139. Pierson (2006) Dating young geomorphic surfaces using age of colonizing Douglas fir in southwestern Washington and northwestern Oregon, USA
     Dating of dynamic, young (<500 years) geomorphic landforms, particularly volcanofluvial features, requires higher precision than is possible with radiocarbon dating. Minimum ages of recently created landforms have long been obtained from tree-ring ages of the oldest trees growing on new surfaces. But to estimate the year of landform creation requires that two time corrections be added to tree ages obtained from increment cores: (1) the time interval between stabilization of the new landform surface and germination of the sampled trees (germination lag time or GLT); and (2) the interval between seedling germination and growth to sampling height, if the trees are not cored at ground level. The sum of these two time intervals is the colonization time gap (CTG). Such time corrections have been needed for more precise dating of terraces and floodplains in lowland river valleys in the Cascade Range, where significant eruption-induced lateral shifting and vertical aggradation of channels can occur over years to decades, and where timing of such geomorphic changes can be critical to emergency planning. Earliest colonizing Douglas fir (Pseudotsuga menziesii) were sampled for tree-ring dating at eight sites on lowland (<750 m a.s.l.), recently formed surfaces of known age near three Cascade volcanoes – Mount Rainier, Mount St. Helens and Mount Hood – in southwestern Washington and northwestern Oregon. Increment cores or stem sections were taken at breast height and, where possible, at ground level from the largest, oldest-looking trees at each study site. At least ten trees were sampled at each site unless the total of early colonizers was less. Results indicate that a correction of four years should be used for GLT and 10 years for CTG if the single largest (and presumed oldest) Douglas fir growing on a surface of unknown age is sampled. This approach would have a potential error of up to 20 years. Error can be reduced by sampling the five largest Douglas fir instead of the single largest. A GLT correction of 5 years should be added to the mean ring-count age of the five largest trees growing on the surface being dated, if the trees are cored at ground level. This correction would have an approximate error of ±5 years. If the trees are cored at about 1.4 m above the ground surface (breast height), a CTG correction of 11 years should be added to the mean age of the five sampled trees (with an error of about ±7 years).
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