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Research about Virginia

Source-linked reports with geographic coverage including Virginia.

At least 307 records · Page 17Linked to original sources
USGS2007

Post-middle Miocene origin of modern landforms in the eastern Piedmont of Virginia

Diverse late middle Miocene dinoflagellate floras, obtained from two sites along the western edge of the Atlantic Coastal Plain in central Virginia, indicate that the eastern Virginia Piedmont was covered by marine waters about 12-13 Ma. This transgression extended farther westward across the Virginia Piedmont than any other transgression that has been documented. Extensive fluvial deposits that may be associated with this transgression covered earlier stream patterns in the eastern Piedmont and buried them beneath a thin (probably less than 100 foot-thick) veneer of sand and gravel. During the subsequent regression, a linear down-slope stream-drainage pattern developed. Although it has been somewhat modified by later stream captures, it still is easily recognizable. This interval of marine inundation and deposition explains why modern stream patterns in the eastern Piedmont of Virginia strongly resemble the stream patterns in the Coastal Plain and differ from the structurally adjusted trellis stream patterns typical of the western Piedmont, Blue Ridge, and Valley and Ridge regions. Uplift of the modern Southern Appalachian Mountains began at the time of this transgression and was largely completed by the late Pliocene.

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USGS2007

Mystery solved: White deposit on streambeds proves to be diatoms

In the late winter and early spring of 2006 an unusual white deposit was observed on rocks and margins of streambeds in a number of park streams. Inquiries were made to park staff and scientists studying water resources in the park as to what the deposit was and did it pose any type of risk. A number of explanations were proposed, but it was not until samples were collected and examined with a scanning electron microscope that the identity of the deposit was definitively determined.

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USGS2006

Time series and recurrence interval models to predict the vulnerability of streams to episodic acidification in Shenandoah National Park, Virginia

Acid rain affects headwater streams by temporarily reducing the acid‐neutralizing capacity (ANC) of the water, a process termed episodic acidification. The increase in acidic components in stream water can have deleterious effects on the aquatic biota. Although acidic deposition is uniform across Shenandoah National Park (SNP) in north central Virginia, the stream water quality response during rain events varies substantially. This response is a function of the catchment's underlying geology and topography. Geologic and topographic data for SNP's 231 catchments are readily available; however, long‐term measurements (tens of years) of ANC and accompanying discharge are not and would be prohibitively expensive to collect. Transfer function time series models were developed to predict hourly ANC from discharge for five SNP catchments with long‐term water‐quality and discharge records. Hourly ANC predictions over short time periods (≤1 week) were averaged, and distributions of the recurrence intervals of annual water‐year minimum ANC values were model‐simulated for periods of 6, 24, 72, and 168 hours. The distributions were extrapolated to the rest of the SNP catchments on the basis of catchment geology and topography. On the basis of the models, large numbers of SNP streams have 6‐ to 168‐hour periods of low‐ANC values, which may stress resident fish populations. Smaller catchments are more vulnerable to episodic acidification than larger catchments underlain by the same bedrock. Catchments with similar topography and size are more vulnerable if underlain by less basaltic/carbonate bedrock. Many catchments are predicted to have successive years of low‐ANC values potentially sufficient to extirpate some species.

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USGS2006

Geo-botanical evidence of Late Quaternary mass wasting in block field areas of Virginia

Studies of block fields at Massanutten Mountain, Virginia, document and provide information on the magnitude and frequency of mass movement on these coarse-grained slopes. Although Pleistocene periglacial climate may have facilitated original formation of block fields, some block fields now continue to spread downslope during intense runoff events. Present block-field mass wasting may be the principal erosional process in these areas of resistant rock.

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USGS2006

Coincidence and spatial variability of geology, soils, and vegetation, Mill Run watershed, Virginia

The Mill Run watershed is a structurally‐controlled synclinal basin on the eastern limb of the Massanutten Mountain complex of northwestern Virginia. Bedrock contacts are obscured by coarse sandstone debris from exposures near basin divides. Colluvium blankets more than half the basin, masking geomorphic surfaces, affecting vegetation patterns, and contributing to the convexity of the alluvial, terrace, pediment and erosion surfaces. Examination of the bedrock geology, geomorphology, soils and vegetation shows distinct distributional correspondences. Vegetation is strongly interdependent with geomorphology, bedrock geology, and soils. On convex colluvial slopes, mixed hardwood forests are most common. In concave coves and deep gorges, mixed hardwoods are replaced by conifers. In thin colluvium, in poorly developed soils, and on blockfields, chestnut oak is singularly prevalent. Conifers dominate shaley bedrock areas. Soils and surficial sediments have a major effect on near‐surface hydrology. During wet seasons, cemented horizons in the subsurface cause temporary saturation in the superjacent horizons; lateral movement of soil‐water effectively eliminates a vertical component of ground‐water recharge. Vegetation is strongly dependent on water availability and thus reflects the distribution of subsurface barriers and sediment‐soil fades changes.

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USGS2006

The relationship between pH and community structure of invertebrates in streams of the Shenandoah National Park, Virginia

1. A replicated natural experiment was used to assess the influence of pH and low alkalinity on abundance and richness of invertebrate families in streams draining catchments that receive acid deposition. Individual streams were used as the unit of replication, allowing conclusions to refer to a class of streams rather than to particular streams. 2. We also controlled for several factors other than pH and alkalinity, including flow and temperature, that are recognized as determinants of invertebrate distribution. Samples were from indigenous rocks, standardized for size, surface area, and geology. 3. Repeated measures analyses of variance (ANOVA) revealed that invertebrate abundance and richness were significantly lower at pH 5.8 than at pH 7.1 for the total community. Thirty per cent of the forty‐seven families exhibited significantly lower abundance at pH 5.8; thirteen families were absent at pH 5.8. Differences were greatest for Ephemeroptera: species richness was significantly lower at pH 5.8, and 71% of the twenty‐four species were either absent (seven) or found in reduced abundance (ten) in the acidic streams. 4. Stream alkalinity is projected to continue to decrease with continued acid deposition in the Shenandoah National Park. Concurrent decreases in pH may lead to the absence or continued numerical decline of certain Ephemeroptera species in streams that acidify to less than pH 6.0 and/or 50μEql −1 alkalinity.

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USGS2006

Hurricane-induced landslide activity on an alluvial fan along Meadow Run, Shenandoah Valley, Virginia (eastern USA)

Although intense rainfall and localized flooding occurred as Hurricane Isabel tracked inland northwestardly across the Blue Ridge Mountains of central Virginia on September 18–19, 2003, few landslides occurred. However, the hurricane reactivated a dormant landslide along a bluff of an incised alluvial fan along Meadow Run on the western flanks of the Blue Ridge Mountains. Subsequent monitoring showed retrogressive movement involving several landslide blocks for the next several months. Using dendrochronology, aerial photography, and stream discharge records revealed periods of landslide activity. The annual variation of growth rings on trees within the landslide suggested previous slope instability in 1937, 1972, 1993, 1997, and 1999, which correlated with periods of local flood events. The avulsive and migrating nature of Meadow Run, combined with strong erosional force potential during flood stages, indicates that landslides are common along the bluff-channel bank interface, locally posing landslide hazards to relatively few structures within this farming region.

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USGS2006

Earthquakes in Virginia and vicinity 1774 - 2004

This map summarizes two and a third centuries of earthquake activity. The seismic history consists of letters, journals, diaries, and newspaper and scholarly articles that supplement seismograph recordings (seismograms) dating from the early twentieth century to the present. All of the pre-instrumental (historical) earthquakes were large enough to be felt by people or to cause shaking damage to buildings and their contents. Later, widespread use of seismographs meant that tremors too small or distant to be felt could be detected and accurately located. Earthquakes are a legitimate concern in Virginia and parts of adjacent States. Moderate earthquakes cause slight local damage somewhere in the map area about twice a decade on the average. Additionally, many buildings in the map area were constructed before earthquake protection was added to local building codes. The large map shows all historical and instrumentally located earthquakes from 1774 through 2004.

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USGS2006

Reconnaissance borehole geophysical, geological, and hydrological data from the proposed hydrodynamic compartments of the Culpeper Basin in Loudoun, Prince William, Culpeper, Orange, and Fairfax Counties, Virginia

The Culpeper basin is part of a much larger system of ancient depressions or troughs, that lie inboard of the Atlantic Coastal Plain, and largely within the Applachian Piedmont Geologic Province of eastern North America, and the transition region with the neighboring Blue Ridge Geologic Province. This basin system formed during an abortive attempt to make a great ocean basin during the Late Triassic and Early Jurassic, and the eroded remnants of the basins record major episodes of sedimentation, igneous intrusion and eruption, and pervasive contact metamorphism. Altogether, some twenty nine basins formed between what is now Nova Scotia and Georgia. Many of these basins are discontinuous along their strike, and have therefore recorded isolated environments for fluvial and lacustrine sedimentation. Several basins (including the Culpeper, Gettysburg, and Newark basins) are fault-bounded on the west, and Mesozoic crustal stretching has produced assymetrical patterns of basin subsidence resulting in a progressive basin deepening to the west, and a virtual onlap relationship with the pre-basin Proterozoic rocks to the east. A result of such a pattern of basin deepening is the development of sequences of sandstones and siltstones that systemmatically increase in dip towards the accomodating western border faults. A second major structural theme in several of the major Mesozoic basins (including the Culpeper) concerns the geometry of igneous intrusion, as discussed below. Froelich (1982, 1985) and Lee and Froelich (1989) discuss the general geology of the Culpeper basin, and Smoot (1989) discusses the sedimentation environments and sedimentary facies of the Mesozoic with respect to fluvial and shallow lacustrine deposition in the Culpeper basin. Ryan and others, 2007a, b, discuss the role of diabase-induced compartmentalization in the Culpeper basin (and other Mesozoic basins), and illustrate (using alteration mineral suites within the diabase and adjacent hornfels, among other evidence) how this process has played a role in organizing the paleo- and contemporary-flow of crustal fluids at local and regional scales. Within this report, the Newark Supergroup nomenclature of Weems and Olsen (1997) is adopted.

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USGS2006

The Virginia Coastal Plain hydrogeologic framework

A refined descriptive hydrogeologic framework of the Coastal Plain of eastern Virginia provides a new perspective on the regional ground-water system by incorporating recent understanding gained by discovery of the Chesapeake Bay impact crater and determination of other geological relations. The seaward-thickening wedge of extensive, eastward-dipping strata of largely unconsolidated sediments is classified into a series of 19 hydrogeologic units, based on interpretations of geophysical logs and allied descriptions and analyses from a regional network of 403 boreholes. Potomac aquifer sediments of Early Cretaceous age form the primary ground-water supply resource. The Potomac aquifer is designated as a single aquifer because the fine-grained interbeds, which are spatially highly variable and inherently discontinuous, are not sufficiently dense across a continuous expanse to act as regional barriers to ground-water flow. Part of the Potomac aquifer in the outer part of the Chesapeake Bay impact crater consists of megablock beds, which are relatively undeformed internally but are bounded by widely separated faults. The Potomac aquifer is entirely truncated across the inner part of the crater. The Potomac confining zone approximates a transition from the Potomac aquifer to overlying hydrogeologic units. New or revised designations of sediments of Late Cretaceous age that are present only south of the James River include the upper Cenomanian confining unit, the Virginia Beach aquifer and confining zone, and the Peedee aquifer and confining zone. The Virginia Beach aquifer is a locally important ground-water supply resource. Sediments of late Paleocene to early Eocene age that compose the Aquia aquifer and overlying Nanjemoy-Marlboro confining unit are truncated along the margin of the Chesapeake Bay impact crater. Sediments of late Eocene age compose three newly designated confining units within the crater, which are from bottom to top, the impact-generated Exmore clast and Exmore matrix confining units, and the Chickahominy confining unit. Piney Point aquifer sediments of early Eocene to middle Miocene age overlie most of the Chesapeake Bay impact crater and beyond, but are a locally significant ground-water supply resource only outside of the crater across the middle reaches of the Northern Neck, Middle, and York-James Peninsulas. Sediments of middle Miocene to late Miocene age that compose the Calvert confining unit and overlying Saint Marys confining unit effectively separate the underlying Piney Point aquifer and deeper aquifers from overlying shallow aquifers. Saint Marys aquifer sediments of late Miocene age separate the Calvert and Saint Marys confining units across two limited areas only. Sediments of the Yorktown-Eastover aquifer of late Miocene to late Pliocene age form the second most heavily used ground-water supply resource. The Yorktown confining zone approximates a transition to the overlying late Pliocene to Holocene sediments of the surficial aquifer, which extends across the entire land surface in the Virginia Coastal Plain and is a moderately used supply. The Yorktown-Eastover aquifer and the eastern part of the surficial aquifer are closely associated across complex and extensive hydraulic connections and jointly compose a shallow, generally semiconfined ground-water system that is hydraulically separated from the deeper system. Vertical faults extend from the basement upward through most of the hydrogeologic units but may be more widespread and ubiquitous than recognized herein, because areas of sparse boreholes do not provide adequate spatial control. Hydraulic conductivity probably is decreased locally by disruption of depositional intergranular structure by fault movement in the generally incompetent sediments. Localized fluid flow in open fractures may be unique in the Chickahominy confining unit. Some hydrogeologic units are partly to wholly truncated where displacements are large relative to unit thickness, resulting in lateral flow barriers or flow conduits. The tops of the Saint Marys confining unit, YorktownEastover aquifer, and Yorktown confining zone are widely sculpted by erosion that reflects both the present-day topography and buried paleochannels. Fault displacements across the top surfaces of these hydrogeologic units probably have been beveled by erosion. Additionally, erosion has modified the margins of many hydrogeologic units by truncation along the valleys of major rivers and their tributaries, beneath which underlying hydrogeologic units are incised. As a result, the surficial aquifer is in contact with a “patchwork” of underlying hydrogeologic units that create a complex array of hydraulic connections between the confined and unconfined ground-water systems.

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USGS2006

Predicting the vulnerability of streams to episodic acidification and potential effects on aquatic biota in Shenandoah National Park, Virginia

Acidic deposition is one of the most serious environmental problems affecting Shenandoah National Park in north-central Virginia. The park is the third most contaminated park in the National Park System because of the deposition of acid rain. Acid rain affects headwater streams in the park by temporarily reducing the acid-neutralizing capacity (ANC) of the water, a process termed episodic acidification. In turn, the increase in acidic components in streamwater can have deleterious effects on the aquatic biota. Although acidic deposition to the park is relatively uniform across its land area, the water-quality response of streamwater during rain events varies substantially. This response is a function of the underlying geology and topographic attributes of watersheds. Geologic and topographic data for the park's 231 watersheds are readily available; however, long-term (years and tens of years) measurements of streamwater ANC and accompanying discharge are not and would be prohibitively expensive to collect. Modeled predictions of the vulnerability of the park's streams to episodic acidification are an alternative to long-term water-quality monitoring. These predictions can aid park officials in making management decisions.

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USGS2006

The effects of the Chesapeake Bay impact on calcareous nannofossil assemblages: patterns from the Watkins School core, Newport News, Virginia (USA)

The goal of this study was to assess the effect that the Late Eocene Chesapeake Bay bolide impact had on local patterns of calcareous nannofossil species composition, richness and preservation. Although calcareous nannofossil assemblages have been described from a handful of coreholes drilled within the impact structure, this is the first study to examine the calcareous nannofossils from the Watkins School core , which was recovered along the outer rim of the crater. A detailed stratigraphic assessment of the calcareous nannofossil assemblages across the synimpact-postimpact boundary was performed to determine whether the impact produced any local extinction. The results obtained suggest that, despite its size, the Chesapeake Bay impact did not significantly affect the local calcareous nannoplankton community. Little or no change was documented across the synimpact-postimpact boundary in calcareous nannofossil species composition, richness or preservation quality. These findings do not support the existence of a calcareous nannofossil 'dead zone' in this particular core; however, the presence of impact-fractured calcareous nannofossils does attest to the tremendous pressures generated by the impact.

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USGS2005

Effectiveness of a confinement strategy for reducing campsite impacts in Shenandoah National Park

The expansion and proliferation of backcountry campsites is a persistent problem in many parks and protected areas. Shenandoah National Park (SNP) has one of the highest backcountry overnight use densities in the USA national parks system. SNP managers implemented a multi-option backcountry camping policy in 2000 that included camping containment with established campsites. These actions were intended to reduce the number of campsites and the area of camping disturbance at each site. This paper describes a longitudinal adaptive management assessment of the new campsite policies, applying quantitative measures of campsite conditions to evaluate the efficacy of management interventions. Physical campsite measurements combined with qualitative visitor interviews indicated SNP had successfully reduced the number of campsites and aggregate measures of camping-related disturbance in the Park, while minimizing the use of regulations, site facilities and staff resources. Implications for managers of other protected areas are that an established site camping policy can minimize camping disturbance, including the number and size of campsites, provided managers can sustain rehabilitation efforts to close and restore unneeded campsites. Experiential attributes, such as the potential for solitude, can also be manipulated through control over the selection of established campsites. Integrating resource and social science methods also provided a more holistic perspective on management policy assessments. Adaptive management research provided a timely evaluation of management success while facilitating effective modifications in response to unforeseen challenges. Conclusions regarding the effectiveness of a visitor impact containment strategy involving an established site camping option are offered.

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USGS2005

Stream salamander species richness and abundance in relation to environmental factors in Shenandoah National Park, Virginia

Stream salamanders are sensitive to acid mine drainage and may be sensitive to acidification and low acid neutralizing capacity (ANC) of a watershed. Streams in Shenandoah National Park, Virginia, are subject to episodic acidification from precipitation events. We surveyed 25 m by 2 m transects located on the stream bank adjacent to the water channel in Shenandoah National Park for salamanders using a stratified random sampling design based on elevation, aspect and bedrock geology. We investigated the relationships of four species ( Eurycea bislineata , Desmognathus fuscus , D. monticola and Gyrinophilus porphyriticus ) to habitat and water quality variables. We did not find overwhelming evidence that stream salamanders are affected by the acid-base status of streams in Shenandoah National Park. Desmognathus fuscus and D. monticola abundance was greater both in streams that had a higher potential to neutralize acidification, and in higher elevation (>700 m) streams. Neither abundance of E. bislineata nor species richness were related to any of the habitat variables. Our sampling method preferentially detected the adult age class of the study species and did not allow us to estimate population sizes. We suggest that continued monitoring of stream salamander populations in SNP will determine the effects of stream acidification on these taxa.

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USGS2005

The stability of chlorofluorocarbons (CFCs) in ground-water samples archived in borosilicate ampoules

The U.S. Geological Survey (USGS) Chlorofluorocarbon (CFC) Laboratory in Reston, Va., has been measuring concentrations of CFCs in ground-water samples since 1989 to estimate the year that a water sample was recharged to a ground-water flow system. The water samples have been collected in flame-sealed borosilicate ampoules. Typically for each site, three samples were analyzed within days to a few months after collection, and additional samples were archived for extended periods of time (up to four years). The stability of CFC concentrations in the archived water samples from the USGS CFC Laboratory was investigated by analyzing the CFC concentrations in archived water samples and comparing them with the CFC concentrations that were obtained soon after the samples were collected. The archived samples selected for analysis were chosen from sites with a wide variety of hydrogeologic and geochemical conditions. For CFC-11 and CFC-12 concentrations, approximately 14% and 10.5%, respectively, of the archived samples were statistically different (both higher and lower) from the concentrations obtained from analyses conducted soon after the sample collection. Most of the extraneous values were attributed to natural variability of CFC concentrations originally in the water discharged from wells, rather than to microbial degradation within the ampoule on storage.

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USGS2005

Water-quality data from ground- and surface-water sites near concentrated animal feeding operations (CAFOs) and non-CAFOs in the Shenandoah Valley and eastern shore of Virginia, January-February, 2004

Concentrated animal feeding operations (CAFOs) result from the consolidation of small farms with animals into larger operations, leading to a higher density of animals per unit of land on CAFOs than on small farms. The density of animals and subsequent concentration of animal wastes potentially can cause contamination of nearby ground and surface waters. This report summarizes water-quality data collected from agricultural sites in the Shenandoah Valley and Eastern Shore of Virginia. Five sites, three non-CAFO and two dairy-operation CAFO sites, were sampled in the Shenandoah Valley. Four sites, one non-CAFO and three poultry-operation CAFO sites were sampled on the Eastern Shore. All samples were collected during January and February 2004. Water samples were analyzed for the following parameters and constituents: temperature, specific conductance, pH, and dissolved oxygen; concentrations of the indicator organisms Escherichia coli ( E. coli ) and enterococci; bacterial isolates of E. coli , enterococci, Salmonella spp., and Campylobacter spp.; sensitivity to antibiotics of E. coli , enterococci, and Salmonella spp.; arsenic, cadmium, chromium 3+ , copper, nickel, and mercury; hardness, biological oxygen demand, nitrate, nitrite, ammonia, ortho-phosphate, total Kjeldahl nitrogen, chemical oxygen demand, total organic carbon, and dissolved organic carbon; and 45 dissolved organic compounds, which included a suite of antibiotic compounds. Data are presented in tables 5-21 and results of analyses of replicate samples are presented in tables 22-28. A summary of the data in tables 5-8 and 18-21 is included in the report.

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