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At least 613 records · Page 34Linked to original sources

USGS2008

Multi-Disciplinary Approach to Trace Contamination of Streams and Beaches

Concentrations of fecal-indicator bacteria in urban streams and ocean beaches in and around Santa Barbara occasionally can exceed public-health standards for recreation. The U.S. Geological Survey (USGS), working with the City of Santa Barbara, has used multi-disciplinary science to trace the sources of the bacteria. This research is helping local agencies take steps to improve recreational water quality. The USGS used an approach that combined traditional hydrologic and microbiological data, with state-of-the-art genetic, molecular, and chemical tracer analysis. This research integrated physical data on streamflow, ground water, and near-shore oceanography, and made extensive use of modern geophysical and isotopic techniques. Using those techniques, the USGS was able to evaluate the movement of water and the exchange of ground water with near-shore ocean water. The USGS has found that most fecal bacteria in the urban streams came from storm-drain discharges, with the highest concentrations occurring during storm flow. During low streamflow, the concentrations varied as much as three-fold, owing to variable contribution of non-point sources such as outdoor water use and urban runoff to streamflow. Fecal indicator bacteria along ocean beaches were from both stream discharge to the ocean and from non-point sources such as bird fecal material that accumulates in kelp and sand at the high-tide line. Low levels of human-specific Bacteroides, suggesting fecal material from a human source, were consistently detected on area beaches. One potential source, a local sewer line buried beneath the beach, was found not to be responsible for the fecal bacteria.

Fact Sheet↗

USGS2018

Breaching of strike-slip faults and successive flooding of pull-apart basins to form the Gulf of California seaway from ca. 8–6 Ma

The geologic record of the formation of marine basins during continental rifting is uncommonly preserved. Using GIS-based paleotectonic maps, we show that marine basin formation in the Gulf of California–Salton trough oblique rift (Mexico and the United States) occurred in a stepwise manner as crustal thinning lowered elevations within the Gulf of California Shear Zone, and subsidence along strike-slip and transtensional faults linked isolated pull-apart basins. At 8 Ma, the earliest marine conditions in the Gulf of California were restricted to an embayment at its southern mouth. Farther north, the plate boundary was a set of continental strike-slip faults and linked pull-apart basins, similar to the modern Walker Lane in Nevada and California. By ca. 7 Ma, a series of marine incursions breached across strike-slip faults to the Pescadero and Farallon basins. Marine waters then breached a 75–100 km-long transtensional fault zone between the Farallon and Guaymas basins, with intermittent flooding that led to accumulation of extensive evaporite deposits in the Guaymas basin. Marine incursion north of the Guaymas basin via breaches across the Guaymas and Tiburón strike-slip faults and transtensional zones resulted in flooding of the northern >500 km of the oblique rift by 6.5–6.3 Ma. Thus, strike-slip and transtensional faulting promoted localization of plate boundary strain and guided punctuated marine flooding of the Gulf of California seaway. Inception of the narrow, 1500-km-long Gulf of California at ca. 6.3 Ma was followed by complete continental rupture in the Guaymas basin at ca. 6.0 Ma.

Geology↗

USGS1996

The upper mantle structure of the central Rio Grande rift region from teleseismic P and S wave travel time delays and attenuation

The lithosphere beneath a continental rift should be significantly modified due to extension. To image the lithosphere beneath the Rio Grande rift (RGR), we analyzed teleseismic travel time delays of both P and S wave arrivals and solved for the attenuation of P and S waves for four seismic experiments spanning the Rio Grande rift. Two tomographic inversions of the P wave travel time data are given: an Aki-Christofferson-Husebye (ACH) block model inversion and a downward projection inversion. The tomographic inversions reveal a NE-SW to NNE-SSW trending feature at depths of 35 to 145 km with a velocity reduction of 7 to 8% relative to mantle velocities beneath the Great Plains. This region correlates with the transition zone between the Colorado Plateau and the Rio Grande rift and is bounded on the NW by the Jemez lineament, a N52°E trending zone of late Miocene to Holocene volcanism. S wave delays plotted against P wave delays are fit with a straight line giving a slope of 3.0 ± 0.4. This correlation and the absolute velocity reduction imply that temperatures in the lithosphere are close to the solidus, consistent with, but not requiring, the presence of partial melt in the mantle beneath the Rio Grande rift. The attenuation data could imply the presence of partial melt. We compare our results with other geophysical and geologic data. We propose that any north-south trending thermal (velocity) anomaly that may have existed in the upper mantle during earlier (Oligocene to late Miocene) phases of rifting and that may have correlated with the axis of the rift has diminished with time and has been overprinted with more recent structure. The anomalously low-velocity body presently underlying the transition zone between the core of the Colorado Plateau and the rift may reflect processes resulting from the modern (Pliocene to present) regional stress field (oriented WNW-ESE), possibly heralding future extension across the Jemez lineament and transition zone.

Journal of Geophysical Research B: Solid Earth↗

USGS2020

Hydrogeologic framework and simulation of predevelopment groundwater flow, eastern Abu Dhabi Emirate, United Arab Emirates

Groundwater in eastern Abu Dhabi in the United Arab Emirates is an important resource that is widely used for irrigation and domestic supplies in rural areas. The U.S. Geological Survey and the Environment Agency—Abu Dhabi cooperated on an investigation to integrate existing hydrogeologic information and to answer questions about regional groundwater resources in Abu Dhabi by developing a numerical groundwater flow model based on MODFLOW–2005 software. The groundwater flow model developed in this investigation provides an improved understanding of groundwater conditions in the eastern region of the Emirate of Abu Dhabi. The flow model simulates steady-state predevelopment conditions from before the rapid growth of modern pumping in the 1980s and was calibrated with 1,342 groundwater-level observations by use of automated and manual calibration techniques. The calibrated model provides good accuracy, with a mean error of 0.50 meters and a standard error of 5.92 meters for simulated groundwater levels. The results of the regional water budget simulation show that gap recharge, which is groundwater inflow through mountain-front gap alluvium, is the greatest source of water to the aquifer. In the base simulation scenario, gap recharge represents 80 percent of total inflow (119,470 of 149,403 cubic meters per day) and the greatest outflow from the aquifer is from evapotranspiration (93 percent of total outflow). Model scenario and sensitivity results reveal a need for data that more thoroughly and more accurately describe aquifer hydraulic conductivity, inflow to the aquifer from the Oman Mountains, and recharge from precipitation on the piedmont. Additional long-term aquifer pumping test observations would improve understanding of aquifer hydraulic conductivity, which would also improve model accuracy. Future studies can modify the model to understand the effect of land-use change and water use on groundwater supplies and simulate more complex groundwater flow conditions in a predictive mode.

Scientific Investigations Report↗

USGS1976

Large sand waves on the Atlantic Outer Continental Shelf around Wilmington Canyon, off Eastern United States

New seismic-reflection data show that large sand waves near the head of Wilmington Canyon on the Atlantic Outer Continental Shelf have a spacing of 100-650 m and a relief of 2-9 m. The bedforms trend northwest and are asymmetrical, the steeper slopes being toward the south or west. Vibracore sediments indicate that the waves apparently have formed on a substrate of relict nearshore sediments. Although the age of the original bedforms is unknown, the asymmetry is consistent with the dominant westerly to southerly drift in this area which has been determined by other methods; the asymmetry, therefore, is probably modern. Observations in the sand-wave area from a submersible during August 1975, revealed weak bottom currents, sediment bioturbation, unrippled microtopography, and lack of scour. Thus, the asymmetry may be maintained by periodic water motion, possibly associated with storms or perhaps with flow in the canyon head.

Wilmington Canyon↗

USGS2014

The Lepanto Cu–Au deposit, Philippines: A fossil hyperacidic volcanic lake complex

Hyperacidic lakes and associated solfatara in active volcanoes are the expression of magmatic gas expansion from source to surface. Here we show for the first time, that the vein system that comprises the ~ 2 Ma high-sulfidation, Lepanto copper–gold deposit in the Mankayan district (Philippines) was associated with a contemporary hyperacidic volcanic lake complex—possibly the first such lake recognized in the geological record. A 15–20‰ difference in sulfur isotopic composition between barite and sulfides and sulfosalts in the vent fumarole encrustations supports the interpretation that SO 2 -rich volcanic gas vented into the base of the lake and marginal to it and ties the mineralization directly to magmatic gas expansion, fracture propagation, and mineralization that occurred through a series of decompression steps within the feeder fracture network. These data confirm that crater lake environments such as Kawah Ijen (Java, Indonesia) provide modern day analogs of the Lepanto and other high sulfidation Cu–Au depositing environments. We also provide extensive analysis of sulfosalt–sulfide reactions during vein formation within the hyperacidic lake complex. Pyrite ± silica deposited first at high temperature followed by enargite that preserves the vapor–solid diffusion of, for example, antimony, tin, and tellurium into the vapor from the crystallizing solid. Subsolidus, intra-crystalline diffusion continued as temperature declined. Pyrite and enargite are replaced by Fe-tennantite in the lodes which initially has low Sb/(Sb + As) atomic ratios around 13.5% close to the ideal tennantite formula, but evolves to higher ratios as crystallization proceeds. Fumarole encrustation clasts and sulfosalts in the lake sediment are more highly evolved with a larger range of trace element substitutions, including antimony. Substitution of especially Zn, Te, Ag, and Sn into tennantite records metal and semi-metal fractionation between the expanding magmatic gas and deposited sulfide sublimates provides a rare insight into the fate of metals and semi-metals in the shallower parts of fracture arrays that feed modern hyperacidic lakes. These data support a growing understanding of the formation of high-sulfidation gold deposits as the consequence of single-phase expansion of gas from magmatic-gas reservoirs beneath the surface of active volcanoes without the intervention of a later aqueous fluid including groundwater. Aggressive sulfide–sulfosalt reactions, including pitting and the almost complete dissolution of earlier minerals, are persistent characteristics of the vein assemblages and precious metals typically occur late in pits or along brittle fractures. These characteristics support a hypothesis of mineral deposition at temperatures of the order of 600 °C in contrast to available fluid inclusion data from enargite that record temperatures following phase transitions in the sulfosalt during the retrograde devolution of the deposit in the presence of groundwater.

Benguet↗

USGS2017

Isotopic evidence for glacial meltwater recharge to the Cambrian-Ordovician aquifer, north-central United States

The chemistry of water in the Cambrian-Ordovician aquifer in six midwestern states has been studied as part of the Northern Midwest Regional Aquifer-System Analysis of the U.S. Geological Survey. Dissolved-solids concentrations generally increase perpendicular to the direction of regional groundwater flow, from less than 400 mg/liter in southeast Minnesota, southwest Wisconsin, and northeast Iowa to more than 10,000 mg/liter in northwest Missouri. Isotopic ratios of hydrogen and oxygen are significantly depleted from north to south, with an areal distribution approximately parallel to the distribution of dissolved solids. For example, ??18O in southern Iowa and northern Missouri is about 6 parts per thousand lighter than ??18O of modern recharge water in Minnesota and Wisconsin. Covariance between ??18O and ??D of the groundwater, similar to that of modern precipitation, suggests that the differences in isotopic ratios between groundwater and modern recharge water reflect meteoric signatures of water during past recharge events rather than geochemical processes such as isotopic exchange with aquifer materials. The pronounced parallelism between the distribution of isotopes and dissolved solids over large areas probably reflects largescale recharge of Pleistocene glacial meltwater into the aquifer system, which probably had a paleoflow system with a gradient from northeast to southwest rather than from northwest to southeast. ?? 1984.

Quaternary Research↗

USGS2020

Automated location correction and spot height generation for named summits in the coterminous United States

Spot elevations published on historical U.S. Geological Survey topographic maps were established as needed to enhance information imparted by the quadrangle’s contours. In addition to other features, labels were routinely placed on mountain summits. While some elevations were established through field survey triangulation, many were computed during photogrammetric stereo-compilation. Today, Global Navigation Satellite System (GNSS) receivers have replaced expensive triangulation methods. However, since GNSS measurements require visiting the feature location, a national dataset containing high-accuracy spot elevations has not yet been created. Consequently, modern U.S. Topo maps are devoid of mountain peak or other spot elevations. Still, topographic map users continue to demand the display of spot heights. Therefore, a pilot study was conducted to evaluate the feasibility of automatically generating elevation values at named U.S. summits using available elevation data. The devised method uses an uphill stepping technique to find the most likely highest point in subsequently higher-resolution elevation models. Resulting elevation values are compared to other published sources. Results from 196 summits indicate that values derived from lidar are generally higher, whereas those populated from the one-third arc-second USGS Seamless 3DEP elevation dataset are generally lower. A thorough understanding of these relationships require the evaluation of more points.

International Journal of Digital Earth↗

USGS1993

A speculative history of the San Andreas fault in the central Transverse Ranges, California

It is generally accepted that the San Andreas fault formed between 4 and 5 Ma and that rocks west of it are now part of the Pacific plate, moving northwest relative to North America at 5 to 6 cm/yr. This model is inconsistent with the geologic record in the central Transverse Ranges. Right-lateral shear began in the vicinity of the San Andreas fault system in early Miocene time. The San Andreas fault system in the central Transverse Ranges has since evolved through three major phases; this development has led to a generally simpler, more throughgoing main trace. Slip rates on the San Andreas system were about 1 cm/yr in the Miocene, increasing to their current level of 3.5 cm/yr between 4 and 5 Ma. The modern San Andreas fault still only accounts for just over half the current relative plate rate and retains kinematic complexities inherited from its earliest geometry. The Early San Andreas transform system originated during early Miocene time in one of three transtensive zones that lay interior to the continent and east of the locus of transform motion between the Pacific and North American plates. The current three-fold division of motion in the plate boundary between the San Andreas fault, a coastal system, and an eastern California system dates to this time, as does the “anomalous” trend of the San Andreas fault through the Transverse Ranges. Basins and volcanic centers associated with this transtensive zone became dismembered as faults became integrated into a throughgoing system. Early motion led to juxtaposition of different rocks across faults now recognized as part of the Early San Andreas transform system, and to the development of sedimentary provincialism associated with uplift along the fault zone. Middle Miocene basins, including the Caliente, Cajon, Crowder, and Santa Ana basins that had previously received most of their sediments from sources far to the east, began to reflect local Transverse Ranges provenance. At least 100 km of slip is associated with the Early San Andreas transform system during early and middle Miocene time. Slip across the geometrically complex late Miocene San Gabriel transform system—which includes the San Gabriel, Cajon Valley, and early Punchbowl faults—produced uplift in the proto-Transverse Ranges at a postulated restraining bend in the fault system. Compressional structures associated with this restraining bend include the Squaw Peak and Liebre Mountain thrusts, related east-striking late Miocene reverse faults and folds, and, perhaps, northeast-striking left-lateral faults in the San Gabriel Mountains. Narrow fault-controlled basins formed during this period, including the Ridge basin, Devil’s Punchbowl basin, Mill Creek basin, and part of the Santa Ana Sandstone basin. Offset of structures and relief associated with the proto-Transverse Ranges provides the best evidence for late Miocene restorations of the modern San Andreas fault. As much as 60 km of offset is associated with the late Miocene San Gabriel transform system. Between 4 and 5 Ma, the modern San Andreas fault became the dominant member of the plate boundary system, cutting through the proto-Transverse Ranges and connecting more northerly striking traces to the north and south. The slip rate across the San Andreas fault system accelerated from 1 cm/yr to its current slip rate of 3.5 cm/yr prior to 4 Ma. The Pliocene rocks in the central Transverse Ranges do not contain evidence for relief as great as that of late Miocene or Quaternary time. The Pliocene trace of the modern San Andreas fault may have temporarily “solved” the geometric problem that led to late Miocene uplift. About 90 km of right-lateral displacement occurred on the modern San Andreas fault during Pliocene time. During Quaternary time new regions of localized vertical deformation developed in the Transverse Ranges, apparently as the result of new geometric problems within the Pliocene solution to the restraining geometry of the fault system. Left-lateral motion on east-striking faults, probably due to a northward increase in Basin and Range extension, kinked the San Andreas fault at both ends of the Transverse Ranges, producing regions of extreme shortening and uplift. The development of young right-lateral faults through the Peninsular Ranges, including the San Jacinto and Elsinore faults, also contributed to renewed uplift in the Transverse Ranges. Sixty kilometers of right-lateral slip occurred across the San Andreas fault zone during Quaternary time.

California↗

USGS2013

Status and understanding of groundwater quality in the Madera, Chowchilla Study Unit, 2008: California GAMA Priority Basin Project

Groundwater quality in the approximately 860-square-mile Madera and Chowchilla Subbasins (Madera-Chowchilla study unit) of the San Joaquin Valley Basin was investigated as part of the Priority Basin Project of the Groundwater Ambient Monitoring and Assessment (GAMA) Program. The study unit is located in California's Central Valley region in parts of Madera, Merced, and Fresno Counties. The GAMA Priority Basin Project is being conducted by the California State Water Resources Control Board in collaboration with the U.S. Geological Survey (USGS) and the Lawrence Livermore National Laboratory. The Project was designed to provide statistically robust assessments of untreated groundwater quality within the primary aquifer systems in California. The primary aquifer system within each study unit is defined by the depth of the perforated or open intervals of the wells listed in the California Department of Public Health (CDPH) database of wells used for municipal and community drinking-water supply. The quality of groundwater in shallower or deeper water-bearing zones may differ from that in the primary aquifer system; shallower groundwater may be more vulnerable to contamination from the surface. The assessments for the Madera-Chowchilla study unit were based on water-quality and ancillary data collected by the USGS from 35 wells during April-May 2008 and water-quality data reported in the CDPH database. Two types of assessments were made: (1) status , assessment of the current quality of the groundwater resource, and (2) understanding , identification of natural factors and human activities affecting groundwater quality. The primary aquifer system is represented by the grid wells, of which 90 percent (%) had depths that ranged from about 200 to 800 feet (ft) below land surface and had depths to the top of perforations that ranged from about 140 to 400 ft below land surface. Relative-concentrations (sample concentrations divided by benchmark concentrations) were used for evaluating groundwater quality for those constituents that have Federal or California regulatory or non-regulatory benchmarks for drinking-water quality. A relative-concentration (RC) greater than 1.0 indicates a concentration above a benchmark. RCs for organic constituents (volatile organic compounds and pesticides) and special-interest constituents (perchlorate) were classified as "high" (RC is greater than 1.0), "moderate" (RC is less than or equal to 1.0 and greater than 0.1), or "low" (RC is less than or equal to 0.1). For inorganic constituents (major and minor ions, trace elements, nutrients, and radioactive constituents), the boundary between low and moderate RCs was set at 0.5. The assessments characterize untreated groundwater quality, not the quality of treated drinking water delivered to consumers by water purveyors; drinking-water benchmarks, and thus relative-concentrations, are used to provide context for the concentrations of constituents measured in groundwater. Aquifer-scale proportion was used in the status assessment as the primary metric for evaluating regional-scale groundwater quality. High aquifer-scale proportion is defined as the percentage of the area of the primary aquifer system with RCs greater than 1.0 for a particular constituent or class of constituents; moderate and low aquifer-scale proportions are defined as the percentages of the area of the primary aquifer system with moderate and low RCs, respectively. Percentages are based on an areal, rather than a volumetric basis. Two statistical approaches--grid-based, which used one value per grid cell, and spatially weighted, which used multiple values per grid cell--were used to calculate aquifer-scale proportions for individual constituents and classes of constituents. The spatially weighted estimates of high aquifer-scale proportions were within the 90% confidence intervals of the grid-based estimates for all constituents except iron. The status assessment showed that inorganic constituents had greater high and moderate aquifer-scale proportions in the Madera-Chowchilla study unit than did organic constituents. RCs for inorganic constituents with health-based benchmarks were high in 37% of the primary aquifer system, moderate in 30%, and low in 33%. The inorganic constituents contributing most to the high aquifer-scale proportion were arsenic (13%), uranium (17%), gross alpha particle activity (20%), nitrate (6.7%), and vanadium (3.3%). RCs for inorganic constituents with non-health-based benchmarks were high in 6.7% of the primary aquifer system, and the constituent contributing most to the high aquifer-scale proportion was total dissolved solids (TDS). RCs for organic constituents with health-based benchmarks were high in 10% of the primary aquifer system, moderate in 3.3%, and low in 40%; organic constituents were not detected in 47% of the primary aquifer system. The fumigant 1,2-dibromo-3-chloropropane (DBCP) was the only organic constituent detected at high RCs. Seven organic constituents were detected in 10% or more of the primary aquifer system: DBCP; the fumigant additive 1,2,3-trichloropropane; the herbicides simazine, atrazine, and diuron; the trihalomethane chloroform; and the solvent tetrachloroethene (PCE). RCs for the special-interest constituent perchlorate were moderate in 20% of the primary aquifer system. The second component of this study, the understanding assessment , identified the natural and human factors that may affect groundwater quality by evaluating statistical correlations between water-quality constituents and potential explanatory factors, such as land use, position relative to important geologic features, groundwater age, well depth, and geochemical conditions in the aquifer. Results of the statistical evaluations were used to explain the distribution of constituents in the study unit. Depth to the top of perforations in the well and groundwater age were the most important explanatory factors for many constituents. High and moderate RCs of nitrate, uranium, and TDS and the presence of herbicides, trihalomethanes, and solvents were all associated with depths to the top of perforations less than 235 ft and modern- and mixed-age groundwater. Positive correlations between uranium, bicarbonate, TDS, and the proportion of calcium and magnesium in the total cations suggest that downward movement of recharge from irrigation water contributed to the elevated concentrations of these constituents in the primary aquifer system. High and moderate RCs of arsenic were associated with depths to the top of perforations greater than 235 ft, mixed- and pre-modern-age groundwater, and location in sediments from the Chowchilla River alluvial fan, suggesting that increased residence time and appropriate aquifer materials were needed for arsenic to accumulate in the groundwater. High and moderate RCs of fumigants were associated with depths to the top of perforations of less than 235 ft and location south of the city of Madera; low RCs of fumigants were detected in wells dispersed across the study unit with a range of depths to top of perforations.

California↗

USGS1993

Stable isotope study of fluid inclusions in fluorite from Idaho: Implications for continental climates during the Eocene

Isotopic studies of fluid inclusions from meteoric water-dominated epithermal ore deposits offer a unique opportunity to study paleoclimates because the fluids can provide direct samples of ancient waters. The oxygen and hydrogen isotope compositions of meteoric waters vary because of changes in climatic variables such as mean annual temperature of precipitation, relative humidity, origin and history of air masses, and the isotope composition of the oceans. Inclusion fluids found in fluorite (CaF 2 ) are especially useful because their host is devoid of oxygen or hydrogen, thus precluding postentrapment isotope exchange. Fluorite-hosted fluid inclusions from the Eocene (51-50 Ma) epithermal deposits of the Bayhorse mining district, northeastern Idaho, have low salinities, most less than 0.6 equivalent wt% NaCl, and low to moderate homogenization temperatures (98 to 146 °C), indicating meteoric origins for the fluids. Oxygen and hydrogen isotope data on inclusion fluids are almost identical to those of modern meteoric waters in the area. The equivalence of the isotope composition of the Eocene inclusion fluids and modern meteoric waters indicates that the Eocene climatic conditions were similar to those today. This conclusion supports the climate modeling of Sloan and Barron, who suggested that the climates of continental interiors do not reflect the magnitude of warming preserved by the deep-ocean paleoclimate record during the Eocene.

Geology↗

USGS2011

The human dimension of fire regimes on Earth

Humans and their ancestors are unique in being a fire‐making species, but ‘natural’ (i.e. independent of humans) fires have an ancient, geological history on Earth. Natural fires have influenced biological evolution and global biogeochemical cycles, making fire integral to the functioning of some biomes. Globally, debate rages about the impact on ecosystems of prehistoric human‐set fires, with views ranging from catastrophic to negligible. Understanding of the diversity of human fire regimes on Earth in the past, present and future remains rudimentary. It remains uncertain how humans have caused a departure from ‘natural’ background levels that vary with climate change. Available evidence shows that modern humans can increase or decrease background levels of natural fire activity by clearing forests, promoting grazing, dispersing plants, altering ignition patterns and actively suppressing fires, thereby causing substantial ecosystem changes and loss of biodiversity. Some of these contemporary fire regimes cause substantial economic disruptions owing to the destruction of infrastructure, degradation of ecosystem services, loss of life, and smoke‐related health effects. These episodic disasters help frame negative public attitudes towards landscape fires, despite the need for burning to sustain some ecosystems. Greenhouse gas‐induced warming and changes in the hydrological cycle may increase the occurrence of large, severe fires, with potentially significant feedbacks to the Earth system. Improved understanding of human fire regimes demands: (1) better data on past and current human influences on fire regimes to enable global comparative analyses, (2) a greater understanding of different cultural traditions of landscape burning and their positive and negative social, economic and ecological effects, and (3) more realistic representations of anthropogenic fire in global vegetation and climate change models. We provide an historical framework to promote understanding of the development and diversification of fire regimes, covering the pre‐human period, human domestication of fire, and the subsequent transition from subsistence agriculture to industrial economies. All of these phases still occur on Earth, providing opportunities for comparative research.

Journal of Biogeography↗

USGS2016

St. Louis area earthquake hazards mapping project; seismic and liquefaction hazard maps

We present probabilistic and deterministic seismic and liquefaction hazard maps for the densely populated St. Louis metropolitan area that account for the expected effects of surficial geology on earthquake ground shaking. Hazard calculations were based on a map grid of 0.005°, or about every 500 m, and are thus higher in resolution than any earlier studies. To estimate ground motions at the surface of the model (e.g., site amplification), we used a new detailed near‐surface shear‐wave velocity model in a 1D equivalent‐linear response analysis. When compared with the 2014 U.S. Geological Survey (USGS) National Seismic Hazard Model, which uses a uniform firm‐rock‐site condition, the new probabilistic seismic‐hazard estimates document much more variability. Hazard levels for upland sites (consisting of bedrock and weathered bedrock overlain by loess‐covered till and drift deposits), show up to twice the ground‐motion values for peak ground acceleration (PGA), and similar ground‐motion values for 1.0 s spectral acceleration (SA). Probabilistic ground‐motion levels for lowland alluvial floodplain sites (generally the 20–40‐m‐thick modern Mississippi and Missouri River floodplain deposits overlying bedrock) exhibit up to twice the ground‐motion levels for PGA, and up to three times the ground‐motion levels for 1.0 s SA. Liquefaction probability curves were developed from available standard penetration test data assuming typical lowland and upland water table levels. A simplified liquefaction hazard map was created from the 5%‐in‐50‐year probabilistic ground‐shaking model. The liquefaction hazard ranges from low (<40% of area expected to liquefy) in the uplands to severe (>60% of area expected to liquefy) in the lowlands. Because many transportation routes, power and gas transmission lines, and population centers exist in or on the highly susceptible lowland alluvium, these areas in the St. Louis region are at significant potential risk from seismically induced liquefaction and associated ground deformation

Alabama, Arkansas, Illinois, Indiana, Iowa, Kentuc↗

USGS1985

Simulated effects of increased recharge on the ground-water flow system of Yucca Mountain and vicinity, Nevada-California

A study was performed to assess the potential effects of changes in future climatic conditions on the groundwater system in the vicinity of Yucca Mountain, the site of a potential mined geologic repository for high-level nuclear wastes. These changes probably would result in greater rates of precipitation and, consequently, greater rates of recharge. The study was performed by simulating the groundwater system, using a two-dimensional, finite-element, groundwater flow model. The simulated position of the water table rose as much as 130 meters near the U.S. Department of Energy 's preferred repository area at Yucca Mountain for a simulation involving a 100-percent increase in precipitation compared to modern-day conditions. Despite the water table rise, no flooding of the potential repository would occur at its current proposed location. According to the simulation, springs would discharge south and west of Timber Mountain, along Fortymile Canyon, in the Amargosa Desert near Lathrop Wells and Franklin Lake playa, and near Furnace Creek Ranch in Death Valley, where they presently discharge. Simulated directions of groundwater flow paths near the potential repository area generally would be the same for the baseline (modern-day climate) and the increased-recharge simulations, but the magnitude of flow would increase by 2 to 4 times that of the baseline-simulation flow. (USGS)

California, Nevada↗

USGS1969

The relationship between fluids in some fresh alpine-type ultramafics and possible modern serpentinization, western United States

Calcium hydroxide waters issue from four partly serpentinized Alpine-type ultramafic bodies in the western United States. The occurrence of calcium-hydroxide-type water is restricted to fresh Alpine-type ultramafic rocks. The calcium hydroxide waters are unsaturated with Mg end-member olivine and pyroxene but supersaturated with Mg end-member brucite and serpentine and thus have chemical potentials to cause Serpentinization. The calcium hydroxide waters are isotopically similar to the common magnesium bicarbonate meteoric waters peculiar to ultramafic rocks and serpentinites. Some Serpentinization is apparently a near-surface phenomenon occurring at present. The Serpentinization takes place at nearly constant composition, except for loss of CaO. © 1969, The Geological Society of America, Inc.

Geological Society of America Bulletin↗

USGS2012

Kinematics of the New Madrid seismic zone, central United States, based on stepover models

Seismicity in the New Madrid seismic zone (NMSZ) of the central United States is generally attributed to a stepover structure in which the Reelfoot thrust fault transfers slip between parallel strike-slip faults. However, some arms of the seismic zone do not fit this simple model. Comparison of the NMSZ with an analog sandbox model of a restraining stepover structure explains all of the arms of seismicity as only part of the extensive pattern of faults that characterizes stepover structures. Computer models show that the stepover structure may form because differences in the trends of lower crustal shearing and inherited upper crustal faults make a step between en echelon fault segments the easiest path for slip in the upper crust. The models predict that the modern seismicity occurs only on a subset of the faults in the New Madrid stepover structure, that only the southern part of the stepover structure ruptured in the A.D. 1811–1812 earthquakes, and that the stepover formed because the trends of older faults are not the same as the current direction of shearing.

Geology↗

USGS2013

Generalized surficial geologic map of the Fort Irwin Area, San Bernardino County, California

The geology and landscape of the Fort Irwin area, typical of many parts of the Mojave Desert, consist of rugged mountains separated by broad alluviated valleys that form the main coarse-resolution features of the geologic map. Crystalline and sedimentary rocks, Mesozoic and older in age, form most of the mountains with lesser accumulations of Miocene sedimentary and volcanic rocks. In detail, the area exhibits a fairly complex distribution of surficial deposits resulting from diverse rock sources and geomorphology that has been driven by topographic changes caused by recent and active faulting. Depositional environments span those typical of the Mojave Desert: alluvial fans on broad piedmonts, major intermittent streams along valley floors, eolian sand dunes and sheets, and playas in closed valleys that lack through-going washes. Erosional environments include rocky mountains, smooth gently sloping pediments, and badlands in readily eroded sediment. All parts of the landscape, from regional distribution of mountains, valleys, and faults to details of degree of soil development in surface materials, are portrayed by the surficial geologic map. Many of these attributes govern infiltration and recharge, and the surface distribution of permeable rock units such as Miocene sedimentary and volcanic rocks provides a basis for evaluating potential groundwater storage. Quaternary faults are widespread in the Fort Irwin area and include sinistral, east-striking faults that characterize the central swath of the area and the contrasting dextral, northwest-striking faults that border the east and west margins. Bedrock distribution and thickness of valley-fill deposits are controlled by modern and past faulting, and faults on the map help to identify targets for groundwater exploration.

California↗

USGS2018

Chemical and isotopic characteristics of methane in groundwater of Ohio, 2016

In 2016, the U.S. Geological Survey, in cooperation with the Ohio Water Development Authority, investigated the hydrogeologic setting, chemical and isotopic characteristics, and origin of methane in groundwater of Ohio. Understanding the occurrence and distribution of methane in groundwater is important in terms of public safety because methane in water wells can pose a risk of explosion. In addition, documenting the chemical and isotopic characteristics of methane in groundwater can make an important contribution to future stray gas investigations. Water samples were collected from 15 domestic water wells known to produce methane, which were in 12 counties in diverse parts of Ohio. The wells were 75–345 feet deep and tapped a range of aquifer types, including glacial deposits and bedrock of Upper Ordovician, Upper Devonian, Lower Mississippian, and Pennsylvanian ages. Although the hydrogeologic settings were varied, there was a broad similarity among the well sites in that the bedrock was predominantly shale and the glacial deposits were predominantly clay. The wells were sampled for dissolved inorganic constituents; dissolved organic carbon; methane and other dissolved gases; stable isotopes (carbon, hydrogen, and oxygen) of methane, water, and dissolved inorganic carbon; and carbon-14 of methane. Gas composition and stable isotopes of methane were used to differentiate thermogenic and microbial methane. The degree of fractionation of hydrogen and carbon isotopes was used to evaluate the pathway of microbial methanogenesis (carbon dioxide [CO 2 ] reduction or acetate fermentation) and the effects of secondary processes such as oxidation, mixing, and migration. The concentration of carbon-14 of methane was used to evaluate the relative age of the carbon source. The quality of water from the 15 wells differed greatly; water types ranged from CaMgHCO 3 to NaCl, and total dissolved solids concentrations ranged from 318 to 2,940 milligrams per liter (mg/L). Methane concentrations ranged from 1.2 to 120 mg/L. Of the 15 samples, 12 had methane concentrations greater than 28 mg/L, the level that can pose a risk of explosion. Of the 15 samples, 12 had chemical and isotopic characteristics or "signatures" consistent with microbial methane formed by CO 2 reduction. CO 2 reduction is commonly associated with microbial degradation of organic matter in anaerobic aquifers and with the formation of microbial shale gas and coalbed methane along margins of sedimentary basins. Two of 15 samples were interpreted as having a component of thermogenic methane based on the δ 13 C of methane (−50.96 and −47.74 parts per thousand [per mil]) and gas dryness (28 and 5). One of 15 samples (from the shallowest well) had chemical and isotopic characteristics consistent with methane oxidation by sulfate reduction based on light δ 13 C of dissolved inorganic carbon (−31.6 per mil) and evidence of sulfate reduction in terms of the odor and appearance of the water. For the 12 samples interpreted as microbial methane formed by CO 2 reduction, the δ 13 C of methane varied from −75 to −56 per mil. Multiple samples from the same aquifer demonstrated a general trend of increasing δ 13 C of methane with depth. Samples with lighter δ 13 C of methane (−75 to −62 per mil) were from shallower wells (or wells with shallow open intervals), and the isotopic signature of the water was consistent with modern or postglacial groundwater recharge. Three samples with heavier δ 13 C of methane (−61 to −56 per mil) were from deeper wells or more confined aquifers where the isotopic signature of water was consistent with older (glacial) recharge. In addition, δ 13 C of dissolved inorganic carbon was enriched (+12 to +18.9 per mil), and carbon-14 of methane was consistent with carbon associated with Paleozoic bedrock or older glacial deposits. These observations are generally consistent with increased Rayleigh-type fractionation at greater depths; however, other interpretations are possible. Isotopic signatures can be ambiguous, especially in areas with complex geologic histories that include multiple episodes of migration, mixing, and (or) oxidation. Many of the wells were in proximity to multiple potential natural and anthropogenic pathways of methane migration; however, it is not possible to determine if the methane in any of the wells is related to human activities based on the chemical and isotopic data collected for this study.

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