USGS Science⌕ Search

SEARCH · USGS Science

Results for “Alaska Reflections”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 397 records · Page 22Linked to original sources
USGS2018

Strain partitioning in southeastern Alaska: Is the Chatham Strait Fault active?

A 1200 km-long transform plate boundary passes through southeastern Alaska and northwestern British Columbia and represents one of the most seismically active, but poorly understood continental margins of North America. Although most of the plate motion is accommodated by the right-lateral Queen Charlotte–Fairweather Fault (QCFF) System, which has produced at least six M > 7 earthquakes since 1920, seismic hazard ass essments also include the Chatham Strait Fault (CSF) as a potentially active, 400 km-long strike slip fault that cuts northward through southeastern Alaska, connecting with the Eastern Denali Fault. Nearly the entire length of the CSF is submerged beneath Chatham Strait and Lynn Canal and has never been systematically imaged using high-resolution marine geophysical approaches. In this study we present an integrated analysis of new marine seismic reflectiondata ac quired across Lynn Canal and tectonic block modeling constrained by data from continuous and campaign GPS sites. Seismic profiles cross the CSF at twelve locations spanning ∼50 km of fault length; they reveal thick (up to 300 m) packages of glaciomarine sedimentary facies emplaced on an unconformity su rface that formed during the Last Glacial Maximum (LGM). Localized warping of post-LGM stratigraphy (∼13.9 kyr B.P. to present) appears to correlate with sediment drape on basement topography and current-controlled deposition. There is no evidence for an active fault along the axis of Lynn Canal in the seismic reflection data. Crustal block models constrained by GPS data allow, but do not require, a maximum slip rate o f 2–3 mm/yr along the CSF; higher slip rates on the CSF result in significant misfit to GPS data in the surrounding region. Based on the combined marine geophysical and GPS observations, it is plausible that the CSF has not generated resolvable coseismic deformation in the last ∼13 ka and that the modern slip-rate is <1 mm/yr. We propose that models for strain transfer between the QCFF and the Denali Fault, and seismic hazard maps in general, may need to be reevaluated.

Alaska↗
USGS1983

Tin granites of Seward Peninsula, Alaska

Seven granite plutons, spatially and genetically related to tin metalization, are exposed in a 170-km-long belt across northwestern Seward Peninsula, Alaska. These plutons are cupolas and epizonal composite stocks that consist of several textural varieties of biotite granite, including medium- to coarse-grained seriate biotite granite, porphyritic biotite granite with an aplitic groundmass, and fine- to medium-grained equigranular biotite granite. The common accessory minerals are fluorite, allanite, apatite, and zircon. Other accessory minerals that are locally present include tourmaline, sphene, opaque oxide minerals, and late-forming (deuteric) muscovite and chlorite. The granites range in major-element contents as follows: SiO 2 , 72.5% to 76.6%; A1 2 O 3 , 12.7% to 14.3%; Na 2 O, 2.9% to 4.0%; K 2 O, 3.9% to 5.6%; and CaO, 0.6% to 1.2%. The sum of FeO + Fe 2 O 3 + MgO ranges from 0.3% to 2.4%; and the K 2 O to Na 2 O ratio from 1.1 to 1.8. The 0.1% to 0.9% F and 0.01% to 0.2% Cl reflect the over-all volatile-rich nature of the granites. The granites contain average or below-average concentrations of Co, Sc, Cr, and Zn, and generally above-average to distinctly high concentrations of Th, U, Hf, and Ta. The large cations emphasize the evolved nature of the granites; the Rb/Sr ratio is as high as 90 in some samples. Initial 87 Sr/ 86 Sr ratios range from 0.708 to as high as 0.720. The three Rb-Sr isochrons defined by the data agree with K-Ar age determinations and show that the stocks were emplaced during the Late Cretaceous, between about 70 and 80 m.y. ago. The field, petrologic, and geochemical data indicate that the plutons had a multistage origin that involved large-scale melting of sialic crust, emplacement of magmas derived from batholithic fractionation at depth, and subsequent evolution of these magmas to generate small volumes of more highly evolved residual magmas. Although evolution of the granite complexes was largely governed by crystal-melt fractionation, some minor-element variations in the highly evolved granites cannot be explained by this process. For example, the distribution of rubidium and the light rare-earths appears to have been influenced by volatile depletion at the final stages of crystallization. The field data, petrologic data, and variation trends, such as distinct shifts toward higher albite contents in the residual granites, suggest that the coexistence of a volatile phase was important in their evolution. These results require that models seeking to explain compositional gradients in high-level granite (rhyolite) systems fully consider the role of a coexisting volatile phase.

Alaska↗
USGS2009

Linking marine and freshwater growth in western Alaska Chinook salmon Oncorhynchus tshawytscha

The hypothesis that growth in Pacific salmon Oncorhynchus spp. is dependent on previous growth was tested using annual scale growth measurements of wild Chinook salmon Oncorhynchus tshawytscha returning to the Yukon and Kuskokwim Rivers, Alaska, from 1964 to 2004. First-year marine growth in individual O. tshawytscha was significantly correlated with growth in fresh water. Furthermore, growth during each of 3 or 4 years at sea was related to growth during the previous year. The magnitude of the growth response to the previous year's growth was greater when mean year-class growth during the previous year was relatively low. Length (eye to tail fork, LETF) of adult O. tshawytscha was correlated with cumulative scale growth after the first year at sea. Adult LETF was also weakly correlated with scale growth that occurred during freshwater residence 4 to 5 years earlier, indicating the importance of growth in fresh water. Positive growth response to previous growth in O. tshawytscha was probably related to piscivorous diet and foraging benefits of large body size. Faster growth among O. tshawytscha year classes that initially grew slowly may reflect high mortality in slow growing fish and subsequent compensatory growth in survivors. Oncorhynchus tshawytscha in this study exhibited complex growth patterns showing a positive relationship with previous growth and a possible compensatory response to environmental factors affecting growth of the age class.

Alaska↗
USGS2007

Geologic Mapping and Mineral Resource Assessment of the Healy and Talkeetna Mountains Quadrangles, Alaska Using Minimal Cloud- and Snow-Cover ASTER Data

On July 8, 2003, ASTER acquired satellite imagery of a 60 km-wide swath of parts of two 1:250,000 Alaska quadrangles, under favorable conditions of minimal cloud- and snow-cover. Rocks from eight different lithotectonic terranes are exposed within the swath of data, several of which define permissive tracts for various mineral deposit types such as: volcanic-hosted massive sulfides (VMS) and porphyry copper and molybdenum. Representative rock samples collected from 13 different lithologic units from the Bonnifield mining district within the Yukon-Tanana terrane (YTT), plus hydrothermally altered VMS material from the Red Mountain prospect, were analyzed to produce a spectral library spanning the VNIR-SWIR (0.4 - 2.5 ?m) through the TIR (8.1 - 11.7 ?m). Comparison of the five-band ASTER TIR emissivity and decorrelation stretch data to available geologic maps indicates that rocks from the YTT display the greatest range and diversity of silica composition of the mapped terranes, ranging from mafic rocks to silicic quartzites. The nine-band ASTER VNIR-SWIR reflectance data and spectral matched-filter processing were used to map several lithologic sequences characterized by distinct suites of minerals that exhibit diagnostic spectral features (e.g. chlorite, epidote, amphibole and other ferrous-iron bearing minerals); other sequences were distinguished by their weathering characteristics and associated hydroxyl- and ferric-iron minerals, such as illite, smectite, and hematite. Smectite, kaolinite, opaline silica, jarosite and/or other ferric iron minerals defined narrow (< 250 m diameter) zonal patterns around Red Mountain and other potential VMS targets. Using ASTER we identified some of the known mineral deposits in the region, as well as mineralogically similar targets that may represent potential undiscovered deposits. Some known deposits were not identified and may have been obscured by vegetation- or snow-cover, or were too small to be resolved.

Open-File Report↗
USGS2010

The use of genetics for the management of a recovering population: temporal assessment of migratory peregrine falcons in North America

Background:Our ability to monitor populations or species that were once threatened or endangered and in the process of recovery is enhanced by using genetic methods to assess overall population stability and size over time. This can be accomplished most directly by obtaining genetic measures from temporally-spaced samples that reflect the overall stability of the population as given by changes in genetic diversity levels (allelic richness and heterozygosity), degree of population differentiation (F ST and D EST ), and effective population size (N e ). The primary goal of any recovery effort is to produce a long-term self-sustaining population, and these measures provide a metric by which we can gauge our progress and help make important management decisions. Methodology/Principal Findings:The peregrine falcon in North America ( Falco peregrinus tundrius and anatum ) was delisted in 1994 and 1999, respectively, and its abundance will be monitored by the species Recovery Team every three years until 2015. Although the United States Fish and Wildlife Service makes a distinction between tundrius and anatum subspecies, our genetic results based on eleven microsatellite loci, including those from Brown et al. (2007), suggest no differentiation and warrant delineation of a subspecies in its northern latitudinal distribution from Alaska through Canada into Greenland. Using temporal samples collected at Padre Island, Texas during migration (seven temporal time periods between 1985-2007), no significant differences in genetic diversity or significant population differentiation in allele frequencies between time periods were observed and were indistinguishable from those obtained from tundrius/anatum breeding locations throughout their northern distribution. Estimates of harmonic mean N e were variable and imprecise, but always greater than 500 when employing multiple temporal genetic methods. These results, including those from simulations to assess the power of each method to estimate Ne, suggest a stable population consistent with data from field-based monitoring indicating that this species is stable or continuing to increase in abundance. Therefore, historic and continuing efforts to prevent the extinction of the peregrine falcon in North America appear successful, further highlighting the importance of archiving samples for continual assessment of population recovery and long-term viability.

PLoS ONE↗
USGS2007

Geochemical and sulfur-isotopic signatures of volcanogenic massive sulfide deposits on Prince of Wales Island and vicinity, southeastern Alaska

Stratabound volcanogenic massive sulfide (VMS) deposits on Prince of Wales Island and vicinity, southeastern Alaska, occur in two volcanosedimentary sequences of Late Proterozoic through Cambrian and of Ordovician through Early Silurian age. This study presents geochemical data on sulfide-rich samples, in situ laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) of sulfide minerals, and sulfur-isotopic analyses of sulfides and sulfates (barite) for identifying and distinguishing between primary sea-floor signatures and later regional metamorphic overprints. These datasets are also used here in an attempt to discriminate the VMS deposits in the older Wales Group from those in the younger Moira Sound unit (new informal name). The Wales Group and its contained VMS deposits have been multiply deformed and metamorphosed from greenschist to amphibolite grade, whereas the Moira Sound unit and related VMS deposits are less deformed and generally less metamorphosed (lower to middle greenschist grade). Variations in the sulfide mineral assemblages and textures of the VMS deposits in both sequences reflect a combination of processes, including primary sea-floor mineralization and sub-sea-floor zone refining, followed by metamorphic recrystallization. Very coarse grained (>1 cm diam) sulfide minerals and abundant pyrrhotite are restricted to VMS deposits in a small area of the Wales Group, at Khayyam and Stumble-On, which record high-grade metamorphism of the sulfides. Geochemical and sulfur-isotopic data distinguish the VMS deposits in the Wales Group from those in the Moira Sound unit. Although base- and precious-metal contents vary widely in sulfide-rich samples from both sequences, samples from the Moira Sound generally have proportionately higher Ag contents relative to base metals and Au. In situ LA-ICP-MS analysis of trace elements in the sulfide minerals suggests that primary sea-floor hydrothermal signatures are preserved in some samples (for example, Mn, As, Sb, and Tl in pyrite from the Moira Sound unit), whereas in other samples the signatures are varyingly annealed, owing to metamorphic overprinting. A limited LA-ICP-MS database for sphalerite indicates that low-Fe sphalerite is preferentially associated with the most Au rich deposits, the Niblack and Nutkwa. Sulfur-isotopic values for sulfide minerals in the VMS deposits in the Wales Group range from 5.9 to 17.4 permil (avg 11.5?2.7 permil), about 5 to 6 permil higher than those in the Moira Sound unit, which range from -2.8 to 10.4 permil (avg 6.1?4.0 permil). This difference in 34Ssulfide values reflects a dominantly seawater sulfate source of the sulfides and is linked to the 34S values of contemporaneous seawater sulfate, which were slightly higher during the Late Proterozoic through Cambrian than during the Ordovician through Early Silurian.

Alaska↗
USGS2018

Energy allocation and feeding ecology of juvenile chum salmon (Oncorhynchus keta) during transition from freshwater to saltwater

Pacific salmon (Oncorhynchus spp.) populations near their northern range extent in the Arctic-Yukon-Kuskokwim region of Alaska have undergone major changes in population trajectory and illuminated the lack of basic information on juvenile ecology. This study fills information gaps on the early life history of chum salmon at northern latitudes. Energy allocation was examined in the context of distribution, feeding intensity, and diet during a critical life history period for a single cohort of juvenile chum salmon (O. keta) as they transition from freshwater to saltwater in Kuskokwim Bay from mid-May to early June. Juvenile chum salmon were primarily captured in the river mouth and plume. Energy density (kJ g−1 dry mass) was related to fork length, timing (day-of-year), and capture location in a general additive model. The smallest fish had slightly higher energy densities, but the change in energy density with fish size was minimal and consistent with allocating energy toward somatic growth rather than lipid storage. Fish captured earlier had higher energy density, likely reflecting the presence of residual yolk lipids during early migration. Fish captured in the river mouth and plume had higher energy densities. Feeding intensity was highest among small fish captured later within the river plume. Diet was dominated by surface prey (insects and calanoid copepods) rather than epibenthic harpacticoid copepods as commonly observed. These results provide the first data on energy allocation of juvenile chum salmon during a critical life history phase and suggest that somatic growth is prioritized over storing lipid at saltwater entry.

Alaska↗
USGS2012

Seismic refraction measurements within the Peninsular terrane, south central Alaska

We present an interpretation of crustal seismic refraction data from the Peninsular terrane, one of the many exotic terranes that have been accreted to the continental margin of southern Alaska in the past 200 m.y. A seismic refraction line was collected along the Glenn Highway in the Copper River Basin of south central Alaska in 1984 and 1985, as part of the U.S. Geological Survey Trans‐Alaska Crustal Transect (TACT) program. P wave velocities of 2.7–3.5 km/s and thicknesses of 1–2 km characterize post‐Lower Jurassic sedimentary rocks that underlie most of the seismic refraction line. An average crustal velocity structure includes the following five velocity divisions. Beneath the sedimentary rocks lie 1–2 km of 4.0–4.6 km/s materials, correlating with andesitic volcaniclastic sedimentary rocks and lava flows of the Lower Jurassic Talkeetna Formation. Below these rocks, seismic velocity increases rapidly, from 5.0 to 6.1 km/s, in 2–3 km. At 7–8 km depth, velocity jumps to 6.3 km/s and increments to 6.6 km/s by 10–12 km depth. Velocities increase from 6.8 to 7.0 km/s between 12 to 20 km depth. At about 22 km depth, a jump in velocity from 7.0 to 7.4 km/s is inferred but is poorly resolved. Depth to the Moho discontinuity could not be determined from our data. The absence of clear PmP reflections may indicate that Moho is deeper than 40 km. Data from two offset shotpoints northeast of the line and within the Wrangellia terrane constrain the deep structure transition between Peninsular and Wrangellia terranes. The 6.3–6.6 km/s material thickens to the northeast, toward the suture between Peninsular and Wrangellia terranes, but southwest of its mapped trace at the West Fork fault. Peninsular terrane crustal structure appears dissimilar to that of continental interiors. It is similar to velocity structures determined for accreted island arc fragments in California, such as the basement of the Great Valley and the Klamath Mountains.

Alaska↗
USGS2001

Hydrologic data from Nation, Kandik, and Yukon rivers, Yukon-Charley Rivers National Preserve, Alaska

Flow data were collected from two adjacent rivers in Yukon?Charley Rivers National Preserve, Alaska?the Nation River (during 1991?2000) and the Kandik River (1994?2000)?and from the Yukon River (1950?2000) at Eagle, Alaska, upstream from the boundary of the preserve. These flow records indicate that most of the runoff from these rivers occurs from May through September and that the average monthly discharge during this period ranges from 1,172 to 2,210 cubic feet per second for the Nation River, from 1,203 to 2,633 cubic feet per second for the Kandik River, and from 112,000 to 224,000 cubic feet per second for the Yukon River. Water-quality data were collected for the Nation River and several of its tributaries from 1991 to 1992 and for the Yukon River at Eagle from 1950 to 1994. Three tributaries to the Nation River (Waterfall Creek, Cathedral Creek, and Hard Luck Creek) have relatively high concentrations of calcium, magnesium, and sulfate. These three watersheds are underlain predominantly by Paleozoic and Precambrian rocks. The Yukon River transports 33,000,000 tons of suspended sediment past Eagle each year. Reflecting the inputs from its major tributaries, the water of the Yukon River at Eagle is dominated by calcium?magnesium bicarbonate.

Open-File Report↗
USGS2019

The benthic foraminifera cassidulina from the Arctic Ocean: Application to paleoceanography and biostratigraphy

We investigated the morphology, biostratigraphy, shell stable isotope composition and paleogeography of the common Arctic benthic foraminifera, Cassidulina teretis (Tappan 1951) (sometimes assigned to Islandiella (Nørvang 1958), for application to Quaternary paleoceanography. Cassidulina teretis, which has been studied by several generations of Arctic foraminiferal specialists, is used in Arctic Ocean paleoceanographic reconstructions based on foraminiferal assemblages and, increasingly, isotope shell chemistry. Here we review its modern and fossil distribution including discussions of its taxonomy, ecology, biostratigraphy and shell chemistry. Cassidulina teretis Tappan 1951, originally described from the Gubik Formation, northern Alaska coastal plain, has variability in test size, apertural morphology and development of an umbilical boss representing intra- and inter-population differences across the Arctic and subarctic in modern, Quaternary and Pliocene assemblages. Nonetheless, our studies and those previously published lead us to conclude that populations from the Arctic Ocean represent a single species proposed by Tappan as Cassidulina teretis. Its modern distribution is mainly 200 to 1000 m water depth, often living within the core of the relatively warm Atlantic Layer. However, shallower occurrences suggest other factors, such as food supply, are also critical to its ecology. The Holocene distribution of Cassidulina teretis in the Beaufort Sea boundary indicate millennial-scale changes in relative abundance related to changing Atlantic Layer influence, sea-ice cover, surface productivity and food availability. There are extremely large changes in its abundance during the last deglacial interval on the Yermak Plateau, Barents Sea slope and the Laptev Sea reflecting rapid ocean changes during the Bølling-Allerød, Younger Dryas, and Preboreal. Similarly, C. teretis abundance changes during the last 300,000 years allow us to use it, at least regionally, as a useful biostratigraphic marker. The stable isotopic composition of Cassidulina teretis tests holds promise for establishing an isotope stratigraphy across the Arctic Ocean and perhaps also in the Nordic Seas, off Iceland and in the northern North Atlantic Ocean, once disequilibrium values and offsets from other Arctic benthic species are more firmly established.

Micropaleontology↗
USGS2021

Extreme Quaternary plate boundary exhumation and strike slip localized along the southern Fairweather fault, Alaska, USA

The Fairweather fault (southeastern Alaska, USA) is Earth’s fastest-slipping intracontinental strike-slip fault, but its long-term role in localizing Yakutat–(Pacific–)North America plate motion is poorly constrained. This plate boundary fault transitions northward from pure strike slip to transpression where it comes onshore and undergoes a <25°, 30-km-long restraining double bend. To the east, apatite (U-Th)/He (AHe) ages indicate that North America exhumation rates increase stepwise from ~0.7 to 1.7 km/m.y. across the bend. In contrast, to the west, AHe age-depth data indicate that extremely rapid 5–10 km/m.y. Yakutat exhumation rates are localized within the bend. Further northwest, Yakutat AHe and zircon (U-Th)/He (ZHe) ages gradually increase from 0.3 to 2.6 Ma over 150 km and depict an interval of extremely rapid >6–8 km/m.y. exhumation rates that increases in age away from the bend. We interpret this migration of rapid, transient exhumation to reflect prolonged advection of the Cenozoic–Cretaceous sedimentary cover of the eastern Yakutat microplate through a stationary restraining bend along the edge of the North America plate. Yakutat cooling ages imply a long-term strike-slip rate (54 ± 6 km/m.y.) that mimics the millennial (53 ± 5 m/k.y.) and decadal (46 mm/yr) rates. Fairweather fault slip can account for all Pacific–North America relative plate motion throughout Quaternary time and indicates stability of highly localized plate boundary strike slip on a single fault where extreme rock uplift rates are persistently localized within a restraining bend.

Alaska↗
USGS2016

An exploratory assessment of thiamine status in western Alaska Chinook salmon (Oncorhynchus tshawytscha)

This study was conducted to investigate the thiamine status of Chinook salmon Oncorhynchus tshawytscha . Egg thiamine levels in Yukon and Kuskokwim River Chinook were examined in 2001 and 2012. Muscle and liver thiamine in Chinook, coho O. kisutch , chum O. keta , and pink O. gorbuscha salmon were measured in northern Bering Sea juveniles and the percentage of the diet containing thiaminase, an enzyme that destroys thiamine, was calculated. Only 23% of the eggs were thiamine replete (> 8.0 nmol·g -1 ) in 2012. Seventy-four percent of the eggs had thiamine concentrations (1.5–8.0 nmol·g -1 ) which can lead to mortality from secondary eff ects of thiamine defi ciency. Only 3% of the eggs had < 1.5 nmol·g -1 associated with overt fry mortality. In 2001 egg thiamine in upper Yukon Chinook was 11.7 nmol·g -1 which was higher than that measured in 2012 (6.2 nmol·g -1 ) and paralleled Chinook productivity. Total thiamine (nmol·g -1 ) in Bering Sea Chinook muscle (3.8) was similar to coho (4.15), but lower than in chum (8.9) and pink salmon (9.6). Thiaminase-containing prey in Chinook (63%) and coho (36%) stomachs were elevated compared to those of chum (3%) and pink (5%) salmon. These results provide evidence of egg thiamine being less than fully replete. Thiamine deficiency was not observed in juvenile muscle tissue, but differences were present among species reflecting the percentage of diet containing thiaminase. Additional studies are recommended.

Alaska↗
USGS1994

Earthquake classification, location, and error analysis in a volcanic environment: implications for the magmatic system of the 1989-1990 eruptions at redoubt volcano, Alaska

Determination of the precise locations of seismic events associated with the 1989-1990 eruptions of Redoubt Volcano posed a number of problems, including poorly known crustal velocities, a sparse station distribution, and an abundance of events with emergent phase onsets. In addition, the high relief of the volcano could not be incorporated into the hypoellipse earthquake location algorithm. This algorithm was modified to allow hypocenters to be located above the elevation of the seismic stations. The velocity model was calibrated on the basis of a posteruptive seismic survey, in which four chemical explosions were recorded by eight stations of the permanent network supplemented with 20 temporary seismographs deployed on and around the volcanic edifice. The model consists of a stack of homogeneous horizontal layers; setting the top of the model at the summit allows events to be located anywhere within the volcanic edifice. Detailed analysis of hypocentral errors shows that the long-period (LP) events constituting the vigorous 23-hour swarm that preceded the initial eruption on December 14 could have originated from a point 1.4 km below the crater floor. A similar analysis of LP events in the swarm preceding the major eruption on January 2 shows they also could have originated from a point, the location of which is shifted 0.8 km northwest and 0.7 km deeper than the source of the initial swarm. We suggest this shift in LP activity reflects a northward jump in the pathway for magmatic gases caused by the sealing of the initial pathway by magma extrusion during the last half of December. Volcano-tectonic (VT) earthquakes did not occur until after the initial 23-hour-long swarm. They began slowly just below the LP source and their rate of occurrence increased after the eruption of 01:52 AST on December 15, when they shifted to depths of 6 to 10 km. After January 2 the VT activity migrated gradually northward; this migration suggests northward propagating withdrawal of magma from a plexus of dikes and/or sills located in the 6 to 10 km depth range. Precise relocations of selected events prior to January 2 clearly resolve a narrow, steeply dipping, pencil-shaped concentration of activity in the depth range of 1-7 km, which illuminates the conduit along which magma was transported to the surface. A third event type, named hybrid, which blends the characteristics of both VT and LP events, originates just below the LP source, and may reflect brittle failure along a zone intersecting a fluid-filled crack. The distribution of hybrid events is elongated 0.2-0.4 km in an east-west direction. This distribution may offer constraints on the orientation and size of the fluid-filled crack inferred to be the source of the LP events. ?? 1994.

Journal of Volcanology and Geothermal Research↗
USGS2026

Warming causes modest increase in the consumptive demands of invasive Northern Pike (Esox lucius) in Alaska freshwaters

Warming freshwaters can have profound effects on species composition and community structure and can increase the consumptive demand of predators. Here we explore synergistic impacts of warming and invasion within a freshwater community in Southcentral Alaska (USA). We quantified changes in population structure and predator diet composition using observed data for an introduced population of Northern Pike ( Esox lucius ) spanning a decade of warming temperatures and declining salmon returns. We used bioenergetics models to estimate past and contemporary predator consumptive demands and then estimated future consumption demands by applying forecasted future simulated temperatures under high emissions scenarios for the mid and late century compared to a baseline from the last twenty years. During the last decade, the population structure of Northern Pike shifted towards younger individuals with increased growth rates in young of year and Age-1 fish. The biomass of juvenile salmon in Northern Pike diets decreased 30–74% across all age classes of predators, corresponding to a 42% reduction of mean abundance of adult Chinook Salmon ( Oncorhynchus tshawytscha ) in the system from 2014–2018 to 2019–2023. Consumption of all fish species was highly variable and all increased, 5% to 63%, consistent with prey switching towards other fishes reflecting possible declines in availability of preferred salmon prey. Bioenergetic simulations revealed modest increases in total per-capita consumption of prey by Northern Pike across mid-century and late-century scenarios, with the largest increases in consumption predicted in individuals three years of age and greater. We also observed increased numbers of Coho Salmon ( Oncorhynchus kisutch ) in diets and smaller mean size suggesting a shift to young of year individuals as well as an absence of Sockeye Salmon ( Oncorhynchus nerka ) from diets, which differed from historical baseline data. These findings collectively suggest that changing thermal regimes may have modest but meaningful overall effects, disproportionately affecting the consumptive demands of larger Northern Pike, and may increase total consumption enough to appreciably increase mortality of salmon and other preferred prey.

Alaska↗
USGS2008

Modeling and dynamic monitoring of ecosystem performance in the Yukon River Basin

Central Alaska is ecologically sensitive and experiencing stress in response to marked regional warming. Resource managers would benefit from an improved ability to monitor ecosystem processes in response to climate change, fire, insect damage, and management policies and to predict responses to future climate scenarios. We have developed a method for analyzing ecosystem performance as represented by the growing season integral of normalized difference vegetation index (NDVI), which is a measure of greenness that can be interpreted in terms of plant growth or photosynthetic activity (gross primary productivity). The approach illustrates the status and trends of ecosystem changes and separates the influences of climate and local site conditions from the influences of disturbances and land management. We emphasize the ability to quantify ecosystem processes, not simply changes in land cover, across the entire period of the remote sensing archive (Wylie and others, 2008). The method builds upon remotely sensed measures of vegetation greenness for each growing season. By itself, however, a time series of greenness often reflects annual climate variations in temperature and precipitation. Our method seeks to remove the influence of climate so that changes in underlying ecological conditions are identified and quantified. We define an "expected ecosystem performance" to represent the greenness response expected in a particular year given the climate of that year. We distinguish "performance anomalies" as cases where the ecosystem response is significantly different from the expected ecosystem performance. Maps of the performance anomalies (fig. 1) and trends in the anomalies give valuable information on the ecosystems for land managers and policy makers at a resolution of 1 km to 250 m.

Fact Sheet↗
USGS2006

Interferometric synthetic aperture radar: Building tomorrow's tools today

A synthetic aperture radar (SAR) system transmits electromagnetic (EM) waves at a wavelength that can range from a few millimeters to tens of centimeters. The radar wave propagates through the atmosphere and interacts with the Earth&rsquo;s surface. Part of the energy is reflected back to the SAR system and recorded. Using a sophisticated image processing technique, called SAR processing (Curlander and McDonough, 1991), both the intensity and phase of the reflected (or backscattered) signal of each ground resolution element (a few meters to tens of meters) can be calculated in the form of a complex-valued SAR image representing the reflectivity of the ground surface. The amplitude or intensity of the SAR image is determined primarily by terrain slope, surface roughness, and dielectric constants, whereas the phase of the SAR image is determined primarily by the distance between the satellite antenna and the ground targets, slowing of the signal by the atmosphere, and the interaction of EM waves with ground surface. Interferometric SAR (InSAR) imaging, a recently developed remote sensing technique, utilizes the interaction of EM waves, referred to as interference, to measure precise distances. Very simply, InSAR involves the use of two or more SAR images of the same area to extract landscape topography and its deformation patterns.

Alaska Satellite Facility News and Notes↗
USGS2010

Emission of SO 2 , CO 2 , and H 2 S from Augustine Volcano, 2002-2008: Chapter 26 in The 2006 eruption of Augustine Volcano, Alaska

Airborne surveillance of gas emissions from Augustine Volcano and other Cook Inlet volcanoes began in 1990 to identify baseline emission levels during noneruptive conditions. Gas measurements at Augustine for SO 2 , CO 2 , and H 2 S showed essentially no evidence of anomalous degassing through spring 2005. Neither did a measurement on May 10, 2005, right after the onset of low level seismicity and inflation. The following measurement, on December 20, 2005, showed Augustine to be degassing about 600 metric tons per day (t/d) of SO 2 , and by January 4, 2006, only 7 days before the first explosive event, SO 2 emissions had climbed to ten times that amount. Maximum emission rates measured during the subsequent eruption were: 8,930 t/d SO 2 (February 24, 2006), 1,800 t/d CO 2 (March 9, 2006), and 4.3 t/d H 2 S (January 19, 2006). In total, 45 measurements for SO 2 were made from December 2005 through the end of 2008, with 19 each for CO 2 and H 2 S during the same period. Molar CO 2 /SO 2 ratios averaged about 1.6. In general, SO 2 emissions appeared to increase during inflation of the volcanic edifice, whereas CO 2 emissions were at their highest during the period of deflation associated with the vigorous effusive phase of the eruption in March. High SO 2 was probably associated with degassing of shallow magma, whereas high CO 2 likely reflected deep (>4 km) magma recharge of the sub-volcanic plumbing system, For the 2005&ndash;6 period, the volcano released a total of about 1.5&times;10 6 tons of CO 2 to the atmosphere, a level similar to the annual output of a medium-sized natural-gas-fired powerplant. Augustine also emitted about 8&times;10 5 tons of SO 2 , similar to that produced by the 1976 and 1986 eruptions of the volcano.

Alaska↗
USGS2008

Adult survival of Black-legged Kittiwakes Rissa tridactyla in a Pacific colony

Breeding Black-legged Kittiwakes Rissa tridactyla survived at a mean annual rate of 0.926 in four years at a colony in Alaska. Survival rates observed in sexed males (0.930) and females (0.937) did not differ significantly. The rate of return among nonbreeding Kittiwakes (0.839) was lower than that of known breeders, presumably because more nonbreeders moved away from the study plots where they were marked. Individual nonbreeders frequented sites up to 5 km apart on the same island, while a few established breeders moved up to 2.5 km between years. Mate retention in breeding Kittiwakes averaged 69% in three years. Among pairs that split, the cause of changing mates was about equally divided between death (46%) and divorce (54%). Average adult life expectancy was estimated at 13.0 years. Combined with annual productivity averaging 0.17 chick per nest, the observed survival was insufficient for maintaining population size. Rather, an irregular decline observed in the study colony since 1981 is consistent with the model of a closed population with little or no recruitment. Compared to their Atlantic counterparts, Pacific Kittiwakes have low productivity and high survival. The question arises whether differences reflect phenotypic plasticity or genetically determined variation in population parameters.

Alaska↗