472. Ewen (2023) Glacial loss and threatened fish: The future of Mount Rainier's cold-water Bull Trout habitats
     Glaciers play a key ecological role in the river systems that they support. Cold-water reaches supplied by glacial ice serve as critical habitats for aquatic organisms that rely on specific thermal ranges to survive. Federally threatened Bull Trout (Salvelinus confluentus) require very cold temperatures, like those found in glacial systems, to complete their life cycles. However, glaciers are retreating due to climate change and are expected to continue diminishing throughout this century. Decreased glacial extent could result in warmer stream temperatures downstream from glaciers and, depending on the magnitude of stream temperature increase, cold-water habitats relied upon by Bull Trout and other sensitive species could shrink. This issue is particularly relevant to Mount Rainier (Washington State, USA). Mount Rainier’s dense concentration of glaciers supports several rivers that provide crucial cold-water spawning habitats for Bull Trout. Future scenarios in which Bull Trout spawning habitats are impacted by glacial decline resulting from increased air temperatures have yet to be widely studied on Mount Rainier. To explore the future of Mount Rainier’s cold-water habitats, I used hourly stream temperature data collected in the glacially-fed White River and Carbon River watersheds, designated as critical Bull Trout spawning habitat by the Endangered Species Act, from June – October in 2021. Based on these empirical stream temperature data, I fit spatial stream network models to each watershed, representing contemporary thermal conditions as a function of current glacial extent and air temperature. Using seven-day average daily maximum (7DADM) stream temperature as my thermal metric and September as my time frame, I focused predictions during Bull Trout spawning season in the White and Carbon rivers. To then simulate future climate change impacts to spawning habitats, I adjusted the models to predict stream temperature in both mid-century and late-century scenarios of air temperature rise, coupled with 20%, 40%, and 80% declines in glacial extent. The average 7DADM temperature predicted for contemporary conditions was 6.3°C in the White River watershed and 8.1°C in the Carbon. As air temperature values increased and glacial size decreased, stream temperatures increased to a maximum of 15.7°C (an increase of 9.4°C) in the White River watershed and up to 12.7°C (an increase of 4.6°C) in the Carbon. The proportion of river kilometers that may be thermally viable for Bull Trout spawning, classified as 12°C, significantly declined in both watersheds by late-century. Site-specific thermal predictions for individual spawning streams found that a few streams may provide cold-water habitats in the coming decades, while most will likely warm beyond a spawning thermal threshold. These results can be utilized by resource managers seeking to conserve Bull Trout and protect the most critical, enduring cold-water habitats. My models can furthermore be used as baselines for future modeling efforts in these or similar glacial systems.
543. Wood and Peters (2026) Influence of modeling assumptions on pedestrian evacuation success for non-eruptive lahar hazards at Mount Rainier, Washington
     Previous efforts to characterize lahar threats posed to communities downstream of volcanoes have focused primarily on delineating hazard zones that lack information on lahar-arrival times and exposure estimates that implicitly treat threats to be the same regardless of distance from the volcano. Estimated lahar-arrival times, travel times for individuals to leave hazard zones, and possible evacuation delays related to event identification, warning dissemination, and evacuee behavior are important, but often overlooked, aspects of understanding the societal threats posed by lahars. These temporal considerations are important for unexpected lahars that could occur due to slope failure in the absence of precursory volcanic unrest or eruption. This case study examines the role of time in lahar evacuations by quantifying population exposure and evacuation potential for non-eruptive lahar hazards associated with Mount Rainier, Washington. Lahars could directly affect tens of thousands of residents and employees, thousands of students at primary and secondary schools, and hundreds of individuals at long-term residential care facilities. Geospatial path-distance modeling quantified evacuation potential for 736 scenarios that represent combinations of lahar sources, evacuation destinations, pedestrian travel speeds, and a range of departure-delay assumptions. Depending on location, some communities may have substantial loss of life in tens of minutes after lahar initiation, whereas other communities may be managing large-scale evacuations over several hours. Estimates of evacuation success based on a range of scenarios provide individuals in hazard zones and risk-reduction agencies with insights on how their actions may increase or decrease the number of people that survive future lahars.
542. Raup et al. (2025) Tracking extinct glaciers in GLIMS
     Global Land Ice Measurements from Space (GLIMS), an initiative to build and distribute a database of global glacier data, has recently begun to track glaciers that have recently disappeared. GLIMS provides a definition of “extinct” glaciers for our community, and the final determination of extinction is left to local experts. There are currently 181 glaciers in the GLIMS Glacier Database that are marked as “extinct”, though we recognize that there have been many more reported in the literature. GLIMS welcomes more submissions to make the list more complete.
541. Carlson et al. (2026) Disappearing glaciers of the Oregon Cascades, USA
     The Oregon Cascades had 35 named glaciers on seven volcanoes in the 1980s, with 34 of those glaciers remaining by 2000. Here, we document the glaciers that fall into the Global Glacier Casualty List categories based on five years of field observations of these 34 glaciers. Five glaciers have disappeared, four have almost disappeared and eight are critically endangered. Thus, half of the Oregon Cascades named glaciers have disappeared, almost disappeared, or reached critically endangered status in the 21st century. Between 1980 and 2024, the May–October ablation season of the Oregon Cascades region warmed at ∼0.3°C per decade, with a 2020–24 mean temperature ∼1.7°C warmer than the 1975–84 mean. In contrast, there was no significant trend in November–April accumulation season precipitation. Given the significant rise in melt-season temperature, we attribute ongoing glacier disappearance in the Oregon Cascades to the warming climate.
540. Ghent et al. (2026) When every second counts: Parental decision-making in Mt Rainier’s lahar inundation zone
     Mount Rainier, a heavily glaciated stratovolcano in Washington State [USA], has a documented history of producing major lahars. The potential for future high-magnitude flows threatens approximately 90,000 downstream residents and has prompted one of the nation’s most extensive volcanic monitoring systems, including a specialized lahar detection network. Because portions of Rainier’s west flank are composed of hydrothermally altered, unstable rock, the region is especially vulnerable to “no-notice” lahars triggered by sudden, non-eruptive slope failure. In response, schools in at-risk zones have conducted lahar evacuation drills – now a legal requirement – for over two decades, demonstrating that on-foot evacuation is the most effective strategy for student and staff safety. Despite these efforts, many parents report an intention to retrieve their children from school during an emergency lahar evacuation, contradicting official guidance. Such actions could obstruct evacuation routes, delay emergency response, and increase personal risk, especially in areas where modeled lahar arrival times are under one hour. Parent decision-making thus presents a critical, yet understudied, variable in evacuation planning and is considered integral to the success of city-wide evacuations. Here we present the ongoing work from focus groups held with local parents to explore motivations behind their intentions. Topics of discussion within the focus groups include parents’ general understanding of lahar hazards, their intended actions, their confidence in school evacuation plans, and underlying factors in their decision-making. These insights can support more effective communication and preparedness strategies by emergency managers and school officials, while also contributing to broader discussions about protective action decision-making in rapid-onset hazards beyond volcanic settings.
539. Conner et al. (2026) Quantifying seismic properties of a river channel at Mount Rainier for use in debris flow monitoring and analysis
     Theoretical models that relate debris flow properties to their seismic signature suggest seismic methods may be used to remotely characterize properties of these events. However, the complexity of debris flow sources and poorly constrained material properties in near‐surface environments limit our ability to determine important attributes of debris flows, such as volume and particle size distribution, from seismic records alone. In this study, we explore the sensitivity of debris flow seismic signals to subsurface seismic characteristics using an established debris flow seismicity model and subsurface properties derived from active‐source measurements in the Tahoma Creek stream channel at Mount Rainier, United States. Using refraction and multichannel analysis of surface waves, we estimate 1D primary and secondary wave velocity profiles to a depth of 11 m and calculate the frequency‐varying phase velocity (⁠v_c) and Rayleigh‐wave quality factor (⁠Q_R⁠) for frequencies between 9 and 50 Hz. We find that the Tahoma Creek stream channel has low ⁠v_c, varying with frequency between 226 and 434 m/s, and is highly attenuating, with Q_R⁠ estimated below 13.3 at all analyzed frequencies. We model the seismic signal of a hypothetical debris flow in Tahoma Creek using our measured values and compare the results against the same model but varying v_c and ⁠Q_R over a range of frequency‐independent, single values commonly used in the literature when measurements are not available (⁠v_c = 250-750 m/s, ⁠Q_R = 3-33⁠). We find that the power spectral densities of the modeled debris flows vary by orders of magnitude within the subset of our test values, highlighting the benefits of measuring material properties when using modeled debris flow seismic signals for quantitative monitoring.

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The U.S. Geological Survey Cascades Volcano Observatory and the University of Washington Pacific Northwest Seismic Network continue to monitor Washington and Oregon volcanoes closely and will issue additional notifications as warranted.

Website Resources

For images, graphics, and general information on Cascade Range volcanoes: https://www.usgs.gov/observatories/cvo
For seismic information on Oregon and Washington volcanoes: http://www.pnsn.org/volcanoes
For information on USGS volcano alert levels and notifications: https://www.usgs.gov/programs/VHP/volcano-notifications-deliver-situational-information

Jon Major, Scientist-in-Charge, Cascades Volcano Observatory, jjmajor@usgs.gov

General inquiries: vhpweb@usgs.gov