114. Symonds et al. (2003) Scrubbing masks magmatic degassing during repose at Cascade-Range and Aleutian-Arc volcanoes
     Between 1992 and 1998, we sampled gas discharges from ≤173°C fumaroles and springs at 12 quiescent but potentially restless volcanoes in the Cascade Range and Aleutian Arc (CRAA) including Mount Shasta, Mount Hood, Mount St. Helens, Mount Rainier, Mount Baker, Augustine Volcano, Mount Griggs, Trident, Mount Mageik, Aniakchak Crater, Akutan, and Makushin. For each site, we collected and analyzed samples to characterize the chemical (H₂O, CO₂, H₂S, N₂, CH₄, H₂, HCl, HF, NH₃, Ar, O₂, He) and isotopic (δ¹³C of CO2, ³He/⁴He, ⁴⁰Ar/³⁶Ar, δ³⁴S, δ¹³C of CH₄, δ¹⁵N, and δD and δ¹⁸O of water) compositions of the gas discharges, and to create baseline data for comparison during future unrest. The chemical and isotopic data show that these gases contain a magmatic component that is heavily modified from scrubbing by deep hydrothermal (150° - 350°C) water (primary scrubbing) and shallow meteoric water (secondary scrubbing). The impact of scrubbing is most pronounced in gas discharges from bubbling springs; gases from boiling-point fumaroles and superheated vents show progressively less impact from scrubbing. The most effective strategies for detecting gas precursors to future CRAA eruptions are to measure periodically the emission rates of CO₂ and SO₂, which have low and high respective solubilities in water, and to monitor continuously CO₂ concentrations in soils around volcanic vents. Timely resampling of fumaroles can augment the geochemical surveillance program by watching for chemical changes associated with drying of fumarolic pathways (all CRAA sites), increases in gas geothermometry temperatures (Mount Mageik, Trident, Mount Baker, Mount Shasta), changes in δ¹³C of CO₂ affiliated with magma movement (all CRAA site), and increases in ³He/⁴He coupled with intrusion of new magma (Mount Rainier, Augustine Volcano, Makushin, Mount Shasta). Repose magmatic degassing may discharge substantial amounts of S and Cl into the edifices of Mount Baker and several other CRAA volcanoes that is trapped by primary and secondary scrubbing. The consequent acidic fluids produce ongoing alteration in the 0.2- to 3-km-deep hydrothermal systems and in fields of boiling-point fumaroles near the surface. Such alteration may influence edifice stability and contribute to the formation of more-hazardous cohesive debris flows. In particular, we recommend further investigation of the volume, extent, and hazards of hydrothermal alteration at Mount Baker. Other potential hazards associated with the CRAA volcano hydrothermal systems include hydrothermal eruptions and, for deeper systems intruded by magma, deep-seated edifice collapse.
482. Wright et al. (2023) Development of a volcanic risk management system at Mount St. Helens: 1980 to present
     Here, we review volcanic risk management at Mount St. Helens from the perspective of the US Geological Survey’s (USGS) experience over the four decades since its 18 May 1980 climactic eruption. Prior to 1980, volcano monitoring, multidisciplinary eruption forecasting, and interagency coordination for eruption response were new to the Cascade Range. A Mount St. Helens volcano hazards assessment had recently been published and volcanic crisis response capabilities tested during 1975 thermal unrest at nearby Mount Baker. Volcanic unrest began in March 1980, accelerating the rate of advance of volcano monitoring, prompting coordinated eruption forecasting and hazards communication, and motivating emergency response planning. The destruction caused by the 18 May 1980 eruption led to an enormous emergency response effort and prompted extensive coordination and planning for continuing eruptive activity. Eruptions continued with pulsatory dome growth and explosive eruptions over the following 6 years and with transport of sediment downstream over many more. In response, USGS scientists and their partners expanded their staffing, deployed new instruments, developed new tools (including the first use of a volcanic event tree) for eruption forecasting, and created new pathways for agency internal and external communication. Involvement in the Mount St. Helens response motivated the establishment of response measures at other Cascade Range volcanoes. Since assembly during the early and mid-1990s, volcano hazard working groups continue to unite scientists, emergency and land managers, tribal nations, and community leaders in common cause for the promotion of risk reduction. By the onset of renewed volcanic activity in 2004, these new systems enabled a more efficient response that was greatly facilitated by the participation of organizations within volcano hazard working groups. Although the magnitude of the 2004 eruptive sequence was much smaller than that of 1980, a new challenge emerged focused on hazard communication demands. Since 2008, our understanding of Mount St. Helens volcanic system has improved, helping us refine hazard assessments and eruption forecasts. Some professions have worked independently to apply the Mount St. Helens story to their products and services. Planning meetings and working group activities fortify partnerships among information disseminators, policy and decision-makers, scientists, and communities. We call the sum of these pieces the Volcanic Risk Management System (VRMS). In its most robust form, the VRMS encompasses effective production and coordinated exchange of volcano hazards and risk information among all interested parties.
481. Fountain et al. (2023) Inventory of glaciers and perennial snowfields of the conterminous USA
     This report summarizes an updated inventory of glaciers and perennial snowfields of the conterminous United States. The inventory is based on interpretation of mostly aerial imagery provided by the National Agricultural Imagery Program, US Department of Agriculture, with some satellite imagery in places where aerial imagery was not suitable. The inventory includes all perennial snow and ice features ≥ 0.01 km². Due to aerial survey schedules and seasonal snow cover, imageries acquired over a number of years were required. The earliest date is 2013 and the latest is 2020, but more than 73% of the outlines were acquired from 2015 imagery. The inventory is compiled as shapefiles within a geographic information system that includes feature classification, area, and location. The inventory identified 1331 (366.52 ± 14.34 km²) glaciers, 1176 (31.01 ± 9.30 km²) perennial snowfields, and 35 (3.57 km² ± no uncertainty) buried-ice features. The data including both the shapefiles and tabulated results are publicly available at https://doi.org/10.15760/geology-data.03 (Fountain and Glenn, 2022).
480. Schwat et al. (2023) Multi-decadal erosion rates from glacierized watersheds on Mount Baker, Washington, USA, reveal topographic, climatic, and lithologic controls on sediment yields
     Understanding land surface change in and sediment export out of proglacial landscapes is critical for understanding geohazard and flood risks over engineering timescales and characterizing landscape evolution over geomorphic timescales. We used automated Structure from Motion software to process historical aerial photographs and, with modern lidar data, generated a high-resolution DEM time series with coverage over 10 glacierized watersheds on Mount Baker, Washington, USA for the time period between 1947 and 2015. We measured basin-wide sediment yields and sediment redistribution on hillslopes and in stream channels. Slopes within most measured erosion sites are above theoretical and observed debris-flow thresholds. We observed significant erosion of hillslopes and limited deposition on hillslopes and in stream channels. Sediment delivery ratios during time periods with net erosion averaged 0.73. We determined, consistent with previous field observations, that debris flows originating from moraines are a primary erosion mechanism in proglacial zones on Mount Baker. Time series measurements indicate that temporal variability in erosion rates is associated with climate oscillations, with higher erosion rates during cooler-wetter periods. Basin-wide sediment yield is positively correlated with lithology (r2 = 0.54), hillslope angle (r2 = 0.52), drainage area (r2 = 0.82), and negatively correlated with stream channel slope (r2 = 0.67). Topographic differences between high and low yielding basins indicate that spatial variability in erosion on Mount Baker is sensitive to Pleistocene and Holocene glacial and volcanic activity. Specific sediment yields in six basins averaged 4600 ton/km2/yr, consistent with global measurements in glacierized catchments. Specific sediment yield decreased with increasing basin area, with total loads in the downstream main stem Nooksack River estimated between 480 and 820 ton/km2/yr. Proglacial sediment yields account for between 18 and 32 % of total sediment load in the main stem Nooksack River and exceed contributions by bluff and terrace erosion, which account for between 8 and 13 % of total load. Our findings indicate that erosion in glacierized basins is sensitive to decadal climate oscillations and that high proglacial sediment yields provide an important contribution to river systems downstream, particularly in catchments where upland topography and lithology is favorable.
479. Yang et al. (2023) Hydromechanical coupling mechanism and an early warning method for paraglacial debris flows triggered by infiltration: Insights from field monitoring in Tianmo gully, Tibetan Plateau
     Deglaciation has intensified in alpine regions with climate warming, causing increasingly intense paraglacial debris flows (PDFs). Examining the hydromechanical mechanism and initiation of PDFs is essential to disaster relief in downstream areas. However, the establishment of source initiation of PDFs and early warning criteria are hampered by a lack of in situ observations of PDFs; therefore, providing a PDF early warning is still challenging. In this study, on the basis of long-time series field monitoring of rainfall, temperature, soil moisture, and surface displacement in the Tianmo gully, southeast of the Tibetan Plateau, the initiation mechanism of PDFs and the evolutions of the effective saturation, matrix suction, and suction stress were analyzed by combining the hydromechanical coupling analysis method of a slope for a long-term sequence. The measured evidence for the formation and evolution process of slope stability in PDF source area was provided under the conditions of precipitation and ablation. Furthermore, through the inversion of the key slope stability parameters, the thresholds of the hydraulic factors for the provenance slope failure were established, which could be used for early warning of PDFs. This study provides theoretical reference and long-time field data for monitoring and early warning of PDFs in paraglacial hazard-prone areas under global warming sequences.
478. Selander et al. (2023) Mapping bedrock outcrops: An assessment of algorithms and their performance across diverse landscapes
     Accurately mapping bedrock outcrops is important to geomorphology, hydrology, ecology, and hazard management. Airborne lidar has proven useful to identify bedrock exposure from topographic data alone. However, there is a need to test these topographic proxies across diverse environments. We developed a new algorithm that uses both slope and curvature to classify bedrock and evaluate its success with respect to two existing classifiers, a slope-threshold method and a roughness-threshold method, for six different landscapes shaped by different erosional processes. Accuracy of binary classifiers are quantified using the F1 score and the normalized Matthews Correlation Coefficient. By analyzing topographic proxies across gradients in bedrock fraction, we show that normalized Matthew Correlation Coefficient is a more robust measure of accuracy than F1 score when the data is imbalanced (i.e., where either soil or bedrock is more prevalent). We found moderate success in mapping bedrock with all three methods for half of the landscapes (flanks of an active stratovolcano, Mount Rainier, Washington; horst and graben landscape, Canyonlands National Park, Utah; bedrock canyon, Boulder Creek, Colorado). Our new algorithm performed slightly better than the other two methods. None of the methods were successful in a sequence of coastal terraces and sea cliffs (Santa Cruz County, California), a glacially scoured landscape (Southern Wind River Range, Wyoming), and a fluvially incised chaparral canyon (Mission Trails, San Diego, California). All classifiers are confounded by erosional processes that produce smooth, low gradient, bedrock surfaces and/or sediment transport processes that increase roughness. While our new algorithm leverages the success of both slope- and roughness-threshold methods, results emphasize the importance of considering the geomorphic context when choosing among algorithms.

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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