174. Barnhardt and Sherrod (2006) Evolution of a Holocene delta driven by episodic sediment delivery and coseismic deformation, Puget Sound, Washington, USA
     Episodic, large-volume pulses of volcaniclastic sediment and coseismic subsidence of the coast have influenced the development of a late Holocene delta at southern Puget Sound. Multibeam bathymetry, ground-penetrating radar (GPR) and vibracores were used to investigate the morphologic and stratigraphic evolution of the Nisqually River delta. Two fluvial–deltaic facies are recognized on the basis of GPR data and sedimentary characteristics in cores, which suggest partial emplacement from sediment-rich floods that originated on Mount Rainier. Facies S consists of stacked, sheet-like deposits of andesitic sand up to 4 m thick that are continuous across the entire width of the delta. Flat-lying, highly reflective surfaces separate the sand sheets and comprise important facies boundaries. Beds of massive, pumice- and charcoal-rich sand overlie one of the buried surfaces. Organic-rich material from that surface, beneath the massive sand, yielded a radiocarbon age that is time-correlative with a series of known eruptive events that generated lahars in the upper Nisqually River valley. Facies CF consists of linear sandbodies or palaeochannels incised into facies S on the lower delta plain. Radiocarbon ages of wood fragments in the sandy channel-fill deposits also correlate in time to lahar deposits in upstream areas. Intrusive, sand-filled dikes and sills indicate liquefaction caused by post-depositional ground shaking related to earthquakes. Continued progradation of the delta into Puget Sound is currently balanced by tidal-current reworking, which redistributes sediment into large fields of ebb- and flood-oriented bedforms.
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