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The glaciers of the North Cascades have experienced mass loss and terminus retreat due to climate change. The meltwater from these glaciers provides a flux of cold glacier meltwater into the river systems, which supports salmon spawning during the late summer dry season. The Nooksack Indian Tribe monitors the outlet flow of the Sholes Glacier within the North Cascades range with the goal of understanding the health of the glacier and the ability of the Tribe to continue to harvest sustainable populations of salmon. This study compares the UAV derived glacier ablation with the discharge data collected by the Tribe. We surveyed the Sholes Glacier twice throughout the 2020 melt season and, using Structure-from-Motion technology, generated high resolution multispectral orthomosaics and Digital Elevation Models (DEMs) of the glacier on each of the survey dates. The DEMs were differenced to reveal the surface height change of the glacier. The spectral data of the orthomosaics were used to conduct IsoData unsupervised classification. This process divided the survey area into Snow, Ice, and Rock classes that were then used to attribute the surface height changes of the DEMs to either snow or ice melt. The analysis revealed the glacier lost an average thickness of −0.132 m per day (m d−1) with snow and ice losing thickness at similar rates, −0.130 m d−1 and −0.132 m d−1 respectively. DEM differencing reveals that a total of −550,161 ± 45,206 m3 water equivalent (w.e.) was discharged into Wells Creek between the survey dates whereas the stream gauge station measured a total discharge of 350,023 m3. This study demonstrates the ability to spectrally classify the UAV data and derive discharge measurements while evaluating the small-scale spatial variability of glacier melt. Assessing ablation in small alpine glaciers is of great importance to downstream communities, like the Nooksack Indian Tribe who seek to understand the magnitude and timing of glacier melt in order to better protect their salmon populations. With this paper, we provide a baseline for future glacier monitoring and the potential to connect the snow surface properties with the rate of snow melt into a warming future.

Lepidoptera at a single mid-elevation site in the central Cascade Range in Washington state were surveyed for six full seasons spanning 11 years (2009–2011, 2017–2019). Sampling was performed continuously with a blacklight trap, and was supplemented with pheromone traps, searches for immature stages, day collecting, observation, photography, and sugar bait traps. The habitat is forested transition zone, including old growth forest, slightly east of the Cascade divide in the southern part of the North Cascades ecoregion. The fauna of 822 species is categorized by the number of seasons each species was found over the span of the study. The higher-order distribution of the fauna within Lepidoptera, impact of sampling methods, annual and multi-year fluctuations in abundance, and local climate effects on flight period are presented. Taxonomic challenges and noteworthy records are discussed. Representative species and genitalia are illustrated. [ABSTRACT FROM AUTHOR]

Glacial retreat from the North Cascade Range after the Last Glacial Maximum (LGM) at approximately 21 ka until the end of the Pleistocene at 11.6 ka was complex and included both continental and alpine glaciers. Alpine valley glaciers reached their maximum extent before 21.4 ka, then underwent a punctuated retreat to valley heads. In the south, beyond the reach of ice sheet glaciation, several end moraines were deposited after the LGM. Moraines marking a re-advance of alpine glaciers to 5 km below modern glaciers were deposited from 13.7 to 11.6 ka. The Cordilleran Ice Sheet flowed south from near 52° north latitude in British Columbia into the North Cascades. At its maximum size the ice sheet covered more than 500 km2 and had a surface elevation of 2200 m in upper Skagit valley. Deglaciation commenced about 16 ka by frontal retreat of ice flanking the mountains. Surface lowering eventually exposed regional hydrologic divides and stranded ice masses more than 1000 m thick in valleys. Isolated fragments of the ice sheet disintegrated rapidly from 14.5 to 13.5 ka, with the pattern of deglaciation in each valley controlled by valley orientation, topography, and climate. Like alpine glaciers to the south, retreat of the ice sheet remnants was slowed by millennial scale climate fluctuations that produced at least one large recessional moraine, and multiple lateral moraines and kame terraces from elevations of 200-1400 m in most valleys. Large volumes of glacial meltwater flowed through the North Cascades and was concentrated in the Skagit and Methow rivers. Outburst floods from deep proglacial lakes spilled across divides and down steep canyons, depositing coarse gravel terraces and alluvial fans at valley junctions. Climate at the LGM was characterized by a mean summer temperature 6 to 7 ºC cooler than today, and 40% lower mean annual precipitation. Persistence of this climate for thousands of years before the LGM caused a 750-1000 m decrease in alpine glacier equilibrium line altitudes (ELA). In the southern North Cascades at 16 ka, glacial ELAs were 500-700 m lower than today, and during advances from 13.7 to 11.6 ka alpine glacier ELAs were 200-400 m lower.

Anthropogenic and natural habitat fragmentation inhibit movement of animals through landscapes. An important challenge for connectivity conservation is determining which conditions facilitate or limit movements, so that these areas can be prioritized for protection or restoration. We examine Canada lynx Lynx canadensis habitat connectivity in the fragmented North Cascade Mountains of Washington, as an example of a highly mobile species that is specialized both on prey and in habitat needs. We identify lynx Habitat Concentration Areas based on Core Habitat Models, parameterize resistance surfaces from our Matrix Habitat Model, and develop linkages of habitat lynx use to move between patches of high quality habitat. We identify a number of linkages for lynx comprised of habitat conditions that differed from high quality core patches identified from our habitat modeling. Radio‐locations from lynx confirm lower‐quality habitats of low resistance to movement were used by traveling lynx. Our results thus suggest traveling lynx do indeed use a much broader range of habitats than do lynx moving within core areas. For lynx in the North Cascades, our results show that maintaining connectivity will require preserving habitats and linkages that would previously have been deemed unsuitable for lynx. Maintaining connectivity for lynx is particularly important given the many recent large wildfires in this region that have reduced the number of mature forest stands that form prime habitat for lynx. Policy implications. Our results strongly suggest that habitat connectivity models should be based on empirical information of animal location data and focused on matrix habitat analysis. Traveling predators use a wide suite of habitats, resulting in more and broader linkage zones that should inform conservation efforts. Failure to identify these areas of functional connectivity could result in the oversight of usable linkage zones, leaving them without protection and vulnerable to degradation. Habitat fragmentation often inhibits the movements of animals across landscapes. We identify areas of connectivity for Canada lynx as an example of a highly mobile carnivore that is specialized in habitat needs. We base our connectivity models on a Travel Habitat analysis revealing a broader range of habitats and thus areas of connectivity used by traveling lynx than by lynx in core habitat. We suggest that basing connectivity models on Travel Habitat analyses will better inform conservation efforts on fragmented landscapes. [ABSTRACT FROM AUTHOR]

Thalénite-(Y), ideally Y3Si3O10F, is a heavy-rare-earth-rich silicate phase occurring in granite pegmatites that may help to illustrate rare-earth element (REE) chemistry and behaviour in natural systems. The crystal structure and mineral chemistry of thalénite-(Y) were analysed by electron microprobe analysis, X-ray diffraction and micro-Raman spectroscopy from a new locality in the peralkaline granite of the Golden Horn batholith, Okanogan County, Washington State, USA, in comparison with new analyses from the White Cloud pegmatite in the Pikes Peak batholith, Colorado, USA. The Golden Horn thalénite-(Y) occurs as late-stage sub-millimetre euhedral bladed transparent crystals in small miarolitic cavities in an arfvedsonite-bearing biotite granite. It exhibits growth zoning with distinct heavy-rare-earth element (HREE) vs. light-rare-earth element (LREE) enriched zones. The White Cloud thalénite-(Y) occurs in two distinct anhedral and botryoidal crystal habits of mostly homogenous composition. In addition, minor secondary thalénite-(Y) is recognized by its distinct Yb-rich composition (up to 0.8 atoms per formula unit (apfu) Yb). Single-crystal X-ray diffraction analysis and structure refinement reveals Y-site ordering with preferential HREE occupation of Y2 vs. Y1 and Y3 REE sites. Chondrite normalization shows continuous enrichment of HREE in White Cloud thalénite-(Y), in contrast to Golden Horn thalénite-(Y) with a slight depletion of the heaviest REE (Tm, Yb and Lu). The results suggest a hydrothermal origin of the Golden Horn miarolitic thalénite-(Y), compared to a combination of both primary magmatic followed by hydrothermal processes responsible for the multiple generations over a range of spatial scales in White Cloud thalénite-(Y). [ABSTRACT FROM AUTHOR]

Alpine treelines are expected to move upward in a warming climate, but downward in response to increases in wildfire. We studied the effects of fire on vegetation structure and composition across four alpine treeline ecotones extending from Abies lasiocarpa/Picea engelmannii forests at lower elevations, through Pinus albicaulis/Larix lyallii parkland, to alpine tundra. We estimated the probabilities of burning and transitions between states following fire among four canopy-cover (structural) classes: nonforest (0% tree cover), sparse woodland (<10% tree cover), open forest (10-40% tree cover), and closed forest (>40% tree cover). We also evaluated changes in the size structure and composition of live overstory trees (≥1.4 m height) due to mortality following fire. The severity and resulting effects of fire varied among structural classes: Non-forest was less likely to burn than the landscape as a whole; open forest was more likely to remain forest than to change to non-forest; and closed forest never changed to non-forest, irrespective of burn severity. Higher-severity fires caused greater mortality of larger-diameter trees than of smaller-diameter trees. Our results suggest that structural components of the alpine treeline will not respond unidirectionally to a warming climate nor to an increase in fire. Instead, the ecotone will expand bidirectionally and develop larger, more heterogeneous patches of vegetation. [ABSTRACT FROM AUTHOR]

Abstract: The metasupracrustal units within the north central Chelan block of the North Cascades Range, Washington, are investigated to determine mechanisms and timescales of supracrustal rock incorporation into the deep crust of continental magmatic arcs. Zircon U‐Pb and Hf‐isotope analyses were used to characterize the protoliths of metasedimentary and metaigneous rocks from the Skagit Gneiss Complex, metasupracrustal rocks from the Cascade River Schist, and metavolcanic rocks from the Napeequa Schist. Skagit Gneiss Complex metasedimentary rocks have (1) a wide range of zircon U‐Pb dates from Proterozoic to latest Cretaceous and (2) a more limited range of dates, from Late Triassic to latest Cretaceous, and a lack of Proterozoic dates. Two samples from the Cascade River Schist are characterized by Late Cretaceous protoliths. Amphibolites from the Napeequa Schist have Late Triassic protoliths. Similarities between the Skagit Gneiss metasediments and accretionary wedge and forearc sediments in northwestern Washington and Southern California indicate that the protolith for these units was likely deposited in a forearc basin and/or accretionary wedge in the Early to Late Cretaceous (circa 134–79 Ma). Sediment was likely underthrust into the active arc by circa 74–65 Ma, as soon as 7 Ma after deposition, and intruded by voluminous magmas. The incorporation of metasupracrustal units aligns with the timing of major arc magmatism in the North Cascades (circa 79–60 Ma) and may indicate a link between the burial of sediments and pluton emplacement. [ABSTRACT FROM AUTHOR]

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The North Cascades Ecoregion in the United States occurs in portions of nine counties of north central Washington state. There are 18 species found here, in nine genera and five families (Acanthodrilidae, Lumbricidae, Megascolecidae, Ocnerodrilidae and Sparganophilidae). Four of the species are native (endemic) to North America; all others are European (exotic) introductions. A description of the ecoregion and three colour photographs are also included. [ABSTRACT FROM AUTHOR]

A stationary response of tree radial growth to climatic variables is assumed as a basis for climatic reconstructions and future growth projections in response to climate change. Mountain hemlock ( Tsuga mertensiana (Bong.) Carrière) trees on the western slopes of the North Cascade Range (Washington, USA) were examined for stability in growth response to climatic influences at a small spatial scale. Moving correlation functions demonstrate that climate-growth interactions are nonstationary over time, alternating between periods of significant and nonsignificant responses. Correlations between growth and winter precipitation have weakened, becoming statistically insignificant in the last decade, but correlations with spring temperature and previous-year summer temperature have strengthened, becoming statistically significant. The Pacific Decadal Oscillation influences patterns in climate-growth correlations but does not seem to account for the most recent changes in correlation strength. At an interannual scale, growth differs between El Niño Southern Oscillation phases, specifically between El Niño and La Niña years and between La Niña and neutral phase years. The variability in growth response to climate at interannual and interdecadal time frames, especially with the climate changes emerging in recent decades, will challenge the reliability and accuracy of reconstruction and predictive models. [ABSTRACT FROM AUTHOR]

Warmer and drier climate over the past few decades has brought larger fire sizes and increased annual area burned in forested ecosystems of western North America, and continued increases in annual area burned are expected due to climate change. As warming continues, fires may also increase in severity and produce larger contiguous patches of severely burned areas. We used remotely sensed burn-severity data from 125 fires in the northern Cascade Range of Washington, USA, to explore relationships between fire size, severity, and the spatial pattern of severity. We examined relationships between climate and the annual area burned and the size of wildfires over a 25-year period. We tested the hypothesis that increased fire size is commensurate with increased burn severity and increased spatial aggregation of severely burned areas. We also asked how local ecological controls might modulate these relationships by comparing results over the whole study area (the northern Cascade Range) to those from four ecological subsections within it. We found significant positive relationships between climate and fire size, and between fire size and the proportion of high severity and spatial-pattern metrics that quantify the spatial aggregation of high-severity areas within fires, but the strength and significance of these relationships varied among the four subsections. In areas with more contiguous subalpine forests and less complex topography, the proportion and spatial aggregation of severely burned areas were more strongly correlated with fire size. If fire sizes increase in a warming climate, changes in the extent, severity, and spatial pattern of fire regimes are likely to be more pronounced in higher-severity fire regimes with less complex topography and more continuous fuels. [ABSTRACT FROM AUTHOR]

Abstract: The crystalline core of the North Cascades is part of a thick (>55 km) 96–45 Ma continental magmatic arc. The highest-grade part of the arc is the Skagit Gneiss Complex that includes partially migmatitic amphibolite-facies orthogneiss, layered biotite gneiss, and paragneiss. The typically NW-striking foliation and gently SE-plunging lineation formed mostly between 69 and 51 Ma. In the study area to the north, four fold generations are recorded some of which formed from 51 to 46 Ma. The upright kilometer-scale folds in the study area are similar to Eocene folds in the southern part of the Skagit Gneiss Complex and implies at least an abbreviated interval of regional shortening during an extended period of overall transtension. Latest ductile deformation is marked by strong subhorizontal constrictional fabrics in granodiorite, which intrudes all other major units and structures at 46–45 Ma. Microstructures record relatively low-temperature (300–400 °C) and medium- to high-temperature (≥450 °C) ductile deformation, which are focused in kilometer-scale domains. Orientation, sequence, and timing of deformation are similar in the northern and southern portions of the Skagit Gneiss Complex, but structures differ in the central portion that apparently do not record the brief interval of shortening. [Copyright &y& Elsevier]

Mount Baker, North Cascades, WA, has a current glacierized area of 38.6 km2. From 1984 to 2010, the North Cascade Glacier Climate Project has monitored the annual mass balance (Ba), accumulation area ratio (AAR), terminus behaviour and longitudinal profiles of Mount Baker glaciers. The Ba on Rainbow, Easton and Sholes Glaciers from 1990 to 2010 averaged −0.52 m w.e. a−1(m a−1). Terminus observations on nine principal Mount Baker glaciers, 1984-2009, indicate retreat ranging from 240 to 520 m, with a mean of 370 m or 14 m a−1. AAR observations on Rainbow, Sholes and Easton Glaciers for 1990-2010 indicate a mean AAR of 0.55 and a steady state AAR of 0.65. A comparison of Ba and AAR on these three glaciers yields a relationship that is used in combination with AAR observations made on all Mount Baker glaciers during 7 years to assess Mount Baker glacier mass balance. Utilizing the AAR-Ba relationship for the three glaciers yields a mean Ba of −0.55 m a−1 for the 1990-2010 period, 0.03 m a−1 higher than the measured mean Ba. The mean Ba based on the AAR-Ba relationship for the entire mountain from 1990 to 2010 is −0.57 m a−1. The product of the mean observed mass balance gradient determined from 11 000 surface mass balance measurements and glacier area in each 100-m elevation band on Mount Baker yields a Ba of −0.50 m a−1 from 1990-2010 for the entire mountain. The median altitude of the three index glaciers is lower than that of all Mount Baker glaciers. Adjusting the balance gradient for this difference yields a mean Ba of −0.77 m a−1 from 1990 to 2010. All but one estimate converge on a loss of −0.5 m a−1 for Mount Baker from 1990 to 2010. This equates to an 11-m loss in glacier thickness, 12-20% of the entire 1990 volume of glaciers on Mount Baker. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Synorogenic basin development and subsequent collapse and loading provide important constraints on the Late Cretaceous crustal structure of the North America Cordillera. High grade metasedimentary rocks of the Swakane Gneiss in the North Cascades have been interpreted to include ca. 73Ma detrital zircon that requires a protolith age considerably younger than metamorphic ages of adjacent terranes. This detrital interpretation requires rapid loading rates of 7–8mm/yr, heating to 750°C in <5myr, and partial exhumation prior to ca. 68Ma. We present new U–Pb zircon and Sm–Nd garnet dates for the Swakane Gneiss that directly date metamorphism and provide a basis for evaluating this model of Late Cretaceous deposition, loading, and crustal structure. Garnet preserves compositional evidence for growth during high pressure amphibolite-facies metamorphism and little subsequent modification. New garnet–rock Sm–Nd isochrons of 73.5±1.2, 71.3±2.8, and 65.8±0.7Ma, tightly constrain the timing of garnet growth. Swakane Gneiss zircons preserve complex magmatic, detrital, and metamorphic histories. Most zircons have distinct cores and homogeneous overgrowths. Detrital zircon cores include significant Proterozoic and Mesozoic components with low U/Th ratios. Homogeneous metamorphic zircon rims have high U/Th (>5) and define an array of concordant U–Pb dates from 75 to 63Ma. The new zircon U–Pb and garnet Sm–Nd ages establish that the youngest regional metamorphism was diachronous and occurred between 75 and 63Ma. Our dataset precludes post 73Ma deposition and instead suggests that sedimentation occurred after ca. 91Ma and ended before ca. 75Ma. Using these age constraints for deposition and metamorphism, we propose new loading rates of 1–3mm/yr and conclude that the Swakane Gneiss protolith was likely deposited in a small, short-lived, intra-arc basin that subsided, filled in, and collapsed quickly due to overthrusting of arc crust. [Copyright &y& Elsevier]

Amphibole fractionation in the deep roots of subduction-related magmatic arcs is a fundamental process for the generation of the continental crust. Field relations and geochemical data of exposed lower crustal igneous rocks can be used to better constrain these processes. The Chelan Complex in the western U.S. forms the lowest level of a 40-km thick exposed crustal section of the North Cascades and is composed of olivine websterite, pyroxenite, hornblendite, and dominantly by hornblende gabbro and tonalite. Magmatic breccias, comb layers and intrusive contacts suggest that the Chelan Complex was build by igneous processes. Phase equilibria, textural observations and mineral chemistry yield emplacement pressures of ∼1.0 GPa followed by isobaric cooling to 700°C. The widespread occurrence of idiomorphic hornblende and interstitial plagioclase together with the lack of Eu anomalies in bulk rock compositions indicate that the differentiation is largely dominated by amphibole. Major and trace element modeling constrained by field observations and bulk chemistry demonstrate that peraluminous tonalite could be derived by removing successively 3% of olivine websterite, 12% of pyroxene hornblendite, 33% of pyroxene hornblendite, 19% of gabbros, 15% of diorite and 2% tonalite. Peraluminous tonalite with high Sr/ Y that are worldwide associated with active margin settings can be derived from a parental basaltic melt by crystal fractionation at high pressure provided that amphibole dominates the fractionation process. Crustal assimilation during fractionation is thus not required to generate peraluminous tonalite. [ABSTRACT FROM AUTHOR]

Continental crust is displaced in strike-slip fault zones through lateral and vertical movement that together drive burial and exhumation. Pressure –temperature–deformation ( P–T–d) histories of orogenic crust exhumed in transcurrent zones record the mechanisms and conditions of these processes. The Skagit Gneiss Complex, a migmatitic unit of the North Cascades, Washington (USA), was metamorphosed at depths of ∼25–30 km in a continental arc under contraction, and is bounded on its eastern side by the long-lived transcurrent Ross Lake fault zone (RLFZ). The P–T–d conditions recorded by rocks on either side of the RLFZ vary along the length of the fault zone, but most typically the fault separates high-grade gneiss and plutons from lower-grade rocks. The Ruby Mt–Elijah Ridge area at the eastern margin of the Skagit Gneiss exposes tectonic contacts between gneiss and overlying rocks; the latter rocks, including slivers of Methow basin deposits, are metamorphosed and record higher-grade metamorphism than in correlative rocks along strike along the RLFZ. In this area, the Skagit Gneiss and overlying units all yield maximum P–T conditions of 8–10 kbar at >650 °C, indicating that slices of basin rocks were buried to similar mid-crustal depths as the gneiss. After exhumation of fault zone rocks to <15 km depth, intrusion of granitoid plutons drove contact metamorphism, resulting in texturally late andalusite–cordierite in garnet schist. In the Elijah Ridge area of the RLFZ, an overlapping step-over or series of step-overs that evolved through time may have facilitated burial and exhumation of a deep slice of the Methow basin, indicating that strike-slip faults can have major vertical displacement (tens of kilometres) that is significant during the crustal thickening and exhumation stages of orogeny. [ABSTRACT FROM AUTHOR]

Abstract: Active debris flow fans in the North Cascade Foothills of Washington State constitute a natural hazard of importance to land managers, private property owners and personal security. In the absence of measurements of the sediment fluxes involved in debris flow events, a morphological-evolutionary systems approach, emphasizing stratigraphy, dating, fan morphology and debris flow basin morphometry, was used. Using the stratigraphic framework and 47 radiocarbon dates, frequency of occurrence and relative magnitudes of debris flow events have been estimated for three spatial scales of debris flow systems: the within-fan site scale (84 observations); the fan meso-scale (six observations) and the lumped fan, regional or macro-scale (one fan average and adjacent lake sediments). In order to characterize the morphometric framework, plots of basin area v. fan area, basin area v. fan gradient and the Melton ruggedness number v. fan gradient for the 12 debris flow basins were compared with those documented for semi-arid and paraglacial fans. Basin area to fan area ratios were generally consistent with the estimated level of debris flow activity during the Holocene as reported below. Terrain analysis of three of the most active debris flow basins revealed the variety of modes of slope failure and sediment production in the region. Micro-scale debris flow event systems indicated a range of recurrence intervals for large debris flows from 106−3645 years. The spatial variation of these rates across the fans was generally consistent with previously mapped hazard zones. At the fan meso-scale, the range of recurrence intervals for large debris flows was 273−1566 years and at the regional scale, the estimated recurrence interval of large debris flows was 874 years (with undetermined error bands) during the past 7290 years. Dated lake sediments from the adjacent Lake Whatcom gave recurrence intervals for large sediment producing events ranging from 481−557 years over the past 3900 years and clearly discernible sedimentation events in the lacustrine sediments had a recurrence interval of 67−78 years over that same period. [Copyright &y& Elsevier]

The Skymo Complex in the North Cascades, Washington, is a layered mafic intrusion within the Ross Lake fault zone, a major orogen-parallel structure at the eastern margin of the Cascades crystalline core. The complex is composed dominantly of troctolite and gabbro, both with inclusions of primitive olivine gabbro. Low-pressure minerals in the metasedimentary contact aureole and early crystallization of olivine + plagioclase in the mafic rocks indicate the intrusion was emplaced at shallow depths (<12 km). The Skymo rocks have trace-element characteristics of arc magmas, but the association of Mg-rich olivine (Fo88-80) with relatively sodic plagioclase (An75-60) and the Al/Ti ratios of clinopyroxene are atypical of arc gabbros and more characteristic of rift-related gabbros. A Sm-Nd isochron indicates crystallization in the early Tertiary (ca. 50 Ma), coeval with the nearby Golden Horn alkaline granite. Mantle melting to produce Skymo magma likely occurred in a mantle wedge with a long history of arc magmatism. The Skymo mafic complex and the Golden Horn granite were emplaced during regional extension and collapse of the North Cascades orogen and represent the end of large-scale magmatism in the North Cascades continental arc. [ABSTRACT FROM AUTHOR]

Three lines of evidence indicate that North Cascade (Washington, USA) glaciers are currently in a state of disequilibrium. First, annual balance measured on nine glaciers yields a mean cumulative balance for the 1984–2004 period of −8·58 m water equivalent (w.e.), a net loss of ice thickness exceeding 9·5 m. This is a significant loss for glaciers that average 30–50 m in thickness, representing 18–32% of their entire volume.Second, longitudinal profiles completed in 1984 and 2002 on 12 North Cascade glaciers confirm this volume change indicating a loss of −5·7 to −6·3 m in thickness (5·0–5·6 m w.e.) between 1984 and 2002, agreeing well with the measured cumulative balance of −5·52 m w.e. for the same period. The change in thickness on several glaciers has been equally substantial in the accumulation zone and the ablation zone, indicating that there is no point to which the glacier can retreat to achieve equilibrium. Substantial thinning along the entire length of a glacier is the key indicator that a glacier is in disequilibrium.Third, North Cascade glacier retreat is rapid and ubiquitous. All 47 glaciers monitored are currently undergoing significant retreat or, in the case of four, have disappeared. Two of the glaciers where mass balance observations were begun, Spider Glacier and Lewis Glacier, have disappeared. The retreat since 1984 of eight Mount Baker glaciers that were all advancing in 1975 has averaged 297 m. These observations indicate broad regional continuity in glacial response to climate. Copyright © 2006 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The origin of broadly orogen-parallel (NW–SE) mineral lineations in Cretaceous and Paleogene arc plutons and amphibolite–facies metamorphic rocks (paleodepths of <10–40km) of the North Cascades (Cascades core) is controversial, particularly the kinematic significance of these lineations and their relationship to regional displacement fields. Outcrop- to map-scale structures are dominated by fold interference. Lineations are commonly parallel to the maximum finite strain axis, which is interpreted to result from nearly coaxial superposed folding and strain accumulation. This is compatible with the better development of kinematic indicators in lineation-normal sections rather than in lineation-parallel sections in much of the region. The fold-dominated strain pattern has been locally modified by steep SW-vergent, reverse shear zones with down-dip lineation that are localized next to plutons, and near the Windy Pass thrust where weak lineation is at a high angle to the inferred displacement direction. During Eocene exhumation, top-to-N to -NNE displacement on subhorizontal surfaces was superposed on fold-related fabrics in the deepest exposed levels of the orogen. The resultant lineation is subparallel to the inferred slip direction, compatible with widespread kinematic indicators in lineation-parallel surfaces. Mineral lineations in the Cascades core are thus composite, formed from pre-96 to ∼45Ma, and are typically parallel to the direction of local maximum stretch and only locally to regional displacement. They formed by multiple mechanisms that were partitioned at a variety of scales, and under multiple boundary conditions, including: multi-scale folding, shear zone displacement, and flow in structural aureoles imposed by pluton emplacement. Local deformation, and not orogen-scale flow, dominated outcrop-scale structures, and pre-existing anisotropy and relative strengths of adjacent layers played an important role in development of final outcrop-scale structures. [Copyright &y& Elsevier]

Abstract: We used logistic regression to derive scaled resource selection functions (RSFs) for female black bears at two study areas in the North Cascades Mountains. We tested the hypothesis that the influence of roads would result in potential habitat effectiveness (RSFs without the influence of roads) being greater than realized habitat effectiveness (RSFs with roads). Roads consistently had a negative influence on black bear RSFs across seasons and study areas. Roads reduced habitat effectiveness during all seasons at both study areas and changes in the potential habitat values ranged from 1.7% to 16.9%. The greatest reduction in habitat values occurred during the early-season on the west-side study area due to high open road densities. These results support the hypothesis that roads reduce habitat effectiveness for black bears. The influence of roads could be reduced through road closures to reduce open road densities and limit traffic volumes. We then used the scaled RSFs in a habitat-based population model to assess the influences of timber harvest and roads on potential black bear population sizes. On the west-side study area the potential black bear population size was most influenced by moderate use roads and timber harvest during the early-season (41% reduction). On the east-side study area, low use roads had the greatest effect on potential black bear population during the early-season (10% reduction). During the late-season, in both study areas, roads had less influence on the potential population sizes as bears were able to access habitats away from roads. The habitat-population model provided reasonable estimates of bear densities compared to other study areas with similar habitats and could be extrapolated to estimate potential black bear populations in other areas with similar habitats. This approach may provide a useful link between the landscape ecology and population biology of black bears, and could eventually be useful in the development of habitat-based population viability analyses. [Copyright &y& Elsevier]

Kulshan caldera (4.5×8 km), at the northeast foot of Mount Baker, is filled with rhyodacite ignimbrite (1.15 Ma) and postcaldera lavas and is only the third Quaternary caldera identified in the Cascade arc. A gravity traverse across the caldera yields a steep-sided, symmetrical, complete Bouguer anomaly of −16 mGal centered over the caldera. Density considerations suggest that the caldera fill, which is incised to an observed thickness of 1 km, may be about 1.5 km thick and is flat-floored, overlying a cylindrical piston of subsided metamorphic rocks. Outflow sheets have been stripped by advances of the Cordilleran Ice Sheet, but the climactic fallout (Lake Tapps tephra) is as thick as 30 cm some 200 km south of the caldera. Ten precaldera units, which range in 40Ar/39Ar age from 1.29 to 1.15 Ma, are dikes and erosional scraps that probably never amounted to a large edifice. A dozen postcaldera rhyodacite lavas and dikes range in age from 1.15 to 0.99 Ma; rhyodacites have subsequently been absent, the silicic reservoir having finally crystallized. At least 60 early Pleistocene intermediate dikes next intruded the caldera fill, helping energize an acid–sulfate hydrothermal system and constituting the main surviving record of an early postcaldera andesite–dacite pile presumed to have been large. Most of the pre- and postcaldera rhyodacites were dated by 40Ar/39Ar or K–Ar methods, and 13 were drilled for remanent magnetic directions. In agreement with the radiometric ages, the paleomagnetic data indicate that eruptions took place before, during, and after the Jaramillo Normal Polarity Subchron, and that one rhyodacite with transitional polarity may represent the termination of the Jaramillo. Most of the biotite–hornblende–orthopyroxene–plagioclase rhyodacite lavas, dikes, and tuffs are in the range 68–73% SiO2, but there were large compositional fluctuations during the 300-kyr duration of the rhyodacite episode. The rhyodacitic magma reservoir was wider (11 km) than the caldera that collapsed into it (8 km). [Copyright &y& Elsevier]