103. Sanford (2011) Glacial changes between 1985-2009 and implications for volcanic hazards at Mt. Rainier, Washington
     Glaciers throughout the world have shown decreases in size in recent years (WGMS, 2008). Because of their sensitivity to temperature and precipitation changes, glaciers are good indicators for climate change (Nylen, 2001). Glaciers located in temperate areas are especially sensitive to warming due to their relatively quick flow and high mass turnover (WGMS, 2008). In areas with significant amounts of glaciation, a warmer climate can have a considerable effect. A ~0.6°C increase in the mean global temperature is responsible for the overall retreat of mountain glaciers since the early 20th century (Hock et al., 2005). Further decreases are expected due to increased global warming as predicted by General Circulation Models (Hock et al., 2005). Several potentially active volcanoes with rapidly thinning glaciers are located in Mexico, Columbia, Chile, and Tanzania (Tuffen, 2010). Tuffen (2010) estimates that if the current rate of thinning continues glaciated volcanoes would lose a large portion of ice. At Popocatépetl in Mexico, this has already happened. The amount of ice on Popocatépetl decreased 53% from 1996-2001, which was partially due to eruptive activity (Julio-Miranda et al., 2008). Other mountain glaciers around the world have also experienced decreases in areal extent. The World Glacier Monitoring Service (WGMS) reports that annual melting rates of mountain glaciers have doubled since the turn of the century (WGMS, 2008). New records for ice loss were also set in 2003, 2004, and 2006 (WGMS, 2008). Significant glacier changes could affect local hazards due to the decrease in glacial coverage and the increase in melt water. Glaciers, ice caps, and ice sheets cover approximately 10% of Earth‟s surface and contain 75% of its freshwater (UNEP, 1992; Nylen, 2001). Hazards in volcanic regions that could occur as a result of melting glaciers include lahars, debris/ice avalanches, eruptions, and jökulhlaups (glacier outburst floods) (Hoblitt et al., 1998). Recent changes in glacial extent on Mt. Rainier could increase hazard risks due to the increase in melt water and steep exposed slopes (Crandell, 1971). The large amounts of loose debris, along with slopes that have been weakened as a result of hydrothermal alteration, also increase hazard risks at Mt. Rainier (Reid et al., 2001). The amount and rate at which Mt. Rainier glaciers are retreating is important for determining risks from hazards such as lahars, debris avalanches, eruptions, and jökulhlaups. Remote sensing provides an alternative method of monitoring glaciers changes as opposed to ground surveys or aerial photographic surveys. Glacier mapping using satellite images is generally less expensive and involves a smaller amount of labor than ground and aerial surveys (Sidjak and Wheate, 1999). Many studies have used Landsat images to map and interpret glacier changes around the world in places such as Iceland, British Columbia, Austria, and Peru (Williams et al., 1997; Sidjak and Wheate, 1999; Paul, 2002; Silverio and Jaquet, 2005). They show that satellite images are useful for collecting data on glacier extent, which can then be used for water management and climate monitoring purposes (Sidjak and Wheate, 1999). They are especially useful in places like the Tibetan Plateau, where areas with rugged terrain and lack of access make ground surveys very difficult or impossible (Zhen et al., 1998). This study concentrates on the changes in glacier areal extent that have occurred at Mt. Rainier and some of the possible consequences of those changes in terms of volcanic hazards. The first objective of this study is to measure the changes in glacier area from 1985-2009 at Mt. Rainier with satellite images. This study maps the areal extents of glaciers and groups of glaciers on Mt. Rainier as a function of time and then examines the rate of ice loss or gain for each glacier/glacier group as well as the rate of total ice loss or gain. These measurements are compared with measurements made by the United States Geological Survey (USGS) and the Global Land Ice Measurements from Space (GLIMS) project. The second objective is to determine the possibility of an increased risk for eruptions at Mt. Rainier due to the removal of glaciers from its slopes. This study examines the relationship between glacier change and eruption rates in the past by comparing the modeled glacier area at Mt. Rainier for the last 10 ka to the eruptive history of Mt. Rainier and other Cascade volcanoes during the same period. Any correlations between times of deglaciation and increases in eruption rates could help in predicting future volcanic activity resulting from continued glacial retreat at Mt. Rainier.
538. Wall et al. (2026) Origin and evolution of mafic volcanism associated with 3 m.y. of andesite production at the Goat Rocks volcanic cluster, southern Washington Cascade Range
     More than 3 m.y. of mafic volcanism near the Goat Rocks volcanic cluster in the southern Washington Cascade Range, USA, lends insight into the evolution of basalts and the subarc mantle at a long-lived, major arc volcanic locus. We contribute field observations, 40Ar/39Ar dates, paleomagnetic directions, and bulk rock and mineral compositions to characterize nine mafic units that erupted in association with the Goat Rocks volcanic cluster. The time frame of mafic volcanism, ca. 3.6 Ma to 60 ka, encompasses the lifespan of the central volcanic cluster (3.1 Ma to 115 ka), with a lull from ca. 2.7 Ma to 1.4 Ma. A climactic period of voluminous mafic activity and far-traveled lava flows, including construction of the Hogback Mountain shield volcano, coincided with voluminous andesite eruptions from the central volcanic cluster. The basaltic rocks in the Goat Rocks area are calc-alkaline to barely tholeiitic and have high field strength element depletion relative to large-ion lithophile elements characteristic of calc-alkaline basalts (CAB) of the Cascade volcanic arc. Unlike at neighboring andesitic volcanic centers (Mounts Adams, St. Helens, and Rainier), no other mafic end members such as high-aluminum olivine tholeiite (HAOT) or intraplate-type basalt (IPB) are present at or near the Goat Rocks volcanic cluster, although some of the calc-alkaline basalts in this study have IPB-like affinities. The Goat Rocks mafic units exhibit two main temporal trends in composition: (1) the most primitive basalts erupted earlier, compared to less primitive and more evolved compositions later, and (2) high field strength element concentrations are higher in the younger basalt units relative to the oldest two. In contrast to these temporal trends, the mafic units define two compositional groups that recur through time, a low-Sr and a high-Sr group, each with distinct trace element and Sr and Nd isotope ratios. Although radiogenic isotope ratios are generally aligned with High Cascades CAB and HAOT, some extend toward IPB of Mount Adams and Simcoe Mountains volcanic field. Olivine-dominated crystal fractionation at shallow pressure from a small range of parent magma compositions accounts for much of the variation among the basalts and basaltic andesites. A high-pressure fractionation model is plausible for only one of the youngest basalt units (basalt of Walupt Lake volcano). Mafic recharge and crustal assimilation accounts for the incompatible-element enriched composition of basaltic andesites erupted during construction of the largest andesitic centers, further supporting sustained basalt mass flux and thermal energy driving andesite genesis. We model the most primitive members of the Goat Rocks mafic units as partial melts of successively less depleted mantle in time. Variable degrees of fluxing with fluids and melts from subduction explain the distinction between high-Sr and low-Sr groups. We propose that mantle metasomatism by ancestral subduction and fluid-flux melting is heterogeneously distributed through the local subarc mantle and played a greater role in the genesis of the high-Sr basalt group. The limited range of primitive basalt types around the Goat Rocks volcanic cluster contrasts with the much greater diversity of basalts throughout the southern Washington to northern Oregon Cascade arc. On the other hand, the central volcanic cluster encompasses nearly the entire diversity observed at neighboring composite volcanoes. In the case of the Goat Rocks area at least, and perhaps attributable to the entire region, this means that the genesis of diverse intermediate magmas is independent from and does not require vastly different parental basalt compositions.
537. Black et al. (2026) Forest-floor burial in 1507 by the largest Mount Rainier lahar of the past millennium
     New dating of lahar-killed trees underscores volcano hazards in the Puget Sound metropolitan area. Beginning as a landslide from the west flank of Mount Rainier, Washington, USA, the Electron Mudflow, which was the largest lahar of the last millennium, swept more than 60 km down the Puyallup River drainage into areas now densely populated. Wiggle matching of seven radiocarbon ages from buried, bark-bearing Douglas-fir (Pseudotsuga menziesii) trees brackets the mudflow’s age between 1477 and 1522 CE with 99.7% certainty. To narrow this date, we applied dendrochronology crossdating on samples collected from 21 trees killed by the lahar, measuring 86 time series for statistical verification. The four bark-bearing trees died the same year while the final rings in all other trees had decayed, exposing rings formed in earlier years. When averaged together, the crossdated measurements form a 475 yr master chronology that was correlated against absolutely dated tree-ring chronologies in the region. The Electron chronology best matched with chronologies from low-elevation sites, especially a Douglas-fir chronology from Vancouver Island, Canada, to show that the Electron trees died in 1507 CE. Latewood in the final ring was beginning to form, indicating the mudflow likely occurred in the late-summer months. What caused the Electron Mudflow is unknown, but this precise date will help to assess possible relationships with other events, assist in interpreting Indigenous narratives about the mudflow, and increase awareness of potential lahar hazards.
536. Koepfli et al. (2025) Discovering spatial variability of critical zone processes at Mount Rainier using DAS
     Mount Rainier (4392 m a.s.l.), an active stratovolcano located ~95 km south-east of Seattle, WA, USA, poses hazards due to its steep glaciated slopes and highly porous volcanic surface. The combination of snowmelt, rainfall, and unstable surface materials frequently triggers debris flows and lahars, threatening downstream communities. At the same time, Mount Rainier’s glaciers play a crucial hydrological role, storing water that sustains rivers and therefore agriculture across the heavily populated lowlands during dry summer months. To better understand the shallow subsurface (critical zone) and its connection to the surface, we collected data using Distributed Acoustic Sensing (DAS) along a ~40 km fiber-optic cable that spans over ~1000 m elevation and crosses diverse lithologies. We analyze ambient seismic noise by using auto- and cross-correlations to image and monitor near subsurface conditions and compare our results with data from nearby weather stations, river gauges, and soil pits. We identify various coherent fiber sections and link the frequency content of seismic noise sources to local hydrological settings. We also find an increased signal-to-noise ratio for specific lithologies. Observed seismic velocity changes (dv/v) align with nearby ground moisture measurements but vary along the fiber. To explain these spatial variations, we investigate hydrological processes that connect surface conditions and subsurface responses
535. Kenyon (2025) Behind the curtain: Characterizing the Nisqually Watershed of MORA as a means to explore the use of non-contact data sources in mountain hydrology
     Impacts from a changing climate are affecting the hydrology, geomorphology, and overall variability of rivers around the world. Upland water especially prone to these effects. Mountainous rivers are experiencing significant shifts in precipitation patterns and the storage of snow and ice in source areas, resulting in stark changes to hydrologic variability, sediment transport, and fluvial morphodynamics. Most hydrology methods have been developed for use in rivers with a slope of <0.001 m/m, and the advancement of knowledge relevant to steeper rivers with has followed slowly in comparison. This research aims to address gaps in mountain hydrology associated with the measurement of discharge and bedload sediment transport in mountain rivers with a slope ≥0.02 m/m, seeking means to improve our ability to observe hydrologic trends and morphodynamics. Containing widely distributed low-resilience infrastructure, significant increases to precipitation intensities, and glacial recession rates greater than 0.1 m/day, the Nisqually River within Mount Rainier National Park (MORA) exemplifies a nexus of modern land management issues driven by climate stressors of the Pacific Northwest. With this study we seek to further characterize observable surface processes in the Nisqually watershed within MORA, and begin considering new methods and frameworks enabling reliable monitoring of steep mountain rivers. We consider the use of seismic, infrasound, and video analysis data as non-contact methods to measure discharge and sediment transport in steep mountain rivers. The primary non-contact data series can then be supported by remote LiDAR products and Sentinel-1 data to assess changes in the source areas and their potential impacts on observable behaviors. Initial data shows signals in the seismic/infrasound that seem to correlate to both water flow and bedload transport. We hypothesize there will be observable correlations with topography and snowmelt timing seen though remote sensing analysis, but also anticipate site-to-site variability based on substrate and local morphology
534. Conner et al. (2025) Characterizing surges from a debris flow induced by a glacial outburst flood at Mount Rainier, USA
     On 15 August 2023, a small debris flow occurred in Tahoma Creek on the southwest side of Mt. Rainier National Park, Washington, USA. The debris flow originated from an outburst flood from the South Tahoma Glacier. Multiple instruments installed in the Tahoma Creek drainage recorded evidence of the debris flow, including nodal and broadband seismometers, infrasound sensors, a laser rangefinder located about 3.4 km downstream of the glacier, and a timelapse camera that captured images of the glacier terminus. In particular, nodal seismometers with a sampling rate of 500 Hz were deployed roughly every 350 m along approximately 2 km of the stream. After initiation of the debris flow, we find evidence in the seismic data of at least three debris flow surges due to either additional small outbursts from the glacier or the debris flow separating into multiple surge fronts caused by wave development from flow instability. Though the arrivals of the surge fronts are often obscured by higher-frequency signals contributed by the full debris flow, we find that the surges can be tracked as they travel downstream. From the seismic data, we are able to approximate where and when the surges merged or separated from the main flow and estimate the flow velocity of each surge front. As the fronts of debris flows generally contain the largest and most damaging materials in the flow, each surge front increases the hazard associated with an event. The dense instrumentation in the Tahoma Creek drainage allows for an in-depth analysis of the evolution of debris flow surges, providing information on how similar debris flows may behave in the future and contributing to the overall understanding of how debris flows evolve over time.

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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