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At least 1,585 records · Page 88Linked to original sources
USGS2011

Hydrologic conditions and terrestrial laser scanning of post-firedebris flows in the San Gabriel Mountains, CA, U.S.A

To investigate rainfall-runoff conditions that generate post-wildfire debris flows, we instrumented and surveyed steep, small watersheds along the tectonically active front of the San Gabriel Mountains, California. Fortuitously, we recorded runoff-generated debris-flows triggered by one spatially restricted convective event with 28 mm of rainfall falling over 62 minutes. Our rain gages, nested hillslope overland-flow sensors and soil-moisture probes, as well as a time series of terrestrial laser scanning (TLS) revealed the effects of the storm. Hillslope overland-flow response, along two ~10-m long flow lines perpendicular to and originating from a drainage divide, displayed only a 10 to 20 minute delay from the onset of rainfall with accumulated totals of merely 5-10 mm. Depth-stratified soil-moisture probes displayed a greater time delay, roughly 20- 30 minutes, indicating that initial overland flow was Hortonian. Furthermore, a downstream channel-monitoring array recorded a pronounced discharge peak generated by the passage of a debris flow after 18 minutes of rainfall. At this time, only four of the eleven hillslope overland flow sensors confirmed the presence of surface-water flow. Repeat TLS and detailed field mapping using GPS document how patterns of rainsplash, overland-flow scour, and rilling contributed to the generation of metter-scale debris flows. In response to a single small storm, the debris flows deposited irregular levees and lobate terminal snouts on hillslopes and caused wide- spread erosion of the valley axis with ground surface lowering exceeding 1.5 m.

California↗
USGS2007

Effects of invasive plant species on pollinator service and reproduction in native plants at Acadia National Park

Invasive plant species can have profound negative effects on natural communities by competively excluding native species. Berberis thunbergii (Japanese barberry), Frangula alnus (glossy or alder buckthorn) and Lythrum salicaria (purple loosestrife) are invasive species known to reduce native plant diversity and are thus of great concern to Acadia National Park. Pollinators visit them for nectar and pollen. The effects of invasive plant species on pollinator behavior were investigated by comparing pollinator visitation to co-flowering native and invasive species with visitation to native species growing alone. The effect of invasives on pollination of native plants was studied by comparing fruit set in patches of the native species growing near invasives with patches far from invasive species in Acadia National Park. The coflowering pairs were as follows: in the spring native Vaccinium angustifolium (lowbush blueberry) was paired with B. thunbergii; in early summer native Viburnum nudum (wild raisin) was paired with F. alnus ; in late summer native Spiraea alba (meadowsweet) was paired with L. salicaria. We investigated whether these invasives competed with native plants for pollinators in Acadia and thus negatively affected native plant reproduction. Our objectives were to determine: 1) the influence, if any, of each invasive on pollinator visitation to a co-flowering native species, 2) factors that might affect visitation, 3) invasive pollen transfer to native plants, and 4) whether invasives influence native plant reproduction (fruit set). Our findings indicate that at times the number of flower visitors to natives was lower or the species composition of visitors different when invasives were present, that invasives sometimes attracted more pollinators, that generally the invasives were more rewarding as far as nectar and pollen availability for pollinators, and that generally native plant fruit set and seed set was not significantly lowered in the presence of the invasive. In fact, in one year fruit set of S. alba was significantly greater in the presence of L. salicaria. The number of invasive pollen grains on native stigmas was extremely low; on average less than one grain per stigma. These fruit set and pollen deposition findings indicate that native plant reproduction was not adversely affected in the short term by these invasive species and that therefore competition between the native and invasive species for pollinators did not occur. Native bee populations monitored in 2004-2005 at sites with and without B. thunbergii and/or F. alnus indicated a greater abundance of native bees at sites with these invasives present. Native bees collected from the native and invasive plants were compared with historical records to assess whether invasive plants favor different bee species than those that formerly predominated on Mount Desert Island. This does not appear to be the case. Several species of bumble bees (Bombus spp.) as well as nine solitary bee species were found that were not documented by the Procter surveys of 1917-1940. Collecting of native bees was limited to the study plants, which may, in part, explain why some bee species documented in the Procter Surveys were not found in the present research. A field guide for identification of native bumble bees has been produced to help Park Natural Resource personnel monitor the status of native bee populations in Acadia. Other educational materials were also developed, aimed at educating Park visitors by exposing them to: 1) the role of native plants and their bee pollinators in terrestrial ecosystems; 2) the effects of invasive plants on native plant-pollinator mutualisms; 3) the need for conserving native bees and other pollinators; and 4) conservation strategies for protecting and enhancing native plant-pollinator mutualisms in the Park. Based on the present findings, Acadia Park Resource Management personnel should continue to closely

Technical Report↗
USGS2013

Dating North America's oldest petroglyphs, Winnemucca Lake subbasin, Nevada

On the west side of the Winnemucca Lake subbasin, Nevada, distinctive deeply carved meter-scale petroglyphs are closely spaced, forming panels on boulder-sized surfaces of a partially collapsed tufa mound. The large, complex motifs at this side are formed by deeply carved lines and cupules. A carbonate crust deposited between 10 200 and 9800 calibrated years B.P. (ka) coats petroglyphs at the base of the mound between elevations of 1202 and 1206 m. Petroglyphs above the carbonate crust are carved into a branching form of carbonate that dates to 14.8 ka. Radiocarbon dates on a multiple-layered algal tufa on the east side of the basin, which formed at an elevation of 1205 m, as well as a sediment-core-based total inorganic carbon record for the period 17.0–9.5 ka indicate that water level in the Winnemucca Lake subbasin was constrained by spill over the Emerson Pass Sill (1207 m) for most of the time between 12.9 ± 0.3 and ≥9.2 ka. These and other data indicate that the lake in the Winnemucca Lake subbasin fell beneath its spill point between 14.8 and 13.2 ka and also between 11.3 and 10.5 ka (or between 11.5 and 11.1 ka), exposing the base of the collapsed tufa mound to petroglyph carving. The tufa-based 14C record supports decreased lake levels between 14.8–13.2 ka and 11.3–10.5 ka. Native American artifacts found in the Lahontan Basin date to the latter time interval. This does not rule out the possibility that petroglyph carving occurred between 14.8 and 13.2 ka when Pyramid Lake was relatively shallow and Winnemucca Lake had desiccated.

Nevada↗
USGS1998

Spawning ecology of flannelmouth sucker, Catostomus lattipinnis (Catostomidae), in two small tributaries of the lower Colorado river

We report the first published accounts of spawning behavior and spawning site selection of the flannelmouth sucker in two small tributaries of the lower Colorado River in the Grand Canyon, Arizona. Spawning was observed on 20 March 1992 and from 28 March to 10 April 1993 in the Paria River, and from 16 to 19 March 1993 in Bright Angel Creek. Flannelmouth suckers exhibited promiscuous spawning behavior-individual females were typically paired with two or more males for a given event and sometimes changed partners between events. Multiple egg deposits by different females sometimes occurred at one spawning site. Flannelmouth sucker selected substrates from 16 to 32 mm diameter in both streams. Spawning occurred at depths of 10 to 25 cm in the Paria River and 19 to 41 cm in Bright Angel Creek. Mean column water velocities at spawning locations ranged from 0.15 to 1.0 m sec-1 in the Paria River and from 0.23 to 0.89 m sec-1 in Bright Angel Creek. Water temperatures recorded during spawning ranged from 9 to 18??C in the Paria River and 13 to 15??C in Bright Angel Creek. Spawning flannelmouth sucker ascended 9.8 km upstream in the Paria River and 1.25 km in Bright Angel Creek. Spawning females (410-580 mm) were significantly larger than spawning males (385-530 mm) in the Paria River. The mean size of spawning fish in the Paria River was significantly smaller than the entire stock, averaged throughout the study period (380-620 mm). However, fish spawning in 1992-1993 averaged 53 mm larger than fish spawning in the same reach of the Paria River in 1981, indicating a shift in the size structure of this stock.

Environmental Biology of Fishes↗
USGS1999

Surface seismic measurements of near-surface P-and S-wave seismic velocities at earthquake recording stations, Seattle, Washington

We measured P - and S -wave seismic velocities to about 40-m depth using seismic-refraction/reflection data on the ground surface at 13 sites in the Seattle, Washington, urban area, where portable digital seismographs recently recorded earthquakes. Sites with the lowest measured V s correlate with highest ground motion amplification. These sites, such as at Harbor Island and in the Duwamish River industrial area (DRIA) south of the Kingdome, have an average V s in the upper 30 m (V¯ s30 ) of 150 to 170 m/s. These values of V¯ s30 place these sites in soil profile type E (V¯ s30 < 180 m/s). A “rock” site, located at Seward Park on Tertiary sedimentary deposits, has a V¯ s30 of 433 m/s, which is soil type C (V¯ s30 : 360 to 760 m/s). The Seward Park site V¯ s30 is about equal to, or up to 200 m/s slower than sites that were located on till or glacial outwash. High-amplitude P - and S -wave seismic reflections at several locations appear to correspond to strong resonances observed in earthquake spectra. An S -wave reflector at the Kingdome at about 17 to 22 m depth probably causes strong 2-Hz resonance that is observed in the earthquake data near the Kingdome.

Washington↗
USGS1991

Wave processes and geologic responses on the floor of the Yellow Sea

The floor of the Yellow Sea is a geologically mundane surface: it is nearly horizontal, lacks relief, and, with few exceptions, is devoid of conspicuous geomorphologic features. However, it is the principal repository for the prodigious sediment load of the Huanghe (Yellow River); and, due to its inherent shallowness (average depth is 40 m), it is frequently stressed by waves generated by winter storms and typhoons. Analyses of mass physical properties of cores representing the upper few meters of sediment in the central and north-central Yellow Sea (near the Shandong Peninsula), in conjunction with analyses of slope stability, failure modes, and erodibility, permit an assessment of the likelihood and effect of dynamic, transient geologic events on the seabed. Vane shear-strength profiles along with consolidation test data indicate that the present surface of the seabed is in a depositional mode and is compacting normally. in addition, liquid-limit profiles imply that in the study area these neritic sediments have been accumulating in an environment that probably has not been modified significantly since sea level reached its current level. There is no geotechnical evidence in the nine cores recovered that slope failures have occurred, and clasts, sand lenses or other manifestations of mass movements, including flows, also are absent. These observations support previous interpretations of seismic records. Moreover, slope stability analysis for static conditions shows that the sea floor is quite stable. Regardless, shear-stress levels generated by cyclic loading during major storms may approach the sediment shear strengths, and, when coupled with concomitant excess pore pressures, could cause slope failure. Unless the failed beds collapsed or flowed, however, there probably would be little conspicuous evidence of such a failure. in fact, evaluation of the potential of these sediments for disintegrative behavior suggests that they are not prone to either collapse or flow. Storm waves also generate oscillatory bottom currents that may erode the seabed. Whether the sediment is considered as cohesionless or cohesive, typhoons could have the potential to erode at all water depths within the Yellow Sea (i.e., to 90 m), and winter storms to water depths of 60 m or more. However, in the case of cohesive behavior, it could be that the effect of winter storms and most typhoons is generally less extreme. If the sea floor is repeatedly scoured, it is likely limited to the top few centimeters. Despite the fact that storm waves may cause slope failure and are certainly responsible for frequent scouring, they probably leave only a subtle sedimentologic imprint on the seabed.

Yellow Sea↗
USGS1963

Water resources of Red River Parish, Louisiana

Red River Parish is on the eastern flank of the Sabine uplift in northwestern Louisiana. The 'area is underlain by lignitic clay and sand of Paleocene and Eocene age which dip to the east at the rate of about 30 feet per mile. The Red River is entrenched in these rocks in the western part of the parish. Alternating valley filling and erosion during the Quaternary period have resulted in the present lowland with flanking terraces. In the flood-plain area moderate to large quantities of very hard, iron-bearing water, suitable for irrigation, are available to wells in the alluvial sand and gravel of Quaternary age. The aquifer ranges in thickness from 20 to slightly more than 100 feet. It is recharged by downward seepage of rainfall through overlying clay and silt, by inflow from older sands adjacent to and beneath the entrenched valley, and by infiltration from the streams where the water table is below stream level during flood stages or as a result of pumping. Water levels are highest in the middle of the valley. Ground water moves mainly toward the Red River on the east and Bayou Pierre on the west, but small amounts move down the valley. Computations based on water-level and aquifer-test data indicate that the Quaternary alluvium contains more than 330 billion gallons of ground water in storage and that the maximum discharge of ground water to the streams is slightly more than 30 mgd (million gallons per day). At times of high river stage, surface water flows into the aquifer at a rate that depends in part upon the height and duration of the river stage. Moderate supplies of soft, iron-bearing water may be obtained from dissected Pleistocene terrace deposits that flank the flood plains of the Red River and Black Lake Bayou. However, the quantity of water that can be pumped from these deposits varies widely from place to place because of differences in the areal extent and saturated thickness of the segments of the deposits; this extent and thickness are governed in turn by the amount of erosion the deposits have undergone. Beds of fine-grained lignitic sands of Tertiary age contain water of generally good quality to depths of 150 to 450 feet. The thinness and low permeability of the sands restrict their development to low-yield wells. Water from these sands in the western part of the parish, where they lie beneath the alluvial valley, is more mineralized than that from the younger Tertiary sands exposed in the east-central area. Streamflow records have been collected on the principal streams in Red River Parish since 1939. Additional spot low-flow data were obtained on several small streams originating within the parish for a study made in connection with the preparation of this report. Quality-of-water data for streams in the parish were collected on an occasional spot-sampling basis prior to and during this investigation. The largest source of surface water in the parish is the Red River, which drains approximately 63,400 square miles upstream from the parish. The Red River has an average flow of about 13,100 cfs (cubic feet per second), or about 8,500 mgd. Many of the streams that drain the upland area are not dependable sources of supply because their flows are not well sustained during dry seasons. The average annual precipitation over the parish is about 52 inches, of which about 17 inches becomes runoff; this runoff is equivalent to a continuous flow of about 1.25 cfs per square mile. Seasonal and annual runoff varies, but no significant trends have been noticed. The principal surface-water problems in the parish pertain to flood control, drainage, irrigation, and navigation. Flood problems have been alleviated considerably by the operation of Denison Dam (Lake Texoma), the completion of levees on the Red River, channel improvements on Bayou Pierre, and the completion of Wallace Lake reservoir on Cypress Bayou. There are wet lands along the Red River that would be very productive if properly drained

Water Supply Paper↗
USGS2010

Detrital zircon provenance from three turbidite depocenters of the Middle-Upper Triassic Songpan-Ganzi complex, central China: Record of collisional tectonics, erosional exhumation, and sediment production

To test the idea that the voluminous upper Middle to Upper Triassic turbidite strata in the Songpan-Ganzi complex of central China archive a detrital record of Dabie ultrahigh-pressure (UHP) terrane unroofing, we report 2080 single detrital U-Pb zircon ages by sensitive high-resolution ion microprobe-reverse geometry (SHRIMP-RG) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis from 29 eastern Songpan-Ganzi complex sandstone samples. Low (<0.07) Th/U zircons, consistent with crystallization under UHP conditions, are rare in eastern Songpan-Ganzi complex zircon, and U-Pb ages of low Th/U zircons are incompatible with a Dabie terrane source. An unweighted pair group method with arithmetic mean nearest-neighbor analysis of Kolmogorov-Smirnov two-sample test results reveals that the eastern Songpan-Ganzi complex is not a single contiguous turbidite system but is instead composed of three subsidiary depocenters, each associated with distinct sediment sources. The northeastern depocenter contains zircon ages characterized by Paleozoic and bimodally distributed Precambrian zircon populations, which, together with south-to southeast-directed paleocurrent data, indicate derivation from the retro-side of the Qinling-Dabie (Q-D) collisional orogen wedge. In the central depocenter, the dominantly Paleozoic detrital zircon signature and south-to southwest-oriented paleocurrent indicators reflect a profusion of Paleozoic zircon grains. These data are interpreted to reflect an influx of material derived from erosion of Paleozoic supra-UHP rocks of the Dabie terrane in the eastern Qinling-Dabie orogen, which we speculate may have been enhanced by development of a monsoonal climate. This suggests that erosional unroofing played a significant role in the initial phase of UHP exhumation and likely influenced the petrotectonic and structural evolution of the Qinling-Dabie orogen, as evidenced by compressed Triassic isotherms/grads reported in the Huwan shear zone that bounds the Dabie terrane to the north. The central depocenter deposits reflect a later influx of bimodally distributed Precambrian zircon, signifying either a decrease in the influx of Paleozoic zircon grains due to stalled UHP exhumation and/or dilution of the same influx of Paleozoic zircons by spilling of Precambrian zircon from the northeastern depocenter into the central depocenter basin, perhaps due to infilling and bypass of sediment from the northern depocenter or due to initial collapse and constriction of the eastern Songpan-Ganzi complex basin. The southeastern depocenter of the eastern Songpan-Ganzi complex bears significant Paleozoic, Neoproterozoic, and Paleoproterozoic zircon populations derived from the South China block and Yidun arc complex, likely recording nascent uplift of the Longmenshan deformation belt due to impingement of the Yidun arc complex upon the western margin of the South China block. ?? 2010 Geological Society of America.

Geological Society of America Bulletin↗
USGS2009

A Holocene record of climate-driven shifts in coastal carbon sequestration

A sediment core collected in the mesohaline portion of Chesapeake Bay was found to contain periods of increased delivery of refractory black carbon (BC) and polycyclic aromatic hydrocarbons (PAHs). The BC was most likely produced by biomass combustion during four centennialscale dry periods as indicated by the Palmer Drought Severity Index (PDSI), beginning in the late Medieval Warm Period of 1100 CE. In contrast, wetter periods were associated with increased non-BC organic matter influx into the bay, likely due to greater runoff and associated nutrient delivery. In addition, an overall increase in both BC and non-BC organic matter deposition during the past millennium may reflect a shift in climate regime. The finding that carbon sequestration in the coastal zone responds to climate fluctuations at both centennial and millennial scales through fire occurrence and nutrient delivery has implications for past and future climate predictions. Drought-induced fires may lead, on longer timescales, to greater carbon sequestration and, therefore, represent a negative climate feedback. Copyright 2009 by the American Geophysical Union.

Geophysical Research Letters↗
USGS1991

The September 1988 intracaldera avalanche and eruption at Fernandina volcano, Galapagos Islands

During 14-16 September 1988, a large intracaldera avalanche and an eruption of basaltic tephra and lava at Fernandina volcano, Galapagos, produced the most profound changes within the caldera since its collapse in 1968. A swarm of eight earthquakes (mb 4.7-5.5) occurred in a 14 h period on 24 February 1988 at Fernandina, and two more earthquakes of this size followed on 15 April and 20 May, respectively. On 14 September 1988, another earthquake (mb 4.6) preceded a complex series of events. A debris avalanche was generated by the failure of a fault-bounded segment of the east caldera wall, approximately 2 km long and 300 m wide. The avalanche deposit is up to 250 m thick and has an approximate volume of 0.9 km3. The avalanche rapidly displaced a preexisting lake from the southeast end of the caldera floor to the northwest end, where the water washed up against the lower part of the caldera wall, then gradually seeped into the avalanche deposit and was completely gone by mid-January 1989. An eruption began in the caldera within about 1-2 h of the earthquake, producing a vigorous tephra plume for about 12 h, then lava flows during the next two days. The eruption ended late on 16 September. Most of the eruptive activity was from vents on the caldera floor near the base of the new avalanche scar. Unequivocal relative timing of events is difficult to determine, but seismic records suggest that the avalanche may have occurred 1.6 h after the earthquake, and field relations show that lava was clearly erupted after the avalanche was emplaced. The most likely sequence of events seems to be that the 1988 feeder dike intruded upward into the east caldera wall, dislocated the unstable wall block, and triggered the avalanche. The avalanche immediately exposed the newly emplaced dike and initiated the eruption. The exact cause of the earthquakes is unknown. ?? 1991 Springer-Verlag.

Bulletin of Volcanology↗
USGS2011

Loch Vale watershed long-term ecological research and monitoring program quality assurance report, 2003-09

The Loch Vale watershed project is a long-term research and monitoring program located in Rocky Mountain National Park that addresses watershed-scale ecosystem processes, particularly as they respond to atmospheric deposition and climate variability. Measurements of precipitation depth, precipitation chemistry, discharge, and surface-water quality are made within the watershed and elsewhere in Rocky Mountain National Park. As data collected for the program are used by resource managers, scientists, policy makers, and students, it is important that all data collected in Loch Vale watershed meet high standards of quality. In this report, data quality was evaluated for precipitation, discharge, and surface-water chemistry measurements collected during 2003-09. Equipment upgrades were made at the Loch Vale National Atmospheric Deposition Program monitoring site to improve precipitation measurements and evaluate variability in precipitation depth and chemistry. Additional solar panels and batteries have been installed to improve the power supply, and data completeness, at the NADP site. As a result of equipment malfunction, discharge data for the Loch Outlet were estimated from October 18, 2005, to August 17, 2006. Quality-assurance results indicate that more than 98 percent of all surface-water chemistry measurements were accurate and precise. Records that did not meet quality criteria were removed from the database. Measurements of precipitation depth, precipitation chemistry, discharge, and surface-water quality were all sufficiently complete and consistent to support project data needs.

Colorado↗
USGS2011

Map of debris flows caused by rainfall during 1996 in parts of the Reedsport and Deer Head Point quadrangles, Douglas County, southern Coast Range, Oregon

This 1:12,000-scale map shows an inventory of debris flows caused by rainfall during 1996 in a 94.4 km 2 area in the southern Coast Range of Oregon. This map and associated digital data are part of a larger U.S. Geological Survey study of debris flows in the southern Coast Range. Available evidence indicates that the flows were triggered by a rain storm that occurred between November 17 and 19. The closest rain gage in the Coast Range (Goodwin Peak) recorded 245 mm during the storm. Maximum rainfall intensity during the storm was 13.2 mm/hr on November 18. Debris flows were photogrammetrically mapped from 1:12,000-scale aerial photographs flown in May, 1997. The inventory is presented on imagery derived from LiDAR data acquired in 2008. We classified mapped debris flows into four categories based on the type of debris-flow activity: (1) discrete slide source areas, (2) predominantly erosion, (3) predominantly transport or mixed erosion and deposition, and (4) predominantly deposition. Locations of woody-debris jams are also shown on the map. The area encompassed by debris flows is 2.1 percent of the 94.4 km 2 map area.

Oregon↗
USGS2004

Trace metal records of regional paleoenvironmental variability in Pennsylvanian (Upper Carboniferous) black shales

Regional geochemical differences within a laterally continuous, cyclic Pennsylvanian (Upper Carboniferous) shale in midcontinent North America are interpreted in light of models of glacioeustatic forcing and new views on water-column paleoredox stability and trace-metal behavior in black shale environments. Specifically, we characterize differences in transition metal (Fe, Mn, Mo, V, Ni, Zn, Pb and U) concentrations in black shales of the Hushpuckney Shale Member of the Swope Limestone in Iowa and equivalent black shale beds of the Coffeyville Formation in Oklahoma. Although C-S-Fe systematics and uniform 34S-depleted isotope ratios of pyrite indicate pervasive euxinic deposition (anoxic and sulfidic bottom waters) for these shales, regional variations can be inferred for the efficiency of Mo scavenging and for the rates of siliciclastic sedimentation as expressed in spatially varying Fe/Al ratios. Black shales in Iowa show Mo enrichment roughly five times greater than that observed in coeval euxinic shales in Oklahoma. By contrast, Fe/Al ratios in Oklahoma shales are as much as five times greater than the continental ratio of 0.5 observed in the over- and underlying oxic facies and in the coeval black shales in Iowa. Recent work in modern marine settings has shown that enrichments in Fe commonly result from scavenging in a euxinic water column during syngenetic pyrite formation. In contrast to Fe, the concentrations of other transition metals (Mo, V, Ni, Pb, Zn, U) are typically more enriched in the black shales in Iowa relative to Oklahoma. The transition metal trends in these Paleozoic shales are reasonably interpreted in terms of early fixation in organic-rich sediments due to euxinic water-column conditions. However, regional variations in (1) rates of siliciclastic input, (2) organic reservoirs, including relative inputs of terrestrial versus marine organic matter, and (3) additional inputs of metals to bottom waters from contemporaneous hydrothermal vents are additional key controls that lead to geographic variation in the extent of metal enrichments preserved in ancient organic-rich sediments. Published by Elsevier B.V.

Chemical Geology↗
USGS1992

The Midcontinent rift in the Lake Superior region with emphasis on its geodynamic evolution

The Midcontinent rift is a Middle Proterozoic continental rift which records about 15 m.y. of extension, subsidence, and voluminous volcanism in the period 1109–1094 Ma in the central part of North America. During that time the crust was nearly totally separated and as much as 25 km of subaerial basalts accumulated in a deep central depression. Following extension and volcanism, a longer period of subsidence resulted in development of a post-rift sedimentary basin in which as much a 8 km of fluvial and lacustrine clastic rocks were deposited. Partial inversion of the central depression occurred about 30–50 m.y. after extension to produce the current configuration of a central horst, composed mostly of thick volcanic accumulations, between shallower flanking basins.

Lake Superior↗
USGS2014

Hydrogeology and water quality of the stratified-drift aquifer in the Pony Hollow Creek Valley, Tompkins County, New York

The lithology, areal extent, and the water-table configuration in stratified-drift aquifers in the northern part of the Pony Hollow Creek valley in the Town of Newfield, New York, were mapped as part of an ongoing aquifer mapping program in Tompkins County. Surficial geologic and soil maps, well and test-boring records, light detection and ranging (lidar) data, water-level measurements, and passive-seismic surveys were used to map the aquifer geometry, construct geologic sections, and determine the depth to bedrock at selected locations throughout the valley. Additionally, water-quality samples were collected from selected streams and wells to characterize the quality of surface and groundwater in the study area. Sedimentary bedrock underlies the study area and is overlain by unstratified drift (till), stratified drift (glaciolacustrine and glaciofluvial deposits), and recent post glacial alluvium. The major type of unconsolidated, water-yielding material in the study area is stratified drift, which consists of glaciofluvial sand and gravel, and is present in sufficient amounts in most places to form an extensive unconfined aquifer throughout the study area, which is the source of water for most residents, farms, and businesses in the valleys. A map of the water table in the unconfined aquifer was constructed by using (1) measurements made between the mid-1960s through 2010, (2) control on the altitudes of perennial streams at 10-foot contour intervals from lidar data collected by Tompkins County, and (3) water surfaces of ponds and wetlands that are hydraulically connected to the unconfined aquifer. Water-table contours indicate that the direction of groundwater flow within the stratified-drift aquifer is predominantly from the valley walls toward the streams and ponds in the central part of the valley where groundwater then flows southwestward (down valley) toward the confluence with the Cayuta Creek valley. Locally, the direction of groundwater flow is radially away from groundwater mounds that have formed beneath upland tributaries that lose water where they flow on alluvial fans on the margins of the valley. In some places, groundwater that would normally flow toward streams is intercepted by pumping wells. Surface-water samples were collected in 2001 at four sites including Carter, Pony Hollow (two sites), and Chafee Creeks, and from six wells throughout the aquifer. Calcium dominates the cation composition and bicarbonate dominates the anion composition in groundwater and surface-water samples and none of the common inorganic constituents collected exceeded any Federal or State water-quality standards. Groundwater samples were collected from six wells all completed in the unconfined sand and gravel aquifer. Concentrations of calcium and magnesium dominated the ionic composition of the groundwater in all wells sampled. Nitrate, orthophosphate, and trace metals were detected in all groundwater samples, but none were more than U.S. Environmental Protection Agency or New York State Department of Health regulatory limits.

New York↗
USGS2025

New evidence for eolian activity and mammoths on Santa Rosa Island prior to the Last Glacial Maximum

Sea-level fluctuations due to the growth and decay of continental ice sheets of the Quaternary exert a strong influence on geologic processes along coastlines. The California Channel Islands are no exception to this, and many studies have been conducted that focus on the extremes of these glacial-interglacial cycles, such as the last glacial period (marine isotope stage [MIS] 2) and the last interglacial period (MIS 5). Far less attention has been paid to intermediate time periods between these extremes, such as MIS 4. Here, we present two very different geologic records from this time period that show how sea-level change affected the nature of sedimentation on the northern shore of Santa Rosa Island. On the northwestern coast of Santa Rosa Island, thick eolian sediments accumulated between ~80 ka and ~45 ka due to a lowered sea level that exposed carbonate-rich skeletal sands that had accumulated during the last interglacial period. On the central part of the northern coast of Santa Rosa Island, thick alluvial sediments were deposited between 80 ka and 47 ka, similar to the time of eolian sedimentation to the west. A mammoth tusk discovered within these deposits is only the third stratigraphically controlled mammoth fossil on the Channel Islands that dates prior to MIS 2. Its discovery adds to the evidence that mammoths migrated to the Channel Islands from mainland California prior to the Last Glacial Maximum.

California↗
USGS2008

Record of the Late Devonian Hangenberg global positive carbon-isotope excursion in an epeiric sea setting: Carbonate production, organic-carbon burial and paleoceanography during the late Famennian

Latest Famennian marine carbonates from the mid-continent of North America were examined to investigate the Late Devonian (very late Famennian) Hangenberg positive carbon-isotope (??13 Ccarb) excursion. This global shift in the ?? 13C of marine waters began during the late Famennian Hangenberg Extinction Event that occurred during the Middle Siphonodella praesulcata conodont zone. The post-extinction recovery interval spans the Upper S. praesulcata Zone immediately below the Devonian-Carboniferous boundary. Positive excursions in ?? 13 Ccarb are often attributed to the widespread deposition of organic-rich black shales in epeiric sea settings. The Hangenberg ??13 Ccarb excursion documented in the Louisiana Limestone in this study shows the opposite trend, with peak ??13 Ccarb values corresponding to carbonate production in the U.S. mid-continent during the highstand phase of the very late Famennian post-glacial sea level rise. Our data indicate that the interval of widespread black shale deposition (Hangenberg Black Shale) predates the peak isotope values of the Hangenberg ??13 Ccarb excursion and that peak values of the Hangenberg excursion in Missouri are not coincident with and cannot be accounted for by high Corg burial in epeiric seas. We suggest instead that sequestration and burial of Corg in the deep oceans drove the peak interval of the ??13Ccarb excursion, as a result of a change in the site of deep water formation to low-latitude epeiric seas as the global climate shifted between cold and warm states.

Conference Paper↗
USGS2017

Amplification of earthquake ground motions in Washington, DC, and implications for hazard assessments in central and eastern North America

The extent of damage in Washington, DC, from the 2011 M w 5.8 Mineral, VA, earthquake was surprising for an epicenter 130 km away; U.S. Geological Survey “Did-You-Feel-It” reports suggest that Atlantic Coastal Plain and other unconsolidated sediments amplified ground motions in the city. We measure this amplification relative to bedrock sites using earthquake signals recorded on a temporary seismometer array. The spectral ratios show strong amplification in the 0.7 to 4 Hz frequency range for sites on sediments. This range overlaps with resonant frequencies of buildings in the city as inferred from their heights, suggesting amplification at frequencies to which many buildings are vulnerable to damage. Our results emphasize that local amplification can raise moderate ground motions to damaging levels in stable continental regions, where low attenuation extends shaking levels over wide areas and unconsolidated deposits on crystalline metamorphic or igneous bedrock can result in strong contrasts in near-surface material properties.

Washington, DC↗