140. Jutzeler (2012) Characteristics and origin of subaqueous pumice-rich pyroclastic facies: Ohanapecosh formation (USA) and Dogashima formation (Japan)
     This thesis discusses the processes that generate subaqueous, pumice-rich pyroclastic facies in below wave-base environments. The principal method is field-based facies analysis. I also present grain size distributions and hydraulic sorting ratios of selected samples using a new technique that combines image analysis and functional stereology. Two Tertiary volcaniclastic successions have been studied. The Ohanapecosh Formation (Washington State, United States) is dominated by subaqueous pumice-rich facies derived from subaerial explosive eruptions and subaqueous sediment remobilisation in a continental basin environment. The Dogashima Formation (Izu Peninsula, Japan) contains well-preserved examples of subaqueous pumice-rich facies produced by subaqueous explosive eruptions and below wave-base sediment remobilisation in an oceanic arc setting. The common processes of lithification and welding prevent quantification of grain size by conventional sieving for most clastic rocks in the geological record. In addition, the true grain size distribution of clastic rocks is finer grained than its representation in a random 2D section. I show that image analysis combined with functional stereology can be used to infer 3D volume fractions and weight percent of clast populations >0.25-2 mm from 2D cross-sectional images. Data from synthetic rocks correlate well with results from sieving of the same samples while still unconsolidated. The method can be applied to any type of coarse grained clastic rock, regardless of age, and therefore has a wide application in volcanology and clastic sedimentology. The >800-m-thick Ohanapecosh Formation records voluminous sedimentation of volcanic clasts during the Eocene-Oligocene in the Central Cascades. Most volcaniclastic beds are dominated by angular pumice clasts and fiamme of intermediate composition, now entirely devitrified and altered. Very thick to extremely thick (1–50 m) and very thin to thick (0.001–1 m) beds are laterally continuous and have even thickness; erosion surfaces, cross-beds and other traction structures are almost entirely absent, which strongly suggests a below wave-base environment of deposition for most of the succession. The Chinook Pass Member is mostly composed of extremely thick, graded, matrixsupported, pumice-and-fiamme-rich beds that commonly include a coarse basal breccia comprising sub-rounded dense clasts. The abundance of angular pumice clasts and extreme thickness suggest that this facies was generated by magmatic volatile-driven explosive eruptions, and the sub-rounded dense clasts were probably rounded above wave-base. Thus, these beds are interpreted to have been deposited in a below wave-base setting by subaerial pyroclastic flows that crossed the shoreline, and transformed into eruption-fed, water-supported subaqueous volcaniclastic density currents. Reversely to normally graded pumice breccia facies that contains sub-rounded pumice clasts, wood and accretionary lapilli is interpreted to have formed by settling from pumice rafts, also related to subaerial explosive eruptions. The White Pass Member chiefly contains massive to normally graded volcanic breccia and coarse volcanic breccia that suggest deposition from subaqueous high-concentration density currents and subaqueous debris flows. The abundance of angular pumice clasts suggests minor reworking above wave-base. Very thin to thick interbeds of fine sandstone to mudstone are interpreted to be derived from subaqueous and subaerial sources, and to have mostly been deposited from low density turbidity currents and suspension. The presence of shallow basaltic intrusions and mafic volcanic breccia composed of scoria lapilli and that contains rare beds of accretionary lapilli indicate the presence of intra-basinal scoria cones that may have been partly subaerial. The lateral transition to thinner and finer-grained facies in the Johnson Creek Member and western part of the White Pass Member suggests that the principal sources were to the east of the preserved exposures of the Ohanapecosh Formation. The Pliocene Dogashima Formation (Izu Peninsula, Japan) is composed of three volcaniclastic sequences erupted under water. Dogashima 1 is mostly composed of pumice breccia, shard-rich siltstone, and cross-bedded and planar bedded pumice breccia/sandstone. The base of Dogashima 2 is dominated by very thick, clast-supported, massive grey andesite breccia composed of very coarse andesite clasts with quenched margins. It is gradationally overlain by very thick, clast-supported white pumice breccia. The massive grey andesite breccia is confined to a palæo-valley eroded into beds of Dogashima 1. The white pumice breccia is hydraulically sorted and stratified in proximity to the wall of this palæo-valley, and is stratified and finer grained in the adjacent overbank setting. The top of Dogashima 2 is dominated by very thick cross-bedded pumice breccia-conglomerate and planar bedded pumice breccia that contains coarse pumice clasts. Dogashima 2 has an erosive contact with overall monomictic andesite breccia of Dogashima 3. The similar mineralogy and composition of white andesite pumice and grey andesite clasts in Dogashima 1 and 2 suggests they were co-magmatic and erupted from the same vent. Dogashima 2 is interpreted to record explosive destruction of a subaqueous hot lava dome by a subaqueous, magmatic volatile-driven explosive eruption. Most of the products of this eruption were deposited in two gradational units from cohesionless, water-supported volcaniclastic density currents. Coarse pumice clasts and ash present in overlying planar beds were settled from suspension. This sequence demonstrates that lava or dome effusion on the sea floor can switch to an open-vent, pumice-forming, magmatic volatile-driven explosive activity, as in subaerial analogues. Pumice breccia of Dogashima 1 is interpreted to be the product of precursory explosive activity, whereas Dogashima 3 records a late, dome-building episode. Pumice breccia and dome-related clasts indicate cyclic effusive and explosive activity throughout the Dogashima Formation. Cross-bedded pumice breccia/breccia conglomerate facies in the Dogashima Formation are most likely to be products of resedimentation of pumiceous aggregates, and development and destruction of subaqueous dune fields in a below wave-base, canyon setting. I apply the image analysis and functional stereology method to pumiceous volcaniclastic rocks of the Ohanapecosh and Dogashima formations and the Manukau Sub-Group (New Zealand) and the Sierra La Primavera caldera (Mexico). Samples from these waterlain successions were grouped into three broad facies, on the basis of bed thickness, abundance of matrix and clast size sorting. The volume of pumice clasts, dense clasts and matrix (<2 mm), modal grain size distribution and hydraulic sorting ratio between pumice and dense clasts were used to characterise these three facies. On plots of sorting versus median diameter, the three facies overlap, which suggests that all three facies have overall good hydraulic sorting in their coarse clasts (>2 mm), and that the pumice clasts were fully waterlogged during transport and deposition. In addition, the studied subaqueous volcaniclastic samples overlap with the fields defined by matrix-free subaerial pyroclastic flow deposits, which confirms that outputs from functional stereology and conventional sieving give comparable results. The volcaniclastic successions in the Ohanapecosh and the Dogashima formations include good examples of subaqueous, pumice-rich pyroclastic facies that were erupted onland or under water, and deposited in below wave-base settings. Eruption-fed facies generated by subaqueous pumice-forming explosive eruptions are exemplified by the extremely thick and graded sequence in Dogashima 2 (Dogashima Formation), which contains dense clasts that were deposited hot. Numerous beds of graded, extremely thick, pumice-rich facies in the Ohanapecosh Formation are interpreted to be deposited from eruption-fed, water-supported high concentration density currents that were fed by subaerial pyroclastic flows, primarily because rounded dense clasts, accretionary lapilli and wood in these and associated facies imply that the source vents were subaerial. Resedimentation events can occur during eruptions and after, especially after eruptions that produce large volumes of pyroclasts in unstable environments. However, resedimented facies can be difficult to distinguish from eruption-fed facies in below wave-base successions, essentially because clast reworking below wave-base is minimal during resedimentation. In addition, eruption-fed facies can contain clasts that were previously abraded in above wave-base settings, for example during long-distance transport in subaerial pyroclastic flows, in pumice rafts (e.g. Chinook Pass Member, Ohanapecosh Formation) or during transport in the dense-clast-dominated bedload of subaqueous volcaniclastic density currents (e.g. Dogashima 2). Short-distance transport in pyroclastic flows might not be able to abrade pumice clasts (e.g. the eruption-fed facies in the Chinook Pass Member, Ohanapecosh Formation).
516. Thelen et al. (2024) Monitoring lahars
     Lahars, or debris flows that originate from a volcano (Pierson and Scott, 1985; Pierson, 1995), are among the most destructive, far-reaching, and persistent hazards on stratovolcanoes. Lahars may be triggered by syneruptive rapid melting of snow and ice, lake breakouts, or heavy rains in conjunction with large eruptive columns. Alternatively, lahars can follow eruptions, when clastic deposits are mobilized by heavy rainfall or lake breakouts, occurring sporadically for years to decades after large eruptions. Some lahars can travel many tens of kilometers in river drainages stemming from volcanoes, as during the 1980 eruption of Mount St. Helens (Washington) (for example, Janda and others, 1981), recent eruptions of Redoubt Volcano (Alaska) (fig. H1; Dorava and Meyer, 1994; Waythomas and others, 2013), and the 1991 eruption of Mount Pinatubo (Philippines) (Major and others, 1996; Pierson and others, 1996). Large lahars are less likely in the absence of eruptive activity, but still possible. The Electron Mudflow at Mount Rainier (approximately A.D. 1500), Wash., is an example of a potential noneruptive lahar, likely initiated by a spontaneous collapse of weak rock, that reached the Puget Lowland after it flowed dozens of kilometers without a recognized eruptive trigger (Sisson and Vallance, 2009). The extreme hazard posed by lahars was demonstrated tragically by the 1985 Nevado del Ruiz (Colombia) catastrophe that claimed the lives of more than 20,000 people (Naranjo and others, 1986). The potential to provide warnings of minutes to hours in advance of lahar arrival in a populated area (for example, Voight, 1990) is a strong reason to provide special monitoring attention to the hazard. Populated river valleys are located downstream from many very high threat and high threat volcanoes, and these areas could be affected by lahars (for example, Hoblitt and others, 1998). The volume and mobility of lahars are two characteristics that can influence the extent of downstream effects (for example, George and others, 2022). The flows that reach the farthest downstream are mobile and voluminous. Additionally, entrainment of material as a lahar travels downstream may increase the volume, and a lahar that starts small may grow to a destructive size under certain conditions. Increasingly, stratovolcanoes host recreational enthusiasts who could be affected by relatively localized geologic hazards, such as rainfall-induced debris flows, glacial outburst floods, rockfalls, and avalanches. These types of events can be common on many volcanoes, occurring seasonally in the case of debris flows and several times per year in the case of avalanches and rockfalls (for example, Allstadt and others, 2018). Many very high threat stratovolcanoes, especially within the contiguous United States, have low eruption frequencies (less than once per century), such that monitoring networks could be used more often for detection and characterization of small surface flows than for identification of volcanic unrest. Such information can be used to validate avalanche forecasts, inform rescue efforts, or notify other agencies of potentially damaged infrastructure (for example, roads, powerlines, or trails). Note that although many of these smaller surface flows create seismic and infrasound waves, the signals are typically highly distorted by the complex volcanic topography and geology. In general, the smaller the flow, the weaker the geophysical signals that it generates, and thus a denser geophysical network is required to study smaller flows (for example, Allstadt and others, 2018). Lahar detection may not be an appropriate or necessary monitoring capability for all volcanoes. Some very high threat volcanoes, like Kīlauea and Mauna Loa, have no lahar hazards currently, and thus no detection, tracking, and characterization capabilities for lahars are needed. At other very high threat volcanoes, such as Pavlof Volcano, Alaska, lahars might be common but pose minimal threat because the volcano is so remote. Ideally, the local observatory would understand the combination of hazard and risk associated with surface flows and assign monitoring and detection capabilities appropriately. Several volcano monitoring techniques (for example, Real-Time Seismic Amplitude Measurement [RSAM], amplitude-based locations, and infrasound array processing) can be adapted to also detect, characterize, and track debris flows, lahars, and other surface flows, so instrumentation installed for detecting volcanic unrest and eruptions can have multiple purposes. The utility of instrumentation for the purpose of monitoring unrest and lahars further justifies the importance and utility of a dense network of monitoring stations, even if the volcano remains quiescent.
515. Iezzi et al. (2024) Debris-flow monitoring on volcanoes via a novel usage of a laser rangefinder
     Mount Rainier has had at least 11 large lahars over the last 6,000 years, including one occurring without evidence of eruptive activity. This prompted the creation of a lahar detection system that uses a combination of seismic, infrasound, and tripwires. We test a laser rangefinder placed on a river channel bank for detecting and confirming mass movements flowing past a station as an alternative to the physical tripwires. After testing the device at an experimental debris-flow flume, the laser rangefinder successfully captured a small debris flow on Mount Rainier in 2023, confirming its effectiveness as a lahar detection and monitoring tool. Over the 2-month deployment at Mount Rainier, we find that spurious recordings in the laser rangefinder data (noise) tend to correlate with high humidity, and that periods of noise do not correlate with increased co-located seismic amplitude. Therefore, the impact of the noise on future alarms can be mitigated by coupling a laser rangefinder alarm with that of independent datasets.
514. Seitzinger et al. (2024) Adaptive management in the National Park Service: How Mount Rainier has grown and responded to imminent geomorphic threats
     The Imminent Threats Program at Mount Rainier National Park (MORA) is a novel addition to the typical structure of the National Park Service’s (NPS) Natural and Cultural Resources (NCR) divisions, operating as a branch of the distinguished Geology program. The landscape of MORA is characterized by steep, mountainous terrain; the very nature of the braided, glacier-fed rivers that cascade through this terrain is to change shape and structure constantly as sediment transport conditions vary. Such dynamic geomorphic surface processes pose complicated conditions for maintaining access throughout the park, affecting the integrity and longevity of park infrastructure, such as roadways, bridges, and trails. Recurrent damage to infrastructure proves that traditional maintenance and engineering techniques utilized for repairs do not work in the local environment. The need of a focused geomorphic risk group to address such inertia became identified in the early 2000’s and exists now formally as the Imminent Threats Program. The Imminent Threats technicians conduct scientific monitoring within the park to collect relevant observations of surface processes. This local knowledge is supported by additional literature review and is then used by the technicians to advise and implement holistic engineering designs fit to exist within rather than dominate the environment. The technicians also aim to influence the cultural perception of change and response to infrastructure damage within the agency workplace through their presence at interdisciplinary policy meetings, and also broader society through educational outreach. The long-running success of the projects they’re involved in encourages the Imminent Threats Program to continue to grow and influence the use of adaptive management techniques while responding to reparative needs in the park, ultimately creating improved, effective, and holistic change in resource management at MORA.
513. Todd and Jimenez (2024) Time-lapse monitoring of a small mountain glacier to capture debris flow activity
     South Tahoma Glacier is a 2 km² glacier in Mount Rainier National Park, WA that has produced 31 known debris flows since 1967, more than any other glacier on Mount Rainier. These geologic hazards threaten infrastructure and human lives along Tahoma Creek, downstream from the glacier terminus. The timing of these events and previous research suggests that debris flows from South Tahoma Glacier are most likely triggered by glacial outburst floods, which result when subglacial water storage increases due to (a) increased melt from a period of high temperatures, or (b) late summer or fall precipitation events. We installed a time lapse camera after a series of destructive debris flows in August 2015, and have monitored the glacier terminus from July - September, 2016 - 2023; we will reinstall a time lapse camera in summer 2024. We combine time lapse imagery with meteorological data, high resolution satellite imagery, and digital elevation models to investigate the relationship between recent debris flows and changes to the glacier terminus and proglacial meltwater channels. Our findings will document precursors to and impacts of debris flows from South Tahoma Glacier.
512. Ruzzante and Gleeson (2024) Increasingly hot and dry summers exacerbate low flows and threaten pacific salmon habitat throughout Northwestern North America
     Excessively low stream flows in the late summer can disrupt aquatic life cycles, including those of ecologically and culturally significant species such as Pacific Salmon. Climate change is expected to drive hydrologic changes throughout northwestern North America, but the magnitude and direction of changes to low flows remain highly uncertain. Here we study 375 near-natural catchments, across rainfall-dominated, hybrid, snowmelt-dominated, and glacial regimes throughout the habitat range of Pacific Salmon from California to Alaska. Annual minimum summer discharge has decreased in most catchments; rainfall-dominated and hybrid catchments, which predominate in coastal watersheds and in the southern half of the range, have seen the most severe declines. We predict low flows using linear regression models which significantly outperform existing process-based models. We hindcast low flows back to 1900 and project changes to 2100 under four emissions scenarios. Low flows have historically been driven primarily by summer precipitation and moderately influenced by winter snow accumulation and summer temperature. However, we find that future changes will likely be driven by temperature because the magnitude of projected heating is large compared to the historical variability of temperature. Some further declines in low flows are probably inevitable in rainfall-dominated and hybrid catchments: under a low-emissions scenario, low flows will continue to decline to mid-century but then stabilize. Under a high-emissions scenario, 1-in-50-year low flows could occur almost every summer in rainfall and hybrid catchments. Bold climate action and mitigation strategies are urgently required to safeguard these habitats.

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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