an avalanche. These whumpfs are a clear warning sign of instability in the surrounding terrain. But assessing the collapsed slope itself, if it is steep enough to avalanche, carries much more uncertainty. Can slopes that whumpf and are steep enough to slide still avalanche? The answer to this question supports avalanche mitigators and ski guides in assessing whether to open such slopes. Previous research on collapsed slopes is limited to one study conducted before tests that estimate crack propagation propensity, such as the Propagation Saw Test (PST), were developed. This work showed that weak layer shear strength decreased immediately after collapsing and then increased over time. However, no research has examined crack propagation propensity after a whumpf. Studying propagation propensity is key for assessing how whumpfs immediately affect slope stability. To improve our understanding of changes in propagation propensity following weak layer collapse, we conducted PSTs on a test slope in the hours and days after an unexpected collapse occurred on a layer of surface hoar. Two PSTs at our study site three days prior to this collapse provided an estimate of weak layer propagation propensity. PST cut lengths decreased immediately following the collapse, suggesting that the collapse increased the propagation propensity. However, over the next 4-5 hours, PST cut lengths steadily increased at our site, likely due to ongoing sintering and strengthening in the collapsed weak layer. By the end of day two, we were no longer able to initiate propagation, suggesting substantial stabilization of the weak layer. Our results support prior findings and observations suggesting that slopes may remain capable of producing avalanches immediately after a collapse but likely stabilize over the next day or two. Although this research does not provide answers about precisely when a slope becomes stable after a collapse, it does highlight uncertainties in our understanding and interpretation of the stability of slopes that have whumped.

Montana↗

USGS2026

Patterns of glide avalanche release: Insights from 23 years of observations along the Going-to-the-Sun Road, Montana, USA

Glide avalanches pose a notable hazard during annual spring snow removal operations along the Going-to-the-Sun Road (GTSR) in Glacier National Park (GNP), USA. Glide cracks consistently form on specific slopes near and above the GTSR. Some glide crack locations produce glide avalanches most years (known as repeater paths), whereas others are less predictable and either release or melt in place. Previous studies of glide avalanches have focused on different meteorological, snow-pack, and terrain parameters that influence glide release. The timing of glide avalanche release remains difficult to predict, which can be a challenge. To the authors' knowledge, no previous work has approached the issue of timing by comparing the chronological release order of glide paths within an operation. To address this, we examine the release order of repeater paths along the GTSR and investigate different topographical factors that may influence release timing. To investigate the timing of glide avalanche release, we analyzed a dataset of annually recorded glide avalanches from 2003 to 2025 along the GTSR from mid-March to June. We identified 359 glide avalanches with starting zones covering all aspects between 1,600 and 2,700 meters, and performed analysis on topographic factors including elevation, aspect, slope angle, and bed surface. Additionally, we assessed the likelihood and sequence of the release of seven repeater paths. Seven repeater paths along the GTSR generate glide avalanches nearly every year (65–100% of the study period), with two paths (Peak 7774 and Peak 7850) releasing first in over half of the years observed (p-value < 0.01). These paths have been informally recognized as "indicator paths," though this distinction has not been quantified until now. Identifying factors that drive the timing of glide avalanches using a days-scale operational signal can support the safeguarding of infrastructure and personnel. By examining release order and related variables, this study provides practical insights to inform operations managing glide avalanche hazards. Our methods may help forecasters pinpoint indicator paths and potentially recognize the onset of glide avalanche cycles, offering a framework for other operations.

Montana↗