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At least 1,657 records · Page 92Linked to original sources
USGS2026

Effects of fipronil bait pellets on two cricetid species: Potential implications for plague mitigation and wildlife conservation

We evaluated the effects of fipronil bait pellets on two cricetids that commonly occupy colonies of black-tailed prairie dogs ( Cynomys ludovicianus ; BTPDs): western deer mice ( Peromyscus sonoriensis ) and northern grasshopper mice ( Onychomys leucogaster ). In one experiment, bait pellets (0.96 mg fipronil/bait) were applied at 75 baits/ha to three 1.44-ha plots on a BTPD colony. Mouse abundance declined by 70% from before to 6-10 d after treatment. In a second experiment, bait pellets (0.46 or 1.52 mg fipronil/bait) were applied at 125 baits/ha to four plots (0.85-1.86 ha) on two BTPD colonies; two non-treated plots were baselines (1.09 and 2.06 ha). From before to 11-15 d after treatment, mouse abundance declined by 51%- 67% on the treated plots vs. a decline of 9% on the non-treated plots. Mouse survival from before to 11-15 d after treatment was 51% lower on the treated plots. In a third experiment, bait pellets (0.84 mg fipronil/bait) were applied at 125 baits/acre on two 1.44-ha plots on a BTPD colony; two 1.44-ha non-treated plots were baselines. Mouse survival from before to 30-44 d after treatment was 45% lower on the treated plots; the abundance of deer mice on the treated plots remained similar from before to 30-44 d after treatment, perhaps due to juvenile recruitment and/or immigration. In a laboratory experiment, 33 deer mice offered one bait pellet (0.86 mg fipronil/bait) consumed 27% of their bait, on average (range = 0-100%). Over 3 d, deer mouse mortality was estimated at 53%; mortality increased with fipronil dose, which averaged 11 mg fipronil/kg body mass (range = 3-46 mg/kg). Brain samples were available from 31 deer mice; all tested positive for fipronil sulfone, the primary mammalian metabolite of fipronil, at 19 to 61,205 ng fipronil sulfone/g. Additional experiments could determine if these findings scale up to larger landscapes.

South Dakota↗
USGS2026

A weight-of-evidence system for integrating monitoring and environmental indicators to guide biological conservation and resource management of native taxa

Many state and federal environmental management agencies are charged with using data-driven evidence to conserve and restore threatened and endangered species that are adversely impacted by humans. Yet, statistical analyses of available environmental indicator data do not always promote unambiguous, ecologically-meaningful, evidence-based decisions for managing native biota. Here we modified our multi-step quantitative adaptive management framework to identify natural and anthropogenic environmental indicators that maintain or threaten native species. In a proof-of-concept example, we quantified how three native stream fish taxa responded to nine environmental indicators based on three criteria (i.e., statistical significance, ecological relevance, and agreement with expectations). The resulting Weight of Evidence (WoE) integration identified five groups of indicators, clarified ambiguous trends, and identified promising future directions that would not have emerged from examining a single analysis or a single taxon alone. Our evaluation and categorization of environmental indicators established the biological foundation on which multi-disciplinary sustainability rests. Our research contribution demonstrates how following a structured integration framework can lead to novel insights that benefit conservation across organisms and systems even when employing relatively simple analytical techniques. Our results address the following often ignored questions: How do we systematically link together different analytical components of the same larger problems? How do we ecologically integrate similar and dissimilar results across analyses? How can we identify generalities by comparing multiple taxa?

Kansas↗
USGS2026

Sedimentological and geochemical characterization of lacustrine deposits of the Babouri-Figuil basin, northern Cameroon: Implications for source rocks distribution and petroleum exploration

The West and Central African Rift System (WCARS) refers to the series of Cretaceous rift basins where commercial hydrocarbon accumulations have been discovered. Some of the WCARS frontier basins are currently being investigated to increase our understanding of these basins in light of new commercial discoveries. The present study was performed in the Babouri-Figuil Basin (BFB), which is genetically related to the WCARS and constitutes an area of interest in terms of petroleum prospecting, where the distribution of petroleum source rocks and potential targets for petroleum exploration across the entire basin is poorly understood. For the current study, an integrated facies analysis along with organic and inorganic geochemical techniques were applied to the basin's Cretaceous deposits with the aim of reconstructing the paleodepositional environment, assessing factors that triggered the input of organic matter, and providing a spatial overview of the organic matter accumulation in the basin based on outcrop samples. An alluvial fan-lacustrine-braided river system is inferred from the facies analysis of the stratigraphic sequence consisting of conglomerate, sandstone, siltstone, limestone, marlstone, and claystone. Bulk analysis of organic matter reveals that black shale and massive claystone are the main prospective petroleum source rocks in the basin. Inorganic geochemical analyses reveal the influence of anoxic conditions, moderate to high primary productivity, and low terrigenous inputs in organic matter enrichment. The formations rich in organic matter are predominantly concentrated in the western and eastern parts of the basin which may represent areas with depressions, characterized by high accommodation space. In terms of the regional context of the WCARS rift basins, typical hydrocarbon exploration in the BFB may target basal-conglomerate, sandstone beds situated directly above or/and interbedded with the Lower Cretaceous source rocks, and the Upper Cretaceous sandstone beds. Basement rocks (granite, granodiorite, and gneisses) and oil shale deposits may represent potential unconventional hydrocarbon exploration. The current integrated study provides an insight that should guide future hydrocarbon exploration campaigns in the basin.

Babouri-Figuil basin↗
USGS2026

Bird guilds exhibit varied responses to floodplain forest restoration in the Colorado River delta, Mexico

Grouping species into guilds can be useful to inform management decisions locally and at broader scales because guilds lack species-specificity. We investigated the response of five breeding bird guilds to riparian habitat restoration in the arid Colorado River delta, based on two decades of bird detections (2002–2021) at 230 bird count stations across 7 routes in actively revegetated (“restored”) sites, and 20 routes in non-actively revegetated (“control”) sites. We used guilds based on habitat associations. We also described changes in vegetation and explored their influence on bird species detections and guild dynamics. Riparian forest bird specialists responded positively to active revegetation, but this positive response was delayed and weaker in a river reach where restoration began later and featured less typical riparian vegetation. Birds associated with wetland habitat showed a positive response to restoration in the wettest reach, which had a baseline of high abundance of wetland birds in control sites and relatively abundant macrophyte cover. Conversely, the abundance of desert scrub bird specialists was highest in the driest and least vegetated restored reach. Generalists only exhibited decreased detections in the wettest restored reach. All this occurred while declines of riparian forest, wetland, desert scrub, and generalist bird species observed over a decade prior to restoration had stabilized in control sites. Detections of birds associated with agricultural fields increased in the study area, irrespective of restoration efforts. Our study demonstrates that the choice of bird guilds as ecological indicators can significantly influence the interpretation of restoration outcomes.

Arizona↗
USGS2026

Characterization and modeling approach for planning restoration strategies in a complex basin affected by acid mine drainage

The management of acid mine drainage (AMD) impacted catchments, such as the Odiel River basin, in southwestern Spain, prioritizes reclamation to meet water resources needs. Assessing water composition across its watercourses is needed to identify major AMD contributors and potentially guide remediation efforts. An equilibrium-based mixing model was developed to simulate AMD pollutant load reductions and estimate the impact of selective restorations on water quality in the Odiel River, particularly at the planned Alcolea Reservoir near its outlet. Sampling under varying flow conditions (average vs. high flow) showed a reduction in acidity transport (from 54.0 to 42.5 ton/day), attributed to greater neutralization effects during high flows. Over 90 % of metal-fluxes originate alone from the Riotinto (73.6 %), Tharsis (14.5 %), and San Telmo (5.00 %) mining districts, among many other mines. While geochemical model estimates fit well with observed data (R 2 = 0.99), some deviations in non-conservative constituents (i.e. pH, Fe and Al) were observed (R 2 = 0.73–0.99), likely due to uncertainties in solubility constants and redox/Fe speciation. After evaluating model reliability, two reduction scenarios (50 % and 100 %) were applied to the three primary sources. Full removal of contamination could subtantially improve impounded reservoir water quality, with pH values of 4.93 and 7.64, and a net acidity between 8.75 and 4.63 mg/L eq. CaCO 3 in both average and high flows, respectively. Such differences may be related to flow regime effects on water quality. However, a 50 % reduction is insufficient to meet drinking or irrigation standards, highlighting the need for full and appropriate reclamation. The model offers a management tool for decision-making in the restoration of the Odiel River basin and could be transferable to similar AMD-affected basins worldwide.

Odiel River basin, southwestern Spain↗
USGS2026

Unexpected appetites: Metabarcoding reveals grass carp (Ctenopharyngodon idella) foraging behaviors in the Great Lakes

Grass carp ( Ctenopharyngodon idella ) are herbivorous fish introduced to North America in the 1960s, and they are now established throughout the Mississippi River basin and Laurentian Great Lakes. Despite increasingly intensified management efforts, limited information exists on their foraging ecology. We used DNA metabarcoding to characterize the gut contents of grass carp captured from 2019 to 2022 to evaluate spatial, temporal, and environmental patterns in diet composition across Lake Erie and Lake Michigan. Contrary to long-standing assumptions that grass carp primarily consume submerged aquatic vegetation (SAV), results from Lake Erie’s western and central basins revealed a diet dominated by terrestrial and terrestrial-wetland plant genera, including maples ( Acer ), willows ( Salix ), cottonwoods ( Populus ), and nightshades ( Solanum ). In contrast, fish harvested from Lake Erie’s eastern basin and Lake Michigan tributaries consumed more SAV, particularly pondweeds like Potamogeton and Stuckenia . Diet composition varied by basin, river, and year, but not by ploidy (diploid vs. triploid). Distance-based redundancy analyses identified environmental variables as drivers of diet variability. These findings reframe previous risk assessments which were based on diets from small artificial environments, suggesting greater dietary plasticity and revealing previously overlooked terrestrial-aquatic food web connections. Results presented here could inform management actions and sampling locations. Understanding grass carp foraging behavior in invaded systems can provide a critical tool for refining removal strategies, preventing further expansion, and improving future ecological risk assessments.

Great Lakes↗
USGS2026

Competition between invasive round goby and native slimy sculpin in a coldwater laboratory setting

Slimy sculpin ( Cottus cognatus ) abundance has substantially declined in many regions of the Laurentian Great Lakes coincident with the arrival and range expansions of invasive round goby ( Neogobius melanostomus ). Previous studies have shown that round goby can outcompete native mottled sculpin ( C. bairdii ) for shelter and negatively affect native spoonhead sculpin ( C. ricei ) growth, but direct behavioral interactions of slimy sculpin and round goby have not been observed. We conducted a laboratory experiment in which a pair of slimy sculpin were placed in an aquarium that contained an artificial spawning shelter and one round goby (treatment, n = 10) or no other fish (control, n = 10) for at least 30 days at temperatures reflective of their potential offshore overlap. We measured slimy sculpin egg deposition, aggressive interactions, artificial shelter occupancy, growth, and survival. Slimy sculpin were less likely to occupy shelters and experienced increased intraspecific competition when a round goby was present. In contrast, round goby rarely chased slimy sculpin, slimy sculpin were more likely to chase round goby, and slimy sculpin growth, egg deposition, and survival were not significantly different between groups. Differences in density between treatments and the relative size of fish could confound our observations. However, the dominant slimy sculpin occupied the shelter at similar rates between experimental groups if the round goby was smaller. Our results indicate that larger round goby overlapping with slimy sculpin could affect slimy sculpin shelter and space use, but the Great Lakes environment may create more stress for slimy sculpin than we observed.

Lake Michigan, Lake Superior↗
USGS2026

Describing the seasonal abundance and growth rates of larval fishes across productivity gradients in Lake Huron in 2017

Several of the Laurentian Great Lakes, including Lake Huron, have undergone oligotrophication in the past decades and prey fish biomass has concomitantly declined. One potential mechanism to explain declines in prey fish is slower growth and lower survival at the larval stage. To determine whether reduced productivity affects the growth of larval fish, we sampled larval fishes and their environment approximately monthly from May through August 2017 at nine nearshore to offshore transects across Lake Huron that included North Channel, Georgian Bay, and the main basin. North Channel transects had the highest chlorophyll a concentrations and zooplankton densities. Rainbow smelt ( Osmerus mordax ), burbot ( Lota lota ), bloater ( Coregonus hoyi ), and shiners ( Notropis spp.) were the most abundant larval fish taxa, peaking in June and July. We aged rainbow smelt and bloater using otoliths, and estimates of growth rate revealed rainbow smelt always grew faster. For both species, we explained variation in total length by comparing 16 candidate linear mixed-effects models, with age, chlorophyll a , zooplankton, water temperature, larval fish density, and interactions with age as predictor variables. For rainbow smelt, the full model was best; zooplankton had the greatest effect, but it was negative and opposite from our hypothesis. For bloater, four candidate models were most parsimonious; water temperature had the greatest effect, and it was positive as predicted from our hypothesis. To more effectively evaluate whether zooplankton can limit larval fish growth and survival, we recommend that future designs conduct more frequently sampling within a year even at the expense of fewer transects.

Lake Huron↗
USGS2026

A post-restoration evaluation of fish spawning on Coreyon Reef in Saginaw Bay, Lake Huron

Habitat diversity is important to fisheries for promoting resiliency to interannual environmental variation. Historical land use change resulting in increased sedimentation has impaired fish rock reef habitats in Saginaw Bay, Lake Huron. Pursuant to the recovery of Saginaw Bay’s walleye population, and to benefit other species, came the decision to restore the offshore habitat Coreyon Reef, a 0.8 ha rock reef complex. Following a pre-restoration assessment in 2014–2016 and construction in 2019, we conducted a comprehensive assessment from fall 2020 to spring 2022 to document the restored habitat’s viability for fish spawning. This assessment featured two objectives: (1) to evaluate reproductive usage by lake whitefish and walleye, and (2) to evaluate their corresponding egg incubation environment. We sampled directly on Coreyon Reef and at nearby unrestored control sites for comparison, with gears standardized to the pre-restoration assessment. We confirmed spawning of lake whitefish and walleye on the restored reef less than 2 years post-construction. Relative to the pre-restoration assessment, peak egg deposition increased substantially for walleye and marginally for lake whitefish. However, concurrent reproductive utilization at nearby unrestored sites was consistent or even greater than directly on the restored site. Dissolved oxygen concentration was sufficient for embryo development, but invasive round goby were abundant and consumed eggs. The fish assemblage at our sampling sites was consistent before and after restoration. We predict eggs deposited on the restored site have improved survival relative to unrestored sites, as the new reef structure may protect incubating embryos from predation and sedimentation.

Michigan↗
USGS2026

Seasonal space use and spatial overlap of lake sturgeon populations inhabiting Lake St. Clair

Multi-jurisdictional management of adult lake sturgeon ( Acipenser fulvescens ) requires characterizing seasonal dynamics of their spatial distributions. Despite decades of research into lake sturgeon movement ecology, system-wide spatiotemporal behavior remains poorly understood in large lakes, particularly those with metapopulations differentiated by spawning river or migratory phenotypes. This study described seasonal space use of lake sturgeon populations in Lake St. Clair, a large, shallow lake divided by the international border between the State of Michigan and Province of Ontario. Our objectives were to characterize spatial behavior of adult lake sturgeon by: 1) assessing U.S. and Canadian residency patterns and cross-boundary movements with relevance for interjurisdictional management; 2) identifying seasonally important habitats where sturgeon regularly congregate; and 3) comparing seasonal spatial distributions and behavioral metrics among spawning populations and migratory phenotypes. A large sample of acoustic-tagged adult lake sturgeon of known spawning river and migratory phenotype were detected with a high-density (∼5 km spacing), lake-wide receiver grid. Home ranges estimated via Brownian Bridge movement models indicated near lake-wide use and seasonal variation in areas occupied, total area used, and residency within and across jurisdictional boundaries. Lake sturgeon seasonally congregated in several distinct areas but were not completely segregated by spawning populations or migratory phenotypes. Instead, space use by the two spawning populations followed a seasonally dependent, north-south gradient associated with the location of spawning inlet and outlet rivers. These results suggest that managers consider internationally coordinated approaches, especially for population assessment, that account for seasonal habitat shifts and cross-population and phenotypic mixing.

Michigan, Ontario↗
USGS2026

Spatio-temporal modeling for assessing geoenergy resources: A workflow applied to gas in place variation in coal beds

The ability to estimate spatio-temporal changes in hydrocarbon reservoir properties and energy resources within pore volumes is essential for optimizing production, reservoir management, geologic energy storage, and safety in underground mining operations. In coal seams, predicting remaining methane gas-in-place (GIP) is critical for quantifying producible gas and improving mine safety and productivity through effective ventilation planning. Although such changes are commonly evaluated using physics-based numerical simulation models, these approaches often require extensive data, calibration effort, and time. This study presents a spatio-temporal geostatistical modeling approach that bridges the gap between purely spatial models and full numerical simulations. The method is applied to a case study of coal seam degasification in the Mary Lee coal group, Black Warrior Basin, Alabama, USA, to estimate GIP evolution over time within a selected mining district. The analysis uses published data from prior natural gas production history-matching of degasification using vertical wells. Empirical spatial and temporal statistics were calculated for reservoir pressure and water saturation, and spatio-temporal variogram models were fitted to experimental variograms. These models provided the structural basis for spatio-temporal kriging, integrated with spatial estimates of time-invariant parameters (porosity, density, and thickness) to estimate GIP. This approach enabled estimation of GIP changes over time, including periods without data. Boxplots of GIP estimates indicated systematic depletion and decreasing spatial variability, reflecting the impacts of degasification. Comparison with cumulative gas production from empirical well records showed approximately 85% agreement based on a relative similarity metric. Spatio-temporal GIP estimates were also used to estimate methane emissions to longwall ventilation systems and compared with reported emissions from the U.S. EPA Greenhouse Gas Reporting Program, showing similar distributions (≈80%) given data limitations. Overall, this integrated modeling approach provides time-dependent GIP estimates with broader implications for resource assessment applications.

Alabama↗
USGS2026

Groundwater spatial variability within an atoll island: Assessing shallow aquifer heterogeneity with geophysical and physicochemical measurements

This study examines the spatial variability of shallow groundwater on Dhigelaabadhoo Island using electromagnetic induction surveys, groundwater monitoring, and sediment analyses. The research reveals how variations in island morphology—such as differences in elevation, reef flat width, and sediment composition—affect the spatial distribution of groundwater lenses and the overall aquifer dynamics. Saltwater intrusion is especially pronounced in low elevated areas, with narrow reef flat plate and areas where higher hydraulic conductivity—driven by the presence of coarser sediments—is observed, whereas regions characterized by finer sediments, higher elevation, and wider reef flat plates tend to support more symmetric and less saline groundwater lenses. The geophysical investigations reveal that tidal oscillations alter groundwater movement by markedly changing water levels and conductivity, thereby underscoring the critical need to account for temporal dynamics in atoll coastal aquifer systems and the importance of integrating tidal dynamics into the aquifer zone. The findings highlight the significant role of intrinsic morphological and external hydrodynamic factors in shaping groundwater distribution on atoll islands, offering critical insights for sustainable freshwater resource management.

Dhigelaabadhoo Island↗
USGS2026

Computational electromagnetic geophysics for groundwater system studies: A review on established practices and recent advances

Identifying effective solutions for locating groundwater resources and ensuring the quality of drinking water is increasingly urgent, given the challenges posed by climate change and population growth. This review investigates electromagnetic geophysical imaging techniques, in both time- and frequency-domain, that can provide valuable insights for groundwater assessment. We explore computational electromagnetic methods used to evaluate electromagnetic data and several recent hydrogeophysical case studies. As open-source frameworks for modeling electromagnetic geophysical problems become available, a broader range of researchers can interpret their data with computationally advanced software. We provide an overview of documented open-source codes for evaluating electromagnetic data and analyze various hydrological targets in relation to their electromagnetic surveying technique and the computational method applied. Furthermore, we evaluate the potential of advanced computational techniques, including three-dimensional modeling, non-deterministic inversion and machine learning, to couple geophysical with numerical groundwater modeling and apply it in groundwater system studies. Despite obstacles such as complexity and resource demands, our findings indicate that the quantification and integration of predictive uncertainties from both electromagnetic and hydrological data and simulations would significantly improve the reliability of hydrogeophysical models. This can lead to a deeper understanding of groundwater systems and improved management practices.

Journal of Hydrology↗
USGS2026

Drone–based camera discharge derived from the entropy–based probability concept and image velocimetry algorithms

In June and August 2023, the U.S. Geological Survey (USGS) conducted small Uncrewed Aircraft System (sUAS or drone) flights at five streamgages in the Upper Colorado River Basin, Colorado, USA. The objectives of this research were (1) compare maximum surface velocities and discharges derived from Space-time Image Velocimetry (STIV) and Particle Image Velocimetry (PIV) and (2) evaluate drone-based camera algorithms that rely on the entropy-based probability concept and mid-section method relative to standard discharge measurements. To evaluate the scalability and transferability of the methods, river reaches were selected with varying top widths, depths, and discharges and colocated with existing USGS streamgages. Percent errors between drone-based camera algorithms and hydroacoustic measurements were substantially smaller for large rivers such as the Colorado River, Colorado when compared to small rivers such as the Blue River, Colorado. A Wilcoxon signed-rank test suggests there was no difference between the discharges generated by STIV and PIV algorithms and hydroacoustic measurements. This implies that, if the appropriate algorithms are properly parameterized, drone-based camera discharges are consistent with standard discharge measurements when siting is conducted appropriately.

Colorado↗
USGS2026

Seismic characteristics of the April 2024 eruption of Ruang Volcano, North Sulawesi, Indonesia

The two most recent eruptions of Ruang volcano, in 2002 and 2024, have been large (VEI 4) with very short precursory periods, 3 and 6 days, respectively. Background seismicity at Ruang volcano is generally low with 0–2 volcano-tectonic (VT) earthquakes per day. The 2024 eruptions were preceded by a notable increase in VT earthquakes from 11 to 15 April with a rapid escalation from 16 to 17 April in the form of increased VT swarms, and the appearance of low frequency earthquakes and short bursts of VT drumbeats shortly before the eruption. Similar VT seismic unrest was recorded in March 2015, May 2016, and April 2022, although none of these episodes culminated in an eruption. A comparison of seismic energy release between April 2022 and April 2024 shows distinct differences. In 2024, cumulative seismic energy reached its peak within 5 days, just before the onset of eruption on 17 April. In contrast, during the 2022-episode, energy release followed a more gradual increase over 8 days peaking on 16 April, then declining gradually without leading to eruption. Notably, low frequency (LF) and drumbeat earthquakes were absent in non-eruptive unrest episodes. The transition to proximal LFs in 2024 likely signals pressure fluctuations, intensified magma degassing, and conduit formation, acting as an important precursor to eruption. Additionally, the occurrence of short bursts of drumbeat seismicity likely reflects the onset of the shallow magma ascent and was an important short-term precursor to the eruption. Finally, we examine the potential influence of regional tectonic earthquakes on the escalation of precursory unrest in 2024.

North Sulawesi, Ruang volcano↗
USGS2026

The petrogenesis of Þingmúli volcano, East Fjords, Iceland

In this work we revisit Þingmúli volcano (Þ = Th), a classic locality known as an example of a complete tholeiitic differentiation. Þingmúli is a ~ 9.5 Ma extinct central volcano located in the East Fjords of Iceland, in which the whole compositional spectrum from basalt to rhyolites have erupted. These volcanic products have been previously considered as petrogenetically related by an ideal fractionation trend, regardless any temporal relationship or volumetric considerations. Here we report new whole-rock geochemistry, mineral chemistry, isotope analyses, estimation of residence times of the different eruptive deposits, and an update of the original petrogenetic model. Our results highlight that an enriched source, likely spinel lherzolites, generated transitional-alkaline basaltic melts after 15–20% of partial melting at depths of 40–45 km. Many of these basaltic melts erupted at various stages of the volcano's history, while others remained longer in the volcanic plumbing system. These evolved by fractional crystallisation into basaltic andesite magmas with a residence time of ~5 years based on the crystal size distribution of the plagioclase population. Isotopic differences between the basalts/basaltic andesites ( 87 Sr/ 86 Sr ~ 0.7034; 143 Nd/ 144 Nd ~ 0.51315) and the erupted rhyolites ( 87 Sr/ 86 Sr ~ 0.7037; 143 Nd/ 144 Nd ~ 0.51304) indicate that the latter are not petrogenetically related to the former. Therefore, instead of a fractional crystallisation mechanism to generate the rhyolites, we propose the partial melting of ignimbrite layers located beneath the volcano. The broad range of trace element concentrations in andesites and dacites and their different isotopic values compared to the basalts strongly suggest that these magmas have been generated by magma mixing between basaltic and rhyolitic melts, similar to modern day Icelandic volcanoes such as Hekla. These results highlight the need to revisit previously studied Icelandic classic localities and reassess their traditionally proposed petrogenetic models.

Þingmúli volcano, East Fjords↗
USGS2026

Mineral chemistry perspective on remobilization of stored magma at Kamakai'a Hills, Southwest Rift Zone of Kilauea, Island of Hawai'i, USA

Differentiated magmas stored in the rift zones of Kīlauea have received more attention in recent years following eruption of andesite during the early phase of 2018 lower East Rift Zone activity. Despite this growing interest, some of the most voluminous eruptions of differentiated rift zone magmas remain poorly studied. One such eruption, and the most voluminous exposed differentiated flow field at Kīlauea, is the Kamakaiʻa Hills. This eruption took place in the Southwest Rift Zone of Kīlauea, a region that is hypothesized to contain a long-lived rift zone reservoir. The Kamakaiʻa Hills flow field encompasses >250 × 10 6 m 3 of basaltic andesite and basalt compositions with a mineral assemblage of orthopyroxene + clinopyroxene + plagioclase during its early ʻaʻā phase and clinopyroxene + plagioclase + olivine during its late pāhoehoe phase. To better understand storage conditions and magma accumulation, this study focuses on major, minor, and trace elements from the mineral assemblage present within the early ʻaʻā and late pāhoehoe phases. The diversity of clinopyroxene and plagioclase compositions within the early ʻaʻā and late pāhoehoe phases, as well as diverse compositions of plagioclase and orthopyroxene within the early ʻaʻā phase, suggest multiple magma bodies and limited pre-eruption magma mixing within the broader Kamakaiʻa Hills reservoir. Oscillatory zoning patterns (particularly in clinopyroxene) imply processes such as recharge events, magma mixing or mingling, or convection within a differentially cooling, chemically stratified reservoir over protracted time intervals, whereas only limited resorbed mineral textures indicate incomplete mixing of heat and chemically distinct magmas during the dike intrusion that triggered the eruption. Mineral-mineral and mineral-melt thermobarometry indicate predominantly shallow (≤2.5 km depth) crustal storage conditions of the cooled, differentiated magma (∼1100 °C and cooler for the basaltic andesites) to hotter temperatures for the basalts (all >1100 °C). Despite the known large standard errors estimated for mineral-melt and mineral-mineral barometry (10s to >100 MPa), the calculated pressures and depths broadly correspond with earthquake swarm depths beneath the Kamakaiʻa Hills, and drill core and fluid inclusion barometry storage depths of differentiated magmas within the lower East Rift Zone. The Kamakaiʻa Hills differentiated magmas have H 2 O contents (∼0.5 wt%, using plagioclase-melt hygrometry) equivalent to typical Kīlauea basalts. Our data and interpretations demonstrate a complex, long-lived rift zone storage system that consisted of multiple magma bodies and was mobilized into eruption through intrusion of a hotter and more primitive summit-derived (uprift) magma.

Hawaii↗