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At least 181 records · Page 10Linked to original sources

USGS1988

The Fox permafrost tunnel: A late Quaternary geologic record in central Alaska

The Fox permafrost tunnel, which penetrates 110 m into frozen sediments of Gold-stream valley, provides a continuous exposure of fossiliferous silt and alluvium above schistose bedrock. Deposition of fluvial gravel was followed by a long interval of loess accretion and permafrost aggradation that was punctuated by episodes of thaw and of gullying and redeposition of silt. Imbricated sandy gravel above the bedrock contains lenses of finer alluvium that contain wood fragments and some rooted stumps. Radiocarbon dates indicate that the gravel is older than 40 ka, but absence of mature soil and weathering profiles at its upper contact indicates that fluvial activity must have continued until shortly before loess accretion began at the tunnel site. Silt is the most widespread depositional unit in the tunnel. This deposit is of eolian origin (loess), but some has been redeposited by slope processes. The silt units contain abundant ground ice as pore filings, lenses, wedges, and buried pond ice. Loess accretion was interrupted by a period when little loess accumulated and when large ice wedges formed in the lower loess unit and subsequently were truncated by thaw. Loess began forming sometime before 40 ka and was rapidly accreting by 39 ka under xeric conditions with open vegetation. A sharply decreased rate of loess accretion associated with local erosion and thaw between about 36 and 30 ka is marked by anomalous cation concentration values, lenses of buried sod, fossils indicative of moist to wet substrates, and truncated ice wedges beneath small frozen ponds or streamlets that occupied ice-wedge troughs. A later episode of rapid loess influx under drier conditions began after 30 ka and coincided with glacial advances of late Wisconsin age in the adjoining Alaska Range. Large ice wedges also formed in the upper loess unit, but only their bases are exposed in the tunnel, and their history of development is uncertain. Fanlike deposits of poorly sorted debris near the tunnel portal formed between about 12.5 and 11 ka during deep erosion of loess slopes under moister conditions. The deposits locally form two subunits: the younger over- whelmed a stand of tall willows on the floor of Goldstream valley between about 11.3 and 11.1 ka; the older may have formed about 1,000 yr earlier. Stratigraphic records elsewhere in central Alaska indicate variable middle Wisconsin environments followed by colder and drier conditions that began between 30 and 25 ka and persisted until perhaps 12.5 ka. Widespread loess erosion and redeposition subsequently occurred under moister and probably warmer conditions. Renewed early Holocene loess deposition may have been widespread, but its exact environmental controls are uncertain. Our data challenge three generally accepted concepts of late Quaternary periglacial processes in central Alaska. We contend that (1) many ice-wedge systems may have formed under interstadial conditions rather than full-glacial conditions, (2) episodes of rapid loess influx may have been partly out of phase with episodes of glacier expansion, and (3) redeposition of loess by solifluction, sheetwash, and gully formation may have been episodic and required conditions moister than those under which the loess initially accreted.

Alaska↗

USGS1995

Stratigraphic and structural synthesis of a Miocene extensional terrane, southeast California and west-central Arizona

Detailed stratigraphy and isotopic dating of stratigraphic sections in the Colorado River extensional corridor support a regional correlation of highly faulted Tertiary stratigraphic sequences and provide a chronologic framework for interpreting the evolution of low-angle normal (detachment) faults. On the basis of this correlation, we define six tilting domains in the upper plate of the Whipple, Chemehuevi, and Rawhide detachment faults and identify three discrete episodes of detachment faulting that began in the early Miocene and ended in middle Miocene time. Episodes of rapid detachment faulting are indicated by extreme tilting of upper-plate fault blocks and overlying Miocene sequences, fanning dips of basinal deposits, and angular unconformities that represent short time gaps in the accumulation of syntectonic sequences. During the first episode of detachment faulting at about 20 Ma, the upper plate segmented to form the domains. Basin subsidence and extreme tilting of upper-plate fault blocks and syntectonic deposits characterized the eastern Topock, Crossman, Aubrey, Parker Dam, and Buckskin-Rawhide domains, whereas the western Mopah domain was the site of abundant volcanic activity but no basins or tilting. A second episode of extension at about 18 Ma produced extreme tilts in the Buckskin-Rawhide domain but upper-plate blocks in the Mopah domain tilted moderately. A third regionwide faulting episode between 14 and 12 Ma was due to localized uplift of middle and lower crust and eventual exposure of the detachment faults and their footwalls. The upper-plate fault blocks responded passively to localized slip on the detachment faults. Rapid extension began on the Whipple-Chemehuevi detachment fault at 20 Ma and had shifted southward to the Buckskin-Rawhide detachment fault by 18 Ma; volcanic activity also shifted southward to the Buckskin-Rawhide domain at this time. The southward shift of rapid extension and volcanism probably represents buildup and release of strain at localized sites in the lower plate. Otherwise, stratigraphic and structural relations indicate that the locations of upper-plate basins, faulting and tilting of upper-plate blocks, and position of the breakaway zone remained stable throughout the major phases of extension.

Arizona, California↗

USGS1968

Geology, paleomagnetism, and potassium-argon ages of basalts from Nunivak Island, Alaska

Geologic mapping, paleomagnetic stratigraphy, and potassium-argon dating were used to determine the time and volume relations of tholeiitic and alkalic basalt on Nunivak Island in the Bering Sea near the coast of Alaska. Volcanism on Nunivak Island occurred in distinct episodes separated by quiet intervals that lasted from 1.6 to 0.6 m.y. During the past 6 m.y., tholeiitic basalt was erupted during at least five such episodes, and highly undersaturated alkalic basalt was erupted during at least three episodes. The oldest volcanic rock found on Nunivak Island is an alkalic basalt, succeeded by repeated alternations of tholeiitic and alkalic basalt. During the last episode of tholeiitic volcanism, 130 cu km of basalt erupted during a well-defined interval that lasted from 0.9 to 0.3 m.y. ago. A nearly contemporaneous eruption of alkalic basalt has continued vigorously to historic times and has covered the central part of the island with small cones, flows, and tephra from explosion craters. The volume of alkalic basalt of the latest episode of volcanic activity is from 0.7 to 2.0 percent of the volume of the associated tholeiite. At least one earlier eruption of alkalic basalt occurred in close association with the eruption of tholeiite. As on Hawaii, the highly undersaturated alkalic basalts on Nunivak contain abundant ultramafic inclusions.

Alaska↗

USGS2005

Evidence for New Madrid earthquakes in A.D. 300 and 2350 B.C

Six episodes of earthquake-induced liquefaction are associated with soil horizons containing artifacts of the Late Archaic (3000-500 B.C.) and Early to Middle Woodland (500 B.C.-A.D. 400) cultural periods at the Burkett archaeological site in the northern part of the New Madrid seismic zone, where little information about prehistoric earthquakes has been available. Radiocarbon dating of organic material and analysis of artifacts are used to estimate the ages of the liquefaction features and times of the causative earthquakes. The most recent episode of liquefaction occurred after A.D. 1670, produced small sand dikes, and is probably related to the 1895 Charleston, Missouri earthquake. The preceding episode struck the area in A.D. 300 ± 200 years and generated a sand blow that contains Late Woodland artifacts and buries an Early to Middle Woodland cultural horizon. Four older episodes of liquefaction occurred in 2350 B.C. ± 200 years and may have been produced by a sequence of closely timed earthquakes. The four earlier episodes produced graben structures, sand dikes, and associated sand blows on which a cultural mound was constructed. The Burkett liquefaction features that formed about 2350 B.C. and A.D. 300 are relatively large and similar in age to other liquefaction features in northeastern Arkansas and southeastern Missouri, respectively. If the prehistoric features at the Burkett site and those of similar age elsewhere in the region are the result of the same earthquakes, then this suggests that they were similar in size to the three largest (M 7-8) 1811-1812 New Madrid earthquakes. A New Madrid-type earthquake in A.D. 300 ± 200 years would support an average recurrence time of 500 years. Although this study extends the earthquake chronology back to 2500 B.C., it is uncertain that the record of New Madrid events is complete for the period between 2350 B.C. and A.D. 300. As demonstrated by this study, information about other prehistoric earthquakes may be buried beneath fluvial deposits of the Mississippi River Valley.

Arkansas, Illinois, Kentucky, Missouri, Tennessee↗

USGS1994

Evolution of volcanic rocks and associated ore deposits in the Marysvale volcanic field, Utah

A geological account on the igneous activity and associated mineral deposition in the volcanic field of Marysvale in Utah is presented. Three episodes (34-22 Ma, 22-14 Ma and 9-5 Ma) involved in the volcanic rock eruption and associated mineralization are described. The first episode is believed to have occurred during the time of tectonic convergence when two contrasting suites of rocks, Mount Dutton Formation and Bullion Canyon Volcanics, erupted concurrently. Mineralization during this period was sparse. In the second episode, change from intermediate to bimodal volcanism occurred. During the third episode, basaltic compositions did not change. Although major element constituent had rhyolites similar to that of the second episode, rhyolites had a marked radiogenic isotope characteristic difference.

Utah↗

USGS1987

Geology of the Wadi Ash Shu'bah Quadrangle, Sheet 26 E, Kingdom of Saudi Arabia

The Wadi Ash Shu'bah quadrangle, located in the north-central part of the Arabian Shield, is underlain by nine Precambrian volcano-sedimentary formations and a wide compositional range of Precambrian intrusive rocks. Late Proterozoic to early Paleozoic rocks of the Jibalah Group crop out in the southwestern part of the quadrangle. Paleozoic and younger units are limited to the early Paleozoic Siq Sandstone that crops out in the northwestern part of the quadrangle and small outcrops of Cenozoic basalt and unconsolidated Quaternary sediments. The Hulayfah group, dated at older than 738 Ma, is the oldest volcano-sedimentary unit in the quadrangle and consists of metamorphosed basaltic to andesitic volcanic and subvolcanic rock, and interbedded limestone, sandstone, and silicic volcanic rock. The Maraghan formation is composed of strongly folded, fine-grained sedimentary rock that was deposited between 677 and 621 Ma. The Hadn and Hibshi formations are composed of rhyolitic to rhyodacitic volcanic rock and interbedded continental sedimentary rock that were deposited between 651 and 600 Ma, but are inferred to postdate the Maraghan formation because they are significantly less deformed. Andesitic flows and volcanic breccia in the southeast corner of the quadrangle are mapped as the Jurdhawiyah group; these rocks unconformably overlie the Maraghan formation. The Zarghat formation is a thick sequence of interbedded sedimentary rock and silicic volcanic rock, and unconformably overlies the Hadn formation. It is inferred to have been deposited between 600 and 580 Ma. The Precambrian igneous rocks are organized into four tentative magmatic episodes. Greenstone of the Hulayfah group and dioritic intrusive rocks represent the oldest episode, and are believed to have formed in an ensimatic magmatic arc environment. These rocks were intruded during a second magmatic episode by post-Hulayfah monzogranite and granodiorite. A still younger, post-Hadn magmatic episode is represented by alkali-feldspar granite and syenogranite. The most recent magmatic episode is represented by small diabase and gabbro intrusions that are inferred to have been emplaced during a period of crustal rifting coincident with the deposition of the Jibalah group. The magnesite deposit near the village of Zarghat is the most significant mineral deposit in the quadrangle. However, the Hulayfah group has the most potential for metallic deposits in the area as it contains numerous gossans and ancient mine workings.

Open-File Report↗

USGS1989

Distribution, facies, ages, and proposed tectonic associations of regionally metamorphosed rocks in northern Alaska

Approximately half of the exposed bedrock in northern Alaska has been regionally metamorphosed. The most widespread metamorphic episode that affected northern Alaska occurred under low-grade, initially high-pressure (blueschist-facies) conditions during Mesozoic time. This episode is thought to have been related to the obduction of one or more oceanic terranes onto the continental margin of North America. Rocks whose metamorphism is considered to have been part of this major episode have an aerial distribution of approximately 10,000 km 2 in the southern Brooks Range, 5,000 km 2 across much of the Seward Peninsula, and 800 km 2 in the Ruby geanticline within the southeastern borderlands of the Yukon-Koyukuk basin. In the southern Brooks Range and on the Seward Peninsula, continental rocks experienced a clockwise pressure-temperature path that evolved during Middle Jurassic to late Early Cretaceous time from the low- to high-temperature subfacies of the blueschist facies and, finally, due to decreasing pressure, evolved to the greenschist facies. Metamorphism in the southern Brooks Range was associated with north-vergent compression along a south-dipping subduction zone that emplaced the oceanic rocks of the Angayucham terrane (represented by klippen of ultramafic rocks and prehnite-pumpellyite-facies metabasite, metatuff, metachert, and metasedimentary rocks) onto the continental margin. The present structural and metamorphic relation between the continental blueschistand greenschist-facies rocks and the structurally overlying lower temperature and pressure oceanic prehnite-pumpellyite-facies rocks to the south indicates that postmetamorphic or late metamorphic down-to-the-south, low-angle extensional faulting has dismembered the upper plate and removed much of the section that originally buried the blueschists. High-pressure metamorphism on the Seward Peninsula probably had a similar origin to that in the southern Brooks Range, but remnants of the overriding plate have not been identified, and the mechanism (such as left-lateral strike-slip faulting or oroclinal bending) by which the high-pressure rocks in the two areas were separated is not known. A significant difference between the thermal histories of these two metamorphic belts also is enigmatic: low-grade metamorphism on the Seward Peninsula was followed by intermediate-pressure amphibolite-facies and, locally, granulite-facies metamorphism as well as plutonism in mid-Cretaceous time, but no such high-temperature events have been documented within the high-pressure belt of the southern Brooks Range. In the Ruby geanticline, glaucophane, attesting to high-pressure metamorphism, is sporadically developed both within the continental rocks of the lower plate and, less commonly, near the base of the overlying oceanic thrust sheets. The direction from which the oceanic rocks were thrust and determination of which oceanic sheets were involved is unclear. Although the majority of the metamorphic episodes that affected northern Alaska occurred during the Mesozoic, older episodes have been documented or are suspected in a few areas. Late Proterozoic medium-grade metamorphism has been documented in a small area in the southwestern Brooks Range, Middle to Late Proterozoic or early Paleozoic metamorphism just south of the Ruby geanticline, and middle Paleozoic metamorphism in the eastern Brooks Range. High-temperature, high-pressure metamorphism of klippen in the Yukon-Tanana upland is tentatively considered to have occurred in early Paleozoic time. Metamorphic ages of units in several areas, particularly in the Ruby geanticline and the Yukon-Tanana upland, can be bracketed only between the probable Paleozoic age of their protoliths and the late Early Cretaceous age of postmetamorphic granitoids that intrude them.

Alaska↗

USGS2004

Eruptive history and chemical evolution of the precaldera and postcaldera basalt-dacite sequences, Long Valley, California: Implications for magma sources, current seismic unrest, and future volcanism

The Long Valley Volcanic Field in east-central California straddles the East Sierran frontal fault zone, overlapping the Sierra Nevada and western Basin and Range Provinces. The volcanic field overlies a mature mid-Tertiary erosional surface that truncates a basement composed mainly of Mesozoic plutons and associated roof pendants of Mesozoic metavolcanic and Paleozoic metasedimentary rocks. Long Valley volcanism began about 4 Ma during Pliocene time and has continued intermittently through the Holocene. The volcanism is separable into two basalt-rhyolite episodes: (1) an earlier, precaldera episode related to Long Valley Caldera that climaxed with eruption of the Bishop Tuff and collapse of the caldera; and (2) a later, postcaldera episode structurally related to the north-south-trending Mono-Inyo Craters fissure system, which extends from the vicinity of Mammoth Mountain northward through the west moat of the caldera to Mono Lake. Eruption of the basalt-dacite sequence of the precaldera basalt-rhyolite episode peaked volumetrically between 3.8 and 2.5 Ma; few basalts were erupted during the following 1.8 m.y. (2.5–0.7 Ma). Volcanism during this interval was dominated by eruption of the voluminous rhyolites of Glass Mountain (2.2–0.8 Ma) and formation of the Bishop Tuff magma chamber. Catastrophic rupture of the roof of this magma chamber caused eruption of the Bishop Tuff and collapse of Long Valley Caldera (760 ka), after which rhyolite eruptions resumed on the subsided caldera floor. The earliest postcaldera rhyolite flows (700–500 ka) contain quenched globular basalt enclaves (mafic magmatic inclusions), indicating that basaltic magma had reentered shallow parts of the magmatic system after a 1.8-m.y. hiatus. Later, at about 400 ka, copious basalts, as well as dacites, began erupting from vents mainly in the west moat of the caldera. These later eruptions initiated the postcaldera basalt-rhyolite episode related to the Mono-Inyo Craters fissure system, which has been active through late Pleistocene and Holocene time.

California↗

USGS2018

Characterization of water quality in Bushy Park Reservoir, South Carolina, 2013–15

The Bushy Park Reservoir is the principal water supply for 400,000 people in the greater Charleston, South Carolina, area, which includes homes as well as businesses and industries in the Bushy Park Industrial Complex. Charleston Water System and the U.S. Geological Survey conducted a cooperative study during 2013–15 to assess the circulation of Bushy Park Reservoir and its effects on water-quality conditions, specifically, recurring taste-and-odor episodes. This report describes the water-quality data collected for the study that included a combination of discrete water-column sampling at seven locations in the reservoir and longitudinal water-quality profiling surveys of the reservoir and tributaries to characterize the temporal and spatial water-quality dynamics of Bushy Park Reservoir. Water-quality profiling surveys were conducted with an autonomous underwater vehicle equipped with a multiparameter water-quality-sonde bulkhead. Data collected by the autonomous underwater vehicle included water temperature, dissolved oxygen, pH, specific conductance, turbidity, total chlorophyll as fluorescence (estimate of algal biomass), and phycocyanin as fluorescence (estimate of cyanobacteria biomass) data. Characterization of the water-quality conditions in the reservoir included comparison to established State nutrient guidelines, identification of any spatial and seasonal variation in water-quality conditions and phytoplankton community structures, and assessment of the degree of influence of water-quality conditions related to Foster Creek and Durham Canal inflows, especially during periods of elevated taste-and-odor concentrations. Depth-profile and autonomous underwater vehicle survey data were used to identify areas within the reservoir where greater phytoplankton and cyanobacteria densities were most likely occurring. Water-quality survey results indicated that Bushy Park Reservoir tended to stratify thermally at a depth of about 20 feet from June to early October. The stratification was limited to the deeper portions of the reservoir near the dam and often dissipated within the reservoir near the CWS intake less than a mile upstream from the dam. Where thermally stratified, a corresponding depletion of dissolved oxygen also occurred at about the same depth and resulted in an anoxic hypolimnion below the 25-foot depth and an increase in specific conductance, likely due to re-mobilized metals and phosphorus under reducing conditions. In general, chlorophyll estimated from fluorescence exhibited some spatial variation, but no strong consistent pattern or “hot spot” was observed. Phycocyanin, estimated from relative fluorescence unit output as blue-green algae cell density, periodically seemed to be greater in the upper portion of the reservoir, but those differences may be attributed to increased turbidity and the potential change in phytoplankton community structure that affects fluorescence. Increased phycocyanin was observed at about the 10-foot depth during the summer months. A constant production of 2-methylisoborneol (MIB) near the dam and geosmin in the middle and upper portions of the reservoir appears to be occurring during the summer and early fall in the reservoir, but concentrations of these compounds tend to be between 10 and 15 nanograms per liter, which is at the Charleston Water System treatment threshold. At the Bushy Park Reservoir intake, the dominant taste-and-odor compound tended to be MIB, measured at a 2- or 3-to-1 ratio with geosmin during the summer and fall. During springtime episodes, however, when taste-and-odor compound concentrations typically are elevated above the Charleston Water System treatment threshold, the spatial distribution of geosmin concentrations greater than 15 nanograms per liter (28 to 38 nanograms per liter) was best explained by in situ production in the lower portion of the Bushy Park Reservoir near the dam rather than transport from Foster Creek. This pattern seems to indicate a possible shift in phytoplankton communities (or, at least, cyanobacteria communities) from MIB producers to geosmin producers. The spatial and seasonal assessment of water-quality conditions in Bushy Park Reservoir identified seasonal differences in water chemistry and spatial differences between the upper and lower portions of the reservoir that correspond to the location of elevated geosmin concentrations. On the basis of the spatial and seasonal assessment of actinomycetes concentrations compared to taste-and-odor compound concentrations, cyanobacteria production likely was the dominant source of the taste-and-odor episodes rather than actinomycetes. The lack of spatial and seasonal patterns in actinomycetes concentrations did not correspond to the springtime geosmin concentrations that were elevated above the Charleston Water System treatment threshold in the lower portion of the reservoir. Additionally, actinomycetes concentrations, although ubiquitous, had a median of about 9 and maximum of about 20 colonies per milliliter, which can be considered low for elevated taste-and-odor compound production. Nonetheless, the potential exists for actinomycetes to be a secondary source of taste-and-odor production and could explain some of the ubiquitous occurrence of low-level taste-and-odor production, such as MIB concentrations, observed throughout the summer and early fall months. When evaluated by biovolume, cyanobacteria were not the dominant phytoplankton group in Bushy Park Reservoir during the study period. Dolichospermum planctonicum (previously Anabaena planktonica ) was the dominant genera of the cyanobacteria group during spring periods. The geosmin-producing genera that were identified in the 2014 and 2015 spring communities in Bushy Park Reservoir were not observed in the 1999 and 2000 algal taxonomic data. A more robust examination of phytoplankton species was conducted by using a multivariate analysis that identified seasonal changes in phytoplankton community structure. These seasonal phytoplankton communities appeared to be explained by seasonal changes in water chemistry and may be responsible for episodes of taste-and-odor occurrence, especially geosmin. The most probable source of geosmin identified during the study was D. planctonicum . In a synoptic sampling event during a taste-and-odor episode in April 2015, cyanobacteria, not acinomycetes, also was indicated to be the more prevalent source of the geosmin. Although the Edisto River intake and its associated supply tunnel to the treatment facility had relatively high actinomycetes concentrations (130 and 140 colonies per milliliter, respectively) compared to the Bushy Park intake and tunnel (2 colonies per milliliter), corresponding geosmin concentrations were below 5 nanograms per liter for source water from the Edisto River intake and tunnel. Elevated geosmin concentrations above the Charleston Water System treatment threshold were identified in source waters from the Bushy Park Reservoir. The cyanobacteria community at the sampled sites in April 2015 was statistically similar to the community in the Bushy Park Reservoir in April 2014, when geosmin concentrations also were elevated. The only geosmin-producing genus identified at the Bushy Park intake, however, was D. planctonicum .

South Carolina↗

USGS2019

Use of set blanks in reporting pesticide results at the U.S. Geological Survey National Water Quality Laboratory, 2001-15

Executive Summary Background .—Pesticide results from the U.S. Geological Survey (USGS) National Water Quality Laboratory (NWQL) are used for water-quality assessments by many agencies and organizations. The USGS is committed to providing data of the highest possible quality to the consumers of its data. A cooperator’s inquiries about specific pesticide detections in water revealed potential laboratory contamination issues for some results. Consequently, the USGS conducted an extensive evaluation of potential low-level contamination related to processing or analysis of water-quality samples at NWQL for 21 pesticide compounds of interest to the cooperator. This is the most comprehensive study of NWQL pesticide quality-control (QC) results to date. Purpose and scope .—The purpose of this study was to document protocols used by the NWQL to censor pesticide results and to determine the effects of laboratory contamination—as determined from detections in laboratory set blanks—on pesticide detections in groundwater and surface-water samples. More than 30,000 pesticide results from 113 selected batches of samples (2 percent or less of total batches) analyzed by the NWQL during the 15 years from 2001 to 2015 were reviewed. All laboratory results from the selected batches, including results from environmental (surface water and groundwater) and QC (set-blank, blind-blank, and blind-spike) samples, were evaluated. The study includes results for 21 pesticide compounds analyzed in groundwater and surface-water samples collected across the United States. Eleven pesticide compounds were analyzed by a gas chromatography/mass spectrometry method and 10 compounds by a liquid chromatography/mass spectrometry method. Objectives and methods .—The objectives of this study were to (1) determine the characteristics of laboratory contamination over time, (2) compare distributions of pesticide results in set blanks with distributions in environmental samples, (3) evaluate the potential for false-positive and false-negative reporting of results, and (4) evaluate the effects of reevaluating historical pesticide results using 2017 compound identification protocols on detections of pesticides in groundwater and surface-water samples. The 113 instrument batches selected for this study contained detections of one or more of the 21 pesticide compounds in set blanks or were among those batches with the highest pesticide detection frequencies in set blanks. As a result, the dataset for this study was targeted toward pesticides and batches with laboratory contamination. The objectives were addressed by statistically comparing environmental and set-blank results; computing moving averages of set-blank detection frequencies to identify periods of episodic contamination; and using summary statistics, tabular summaries, and graphical approaches, such as time-series plots and cumulative distribution functions. Results .— Objective 1 : Laboratory contamination, as determined by pesticide detections in set blanks, was found in 13 percent of set-blank results from the 113 targeted batches included in this study (as compared to 6 percent of set-blank results from all 7,620 batches analyzed during the study period). It is estimated that 92 percent of the laboratory contamination during the study period was episodic, meaning that it occurred during discrete periods of time. All 21 of the targeted pesticide compounds had periods of episodic contamination, with most episodes ranging in duration from about 1 to 8 months. The remaining 8 percent of laboratory contamination was random or from a known source (deterministic). Objective 2 : For some compounds, graphs of cumulative distribution functions of the entire distributions of set-blank and environmental samples overlap, suggesting that there is no difference in the distributions of the two types of samples. However, time-series graphs show that detections in set blanks often occur at different times (sometimes separated by years) than detections in environmental samples, indicating clear differences in those distributions, and indicating the importance of evaluating the timing of detections in all sample types. For most compounds detected in set-blank and environmental samples, detection frequencies were significantly greater in set blanks than in groundwater or surface-water samples ( p <0.05). There are several explanations for this finding, including that the 113 batches of samples chosen for this study targeted batches with detections in set blanks or that detections in set-blank samples were historically determined with less stringent identification criteria than for environmental samples (groundwater and surface-water samples). Objective 3 : The false-positive and false-negative rates from blind samples submitted during the study period by the USGS Quality Systems Branch generally were less than 1 and 5 percent, respectively, for the 21 pesticides. The only compound with a false-positive rate greater than 1 percent was flumetsulam (2.6 percent), indicating that there is a higher likelihood of flumetsulam being reported as a detection when it is not present in an environmental sample compared with the reporting of other compounds. Objective 4 : Altogether, for data in targeted batches, NWQL would have reported 0.1 percent of results from groundwater samples and 1.4 percent of results from surface-water samples differently if 2017 identification protocols were applied to historical pesticide results. In most of these cases, detections observed in historical results would change to nondetections. The small percentages of changes that would occur if historical data were reevaluated indicate that historical protocols used by the NWQL to identify detections in environmental samples were robust and produced results that are predominantly consistent with current [2017] practices. Conclusions .—The NWQL produces high-quality pesticide results at environmentally relevant concentrations. NWQL identification protocols and censoring practices are largely effective at minimizing the reporting of false-positive and false-negative results. Laboratory contamination, when it occurred, tended to occur in episodes; thus, evaluating the timing and magnitude of detections in set blanks relative to detections in environmental samples was determined to be an important consideration for analysis of environmental results. Because NWQL censoring practices do not address all types and occurrences of laboratory contamination, options for additional censoring practices are provided for data users with more specific or stringent data-quality objectives. The methods used to analyze the 21 compounds for this report can similarly be applied to all 173 pesticide compounds that were analyzed by the NWQL during the same time period. This study also has helped to identify potential improvements in reporting USGS data, such as conducting more frequent review of set-blank datasets.

Scientific Investigations Report↗

USGS1994

Effects of acid deposition on dissolution of carbonate stone during summer storms in the Adirondack Mountains, New York, 1987-89

This study is part of a long-term research program designed to identify and quantify acid rain damage to carbonate stone. Acidic deposition accelerates the dissolution of carbonate-stone monuments and building materials. Sequential sampling of runoff from carbonate-stone (marble) and glass (reference) microcatchments in the Adirondack Mountains in New York State provided a detailed record of the episodic fluctuations in rain rate and runoff chemistry during individual summer storms. Rain rate and chemical concentrations from carbonate-stone and glass runoff fluctuated three to tenfold during storms. Net calcium-ion concentrations from the carbonatestone runoff, a measure of stone dissolution, typically fluctuated twofold during these storms. High net sulfate and net calcium concentrations in the first effective runoff at the start of a storm indicated that atmospheric pollutants deposited on the stone surface during dry periods formed calcium sulfate minerals, an important process in carbonate stone dissolution. Dissolution of the carbonate stone generally increased up to twofold during coincident episodes of low rain rate (less than 5 millimeters per hour) and decreased rainfall (glass runoff) pH (less than 4.0); episodes of high rain rate (cloudbursts) were coincident with a rapid increase in rainfall pH and also a rapid decrease in the dissolution of carbonate-stone. During a storm, it seems the most important factors causing increased dissolution of carbonate stone are coincident periods of low rain rate and decreased rainfall pH. Dissolution of the carbonate stone decreased slightly as the rain rate exceeded about 5 millimeters per hour, probably in response to rapidly increasing rainfall pH during episodes of high rain rate and shorter contact time between the runoff and the stone surface. High runoff rates resulting from cloudbursts remove calcium sulfate minerals formed during dry periods prior to storms and also remove dissolution products formed in large measure by chemical weathering as a result of episodes of low rain rate and decreased rainfall pH during a storm.

Water-Resources Investigations Report↗

USGS1998

Mesoscale disturbance and ecological response to decadal climatic variability in the American Southwest

Ecological responses to climatic variability in the Southwest include regionally synchronized fires, insect outbreaks, and pulses in tree demography (births and deaths). Multicentury, tree-ring reconstructions of drought, disturbance history, and tree demography reveal climatic effects across scales, from annual to decadal, and from local (<102 km2) to mesoscale (104-106 km2). Climate-disturbance relations are more variable and complex than previously assumed. During the past three centuries, mesoscale outbreaks of the western spruce budworm (Choristoneura occidentalis) were associated with wet, not dry episodes, contrary to conventional wisdom. Regional fires occur during extreme droughts but, in some ecosystems, antecedent wet conditions play a secondary role by regulating accumulation of fuels. Interdecadal changes in fire-climate associations parallel other evidence for shifts in the frequency or amplitude of the Southern Oscillation (SO) during the past three centuries. High interannual, fire-climate correlations (r = 0.7 to 0.9) during specific decades (i.e., circa 1740-80 and 1830-60) reflect periods of high amplitude in the SO and rapid switching from extreme wet to dry years in the Southwest, thereby entraining fire occurrence across the region. Weak correlations from 1780 to 1830 correspond with a decrease in SO frequency or amplitude inferred from independent tree-ring width, ice core, and coral isotope reconstructions. Episodic dry and wet episodes have altered age structures and species composition of woodland and conifer forests. The scarcity of old, living conifers established before circa 1600 suggests that the extreme drought of 1575-95 had pervasive effects on tree populations. The most extreme drought of the past 400 years occurred in the mid-twentieth century (1942-57). This drought resulted in broadscale plant dieoffs in shrublands, woodlands, and forests and accelerated shrub invasion of grasslands. Drought conditions were broken by the post-1976 shift to the negative SO phase and wetter cool seasons in the Southwest. The post-1976 period shows up as an unprecedented surge in tree-ring growth within millennia-length chronologies. This unusual episode may have produced a pulse in tree recruitment and improved rangeland conditions (e.g., higher grass production), though additional study is needed to disentangle the interacting roles of land use and climate. The 1950s drought and the post-1976 wet period and their aftermaths offer natural experiments to study long-term ecosystem response to interdecadal climate variability.Ecological responses to climatic variability in the Southwest include regionally synchronized fires, insect outbreaks, and pulses in tree demography (births and deaths). Multicentury, tree-ring reconstructions of drought, disturbance history, and tree demography reveal climatic effects across scales, from annual to decadal, and from local (<102 km2) to mesoscale (104-106 km2). Climate-disturbance relations are more variable and complex than previously assumed. During the past three centuries, mesoscale outbreaks of the western spruce budworm (Choristoneura occidentalis) were associated with wet, not dry episodes, contrary to conventional wisdom. Regional fires occur during extreme droughts but, in some ecosystems, antecedent wet conditions play a secondary role by regulating accumulation of fuels. Interdecadal changes in fire-climate associations parallel other evidence for shifts in the frequency or amplitude of the Southern Oscillation (SO) during the past three centuries. High interannual, fire-climate correlations (r = 0.7 to 0.9) during specific decades (i.e., circa 1740-80 and 1830-60) reflect periods of high amplitude in the SO and rapid switching from extreme wet to dry years in the Southwest, thereby entraining fire occurrence across the region. Weak correlations from 1780 to 1830 correspond with a decrease in SO frequency or amplitude inferred from independent tree-ring width, ic

Journal of Climate↗

USGS2015

Renewed inflation of Long Valley Caldera, California (2011 to 2014)

Slow inflation began at Long Valley Caldera in late 2011, coinciding with renewed swarm seismicity. Ongoing deformation is concentrated within the caldera. We analyze this deformation using a combination of GPS and InSAR (TerraSAR-X) data processed with a persistent scatterer technique. The extension rate of the dome-crossing baseline during this episode (CA99 to KRAC) is 1 cm/yr, similar to past inflation episodes (1990–1995 and 2002–2003), and about a tenth of the peak rate observed during the 1997 unrest. The current deformation is well modeled by the inflation of a prolate spheroidal magma reservoir &sim;7 km beneath the resurgent dome, with a volume change of &sim;6 × 10 6  m 3 /yr from 2011.7 through the end of 2014. The current data cannot resolve a second source, which was required to model the 1997 episode. This source appears to be in the same region as previous inflation episodes, suggesting a persistent reservoir.

California↗

USGS2015

Delayed dynamic triggering of deep tremor along the Parkfield-Cholame section of the San Andreas Fault following the 2014 M6.0 South Napa earthquake

Large, distant earthquakes are known to trigger deep tectonic tremor along the San Andreas Fault and in subduction zones. However, there are relatively few observations of triggering from regional distance earthquakes. Here we show that a small tremor episode about 12–18 km NW of Parkfield was triggered during and immediately following the passage of surface waves from the 2014 M w 6.0 South Napa main shock. More notably, a major tremor episode followed, beginning about 12 h later, and centered SE of Parkfield near Cholame. This major episode is one of the largest seen over the past several years, containing intense activity for ~3 days and taking more than 3 weeks to return to background levels. This episode showed systematic along-strike migration at ~5 km/d, suggesting that it was driven by a slow-slip event. Our results suggest that moderate-size earthquakes are capable of triggering major tremor and deep slow slip at regional distances.

California↗

USGS2017

Buried soils in a perched dunefield as indicators of late holecene lake-level change in the Lake Superior basin

A stratigraphic analysis of buried soils within the Grand Sable Dunes, a dune field perched 90 m above the southern shore of Lake Superior, reveals a history of eolian activity apparently linked with lake-level fluctuations over the last 5500 yr. A relative rise in the water plane of the Nipissing Great Lakes initially destabilized the lakeward bluff face of the Grand Sable plateau between 5400 and 4600 14 C yr B.P. This led to the burial of the Sable Creek soil by eolian sediments derived from the bluff face. Subsequent episodes of eolian activity appear to be tied to similar destabilizing events; high lake levels may have initiated at least four and perhaps eleven episodes of dune building as expressed by soil burials within the dunes. Intervening low lake levels probably correlate with soil profile development, which varies from the well-developed Sable Creek Spodosol catena to thin organic layers containing in-place stumps and tree trunks. Paleoecological reconstructions available for the area do not imply enough climatic change to account for the episodic dune activity. Burial of soils by fine-fraction sediments links dune-building episodes with destabilization of the lower lake-facing bluff, which is rich in fines.

Michigan↗

USGS2021

Diatom record of holocene moisture variability in the San Bernardino Mountains, California, USA.

Lower Bear Lake, in the San Bernardino Mountains, contains a Holocene paleohydrology record for southern California. The diatom and sediment geochemistry record indicates that the region experienced a wet Early Holocene followed by a gradual decrease in precipitation, which was punctuated by four strong and five weak pluvial episodes. The Lower Bear Lake record is compared with that of Silver Lake, a Mojave River terminal lake with headwaters in the San Bernardino Mountains, which exhibited several pluvial events at roughly the same time. The comparison is extended to records in relative proximity to Bear Lake (Dry Lake, Lake Elsinore, and San Joaquin marsh) and to two lakes with headwaters in the Sierra Nevada (Tulare Lake and Owens Lake). All exhibit a wet Early and early Middle Holocene wet interval and gradual drying through the remainder of the Holocene but differ in the expression of the pluvial episodes observed at Lower Bear Lake. The pluvial episodes are likely the result of changes in the storm track that affects the frequency and magnitude of winter storms in the area. These episodes are controlled by complex oceanic and atmospheric interactions and may be the result of the synchronous interaction of several teleconnections.

California↗

USGS1991

Real-time Seismic Amplitude Measurement (RSAM): a volcano monitoring and prediction tool

Seismicity is one of the most commonly monitored phenomena used to determine the state of a volcano and for the prediction of volcanic eruptions. Although several real-time earthquake-detection and data acquisition systems exist, few continuously measure seismic amplitude in circumstances where individual events are difficult to recognize or where volcanic tremor is prevalent. Analog seismic records provide a quick visual overview of activity; however, continuous rapid quantitative analysis to define the intensity of seismic activity for the purpose of predicing volcanic eruptions is not always possible because of clipping that results from the limited dynamic range of analog recorders. At the Cascades Volcano Observatory, an inexpensive 8-bit analog-to-digital system controlled by a laptop computer is used to provide 1-min average-amplitude information from eight telemetered seismic stations. The absolute voltage level for each station is digitized, averaged, and appended in near real-time to a data file on a multiuser computer system. Raw realtime seismic amplitude measurement (RSAM) data or transformed RSAM data are then plotted on a common time base with other available volcano-monitoring information such as tilt. Changes in earthquake activity associated with dome-building episodes, weather, and instrumental difficulties are recognized as distinct patterns in the RSAM data set. RSAM data for domebuilding episodes gradually develop into exponential increases that terminate just before the time of magma extrusion. Mount St. Helens crater earthquakes show up as isolated spikes on amplitude plots for crater seismic stations but seldom for more distant stations. Weather-related noise shows up as low-level, long-term disturbances on all seismic stations, regardless of distance from the volcano. Implemented in mid-1985, the RSAM system has proved valuable in providing up-to-date information on seismic activity for three Mount St. Helens eruptive episodes from 1985 to 1986 (May 1985, May 1986, and October 1986). Tiltmeter data, the only other telemetered geophysical information that was available for the three dome-building episodes, is compared to RSAM data to show that the increase in RSAM data was related to the transport of magma to the surface. Thus, if tiltmeter data is not available, RSAM data can be used to predict future magmatic eruptions at Mount St. Helens. We also recognize the limitations of RSAm data. Two examples of RSAM data associated with phreatic or shallow phreatomagmatic explosions were not preceded by the same increases in RSAM data or changes in tilt associated with the three dome-building eruptions. ?? 1991 Springer-Verlag.

Bulletin of Volcanology↗

USGS2019

Temporal relationship between the Lassen Volcanic Center and mafic regional volcanism

Monogenetic volcanoes, distributed over large areas, contribute to the growth of monogenetic volcanic fields (MVFs) over thousands to millions of years of activity. It is now accepted that MVFs are also temporally clustered. To reduce uncertainties inherent to this episodic character, it is critical to combine multi-disciplinary studies to improve our knowledge of the temporal evolution of MVFs. The Lassen region, in the southern Cascades, is investigated to compare timing of eruptions at distributed mafic, intermediate, and silicic monogenetic volcanoes considering a new set of 40Ar/39Ar and K-Ar ages, complementing published radiometric ages for the area. Activity over the past 3.5 Ma has been episodic, alternating periods of intense and reduced activity as observed at other MVFs. More specifically, periods of intense regional mafic activity have occurred simultaneously to eruptive sequences at the silicic Lassen Volcanic Center (LVC). The back-arc Caribou Volcanic Field (CVF, ~800 – 15 ka) and forearc volcanoes, active simultaneously with the LVC, are characterized by eruptive sequences that persisted for 20 – 40 kyr, with the most recent eruptions occurring during the last glacial episode. Crater Mountain, a relatively young (282 - 395 ka) shield volcano spatially close to the CVF, confirms the presence of localized higher fluxes of mantle-derived melts that persisted for hundreds of thousand years in the back-arc region. Over the past 3.5 Ma, many small magma batches erupted simultaneously in short-lived episodes within clusters distributed across the Lassen region, including the LVC.

California, Oregon, Washington↗