143. Wright (1964) The alkali feldspars of the Tatoosh Pluton in Mount Rainier National Park
     Twenty five orthoclase microperthites from a shallow intrusion of granodiorite-quartz monzonite have been studied chemically, optically and by xray diffraction. The data presented are: bulk composition; composition and obliquity of the potassium-rich phase; α^* and γ^* for the sodium-rich phase; 2V for both potassium-rich and sodium-rich phases. 2V of each phase is correlated with the composition of that phase on a 2V-composition diagram. Plotting 2V of perthites opposite the bulk composition should be abandoned. The potassic phases of the perthites are structurally intermediate between orthoclase and maximum microclinel average 2V_x and obliquity of this phase increase with decreasrng Ab content. The sodic phases are intermediate betrveen high and low albite; 2V_x increases with the size of the exsolution lamellae in individual crystals and γ^* measured for the sodic phase is higher (closer to low albite), in specimens showing more exsolution. Thus both phases of the perthites exhibit a continuous inversion from a high to low structural state during exsolution. The related processes of exsolution and inversion are discussed in terms of two models of the alkali feldspar solvus. Both models indicate that exsolution, if carried to completion, will result in a perthite consisting of maximum microcline and low albite.
441. Christian et al. (2022) Differences in the transient responses of individual glaciers: A case study of the Cascade Mountains of Washington State, USA
     Mountain glaciers have response times that govern retreat due to anthropogenic climate change. We use geometric attributes to estimate individual response times for 383 glaciers in the Cascade mountain range of Washington State, USA. Approximately 90% of estimated response times are between 10 and 60 years, with many large glaciers on the short end of this distribution. A simple model of glacier dynamics shows that this range of response times entails consequential differences in recent and ongoing glacier changes: glaciers with decadal response times have nearly kept pace with anthropogenic warming, but those with multi-decadal response times are far from equilibrium, and their additional committed retreat stands well beyond natural variability. These differences have implications for changes in glacier runoff. A simple calculation highlights that transient peaks in area-integrated melt, either at the onset of forcing or due to variations in forcing, depend on the glacier's response time and degree of disequilibrium. We conclude that differences in individual response times should be considered when assessing the state of a population of glaciers and modeling their future response. These differences in response can arise simply from a range of different glacier geometries, and the same basic principles can be expected in other regions as well.
440. Acob et al. (2021) Small scale spatial variability of light-absorbing particles in snow on Mount Rainier, Washington State, USA
     Light-absorbing particles (LAP), including black carbon (BC), dust, and light absorbing organics, can be deposited on snow, decreasing albedo and accelerating snowmelt. While other studies have focused on larger scale spatial variability of LAPs, it is important to take smaller scale spatial variability into account as well because there is potential for large variability among these LAP across small spatial scales. The purpose of this study was to analyze the spatial variability of LAP within the Sunrise and Paradise regions on Mount Rainier and evaluate the effect of LAP on snow albedo. In July 2021, we used a Spectral Evolution PSR+ Spectroradiometer to measure snow reflectance at the snow collection sites, and on transects across the snow sampling areas. Snow samples taken from these sites were kept frozen until just prior to analysis, then melted and analyzed for total impurity concentrations using gravimetric filtration, black carbon using a Single Particle Soot Photometer (SP2), organic and elemental carbon using a Sunset- OC-EC Analyzer, and dust and organic content using a Jupiter Simultaneous Thermal Analyzer. LAP were characterized at the submicron scale using a Cytoviva Hyperspectral Imaging Microscope Spectrometer. Our results show that there is large variability in LAP concentration and composition over small spatial scales due to variations in snow topography (snow cups) and variable conditions favorable to algae blooms.
439. Vinnell et al. (2021) Community preparedness for volcanic hazards at Mount Rainier, USA
     Lahars pose a significant risk to communities, particularly those living near snow-capped volcanoes. Flows of mud and debris, typically but not necessarily triggered by volcanic activity, can have huge impacts, such as those seen at Nevado Del Ruiz, Colombia, in 1985 which led to the loss of over 23,000 lives and destroyed an entire town. We surveyed communities around Mount Rainier, Washington, United States, where over 150,000 people are at risk from lahar impacts. We explored how factors including demographics, social effects such as perceptions of community preparedness, evacuation drills, and cognitive factors such as risk perception and self-efficacy relate to preparedness when living within or nearby a volcanic hazard zone. Key findings include: women have stronger intentions to prepare but see themselves as less prepared than men; those who neither live nor work in a lahar hazard zone were more likely to have an emergency kit and to see themselves as more prepared; those who will need help to evacuate see the risk as lower but feel less prepared; those who think their community and officials are more prepared feel more prepared themselves; and benefits of evacuation drills and testing evacuation routes including stronger intentions to evacuate using an encouraged method and higher self-efficacy. We make a number of recommendations based on these findings including the critical practice of regular evacuation drills and the importance of ongoing messaging that focuses on appropriate ways to evacuate as well as the careful recommendation for residents to identify alternative unofficial evacuation routes.
438. Thelen et al. (2021) Investigating location methods of surface events using seismic and infasound data at Mount Rainier
     Mount Rainier, Washington looms large above a vulnerable population of permanent residents and transient tourists. The hazard most likely to impact the largest population is a sector collapse that incorporates water to transform into a mobile lahar. Such sector collapses have occurred most famously 5600 years ago in the Osceola Mudflow and most recently approximately 500 years ago in the Electron Mudflow. Weak, hydrothermally altered rock remains left over in the scar of the Electron Mudflow, and the failure of this rock is the most likely source area for the next lahar. In response to this hazard, the United States Geological Survey (USGS) is building the Rainier Lahar Detection System (RLDS), which when fully implemented, will provide early warning of a lahar to potentially impacted communities. A major part of the system is an enhanced network of seismometers and infrasound arrays that will make Mount Rainier one of the best monitored volcanoes in the Cascades. Thus far, 14 additional seismometers and 9 infrasound arrays have been installed, mainly on the west and south sides of the volcano. Approximately 20 additional sites are proposed to be installed. Several avalanches, rockfalls, icefalls and debris flows (collectively called surface events) have been recorded by the current network since improvements began in 2016. We use this dataset to assess different location methods for these surface events using complementary observations. Specifically, we consider amplitude and amplitude ratio source locations, envelope-based locations and infrasound back azimuths to understand the sensitivity of the individual methods within the RLDS monitoring network. The results of this analysis will help calibrate the RLDS network and inform decisions about the best algorithms to use for rapid detection of larger events that may impact downstream populations.
437. Uhlrich et al. (2021) A 40-year story of river sediment at Mount St. Helens
     The 1980 eruption of Mount St. Helens in Washington State unleashed one of the largest debris avalanches (landslide) in recorded history. The debris avalanche deposited 3.3 billion cubic yards of material into the upper North Fork Toutle River watershed and obstructed the Columbia River shipping channel downstream. From the eruption on May 18, 1980, to September 30, 2018, the Toutle River transported a total of about 405 million tons of sediment into the lower Cowlitz River—enough to bury downtown Portland, Oregon, to a depth of 300 feet. Excluding the massive sediment load from the eruption itself, from October 1, 1980, to September 30, 2018, the Toutle River transported more than 248 million tons of sediment, or an average of 6.5 million tons per year. Increased flood risk to downstream communities is managed by a sediment retention structure, grade building structures, berms, levees, and dredging. Near-real-time monitoring of streamflow and sediment yield is important for effective management of these dynamic mitigation efforts. Since the sediment retention structure began trapping sediment in November 1987, the Toutle River has transported on average 2.8 million tons of sediment per year into the lower Cowlitz River. This is still 10 times greater than pre-eruption levels, with higher sediment transport potentially approaching 50 to 100 times greater during storms. Despite the eruption lasting only a few hours, the socioeconomic effects and mitigation measures for the region continue into the 21st century.

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