431. Reyes and Todd (2021) Temporal changes in proglacial stream temperatures in White River, WA
     Water temperature is a crucial component of water quality. Glaciers and snow in glaciated watersheds supply low temperature water during the summer melt season, which can help to counteract warming stream temperatures due to rising air temperatures and urbanization. Emmons Glacier located on Mount Rainier, WA supplies low temperature water to the Puyallup watershed via the White River. We measured stream temperature in White River at four sites located ~ 0.1 to 4 km from Emmons Glacier terminus. Data was collected using probes that were submerged in the river for 24 - 48 hour periods in June and July, 2016 - 2021. Meltwater temperatures within 0.2 km of the terminus are less than two degrees Celsius. Preliminary results show that meltwater temperature cycles diurnally, with peak temperatures occurring in the afternoon, and minimum temperatures occurring late at night or in the early morning; diurnal meltwater temperature fluctuations near the terminus are within one degree Celsius. These findings suggest that air temperature is the dominant influence on glacial meltwater temperature. At a site 4 km from the terminus, the water is one to five degrees Celsius warmer, and the diurnal temperature shift is larger, up to two degrees Celsius. The consistency of meltwater temperatures at the glacier terminus throughout our findings suggests that glacial melt may mitigate rising stream temperatures downstream.
473. Johnson et al. (2023) Infrasound detection of approaching lahars
     Infrasound may be used to detect the approach of hazardous volcanic mudflows, known as lahars, tens of minutes before their flow fronts arrive. We have analyzed signals from more than 20 secondary lahars caused by precipitation events at Fuego Volcano during Guatemala’s rainy season in May through October of 2022. We are able to quantify the capabilities of infrasound monitoring through comparison with seismic data, time lapse camera imagery, and high-resolution video of a well-recorded event on August 17. We determine that infrasound sensors, deployed adjacent to the lahar path and in small-aperture (10 s of meters) arrays, are particularly sensitive to remote detection of lahars, including small-sized events, at distances of at least 5 km. At Fuego Volcano these detections could be used to provide timely alerts of up to 30 min before lahars arrive at a downstream monitoring site, such as in the frequently impacted Ceniza drainage. We propose that continuous infrasound monitoring, from locations adjacent to a drainage, may complement seismic monitoring and serve as a valuable tool to help identify approaching hazards. On the other hand, infrasound arrays located a kilometer or more from the lahar path can be effectively used to track a lahar’s progression.
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.
471. Muste et al. (2020) Revisiting hysteresis of flow variables in monitoring unsteady flows
     Conventional streamflow monitoring methods entail one-to-one relationships between two flow variables obtained by combining direct flow measurements with statistical analyses. These relationships (i.e. ratings) are used to monitor both steady and unsteady flows despite that in the latter cases the flow variables display an inherent hysteretic behaviour. Such behaviour is prominent if the wave passing through the gauging station is non-kinematic. This paper demonstrates that the index-velocity and continuous slope-area methods are more suitable to monitor unsteady flows in comparison with the widely used stage–discharge approach. Case studies are presented to show that, contrary to current perceptions in practical applications, hysteresis can be captured even in small streams and frequently-occurring run-off events. The paper also highlights the separation of the flow variable hydrographs in unsteady flows. This hysteresis-related aspect is less investigated so far despite having important practical implications for both hydrometric and fluvial transport applications.
470. Varliero et al. (2023) Glacial water: A dynamic microbial medium
     Microbial communities and nutrient dynamics in glaciers and ice sheets continuously change as the hydrological conditions within and on the ice change. Glaciers and ice sheets can be considered bioreactors as microbiomes transform nutrients that enter these icy systems and alter the meltwater chemistry. Global warming is increasing meltwater discharge, affecting nutrient and cell export, and altering proglacial systems. In this review, we integrate the current understanding of glacial hydrology, microbial activity, and nutrient and carbon dynamics to highlight their interdependence and variability on daily and seasonal time scales, as well as their impact on proglacial environments.
469. Fordham et al. (2023) Recurrent debris flows and their downstream fate: Geomorphic drivers of an anomalous sediment load, Suiattle River, Washington State, USA
     Alpine mass wasting events have impacts that extend past their headwater origins, sometimes reaching populated lowlands. Understanding the processes driving these sediment pulses, and how they contribute to basin-scale sediment fluxes, is important for hazard assessment and aquatic habitat management. The Suiattle River, which drains Glacier Peak stratovolcano in Washington State, is a dominant contributor of suspended sediment in the region. Normalized for drainage area, it supplies more suspended sediment than nearly any other river in the area and more than twice as much as the White Chuck River, which drains the opposite flank of the volcano. Despite its importance to the regional sediment budget, geomorphic processes in the basin have received relatively little attention in the literature. In this study, we build on previous work to explore the magnitude, timing and triggering mechanisms of sediment loading events in the basin. We find that outburst flood-triggered debris flows from Chocolate Glacier are of widely varying magnitude and coincide with high temperatures in the late summer. Major debris flow activity initiated in the late 1930s, with at least eight valley-filling debris flows since then. Smaller, more recent debris flows, likely also driven by outburst floods, occur in five of seven years of complete data. In total, the small debris flows and the subsequent autumn flushing events explain ~21% of the ‘anomalous’ sediment load in the basin, while reworking and abrasion of the historic events may explain another ~26%. We speculate that some of the remaining unexplained ‘anomalous’ load could be the result of a feedback between channel lateral instability (originally triggered by the valley-spanning debris flows) and bluff erosion.

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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.

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

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