395. Beason (2020) Stream stage, stream temperature, stream turbidity, stream conductivity, precipitation and air temperature for the Nisqually River at Longmire: Water year 2019
     Mount Rainier is a 4,392 m (14,410 ft) volcano in southwestern Washington State. Braided rivers radiate away from the volcano and are generally glacially-sourced. Approximately 3.22 km³ (0.77 mi³) of glacial ice and perennial snows cover Mount Rainier in 29 named features (Beason, 2017; George and Beason, 2017). The mountain receives an average of 16.3 m (53.3 ft; 640 in) of snow at Paradise and melting snow causes high flows in spring and summer months (NPS, 2020). Fall and winter storms lead to periodic flooding and higher flows. Generally, the lowest river flows occur late in the summer prior to the onset of fall storms and in the middle of winter. Most streams in the park exhibit a braiding or anastomosing character due to their glacial source, however, several of the lower order streams that have non-glacial sources exhibit pool-riffle morphology with very coarse median grain sizes. Average stream gradient ranges from 1 to 4%. The Nisqually River is one of six major stream networks that drain a significant portion of the volcano (the others being the Puyallup, Carbon, West Fork White, White, and Ohanapecosh). The Nisqually River watershed (Figure 1) begins at the Nisqually Glacier and ends at the Nisqually National Wildlife Refuge, emptying into the Puget Sound. The Nisqually River at Longmire has a watershed size of 48.7 km² (18.8 mi²), a mean basin elevation of 1,814 m (5,950 ft) and drains from the summit of Mount Rainier down to 853 m (2,800 ft) at Longmire (Table 1). The drainage basin includes three glaciers (Nisqually, Wilson and Van Trump Glaciers) and the permanent Muir Snowfield. Mean basin slope is 48.2% and has 39.0% canopy cover. Mean annual precipitation in the watershed is approximately 262 cm (103 in) (USGS Stream Stats, 2011). The Nisqually River's headwaters start at the terminus of the Nisqually Glacier, at approximately 1,585 m (5,200 ft). From there, the river cascades down a steep braided stream with very coarse sediment. The river character is a classic braided system with multiple debris flow inputs from Van Trump Creek and other small streams. Stream gage data from the Nisqually River at Longmire within Mount Rainier National Park are presented for water year 2019 (WY2019; October 1, 2018 – September 30, 2019). The Longmire location is one of two year-round real-time gaging stations at the park; the other being on the White River at White River Bridge (see associated water-data reports for that location). Stream statistics are obtained via pressure transducers that are mounted within a stilling well at Longmire. Data from WY2019 was collected by a solar and battery-powered data collector and transmitted to the GOES West satellite where the data was then disseminated to a web-accessible database. Stream gage data is useful for determining critical in-stream flows for aquatic habitats as well as showing the range of temperatures exhibited in park streams during the year.
455. Muneer (2022) Advanced suspended sediment sampling and simulation of sediment pulses to better predict fluvial geomorphic change in river networks
     Sediment, an integral part of rivers and watersheds, is eroded from, stored in, and transported through various watershed components. Rivers often receive sediment in the form of episodic, discrete pulses from a variety of natural and anthropogenic processes, this sediment can be transported downstream along the bed or suspended in the water column. Most sediment measurements are focused on the component suspended in the water column. Recent advances in data collection techniques have substantially increased both the resolution and spatial scale of data on suspended sediment dynamics, which is helpful in linking small, site-scale measurements of transport processes in the field with large-scale modeling efforts. Part of this research evaluates the accuracy of the latest laser diffraction instrument for suspended-sediment measurement in rivers, LISST-SL2 for measuring suspended sediment concentration (SSC), particle size distribution (PSD), and velocity by comparing to concurrent physical samples analyzed in a lab for SSC and PSD, and velocity measured using an acoustic Doppler current profiler (ADCP) at 11 sites in Washington and Virginia during 2018-2020. Another part of this work employs a 1-D river network, bed material transport model to investigate the magnitude, timing, and persistence of downstream changes due to the introduction of sediment pulses in a linear river network. We specifically focus on comparing bed responses between mixed and uniform grain size sediment pulses. Then the model capability is utilized to explore the control of hydrograph structure on debris flow sediment transport through a more complex river network at different time horizons. Another part of this work investigates the effect of differences in spatial distribution of debris flow sediment input to the network by analyzing corresponding tributary and mainstem characteristics. Based on an extensive dataset, our results highlight the need for a correction of the raw LISST-SL2 measurements to improve the estimation of effective density and particle size distribution with the help of a physical sample. Simulation results from the river network model show that bed response is primarily influenced by the sediment-pulse grain size and distribution. Intermediate mixed-size pulses are likely to have the largest downstream impact because finer sizes translate quickly and coarser sizes (median bed gravel size and larger) disperse slowly. Furthermore, a mixed-size pulse, with a smaller median grain size than the bed, increases bed mobility more than a uniform-size pulse. While investigating the hydrologic control on debris flow simulation, this study finds that differences between transport by a 30-year daily hydrograph and simplified hydrographs were greatest in the first few years, but errors decreased to around 10% after 10 years. Our simulation results highlight that the sequence of flows (initial high/low flow) is less important for transport of finer sediment. We show that such network-scale modeling can quantitatively identify geomorphically significant network characteristics for efficient transport from tributaries to the mainstem, and eventually to the outlet. Results suggest that watershed area and slope characteristics are important to predict aggradation hotspots in a network. However, to predict aggradation and fluvial geomorphic responses to variations in sediment supply from river network characteristics more confidently, more widespread (in several other river networks) model applications with field validation would be useful. This work has important implications for river management, as it allows us to better predict geomorphically significant tributaries and potential impact on downstream locations, which are important for river biodiversity. Model results lead the way to use of simplified flow hydrographs for different timescales, which is crucial in large-scale modeling as it is often restricted by computational capacity. Finally, given the ability for reliable quantification of a high-resolution time-series of different suspended-sediment characteristics, in-stream laser diffraction offers great potential to advance our understanding of suspended-sediment transport.
454. Stenner et al. (2022) Development and persistence of hazardous atmospheres in a glaciovolcanic cave system: Mount Rainier, Washington, USA
     Glaciovolcanic cave systems, including fumarolic ice caves, can present variable atmospheric hazards. The twin summit craters of Mount Rainier, Washington, USA, host the largest fumarolic ice cave system in the world. The proximity of fumarole emissions in these caves to thousands of mountaineers each year can be hazardous. Herein we present the first assessment and mapping of the atmospheric hazards in the Mount Rainier caves along with a discussion on the microclimates involved in hazard formation and persistence. Our results are compared to applicable life-safety standards for gas exposure in ambient air. We also describe unique usage of Self-Contained Breathing Apparatus (SCBA) at high altitude. In both craters, subglacial CO2 traps persist in multiple locations due to fumarole output, limited ventilation, and cave morphology. CO2 concentrations, calculated from O2 depletion, reached maximum values of 10.3 % and 24.8 % in the East and West Crater Caves, respectively. The subglacial CO2 lake in West Crater Cave was persistent, with atmospheric pressure as the main factor influencing CO2 concentrations. O2 displacement exacerbated by low O2 partial pressure at the high summit altitude revealed additional cave passages that can be of immediate danger to life and health (IDLH), with O2 partial pressures as low as 68.3 mmHg. Planning for volcanic research or rescue in or around similar cave systems can be assisted by considering the implications of atmospheric hazards. These findings highlight the formation mechanisms of hazardous atmospheres, exploration challenges, the need for mountaineering and public awareness, and the broader implications to volcanic hazard assessment and research in these environments.
453. Sobolewski et al. (2022) Ongoing genesis of a novel glaciovolcanic cave system in the crater of Mount St. Helens, Washington, USA
     Mount St. Helens, one of the highest-risk volcanoes in the Cascade Volcanic Arc, hosts a novel system of glaciovolcanic caves that has formed around the 2004-2008 lava dome. From 2014 to 2021 a multidisciplinary research team systematically explored and mapped these new caves to ascertain their characteristics. Air and fumarole temperatures, volume flow rates, and wind regimes were also monitored. More than 3.0 km of cave passages have formed in a semicircular pattern in the volcanic crater and provide an opportunity to (1) observe cave development over time, (2) identify low temperature fumaroles as the main driving force for cave formation, (3) verify the impact of seasonal snow accumulation on cave climate, and (4) assess heat distribution in subglacial and subaerial portions of the new lava dome. Glaciovolcanic cave systems on Mount St. Helens are comparatively young (<10 years) and the most dynamic in the Pacific Northwest. Observed cave expansion during the study suggests ongoing genesis and future formation of interconnected systems. However, further expansion may also be limited by increasing fumarole temperatures towards the upper parts of the lava dome, cave instability due to snow overload, or variable subglacial volcanic heat output. New glaciovolcanic cave system development provides a unique barometer of volcanic activity on glacier-mantled volcanoes and to study the subglacial environment. We present the results of eight years of initial study within this dynamic cave system, and discuss a pathway towards future longitudinal analyses.
452. Fricke and Lofgren (2022) Predicting impacts of climate change on water supply: Mount Rainier National Park
     Mount Rainier National Park's (MORA) water supply primarily depends on streams and lakes fed by snowmelt and perennial snowfields. The loss of perennial snowfields during the past thirty years, combined with the potential for lower annual snowpack and increased air temperatures, could have profound implications for Park water supplies. Warming temperatures correspond with shifts from solid to liquid precipitation resulting in earlier snowmelt. In response to increasing Park visitation, multiple stressors on sensitive aquatic organisms, and projected climate changes, MORA is taking steps to develop a range of water supply options and park management strategies to adapt to climate change. As a case study, warm winter temperatures during water year 2015 had a profound effect on snowpack in MORA. During the months when most snow is deposited in our mountains (December to March), temperatures typically averaged more than 3°C above normal. Although precipitation was near normal, warmer temperatures caused much of this precipitation to fall as rain, resulting in an unusually low snowpack. These conditions stressed water supplies that are critical to Park operations, and likely stressed sensitive aquatic species (e.g., cold-water fishes and insects) downstream of water supply intakes as a consequence of elevated stream temperatures and low stream flow. Conditions resembling historical droughts, including the recent 2015 event, are projected to be more likely within this century as the climate warms across the region. These changes are likely to coincide with increased Park visitation and greater stresses on sensitive aquatic ecosystems. In order to provide sufficient context for our analysis, we have summarized MORA’s current water supply demands, history of development, issues, changes over time, and potential impacts to aquatic organisms. Focusing on key water supply systems within the Park, we estimated the potential maximum use and storage capacity of existing water. We then scaled region-wide streamflow projections under multiple emission scenarios to water supply intake drainage basins to evaluate future water supply scenarios within the Park. Our findings suggest the most viable immediate options for securing water supplies long-term include increasing system storage capacity and adding groundwater sources. These results can be used to directly inform current Park planning efforts and potential management actions to adapt to changing visitation demands, infrastructure needs, and climate change.
451. Anderson and Shean (2022) Spatial and temporal controls on proglacial erosion rates: A comparison of four basins on Mount Rainier, 1960-2017
     The retreat of alpine glaciers since the mid-19th century has triggered rapid landscape adjustments in many headwater basins. However, the degree to which decadal-scale glacier retreat is associated with systematic or substantial changes in overall coarse sediment export, with the potential to impact downstream river dynamics, remains poorly understood. Here, we use repeat topographic surveys to assess geomorphic change in four partly glaciated basins on a stratovolcano (Mount Rainier) in Washington State at roughly decadal intervals from 1960 to 2017. The proglacial extents of the four basins show distinct geomorphic trajectories, ranging from substantial and sustained net erosion to relatively inactive with net deposition. These different trajectories correspond to differences in initial (1960) valley floor gradients, and can be effectively understood as valley floor grade adjustments. Significant erosion was most often accomplished by debris flows triggered by extreme rainfall or glacial outburst floods, though a single rockfall mobilized more material than all other events combined. Year-to-year runoff events had little measurable geomorphic impact. Exported material tended to accumulate in broad deposits within several kilometers of source areas and largely remained there through the end of the study period. Over 10- to 100-year timescales, we find that the impact of glacier retreat on coarse sediment yield may then vary substantially according to the geometry and storage trends of the newly exposed valley floor; the timing of that response may also be dictated, and potentially obscured, by stochastic and/or extreme events.

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The U.S. Geological Survey and Pacific Northwest Seismic Network (PNSN) continue to monitor these volcanoes closely and will issue additional updates and changes in alert level as warranted.

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For images, graphics, and general information on Cascade Range volcanoes: https://www.usgs.gov/observatories/cvo" target="_blank" title="https://www.usgs.gov/observatories/cvo">https://www.usgs.gov/observatories/cvo">https://www.usgs.gov/observatories/cvo">https://www.usgs.gov/observatories/cvo
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