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Geophysical surveys conducted in the Clear Lake fault zone (Utah) constrain the interpretation of neotectonics and volcanism along a portion of the Colorado Plateau-Basin-and-Range Transition Zone. The fault zone lies within the Sevier Desert, a region marked by numerous Quaternary fault scarps and bimodal volcanism. Lavas as young as 660 a B.P. are usually cut by faults, and many scarps have significant offsets implying the potential for M 7 + earthquakes. The range of scarp heights and uncertainty in scarp-magnitude regressions suggest variations on the order of 0.75 moment magnitude units. In order to characterize the range of deformation styles in the Clear Lake fault zone, three fault scarps were investigated for their patterns of shallow (< 1 km depth) deformation. A suite of methods, including seismic P- and SH-wave surveys, ground-penetrating radar, auger holes, and surface geological mapping produces a more complete view of near-surface Quaternary deformation. Sub-surface faults are expressed as scarps at the ground surface, but with differing tectonic styles: (1) growth strata in the hanging wall of a fault imply aseismic creep; (2) buried lavas draped over buried paleo-scarps indicate multiple slip events; and (3) a complex fault zone is expressed as ramps that step-over from one scarp to another. On a larger scale, the results bear directly on estimating seismic and volcanic hazards. In one locality, evidence of aseismic creep suggests hazard is lower than that inferred from the exposed scarp height or length. By contrast, multiple slip events at other locations indicate that hazards could be underestimated if scarps are assumed to represent single slip events. Finally, the intimate spatial association of Quaternary volcanic vents and faults implies that volcanic and seismic hazards are interrelated, both resulting from crustal extension where eruptive events exploited faults as conduits in the shallow crust. [ABSTRACT FROM AUTHOR]

Abstract: Ease of access, size, and basalt as the dominant bedrock make Oahu an ideal locality for investigating chemical weathering-driven denudation rates as a function of climate (rainfall varies by an order of magnitude), water–rock contact time, and soil thickness. New and compiled surface and groundwater solute data permit calculation of mass balances for solute fluxes from Oahu, revealing that groundwater dominates surface water solute fluxes by a factor of 3–12. Weathering reactions were written consistent with the mineralogy of Oahu soils, permitting denudation rates to be partitioned between dissolved and suspended loads. Total denudation rates, indexed to the leaching of SiO2, vary from 0.016 to 0.063m/ka, with about 70% of Si transport due to dissolved loads. Drier regions of Oahu have distinctly lower denudation rates, and areas with thick weathering profiles have suppressed surface-water solute loads. Indexing denudation in basaltic terranes to dissolved SiO2 rather than other solutes leads to improved estimates of weathering rates. Other approaches require correction for the atmospheric depositions of sea salts based on Cl− abundances in waters that are assumed to derive solely from the ocean via atmospheric deposition. Recent work indicates that Oahu is tectonically emerging at 0.060m/ka. As long as this uplift continues, the net size of the island will slowly increase and the Koolau Range should persist as an orographic trap to precipitation, maintaining relative aridity in the Waianae Range. Comparing emergence and denudation rates suggests that growth of the island will be non-uniform, with arid regions experiencing the greatest emergence with wet regions in balance with denudation. More importantly, however, this work offers an increased appreciation of the controls on the rates and mechanisms of denudation in basaltic and intermediate composition terranes in the tropics. [Copyright &y& Elsevier]

Summary: Many groundwater 14C age models require the assumption of the δ13C value of soil CO2 at the time of recharge. Concurrently, δ13C values of DIC are used to estimate the contribution of “live” carbon from the soil zone and “dead” carbon via the dissolution of calcite. Thus, model ages are critically sensitive to the δ13C value of CO2 in soil. Soil CO2 was sampled monthly throughout Utah representing a variety of elevations, climates, and plant communities where C3 plant assemblages dominate. A δ13C value of ∼−22±1.5‰ (1σ) was obtained where plant growth and soil microbial activity are not strongly suppressed by aridity. During spring and early summer in highly vegetated uplands, a value of −24.0±0.6‰ was found. Used as model age inputs, the associated uncertainties produce errors of ±500 and ±200yr, respectively for model ages of saturated zone waters. At one field station, δ13C values of soil CO2 vary between −8‰ at the soil/atmosphere interface to ∼−23‰ at depth, confounding the choice of model input values depending on where water in the soil column is assumed to acquire its gas. Measurements, inverse models, and forward models of δ13C gradients indicate that during recharge, >50% pore saturation decreases the atmospheric exchange such that isotopic gradients are erased at depths >10–20cm. Thus, large vertical gradients in this key input to model age calculations can be neglected. In summary, this work represents a significant improvement in understanding the origin and variability of δ13C values extant in the vadose zone during recharge, and permit a realistic assessment of the uncertainty in 14C ages of saturated zone waters resulting from the choice of this parameter. [Copyright &y& Elsevier]

Atmospheric particulate matter (PM) in urban areas is derived from natural and anthropogenic sources, but it is difficult to identify how these various sources contribute to air quality. To characterize PM sources in an urban setting, we collected PM in three size fractions (PM 2.5 , PM 10 , and total suspended particulates, TSP) for two-week intervals from 2019 through 2021 in the Wasatch Front of northern Utah. The PM samples were analyzed for major and trace element concentrations and 87Sr/86Sr ratios. Using principal components analysis, we identified mineral dust, urban pollution, and fireworks as the primary PM sources affecting Wasatch Front air quality. Dust contributed Al, Be, Ca, Fe, Mg, Rb, Y, and REEs, which are typical components of carbonate and silicate minerals, with highest concentrations in the TSP fraction. Urban sources produced PM that was enriched in As, Cd, Mo, Pb, Sb, Se, and Tl, and fireworks smoke had high concentrations of Ba, Cr, Cu, K, Sr, and V. Dust events dominated PM chemistry during spring through fall, punctuated by fireworks smoke over the Independence Day holiday, while urban pollution dominated PM chemistry from November through February during winter inversions. 87Sr/86Sr ratios revealed that Sr was sourced from regional playas, local sediment, and fireworks. Strontium released from fireworks had relatively low 87Sr/86Sr ratios that dominated the PM isotopic composition during holidays. Sequential leaching showed that potentially harmful elements such as Se, Cd, and Cu were readily removed by weak acids, suggesting that they are readily available in the environment or through human inhalation. This is the first study to describe seasonal variations in PM chemistry in the Wasatch Front and serves as an example of investigating air quality in complex urban areas impacted by desert dust. • Air quality in a complex urban environment impacted by mineral dust, urban pollution, and fireworks smoke. • Specific trace elements are used to identify impacts from each source. • Strontium isotope ratios identify specific sources of particulate matter. • Sequential leaching results show that harmful trace elements in particulate matter are bioavailable. [ABSTRACT FROM AUTHOR]

Numerous natural and anthropogenic processes in a watershed produce the geochemical composition of a river, which can be altered over time by snowmelt and rainfall events and by built infrastructure (i.e., dams and diversions). Trace element concentrations coupled with isotopic ratios offer valuable insights to disentangle the effects of these processes on water quality. In this study, we measured a suite of 40+ trace and major elements (including As, Cd, Ce, Cr, Cs, Fe, La, Li, Mo, Pb, Rb, Sb, Se, Sr, Ti, Tl, U, and Zn), Sr isotopes ( 87 Sr/ 86 Sr), and stable isotopes of H and O (δD and δ 18 O) to investigate natural and anthropogenic processes impacting the Provo River in northern Utah, USA. The river starts as a pristine mountain stream and passes through agricultural and urban areas, with two major reservoirs and several major diversions to and from the river. We sampled the entire 120 km length of the Provo River at 13 locations from the Uinta Mountains to Utah Valley, as well as two important tributaries, across the range of hydrologic conditions from low flow to snowmelt runoff during the 2013 water year. We also sampled the furthest downstream site in the Utah Valley urban area during a major flood event. Trace element concentrations indicate that a variety of factors potentially influence Provo River chemistry, including inputs from weathering of carbonate/siliciclastic rocks (Sr) and black shales (Se and U), geothermal groundwater (As, Cs, Li, and Rb), soil erosion during snowmelt runoff (Ce, Cr, Fe, La, Pb, and Ti), legacy mining operations (Mo, Sb, and Tl), and urban runoff (Cr, Pb, and Zn). Although specific elements overlap between different groups, the combination of different elements together with isotopic measurements and streamflow observations may act as diagnostic tools to identify sources. 87 Sr/ 86 Sr ratios indicate a strong influence of siliciclastic bedrock in the headwaters with values exceeding 0.714 and carbonate bedrock in the lower reaches of the river with values approaching 0.709. δD and δ 18 O changed little throughout the year in the Provo River, suggesting that the river is primarily fed by snowmelt during spring runoff and snowmelt-fed groundwater during baseflow. Based on nonmetric multidimensional scaling (NMS) water chemistry was unique across the upper, middle, and lower portions of the river, with high temporal variability above the first reservoir but minimal temporal variability below the reservoir. Thus, the results show that dams alter water chemistry by allowing for settling of particle-associated elements and also by homogenizing inflows throughout the year to minimize dilution during snowmelt runoff. Taken together, trace element concentrations and isotopic measurements can be used to evaluate the complex geochemical patterns of rivers and their variability in space and time. These measurements are critical for identifying natural and anthropogenic impacts on river systems. [ABSTRACT FROM AUTHOR]

Highlights: [•] Direct test of lithospheric versus crustal mechanisms of uplift in active collision. [•] Surface uplift rate of 0.5m/ka calculated for Kisar Island in Banda Arc. [•] May be one of the youngest exhumed metamorphic complexes on earth. [•] Active emergence and uplift attributed to combination of thrusting and domal extrusion along shear zone. [•] “Fresh” coral fragments represent possible tsunami deposits. [Copyright &y& Elsevier]

• Hg and DOM concentrations increased dramatically during snowmelt. • Clockwise C-Q hysteresis for filtered THg concentrations. • Hg was predominantly in the dissolved fraction. • DOM was dominated by humic and fulvic acids from soils. • Most Hg and DOM export occurred during the snowmelt period by soil water flushing. The mechanisms of Hg and dissolved organic matter (DOM) transport from watersheds to streams remain unclear, especially in snowmelt dominated montane systems. We characterized total Hg concentrations and DOM characteristics during snowmelt by weekly and/or monthly sampling at three locations in the upper Provo River, northern Utah, over two water years (2016 and 2017). Total Hg concentrations increased from <1 ng/L during baseflow to >7 ng/L during the snowmelt period (April–June), with decreasing concentrations from upstream to downstream. Filtered THg concentrations accounted for 65–75% of the unfiltered concentrations, suggesting that Hg is primarily transported in the dissolved phase. Annual THg loading in the upper Provo River was approximately 1 kg/yr, with ~90% of the flux occurring during the snowmelt period. Filtered THg concentrations were strongly correlated with in-situ fluorescence DOM (fDOM) measurements, allowing for the development of high-resolution proxy THg concentrations. Further, DOM characteristics, evaluated using excitation-emission matrices (EEMs) and parallel factor analysis (PARAFAC), identified the dominance of soil humic and fulvic acid fractions of DOM during runoff. Total Hg concentrations were low in snowpack but elevated in ephemeral streams during snowmelt runoff, indicating that Hg originated from shallow soil water rather than snow. Concentration—discharge relationships revealed clockwise hysteresis patterns, suggesting that Hg was flushed from soils on the rising limb of the hydrograph. Our results demonstrate that a majority of Hg transport occurs with a flux of DOM during the short snowmelt season as shallow soils are flushed by meltwater. The snowmelt-driven Hg pulse is a substantial source to downstream reservoirs and potentially contributes to a fish consumption advisory. [ABSTRACT FROM AUTHOR]