72. Venezky and Rutherford (1997) Preeruption conditions and timing of dacite-andesite magma mixing in the 2.2 ka eruption at Mount Rainier
    Analytical, field, and experimental evidence demonstrate that the Mount Rainier tephra layer C (2.2 ka) preserves a magma mixing event between an andesitic magma (whole rock SiO₂ content of 57–60 wt %) and a dacitic magma (whole rock SiO₂ content of 65±1 wt %). The end-member andesite (a mix of an injected and chamber andesite) and dacite can be characterized on the basis of the homogeneity of the matrix glass and phenocryst rim compositions. Many pumices, however, contain mixtures of the end-members. The end-member dacite contains a microlite-free matrix glass with 74–77 wt % SiO₂, orthopyroxene rims of Mg_57–64, clinopyroxene rims of Mg_66–74, and plagioclase rim anorthite contents of An_45–65. The temperature and oxygen fugacity, from Fe-Ti oxide compositions, are 930±10°C and 0.5–0.75 log units above NNO. The mixed andesite contains Mg_73–84 orthopyroxene rims, Mg_73–78 clinopyroxene rims, An_78–84 plagioclase rims, and Mg_67–74 amphibole rims. The temperature from Fe-Ti oxides, hornblendeplagioclase, and two-pyroxene geothermometry is 1060±15°C, and the oxygen fugacity is approximately one log unit above NNO for the injected andesite. The chamber andesite is estimated to be a magma with a ~64–65 wt % SiO₂ melt at 980°C and a NNO oxygen fugacity. We conclude that the andesitic and dacitic magmas are from separate magma storage regions (at >7 km and ~2.4 km) due to differences in the bimodal whole rock, matrix glass, and phenocryst compositions and the presence or absence of stable hornblende. The time involved from the mixing event through the eruption is limited to a period of 4–5 days based on Fe-Ti oxide reequilibration, phenocryst growth rates, and hornblende breakdown. The eruption sequence is interpreted as having been initiated by an injection of the 1060±15°C andesitic magma into the ~980°C (>7 km) andesite storage region. The mixed andesitic magma then intersected a shallow, ~2.4 km, dacitic storage system on its way toward the surface. The eruption became more dacitic over time, and the final products some show evidence of partial reequilibration between the andesite and dacite.
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.
450. Fordham (2022) Glacier Peak and the chocolate factory: Recurring debris flows from the eastern flank of Glacier Peak stratovolocano, North Cascades, Washington State, USA
     Alpine mass wasting events can have wide ranging impacts that extend past their headwater origins reaching down to lowland population centers. The Suiattle River, which drains the eastern flank of Glacier Peak in the North Cascades of Washington State, is a dominant contributor of suspended sediment in the region. Normalized for drainage area, the Suiattle River supplies more suspended sediment than nearly any other river in the region and more than twice as much as the White Chuck River, which drains the western flank of the volcano. Despite its known importance to the regional sediment budget, the specific geomorphic drivers of the anomalous sediment load on the Suiattle have received relatively little attention in the literature. In this study, I build on previous work to explore the magnitude, timing, triggering mechanisms, and the spatial distribution of sediment loading events in the Suiattle River Basin. My historical analysis shows that major debris flow activity initiated in the late-1930s, with a total of nine historic debris flows since then (RI = 9.3 years). One previously unreported circa late-1940s debris flow was identified from reanalysis of dendrochronology (Slaughter, 2004) and historical aerial imagery. From topographic differencing, I placed a minimum bound of ~4.9 M m3 (±0.6 M m3) on the material incised from the most recent valley filling debris flow deposits. Historical accounts suggest that major debris flows happen at the hottest times of the year in the absence of precipitation, with two eyewitness accounts of debris flows triggered by glacial outburst floods. Historical photos, remote sensing, and field measurements of terrace heights suggest that incision into historic debris flow deposits occurs soon after deposition and tapers after the first few years. To examine smaller more recent debris flows, I created a framework to automatically extract debris flow timing, duration, and magnitude from USGS turbidity and discharge data over the period 2011 to 2020. I identified 28 individual debris flow events that occurred in every year in the record. To evaluate triggering mechanisms, I calculated prior day maximum temperature anomalies for all non-debris flow days and for days when a debris flow started. Debris flow start days were shown to be statistically warmer than non-debris flow days (mean of -0.21 °C and 2.48 °C, respectively; ks test, dm = 0.314, p = 0.007). This suggests that minor debris flows are triggered by high temperatures and, like the historical major debris flows, points to glacier outburst floods as the primary initiation process. I estimate suspended sediment loads attributable to minor debris flows, anomalous sediment flushing events following debris flows, and suspended sediment loads outside of these categories. Together debris flows and flushing account for ~21% of the mean annual load on the Suiattle. At Glacier Peak, Chocolate Glacier is unique. Its high propensity for glacier outburst floods makes it the dominant source of debris flows and suspended sediment, vastly outweighing contributions from other glaciers on the mountain. The frequency and magnitude of debris flows from Chocolate Glacier bare similarities to South Tahoma Glacier at Mount Rainier. Combined, my findings show that debris flows deliver large quantities of sediment to the mainstem river at both annual and decadal timescales. This work is a step toward understanding how sediment supplied from alpine mass wasting events shapes downstream geomorphic processes. My findings have implications for how ongoing climate change may alter cascading hazards in these systems.
449. Almekinder (2022) Using spectral indices to determine the effects of the summer 2021 North American heat wave at Mount Rainier, Washington
     Quality of life at Mount Rainier and the surrounding region is dependent on annual snowpack and subsequent snowmelt. Winter storm observations, snowpack, and the rate of snowmelt all play critical roles in determining the health of the environment. To help analyze these factors, users and consumers rely on remotely sensed data to analyze the past, present, and future of the area. The Normalized Difference Snow Index (NDSI) and Normalized Difference Vegetation Index (NDVI), collected from satellite imagery, are two spectral indices used with analyzing snowpack and vegetation health to assist risk mitigation for wildfires, glacial change, and river ecosystems. This project used NDSI and NDVI to determine if the 2021 North American heat wave had any significant effects on vegetation health, snowpack, and glacial size over a five-year study period. Landsat 8 satellite imagery was acquired, corrected for any atmospheric bias, and processed through GIS techniques. Despite yearly fluctuation of warmer and cooler years, results show a progressive increase in snowmelt with 2021 showing the highest percentage during the study period and the highest differential from the mean of all years in the study. Vegetation labeled as "Healthy" saw the biggest decrease between consecutive years from 2020-2021. Also in 2021, Mount Rainier saw its glaciers recede to their lowest total area since 2005. Conclusions show that general warming trends are occurring in the Pacific Northwest and the heat wave exacerbated total glacial area, total snow area, and vegetation health. This Masters project contributes to future extreme weather anomalies and related results.
448. George et al. (2022) Modeling the dynamics of lahars that originate as landslides on the west side of Mount Rainier, Washington
     Large lahars pose substantial threats to people and property downstream from Mount Rainier volcano in Washington State. Geologic evidence indicates that these threats exist even during the absence of volcanic activity and that the threats are highest in the densely populated Puyallup and Nisqually River valleys on the west side of the volcano. However, the precise character of these threats can be difficult to anticipate. To help predict depths and rates of possible lahar inundation in the area, this report presents the results of simulations of hypothetical future lahars that originate high on the west side of Mount Rainier and travel downstream into the Puyallup and Nisqually River valleys. Many of the results portrayed as still images in the figures of this report are also available as animated files that can be accessed at the web address provided in the figure captions. We simulated eight scenarios, including worst-case scenarios in which the simulated lahars are similar in size and mobility to the approximately 260 million cubic meter (Mm³; 340 million cubic yard) Electron Mudflow lahar that descended from Mount Rainier and inundated the Puyallup River valley about 500 years ago. The other six scenarios place the worst-case scenarios in perspective by simulating lahars that originate from the same source areas but have smaller volumes or lesser mobilities. We perform our simulations using an open-source software package that we developed called D-Claw. The numerical model composing the kernel of D-Claw solves a system of five hyperbolic partial differential equations that describe the depth-averaged dynamics of static or flowing grain-fluid mixtures interacting with three-dimensional topography. In D-Claw, the volume fraction occupied by solid grains is a dependent variable that can freely evolve, enabling simulation of landslide liquefaction and of lahar interaction with static bodies of water. The latter feature facilitates a seamless simulation of a lahar in the Nisqually River valley entering Alder Lake reservoir. In the event of an approximately 260 Mm³ high-mobility lahar originating on the west side of Mount Rainier, our results point to two areas of pronounced hazard. One area, comprising the densely populated lowlands of Orting, Washington, and environs, could be inundated by lahars originating from either the Sunset Amphitheater or Tahoma Glacier headwall areas. In the worst-case scenario we consider for the Orting lowlands, which involves a 260 Mm³ high-mobility lahar originating from a landslide in the Sunset Amphitheater, a flow front approximately 4 meters deep and traveling about 4 meters per second reaches the Orting lowlands about 1 hour after the onset of slope failure. After passing through the Orting lowlands, the simulated lahar slows down and comes to rest in the valleys surrounding Sumner and Puyallup. A second area of pronounced hazard is the stretch of the Nisqually River valley beginning in Mount Rainier National Park and extending downstream to Alder Lake reservoir and Alder Dam. This area would be substantially affected in the worst-case scenario that involves a 260 Mm³ high-mobility lahar originating from the Tahoma Glacier headwall area—the locality identified by a previous study as the sector of Mount Rainier most prone to large-scale gravitational collapse. The simulated lahar passes through the area of Ashford, Washington, within about 20 minutes of the onset of slope failure and reaches the head of Alder Lake within about 50 minutes. The lahar ultimately displaces enough reservoir water to cause overtopping of the 100 meter (330 foot) tall Alder Dam, but consequences of such dam overtopping are not addressed in this report.

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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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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.

Website Resources

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
For seismic information on Oregon and Washington volcanoes: http://www.pnsn.org/volcanoes" target="_blank" title="http://www.pnsn.org/volcanoes">http://www.pnsn.org/volcanoes">http://www.pnsn.org/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" target="_blank" title="https://www.usgs.gov/programs/VHP/volcano-notifications-deliver-situational-information">https://www.usgs.gov/programs/VHP/volcano-notifications-deliver-situational-information">https://www.usgs.gov/programs/VHP/volcano-notifications-deliver-situational-information">https://www.usgs.gov/programs/VHP/volcano-notifications-deliver-situational-information

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

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