47. Kamb (1987) Glacier surge mechanism based on linked cavity configuration of the basal water conduit system
    Based on observations of the 1982–1983 surge of Variegated Glacier, Alaska, a model of the surge mechanism is developed in terms of a transition from the normal tunnel configuration of the basal water conduit system to a linked cavity configuration that tends to restrict the flow of water, resulting in increased basal water pressures that cause rapid basal sliding. The linked cavity system consists of basal cavities formed by ice-bedrock separation (cavitation), ~1 m high and ~10 m in horizontal dimensions, widely scattered over the glacier bed, and hydraulically linked by narrow connections where separation is minimal (separation gap 2) is much larger than that of a tunnel system (~10 m²). A physical model of the linked cavity system is formulated in terms of the dimensions of the "typical" cavity and orifice and the numbers of these across the glacier width. The model concentrates on the detailed configuration of the typical orifice and its response to basal water pressure and basal sliding, which determines the water flux carried by the system under given conditions. Configurations are worked out for two idealized orifice types, step orifices that form in the lee of downglacier-facing bedrock steps, and wave orifices that form on the lee slopes of quasisinusoidal bedrock waves and are similar to transverse "N channels." The orifice configurations are obtained from the results of solutions of the basal-sliding-with-separation problem for an ice mass constituting of linear half-space of linear rheology, with nonlinearity introduced by making the viscosity stress-dependent on an intuitive basis. Modification of the orifice shapes by melting of the ice roof due to viscous heat dissipation in the flow of water through the orifices is treated in detail under the assumption of local heat transfer, which guarantees that the heating effects are not underestimated. This treatment brings to light a melting-stability parameter Ξ that provides a measure of the influence of viscous heating on orifice cavitation, similar but distinct for step and wave orifices. Orifice shapes and the amounts of roof meltback are determined by Ξ. When Ξ ≳ 1, so that the system is "viscous-heating-dominated," the orifices are unstable against rapid growth in response to a modest increase in water pressure or in orifice size over their steady state values. This growth instability is somewhat similar to the jökulhlaup-type instability of tunnels, which are likewise heating-dominated. When Ξ ≲ 1, the orifices are stable against perturbations of modest to even large size. Stabilization is promoted by high sliding velocity v, expressed in terms of a v^-1/2 and v^-1 dependence of Ξ for step and wave cavities. The relationships between basal water pressure and water flux transmitted by linked cavity models of step and wave orifice type are calculated for an empirical relation between water pressure and sliding velocity and for a particular, reasonable choice of system parameters. In all cases the flux is an increasing function of the water pressure, in contrast to the inverse flux-versus-pressure relation for tunnels. In consequence, a linked cavity system can exist stably as a system of many interconnected conduits distributed across the glacier bed, in contrast to a tunnel system, which must condense to one or at most a few main tunnels. The linked cavity model gives basal water pressures much higher than the tunnel model at water fluxes ≳1 m³/s if the bed roughness features that generate the orifices have step heights or wave amplitudes less than about 0.1 m. The calculated basal water pressure of the particular linked cavity models evaluated is about 2 to 5 bars below ice overburden pressure for water fluxes in the range from about 2 to 20 m³/s, which matches reasonably the observed conditions in Variegated Glacier in surge; in contrast, the calculated water pressure for a single-tunnel model is about 14 to 17 bars below overburden over the same flux range. The contrast in water pressures for the two types of basal conduit system furnishes the basis for a surge mechanism involving transition from a tunnel system at low pressure to a linked cavity system at high pressure. The parameter Ξ is about 0.2 for the linked cavity models evaluated, meaning that they are stable but that a modest change in system parameters could produce instability. Unstable orifice growth results in the generation of tunnel segments, which may connect up in a cooperative fashion, leading to conversion of the linked cavity system to a tunnel system, with large decrease in water pressure and sliding velocity. This is what probably happens in surge termination. Glaciers for which Ξ ≲ 1 can go into surge, while those for which Ξ ≳ 1 cannot. Because Ξ varies as α^3/2 (where α is surface slope), low values of Ξ are more probable for glaciers of low slope, and because slope correlates inversely with glacier length in general, the model predicts a direct correlation between glacier length and probability of surging; such a correlation is observed (Clarke et al., 1986). Because Ξ varies inversely with the basal shear stress τ, the increase of τ that takes place in the reservoir area in the buildup between surges causes a decrease in Ξ there, which, by reducing Ξ below the critical value ~1, can allow surge initiation and the start of a new surge cycle. Transition to a linked cavity system without tunnels should occur spontaneously at low enough water flux, in agreement with observed surge initiation in winter.
459. Kellermann (2022) Developing and testing a geomorphic mapping protocol in Mount Rainier National Park, Washington, USA
     The grand landscapes and river systems of Mount Rainier National Park (MORA) are influenced by its glaciovolcanic geology and the temperate climate of the Pacific Northwest. Mapping geomorphic changes is a crucial step to understanding, interacting with, and preserving the pristine environments of the Park. Geologic hazards and large-scale hydrologic events are common within park boundaries, putting infrastructure and cultural and historical sites at risk of permanent damage. In this study, I present a protocol for mapping geomorphic features remotely and in the field, and I test the protocol along an at-risk road segment along the Nisqually River. With ArcGIS Pro, I defined site boundaries with a watershed delineation, designated key geomorphic features custom to the unique environment of the Park, and assigned key attribute domains to further describe each mapped feature. Then, I mapped landform features using LiDAR and aerial imagery in Pro and used ArcGIS Online and Field Maps for in-field mapping with a mobile tablet and a backpack-mounted GNSS receiver. After extensive testing, the protocol is in its preliminary phase and ready to be applied to other park field sites for further testing and repeat mapping projects. The resulting inventory suggests that the protocol is suitable for the remote and rugged characteristics of the Park when paired with recent LiDAR data and favorable GNSS conditions. The standardized methods and taxonomy proposed in the protocol allow for recording landform changes and initial site characterization that can be used to identify locations for hazard mitigation. The protocol is repeatable, providing a standardized format useful for comparison between different locations and timescales. While the protocol is designed for the features found near Mount Rainier, it can be readily modified for other fluvial and hillslope environments. In its final form, this geomorphic mapping protocol will equip MORA geologists and resource managers with a standard approach to documenting MORA's most geologically dynamic and at-risk infrastructure and resources.
458. Todd et al. (2022) Field observations of glacier change in Mount Rainier National Park
     Mount Rainier National Park in Washington State is home to 25 glaciers that flow down the flanks of the 14,411 foot high stratovolcano. Remote-sensing studies of Mount Rainier reveal significant glacier retreat, warranting further field-based research into the nature and impacts of ice loss. We use high-precision GPS measurements and a time-lapse camera to observe glacier change in remote and rugged locations in the park. We measured surface elevation along transects crossing Emmons Glacier, where slower retreat rates have been attributed to its thick debris cover. Steep slopes and unconsolidated sediment on the glacier surface complicate data collection, but preliminary analyses reveal glacier surface lowering rates of approximately 1 - 4 m/year with wide variability across the debris-covered surface. We also use time lapse imagery to document changes at the terminus of South Tahoma Glacier, where damaging debris flows have originated. Preliminary analysis of imagery reveals approximately 10 - 30 abrupt increases in water discharge per summer month, as evidenced by a widening or darkening of meltwater channels. These events do not correspond with large debris flows documented farther downstream, and suggest that smaller outbursts of glacial meltwater are common. Although some field measurements of glacier change at Mount Rainier are limited to summer months when snowpack is at a minimum, short-term data collection in limited-access locations can nevertheless enhance our understanding of remote-sensing observations by providing information at higher geographic and temporal resolution.
457. Jimenez et al. (2022) Debris sources and surface evolution at Emmons Glacier, Mount Rainier in relation to possible landslide deposits on Martian viscous flow features
     Mass wasting events such as landslides occur on Earth and Mars. Landslides can cover glaciers with debris, which can armor the underlying glacier ice from melting. Across the mid-latitudes of Mars, there are buried ice deposits that have been interpreted as possible debris-covered glaciers. In particular, Martian glacier-like forms (GLFs) and Lobate Debris Aprons (LDAs) are stagnant in the current climate but were dynamic in the past and we do not fully understand the co-evolution of debris and ice on Mars. Previous studies have mapped GLFs and LDAs and evaluated their morphologies using high-resolution imagery, topography, and radar. Previous studies have also investigated landslide deposits on Mars. While the mapped mid-latitude flow features and mapped landslide deposits overlap in only very few locations, we use high-resolution imagery and topography to evaluate surface morphology and structure in these locations. This evaluation is informed by our work on the debris-covered Emmons Glacier on Mount Rainier in Washington, USA. In 1963, Emmons Glacier experienced a landslide that covered most of the lower glacier. In this field study, we use high-resolution satellite imagery to map the landslide deposit covering the glacier. We conducted sedimentological analyses to better identify transport paths that landslide and glaciogenic debris has taken since deposition on Emmons Glacier. Field measurements of clast size and angularity were determined via orthogonal axes and using Power Roundness scale, respectively, and have been collected at over 30 sample sites across the debris cover from 2019 to 2022. The surface morphology, debris characteristics, and sediment transport of Emmons Glacier provides a case study in the evolution of a debris-covered glacier following a landslide event. Our on-the-ground analyses of Emmons Glacier deepens our understanding compared to using satellite imagery alone. This terrestrial understanding will be considered in relation to how we may interpret the surface morphologies and surface structures of any locations where mapped landslide deposits may be coincident with mapped GLFs or LDAs on Mars.
456. Beason et al. (2022) A vanishing landscape: Current trends for the glaciers of Mount Rainier National Park, Washington, USA
     Mount Rainier is the most glaciated volcano in the Cascade Range of the western United States and has more glacial ice on its edifice than all other volcanoes in the Cascade Range combined. Measuring rates of glacial ice loss during warming climates are critical to understanding the future impacts to riparian areas downslope of the glaciers, sediment production to braided rivers, aquatic impacts due to increasing stream temperatures, and many other important areas for park resource management. Glacial area has been delineated many times in the last century; most importantly in 1896, 1913, 1971, 1994, 2009, and, most recently, in 2015. Each of these extents represents a snapshot of the surface area of the volcano occupied by glacial ice during those years and provides an opportunity to visualize the health of the glaciers in the park over time. Using aerially derived Structure from Motion (SfM) data acquired in September 2021, as well as other satellite and aerial imagery, glacier area for each of the 29 named glacial features is updated for Mount Rainier and presented here. From these source data, we have mapped not only the extent of ice but estimate the volume of ice from methods developed by other researchers in the past. Overall, our data shows a continuation of gradual yet accelerating loss of glacial ice at Mount Rainier, resulting in significant changes in regional ice volume over the last century. Regional climate change is affecting all glacial features at Mount Rainier, but mostly those smaller cirque glaciers and discontinuous glaciers on the south aspect of the volcano.
455. Muneer (2022) Advanced suspended sediment sampling and simulation of sediment pulses to better predict fluvial geomorphic change in river networks
     Sediment, an integral part of rivers and watersheds, is eroded from, stored in, and transported through various watershed components. Rivers often receive sediment in the form of episodic, discrete pulses from a variety of natural and anthropogenic processes, this sediment can be transported downstream along the bed or suspended in the water column. Most sediment measurements are focused on the component suspended in the water column. Recent advances in data collection techniques have substantially increased both the resolution and spatial scale of data on suspended sediment dynamics, which is helpful in linking small, site-scale measurements of transport processes in the field with large-scale modeling efforts. Part of this research evaluates the accuracy of the latest laser diffraction instrument for suspended-sediment measurement in rivers, LISST-SL2 for measuring suspended sediment concentration (SSC), particle size distribution (PSD), and velocity by comparing to concurrent physical samples analyzed in a lab for SSC and PSD, and velocity measured using an acoustic Doppler current profiler (ADCP) at 11 sites in Washington and Virginia during 2018-2020. Another part of this work employs a 1-D river network, bed material transport model to investigate the magnitude, timing, and persistence of downstream changes due to the introduction of sediment pulses in a linear river network. We specifically focus on comparing bed responses between mixed and uniform grain size sediment pulses. Then the model capability is utilized to explore the control of hydrograph structure on debris flow sediment transport through a more complex river network at different time horizons. Another part of this work investigates the effect of differences in spatial distribution of debris flow sediment input to the network by analyzing corresponding tributary and mainstem characteristics. Based on an extensive dataset, our results highlight the need for a correction of the raw LISST-SL2 measurements to improve the estimation of effective density and particle size distribution with the help of a physical sample. Simulation results from the river network model show that bed response is primarily influenced by the sediment-pulse grain size and distribution. Intermediate mixed-size pulses are likely to have the largest downstream impact because finer sizes translate quickly and coarser sizes (median bed gravel size and larger) disperse slowly. Furthermore, a mixed-size pulse, with a smaller median grain size than the bed, increases bed mobility more than a uniform-size pulse. While investigating the hydrologic control on debris flow simulation, this study finds that differences between transport by a 30-year daily hydrograph and simplified hydrographs were greatest in the first few years, but errors decreased to around 10% after 10 years. Our simulation results highlight that the sequence of flows (initial high/low flow) is less important for transport of finer sediment. We show that such network-scale modeling can quantitatively identify geomorphically significant network characteristics for efficient transport from tributaries to the mainstem, and eventually to the outlet. Results suggest that watershed area and slope characteristics are important to predict aggradation hotspots in a network. However, to predict aggradation and fluvial geomorphic responses to variations in sediment supply from river network characteristics more confidently, more widespread (in several other river networks) model applications with field validation would be useful. This work has important implications for river management, as it allows us to better predict geomorphically significant tributaries and potential impact on downstream locations, which are important for river biodiversity. Model results lead the way to use of simplified flow hydrographs for different timescales, which is crucial in large-scale modeling as it is often restricted by computational capacity. Finally, given the ability for reliable quantification of a high-resolution time-series of different suspended-sediment characteristics, in-stream laser diffraction offers great potential to advance our understanding of suspended-sediment transport.

View More Publications...

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: https://pnsn.org/volcanoes
For information on USGS volcano alert levels and notifications: https://www.usgs.gov/natural-hazards/volcano-hazards/notifications

The U.S. Geological Survey and Pacific Northwest Seismic Network (PNSN) continue to monitor these volcanoes closely and will issue additional updates and changes in alert level 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
Media: Ryan McClymont, PIO, USGS Office of Communications and Publishing rmcclymont@usgs.gov