76. Moran et al. (1999) P wave crustal velocity structure in the greater Mount Rainier area from local earthquake tomography
    We present results from a local earthquake tomographic imaging experiment in the greater Mount Rainier area. We inverted P wave arrival times from local earthquakes recorded at permanent and temporary Pacific Northwest Seismograph Network seismographs between 1980 and 1996. We used a method similar to that described by Lees and Crosson [1989], modified to incorporate the parameter separation method for decoupling the hypocenter and velocity problems. In the upper 7 km of the resulting model there is good correlation between velocity anomalies and surface geology. Many focal mechanisms within the St. Helens seismic zone have nodal planes parallel to the epicentral trend as well as to a north-south trending low-velocity trough, leading us to speculate that the trough represents a zone of structural weakness in which a moderate (M 6.5–7.0) earthquake could occur. In contrast, the western Rainier seismic zone does not correlate in any simple way with anomaly patterns or focal mechanism fault planes, leading us to infer that it is less likely to experience a moderate earthquake. A ∼10 km-wide low-velocity anomaly occurs 5 to 18 km beneath the summit of Mount Rainier, which we interpret to be a signal of a region composed of hot, fractured rock with possible small amounts of melt or fluid. No systematic velocity pattern is observed in association with the southern Washington Cascades conductor. A midcrustal anomaly parallels the Olympic-Wallowa lineament as well as several other geophysical trends, indicating that it may play an important role in regional tectonics.
524. Ring (2025) Exploring thermal occupancy between bull trout and brook trout in glacial headwaters
     Cold, glacially influenced headwater streams are recognized as critical thermal refugia for cold-water fish species such as bull trout (Salvelinus confluentus), which are highly sensitive to warming temperatures and face significant threats from climate change and non-native species. The cold waters of glacial streams not only provide essential thermal conditions for bull trout but may also exclude non-native species like brook trout (Salvelinus fontinalis) that compete with or displace bull trout. My study assesses the distribution of bull and brook trout in two glacial headwater rivers within Mount Rainier National Park, an area that includes federally designated critical habitat for bull trout under the U.S. Endangered Species Act. Using environmental DNA (eDNA) sampling and spatial stream network modeling (SSNM), I examined the relationship between fish presence and water temperature to understand thermal occupancy within glacial headwaters. Results showed that bull trout were widely distributed across the study site and detected at temperatures as low as 3 °C. Brook trout were concentrated in the warmest areas of the study area, being most prevalent between 6 and 8 °C, with the probability of their presence increasing as temperatures increased. Brook trout were nonetheless observed at temperatures as low as 4.25°C, which indicates a lower thermal tolerance than previously documented and calls into question the idea that temperature is a limiting factor for their distribution. My findings present evidence that brook trout may be more tolerant of cold stream temperatures than previously thought, and low stream temperatures may not be as strong of a barrier to invasion. Greater understanding of thermal occupancy of bull trout and brook trout in glacial headwaters is necessary to inform management strategies to mitigate the risk of bull trout extirpation in these vulnerable ecosystems.
523. Field et al. (2025) Best practices for managing bank erosion within the National Park Service and National Wild and Scenic River System
     Riverbank erosion is a natural process that occurs as rivers adjust to disturbance events and to changes in water and sediment delivery over time. The resulting lateral movement of river channels is fundamental to building complex, dynamic, and resilient landscapes. In this sense, bank erosion is crucial to creating healthy rivers and should be preserved whenever possible. However, river managers may deem protection from bank erosion necessary if bank retreat threatens infrastructure, developed land, or other valuable natural and cultural resources. The National Park Service manages over 220,000 miles of rivers, approximately 3,750 of which are part of the National Wild and Scenic River System, encompassing various climatic, geological, watershed, and land use settings. These rivers have unique protections granted under National Park Service policies and the Wild and Scenic River Act, which require any action taken to mitigate bank erosion must minimize impacts to natural processes and river health. This document provides river managers with guidance and tools to ensure that bank erosion management aligns with the protections granted to Wild and Scenic Rivers and rivers managed by the National Park Service. River managers should reference this document during the project conceptual design phase to steer bank erosion management practices toward techniques that maintain the ecological and geomorphic functions of rivers. When evaluating a bank erosion issue, managers are encouraged to determine if erosion can be allowed to continue unimpeded or if offsite measures can be undertaken to slow the rate of bank retreat. A variety of surface treatments and flow deflection treatments are described for situations in which on-site bank protection is deemed necessary. Deformable treatments and those using organic materials, such as live vegetation or logs, are generally favored over those using inert materials, such as concrete and rock riprap.
522. Pang et al. (2025) Long-lived partial melt beneath Cascade Range volcanoes
     Quantitative estimates of magma storage are fundamental to evaluating volcanic dynamics and hazards. Yet our understanding of subvolcanic magmatic plumbing systems and their variability remains limited. There is ongoing debate regarding the ephemerality of shallow magma storage and its volume relative to eruptive output, and so whether an upper-crustal magma body could be a sign of imminent eruption. Here we present seismic imaging of subvolcanic magmatic systems along the Cascade Range arc from systematically modelling the three-dimensional scattered wavefield of teleseismic body waves. This reveals compelling evidence of low-seismic-velocity bodies indicative of partial melt between 5 and 15 km depth beneath most Cascade Range volcanoes. The magma reservoirs beneath these volcanoes vary in depth, size and complexity, but upper-crustal magma bodies are widespread, irrespective of the eruptive flux or time since the last eruption of the associated volcano. This indicates that large volumes of melts can persist at shallow depth throughout eruption cycles beneath large volcanoes.
521. Obryk et al. (2025) Utility of a swath laser rangefinder for characterizing mass movement flow depth and landslide initiation
     Mass movements such as debris flows and landslides are some of the deadliest and most destructive natural hazards occurring mostly in alpine and volcanic settings. With ever-growing populations located downslope from known debris flow channels, early warning systems can help prevent loss of life. Geophysical and technological advances have improved monitoring and detection capabilities in recent years; however, they can often be cost prohibitive and resource intensive, making them less accessible to disadvantaged populations. We tested and validated a readily available and cost-effective two-dimensional swath laser rangefinder in a controlled experimental setting against two independent flow-depth lasers. The swath laser successfully recorded cross-sectional changes in flow depth from four debris flows and a water-only flood, in addition to geomorphic changes associated with landslide initiation. The results suggest that a swath laser could be integrated into systems for debris flow detection and characterization of mass movements in natural settings, thus improving the ability to monitor these hazards.
520. Gendaszek et al. (2025) Spatial stream network modeling of water temperature within the White River Basin, Mount Rainier National Park, Washington
     Water temperature is a primary control on the occurrence and distribution of fish and other ectothermic aquatic species. In the Pacific Northwest, cold-water species such as Pacific salmon (Oncorhynchus spp.) and bull trout (Salvelinus confluentus) have specific temperature requirements during different life stages that must be met to ensure the viability of their populations. Rivers draining Mount Rainier in western Washington, including the White River along its northern flank, support a number of cold-water fish populations, but the spatial distribution of water temperatures, particularly during late-summer baseflow during August and September, and the climatic, hydrologic, and physical processes regulating it are not well constrained. Spatial stream network (SSN) models, which are generalized linear models that incorporate streamwise spatial autocovariance structures, were fit to mean and 7-day average daily maximum water temperature for August and September for the White River Basin. The SSN models were calibrated using water temperature measurements collected in 2010 through 2020. The extent of the models included the White River and its tributaries upstream from its confluence with Silver Creek in Mount Rainier National Park, Washington. SSN models incorporated covariates hypothesized to represent the climatic, hydrologic, and physical processes that influence water temperature. SSN models were fit to the measured data and compared to generalized linear models that lacked spatial autocovariance structures. Statistically significant covariates within the best-fit models included the proportion of ice cover and forest cover within the basin, mean August air temperature, the proportion of consolidated geologic units, and snow-water equivalent. Statistical models that included spatial autocovariance structures had better predictive performance than those that did not. Additionally, models of mean August and September water temperature had better predictive performance than those of 7-day average daily maximum temperature in August and September. Predictions of the spatial distribution of water temperature were similar between August and September with a general warming in the downstream part of the mainstem White River compared to cooler water temperatures in the high-elevation headwater streams. The proportion of ice cover emerged as an inversely related significant covariate to both mean August and September water temperature because streams that receive glacial meltwater are colder than non-glaciated streams. Water temperatures of the upper White River increased downstream and are attributed to warming of water temperature from accumulated solar radiation and inflow of non-glaciated tributaries. Estimated water temperatures for the upper White River model are 3–4 degrees Celsius (°C) warmer for tributaries, but 1–2 °C cooler for the mainstem compared to the regional-scale model. Differences between the upper White River SSN model and the regional-scale NorWeST model are attributed to the fact that the upper White River SSN included water temperature observations specific to the upper White River, whereas water temperature observations from lower elevation streams and downstream from the Mount Rainer National Park boundary were used in the regional scale model.

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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