39. Riedel (1997) Geologic hazard and floodplain management: Mount Rainier General Management Plan
    Mount Rainier National Park (MORA) is in the process of developing a 20-year General Management Plan (GMP) in time for its 100th anniversary celebration in 1999. This report was prepared to assist planners in managing geologic hazards and floodplains in front country development and visitor use sites. NPS management policy in regard to geologic hazards focuses on saving human life, and avoiding hazard if possible. Further, where facilities must be located in hazard areas, design and siting should include mitigating measures to minimize risk to life and human property. At MORA, however, most developed areas are in mapped volcanic hazard zones. The designation of Mount Rainier as a Decade Volcano Study Area by the National Research Council in 1994 underscores the seriousness of the volcanic hazards at Mount Rainier. Due to NPS management policy and the considerable hazards at Mount Rainier, a geologic hazard mitigation approach is presented that avoids unrealistic closer of large areas of the park. On a short time scale of 0-5 years, this approach emphasizes education and contingency planning for response to hazards as means of mitigating volcanic hazards at the park. GMP hazard mitigation is focused on longer time scales. The recommended approach is that no new housing, administrative facilities, concessions or overnight visitor facilities be constructed in high hazard zones. A risk analysis of 23 visitor and administrative sites was conducted to identify the most hazardous and risky sites in the park. This analysis considered hazard, value and vulnerability at each of these sites. Components of hazard in the risk formula included both deterministic and probabilistic factors, while emphasizing the hazard presented by debris flows. Results indicate that White River Campground, Longmire and Cougar Rock Campground are the three sites at highest risk in the park by a large margin. It is recommended that hazard mitigation in the GMP focus on these three areas. White River Campground is by far the most hazardous and risky site at MORA with a hazard score two times greater than that of the next most hazardous site, Camp Schurman. High hazard score at White River Campground is due to the site's proximity to the volcano, location below fractured, hydrothermally weakened rocks on Little Tahoma Peak, and position next to the floodplain of White River. Nonvolcanic geologic hazards are also a concern at MORA. Hazards such as rock falls, snow avalanches and landslides occur at sites scattered throughout the park. The risk analysis and field studies also showed that the portion of Tahoma Woods north of highway 706 is an appropriate place for future developments. Trenches dug in spring 1995 indicate that this site has not been inundated by a debris flow in the past 10,000 years. Further, Tahoma Woods is outside case II and case III debris flow inundation zones, which have the most frequent recurrence intervals. Floodplain management at MORA floows the NPS Floodplain Management Guideline (1993). Ten of 23 developed sites, which are primarily day use areas and entrances, are actions that are excepted from compliance with the guideline. Preliminary floodplain assessments at 13 other sites indicate that only three sites are within regulatory floodplains. Detailed floodplain studies were conducted at Longmire, Carbon Entrance and Ipsut Campground to provide information that will allow these sites to be in compliance with the guideline. Walk-in sites at Ipsut and Loop-C of Ohanapecosh campgrounds are recommended for temporary seasonal closure during periods of high river flow in spring and early winter. Floodplains at MORA are as dynamic as at any NPS area, due to the movement of vast amounts of water and glacial sediment carried by the large rivers down the steep slopes of the volcano. It is estimated that because of rapid rates of deposition and erosion, typical floodplain mapping techniques would be inaccurate in as little as 10 years after completion. Therefore, it is recommended that floodplain boundaries be drawn conservatively, without the use of expensive hydraulic modeling techniques. Further, stream gaging stations place on the large rivers of the park would provide important information to managers on rates of stream channel deposition and channel instability.
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.
538. Wall et al. (2026) Origin and evolution of mafic volcanism associated with 3 m.y. of andesite production at the Goat Rocks volcanic cluster, southern Washington Cascade Range
     More than 3 m.y. of mafic volcanism near the Goat Rocks volcanic cluster in the southern Washington Cascade Range, USA, lends insight into the evolution of basalts and the subarc mantle at a long-lived, major arc volcanic locus. We contribute field observations, 40Ar/39Ar dates, paleomagnetic directions, and bulk rock and mineral compositions to characterize nine mafic units that erupted in association with the Goat Rocks volcanic cluster. The time frame of mafic volcanism, ca. 3.6 Ma to 60 ka, encompasses the lifespan of the central volcanic cluster (3.1 Ma to 115 ka), with a lull from ca. 2.7 Ma to 1.4 Ma. A climactic period of voluminous mafic activity and far-traveled lava flows, including construction of the Hogback Mountain shield volcano, coincided with voluminous andesite eruptions from the central volcanic cluster. The basaltic rocks in the Goat Rocks area are calc-alkaline to barely tholeiitic and have high field strength element depletion relative to large-ion lithophile elements characteristic of calc-alkaline basalts (CAB) of the Cascade volcanic arc. Unlike at neighboring andesitic volcanic centers (Mounts Adams, St. Helens, and Rainier), no other mafic end members such as high-aluminum olivine tholeiite (HAOT) or intraplate-type basalt (IPB) are present at or near the Goat Rocks volcanic cluster, although some of the calc-alkaline basalts in this study have IPB-like affinities. The Goat Rocks mafic units exhibit two main temporal trends in composition: (1) the most primitive basalts erupted earlier, compared to less primitive and more evolved compositions later, and (2) high field strength element concentrations are higher in the younger basalt units relative to the oldest two. In contrast to these temporal trends, the mafic units define two compositional groups that recur through time, a low-Sr and a high-Sr group, each with distinct trace element and Sr and Nd isotope ratios. Although radiogenic isotope ratios are generally aligned with High Cascades CAB and HAOT, some extend toward IPB of Mount Adams and Simcoe Mountains volcanic field. Olivine-dominated crystal fractionation at shallow pressure from a small range of parent magma compositions accounts for much of the variation among the basalts and basaltic andesites. A high-pressure fractionation model is plausible for only one of the youngest basalt units (basalt of Walupt Lake volcano). Mafic recharge and crustal assimilation accounts for the incompatible-element enriched composition of basaltic andesites erupted during construction of the largest andesitic centers, further supporting sustained basalt mass flux and thermal energy driving andesite genesis. We model the most primitive members of the Goat Rocks mafic units as partial melts of successively less depleted mantle in time. Variable degrees of fluxing with fluids and melts from subduction explain the distinction between high-Sr and low-Sr groups. We propose that mantle metasomatism by ancestral subduction and fluid-flux melting is heterogeneously distributed through the local subarc mantle and played a greater role in the genesis of the high-Sr basalt group. The limited range of primitive basalt types around the Goat Rocks volcanic cluster contrasts with the much greater diversity of basalts throughout the southern Washington to northern Oregon Cascade arc. On the other hand, the central volcanic cluster encompasses nearly the entire diversity observed at neighboring composite volcanoes. In the case of the Goat Rocks area at least, and perhaps attributable to the entire region, this means that the genesis of diverse intermediate magmas is independent from and does not require vastly different parental basalt compositions.

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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