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USGS1994

Hydrothermal alteration in oceanic ridge volcanics: A detailed study at the Galapagos Fossil Hydrothermal Field

The Galapagos Fossil Hydrothermal Field is composed of altered oceanic crust and extinct hydrothermal vents within the eastern Galapagos Rift between 85°49′W and 85°55′W. The discharge zone of the hydrothermal system is revealed along scarps, thus providing an opportunity to examine the uppermost mineralized, and highly altered interior parts of the crust. Altered rocks collected in situ by the submersible ALVIN show complex concentric alteration zones. Microsamples of individual zones have been analysed for major/minor, trace elements, and strontium isotopes in order to describe the complex compositional details of the hydrothermal alteration. Interlayered chlorite-smectite and chlorite with disequilibrium compositions dominate the secondary mineralogy as replacement phases of primary glass and acicular pyroxene. Phenocrysts and matrix grains of plagioclase are unaffected during alteration. Using a modification of the Gresens' equation we demonstrate that the trivalent rare earth elements (REEs) are relatively immobile, and calculate degrees of enrichment and depletion in other elements. Strontium isotopic ratios increase as Sr concentrations decrease from least-altered cores to most-altered rims and cross-cutting veins in individual samples, and can be modeled by open system behaviour under low fluid-rock ratio (< 10) conditions following a period of lower-temperature weathering of volcanics within the rift zone. The complex patterns of element enrichment and depletion and strontium isotope variations indicate mixing between pristine seawater and ascending hot fluids to produce a compositional spectrum of fluids. The precipitation of base-metal sulfides beneath the seafloor is probably a result of fluid mixing and cooling. If, as suggested here, the discharge zone alteration occurred under relatively low fluid-rock ratios, then this shallow region must play an important role in determining the exit composition of vent fluids in marine hydrothermal systems.

Geochimica et Cosmochimica Acta↗

USGS2009

Probabilistic tsunami hazard assessment at Seaside, Oregon, for near-and far-field seismic sources

The first probabilistic tsunami flooding maps have been developed. The methodology, called probabilistic tsunami hazard assessment (PTHA), integrates tsunami inundation modeling with methods of probabilistic seismic hazard assessment (PSHA). Application of the methodology to Seaside, Oregon, has yielded estimates of the spatial distribution of 100- and 500-year maximum tsunami amplitudes, i.e., amplitudes with 1% and 0.2% annual probability of exceedance. The 100-year tsunami is generated most frequently by far-field sources in the Alaska-Aleutian Subduction Zone and is characterized by maximum amplitudes that do not exceed 4 m, with an inland extent of less than 500 m. In contrast, the 500-year tsunami is dominated by local sources in the Cascadia Subduction Zone and is characterized by maximum amplitudes in excess of 10 m and an inland extent of more than 1 km. The primary sources of uncertainty in these results include those associated with interevent time estimates, modeling of background sea level, and accounting for temporal changes in bathymetry and topography. Nonetheless, PTHA represents an important contribution to tsunami hazard assessment techniques; viewed in the broader context of risk analysis, PTHA provides a method for quantifying estimates of the likelihood and severity of the tsunami hazard, which can then be combined with vulnerability and exposure to yield estimates of tsunami risk. Copyright 2009 by the American Geophysical Union.

Journal of Geophysical Research C: Oceans↗

USGS1997

Effect of wave-enhanced bottom friction on storm-driven circulation in Massachusetts Bay

Massachusetts Bay is a shallow (35 m average depth) semienclosed embayment, roughly 100 ?? 50 km, which opens into the Gulf of Maine at its eastern boundary. Surface waves associated with winter storm winds from the northeast cause large sediment resuspension events, and wave and circulation fields during these events have a quasi-steady response to the wind stress. Coupled wave, circulation, and boundary layer models indicate that wave-enhanced bottom friction has a significant damping effect on storm-driven circulation in Massachusetts Bay. The simulated response exhibits significant three-dimensional structure, but still can be fundamentally understood using idealized models. The depth-integrated momentum balance is dominated by along-bay stress, pressure gradient, and bottom stress. The effective bottom drag coefficient during typical storm conditions is increased by a factor of 2-5 when wave effects are included, but the mean bottom stress is relatively unaffected by wave effects due to a reduction in bottom currents by 30-50%. The vertical mixing is also relatively unaffected by the waves, and the result is that the increased drag causes a nearly depth-independent offset of the vertical current profiles. The alongshore transport in the bay is reduced 10-50%, depending on wind direction.

Cape Cod Bay, Massachussetts Bay↗

USGS2021

Numerical simulation of the boundary layer flow generated in Monterey Bay, California by the 2010 Chilean tsunami: Case study

This work presents a case study involving the numerical simulation of the unsteady boundary layer generated by the 2010 Chilean tsunami, as measured by field equipment in Monterey Bay, California, USA. A one-dimensional vertical (1DV) boundary layer model is utilized, solving Reynolds-averaged Navier–Stokes equations, coupled with two-equation k – ω turbulence closure. Local effects of convective acceleration (converging–diverging effects) on the boundary layer due to the sloping bed are likewise approximated. Four cases are considered involving simulation of: (1) the long tsunami-induced boundary layer flow in isolation, in combination with either (2) convective acceleration effects or (3) energetic short wind waves, and, finally, (4) all effects combined. Reasonable agreement with field measurements is achieved, with model results similarly showing that the tsunami-induced boundary layer in this case only spans a fraction of the local water depth. Systematic comparison of the various cases likewise elucidates the likely significance of both local converging–diverging effects, as well as interaction with the much shorter period wind waves, on the tsunami-generated boundary layer. In the latter case, analogy is drawn to well-known wave–current boundary layer interaction, with the boundary layer turbulence associated with the short wind waves inducing an effective wave roughness felt by the tsunami-induced flow, which effectively plays the role of the current.

California↗

USGS2016

Ephemerality of discrete methane vents in lake sediments

Methane is a potent greenhouse gas whose emission from sediments in inland waters and shallow oceans may both contribute to global warming and be exacerbated by it. The fraction of methane emitted by sediments that bypasses dissolution in the water column and reaches the atmosphere as bubbles depends on the mode and spatiotemporal characteristics of venting from the sediments. Earlier studies have concluded that hot spots—persistent, high-flux vents—dominate the regional ebullitive flux from submerged sediments. Here the spatial structure, persistence, and variability in the intensity of methane venting are analyzed using a high-resolution multibeam sonar record acquired at the bottom of a lake during multiple deployments over a 9 month period. We confirm that ebullition is strongly episodic, with distinct regimes of high flux and low flux largely controlled by changes in hydrostatic pressure. Our analysis shows that the spatial pattern of ebullition becomes homogeneous at the sonar's resolution over time scales of hours (for high-flux periods) or days (for low-flux periods), demonstrating that vents are ephemeral rather than persistent, and suggesting that long-term, lake-wide ebullition dynamics may be modeled without resolving the fine-scale spatial structure of venting.

Geophysical Research Letters↗

USGS2012

A model for the generation of two-dimensional surf beat

A finite difference model predicting group-forced long waves in the nearshore is constructed with two interacting parts: an incident wave model providing time-varying radiation stress gradients across the nearshore, and a long-wave model which solves the equations of motion for the forcing imposed by the incident waves. Both shallow water group-bound long waves and long waves generated by a time-varying breakpoint are simulated. Model-generated time series are used to calculate the cross correlation between wave groups and long waves through the surf zone. The cross-correlation signal first observed by Tucker (1950) is well predicted. For the first time, this signal is decomposed into the contributions from the two mechanisms of leaky mode forcing. Results show that the cross-correlation signal can be explained by bound long waves which are amplified, though strongly modified, through the surf zone before reflection from the shoreline. The breakpoint-forced long waves are added to the bound long waves at a phase of pi/2 and are a secondary contribution owing to their relatively small size.

Journal of Geophysical Research C: Oceans↗

USGS1977

Compositional variations of young basalts in the Mid-Atlantic Ridge rift valley near lat 36°49′N

Fifty acoustically positioned samples of fresh basalt were collected by the submersible Alvin from the median valley of the Mid-Atlantic Ridge during the French American Mid-Ocean Undersea Study (FAMOUS) in the summer of 1974. The samples show regular compositional variations from the center of the rift valley (central lava flows) out to the rift valley walls (flank lava flows). The central lava samples show higher ratios of olivine relative to clinopyroxene and plagioclase phenocrysts and contain chrome spinel. Glasses of the flank lava samples are enriched in SiO 2 , TiO 2 , K 2 O, H 2 O, and FeO/MgO relative to central lava samples. Studies of the thickness of palagonite and manganese crusts indicate that the flank lava flows are considerably younger than the inferred spreading age of the crust on which they occur. Flank lavas are generally older than central lavas, but notable exceptions occur. The composition of the flank lava glass can be derived by the removal of approximately 29 wt percent of analyzed phenocrysts (in the ratio 5.7 plagioclase, 2.5 olivine, 1.8 clinopyroxene) from the central lava glass. In addition, other processes (possibly involving volatile transfer) must enrich the flank lavas in K 2 O, TiO 2 , and H 2 O. A model is proposed whereby this crystal fractionation occurs in a shallow, narrow (6-km-wide) magma chamber underlying the median valley. The chamber is compositionally zoned, and central lavas are fed from dikes tapping its hotter axial zone, whereas flank lavas are fed from the cooler, differentiated melt on the margins. The nature of the chemical variations in the lavas permits an estimate of the composition and thickness of the cumulates forming at the base of the chamber.

GSA Bulletin↗

USGS2004

The distribution of seabirds and pinnipeds in Marguerite Bay and their relationship to physical features during austral winter 2001

The distribution of seabirds and pinnipeds and their relationship to physical oceanographic variables were investigated as part of the US Southern Ocean Global Ocean Ecosystem Dynamics field program along a study grid centered around Marguerite Bay on the west Antarctic Peninsula during late fall (April-May) and winter (July-August), 2001. Sea-ice conditions during the cruises provided an opportunity to compare the relationship among physical oceanographic variables and species distributions before and after the development of pack ice. During the fall cruise before pack ice development, both sea-ice-affiliated species and open-water-affiliated were observed in the area. The most common ice-affiliated species observed at this time were snow petrel (Pagodroma nivea, 0.7 individuals km-2) and Antarctic petrel (Thalassoica antarctica, 0.2 individuals km-2) and the most common open-water-affiliated species were blue petrel (Halobaena caerulea, 0.4 individuals km-2), cape petrel (Daption capense, 0.2 individuals km-2), and southern fulmar (Fulmarus glacialoides, 0.1 individuals km-2). In addition, Antarctic fur seals (Arctocephalus gazella, 0.1 individuals km-2) and crabeater seals (Lobodon carcinophagus, 0.4 individuals km-2) were observed in low numbers. Akaike's information criterion was used to assess competing models that predicted predator distributions based on physical oceanographic variables proposed to structure predator distribution in previous research. These analyses indicated that predator distributions were primarily associated with water-mass structure and variability in bottom depth during the fall cruise. Crabeater seal, snow petrel, Antarctic petrel, and southern fulmar had higher densities in Inner Shelf Water, particularly near Alexander Island where a coastal current was present. Blue petrel, kelp gull (Larus dominicanus), and southern giant petrel (Macronectes giganteus) were positively associated with variability in bottom depth in April-May, suggesting that hydrographic processes influenced by bathymetry may have been important in structuring bird distributions. After the development of pack ice, during July and August, only sea-ice-affiliated species, including snow petrel (1.0 individuals km-2), Antarctic petrel (0.1 individuals km-2), Ade??lie penguin (Pygoscelis adeliae, 0.4 individuals km-2), and crabeater seal (0.3 individuals km-2), were observed. Seabirds were primarily associated with sea-ice characteristics (e.g. sea-ice concentration, sea-ice type) rather than the water-column environment later in the winter. Results from this study suggest that the timing and extent of sea-ice development in the fall may influence over-winter predation by seabirds and pinnipeds on zooplankton and fish on the western Antarctic Peninsula. Delays in sea-ice development may allow seabirds and pinnipeds access to biologically important areas such as the Inner Shelf Water for a longer period of time thereby increasing predation on zooplankton and fish. ?? 2004 Elsevier Ltd. All rights reserved.

Deep-Sea Research Part II: Topical Studies in Ocea↗

USGS2019

It’s about time: A synthesis of changing phenology in the Gulf of Maine ecosystem

The timing of recurring biological and seasonal environmental events is changing on a global scale relative to temperature and other climate drivers. This study considers the Gulf of Maine ecosystem, a region of high social and ecological importance in the Northwest Atlantic Ocean and synthesizes current knowledge of 1) key seasonal processes, patterns, and events; 2) direct evidence for shifts in timing; 3) implications of phenological responses for linked ecological-human systems; and 4) potential phenology-focused adaptation strategies and actions. Twenty studies demonstrated shifts in timing of regional marine organisms and seasonal environmental events. The most common response was earlier timing, observed in spring onset, spring and winter hydrology, zooplankton abundance, and diadromous fish migrations. Later timing was documented for fall onset, reproduction and fledging in Atlantic puffins, spring and fall phytoplankton blooms, and occurrence of some larval fishes. Changes in event duration generally increased and were detected in zooplankton peak abundance, early life history periods of macro-invertebrates, and lobster fishery landings. Reduced duration was observed in winter-spring ice-affected stream flows. Two studies projected phenological changes, both finding diapause duration would decrease in zooplankton under future climate scenarios. Phenological responses were species-specific and varied depending on the environmental driver, spatial, and temporal scales evaluated. Overall, a wide range of baseline phenology and relevant modeling studies exist, yet surprisingly few document long-term shifts. Results reveal a need for increased emphasis on phenological shifts in the Gulf of Maine, identify opportunities for future research and consideration of phenological changes in adaptation efforts.

Maine↗

USGS1982

Paleomagnetic evidence bearing on Tertiary tectonics of the Tihamat Asir coastal plain, southwestern Saudi Arabia

Paleomagnetic directions determined for an upper Oligocene to lower Miocene dike swarm and from two lower Miocene layered gabbros in the Tihamat Asir coastal plain of southwestern Saudi Arabia are used to test several hypotheses concerning the tectonics of rifting along the eastern margin of the Red Sea. The dikes and gabbros were emplaced during the initial phases of Red Sea rifting and may mark the transition between continental and oceanic crust. Although these rocks have been hydrothermally altered to varying degrees, reliable remanent directions after alternating-field demagnetization were obtained for 23 dikes and for gabbros at Jabal at Tirf and Wadi Liyyah. Twelve of the dikes are reversely magnetized. After the directions of the reversely magnetized dikes are inverted 180?, the mean direction calculated for the normal dikes is approximately 24? more downward than that calculated for the reversed dikes. This result is similar to that found for the As Sarat volcanic field, 100 km to the north, and may be due to a displaced dipole source for the field. The unrotated mean remanent direction for the dikes (inverting reversed dike directions 180?) is D (declination) = 353.2? and I (inclination) = 6.8? with a95 (radius of the cone of 95 percent confidence) = 8.9? whereas directions from the Jabal at Tirf and Wadi Liyyah gabbros lie at D = 176.2?, I = -1.6? (a95 = 7 1 ?) and D = 17.1?, I = 16.3? (a 95 = 8.7?), respectively. Comparing these results with the results from the As Sarat volcanic field, all the paleomagnetic evidence supports a model for approximately 20 ? of westward tilting of the Wadi Damad and Wadi Jizan areas after the emplacement of the Jabal at Tiff gabbro. The Wadi Liyyah area may have been tilted even more toward the Red Sea. The paleomagnetic directions from three widely separated localities in the Jabal at Tirf gabbro are not significantly different, a fact which indicates that the body cooled in approximately its present bowl shape. Evidence suggests that the ratio of normal to reversed dikes may change significantly along a 6-km-long traverse normal to the trend of the dike swarm, possibly reflecting migration of .a spreading axis.

Open-File Report↗

USGS2012

The structure of subtidal currents within and around Lydonia Canyon: Evidence for enhanced cross-shelf fluctuations over the mouth of the canyon

Between October 1980 and April 1981, currents were measured within Lydonia Canyon and on the adjacent shelf and slope. The amplitude of the subtidal currents over the shelf and slope ranged between 10 and 30 cm s −1 , but within the canyon, they were typically smaller than 5 cm s −1 . The subtidal currents had well-defined spatial structures over the shelf and the slope and in the middle and outer portions of the canyon. The along-isobath flow over the shelf and slope was unaltered by the canyon. Currents within the canyon and just above it were driven up and down the canyon by the cross-shelf pressure gradient in geostrophic equilibrium with the along-shelf flow. The measurements suggest that the Coriolis force on the cross-canyon flow, turbulent Reynolds stresses, and acceleration of the along-canyon flow balanced the imposed pressure gradient for flow near the rim of Lydonia Canyon. The Coriolis force was not important in the deeper portions of the canyon, where baroclinic adjustments of the density field began to be an important factor in the momentum balance. A simple model indicates that the magnitude of the horizontal turbulent viscosity coefficient for subtidal flow in this narrow canyon is 10 6 to 10 7 cm 2 s −1 . The mixing indicated by the large amplitude of the viscosity coefficient was probably caused by the strong tidal currents present within Lydonia Canyon. On the shelf, along-isobath currents were locally driven by the large-scale component of the wind field; along-shelf currents were equally correlated with local winds and with winds from sites 700 km northeast of Lydonia Canyon. Wind stress was not correlated with currents over the slope in water deeper than 450 m or with currents within the canyon.

Journal of Geophysical Research - Oceans↗

USGS2003

Fault trends on the seaward slope of the Aleutian Trench: Implications for a laterally changing stress field tied to a westward increase in oblique convergence

Normal faults along the seaward trench slope (STS) commonly strike parallel to the trench in response to bending of the oceanic plate into the subduction zone. This is not the circumstance for the Aleutian Trench, where the direction of convergence gradually changes westward, from normal to transform motion. GLORIA side-scan sonar images document that the Aleutian STS is dominated by faults striking oblique to the trench, west of 179??E and east of 172??W. These images also show a pattern of east-west trending seafloor faults that are aligned parallel to the spreading fabric defined by magnetic anomalies. The stress-strain field along the STS is divided into two domains west and east, respectively, of 179??E. Over the western domain, STS faults and nodal planes of earthquakes are oriented oblique (9??-46??) to the trench axis and (69??-90??) to the magnetic fabric. West of 179??E, STS fault strikes change by 36?? from the E-W trend of STS where the trench-parallel slip gets larger than its orthogonal component of convergence. This rotation indicates that horizontal stresses along the western domain of the STS are deflected by the increasing obliquity in convergence. An analytical model supports the idea that strikes of STS faults result from a superposition of stresses associated with the dextral shear couple of the oblique convergence and stresses caused by plate bending. For the eastern domain, most nodal planes of earthquakes strike parallel to the outer rise, indicating bending as the prevailing mechanism causing normal faulting. East of 172??W, STS faults strike parallel to the magnetic fabric but oblique (10??-26??) to the axis of the trench. On the basis of a Coulomb failure criterion the trench-oblique strikes probably result from reactivation of crustal faults generated by spreading. Copyright 2003 by the American Geophysical Union.

Journal of Geophysical Research B: Solid Earth↗

USGS1981

Significant results from using earth observation satellites for mineral and energy resource exploration

A large number of Earth-observation satellites orbit our world several times each day, providing new information about the land and sea surfaces and the overlying thin layer of atmosphere that makes our planet unique. Meteorological satellites have had the longest history of experimental use and most are now considered operational. The geologic information collected by the Landsat, Polar Orbiting Geophysical Observatory (POGO), Magsat, Heat Capacity Mapping Mission (HCMM) and Seasat land and ocean observation systems is being thoroughly tested, and some of these systems are now approaching operational use. Landsat multispectral images provide views of large areas of the Earth under uniform lighting conditions and can be obtained at a variety of scales and formats. Not only do the Landsat data provide highly useful images showing surficial materials and structures such as folds and faults, but also measurements and computer-derived ratios of the brightness of different rock types, alteration zones, and mineral associations. These data have led to the finding of a variety of new ore deposits. In addition, the combination of Landsat digital data and aeromagnetic data has extended the use of Landsat as an exploration tool which can be used to readily relate surface features to subsurface anomalies. Magsat data, now being collected, are helping refine information on major crustal anomalies that were first recognized during the analysis of POGO data. The more nearly circular orbit, lower altitude, and increased sophistication of its vector magnetometer enable Magsat to provide more precise information than POGO. Information of this type is required to develop crustal models. Although Magsat is designed to operate for only 4–8 months, the number of orbits that it should be able to make will be sufficient to accomplish its mission and to record a major magnetic storm expected in 1980. HCMM is a two-band visible to near-IR (0.55–1.1 μm) and thermal infrared (10.2–12.5 μm) system designed to measure reflected solar energy, determine the heat capacity of rocks and to monitor soil moisture, thermal effluents, plant canopy temperatures and snow cover. Launched in April 1978, it is in sun-synchronous, circular orbit at an altitude of 620 km. It is a relatively low-resolution system with an instantaneous field of view (IFOV) of 500–600 m and a swath width of 716 km. However, the system is designed to detect objects in the range of 260°–340° K with a sensitivity (NEδT) of 0.4°K at 280°. Recording the thermal radiation of urban heat islands and high thermal inertia of quartzite strata in the Appalachian region are two examples of its land applications. Launched in June 1978, Seasat operated for only 100 days, but successfully acquired much information over both sea and land. The collection of synthetic aperture radar (SAR) imagery and radar altimetry was particularly important to geologists. Although there are difficulties in processing and distributing these data in a timely manner, initial evaluations indicate that the radar imagery supplements Landsat data by increasing the spectral range and offering a different look angle. The radar altimeter provides accurate profiles over narrow strips of land (1 km wide) and has demonstrated usefulness in measuring icecap surfaces (Greenland, Iceland, and Antarctica). The Salar of Uyuni in southern Bolivia served as a calibration site for the altimeter and has enabled investigators to develop a land-based smoothing algorithm that is believed to increase the accuracy of the system to 10 cm. Data from the altimeter are currently being used to measure subsidence resulting from ground water withdrawal in the Phoenix-Tucson area.

Advances in Space Research↗

USGS2020

The water-year water balance of the Colorado River Basin

Model‐estimated monthly water balance components (i.e., potential evapotranspiration, actual evapotranspiration, and runoff ( R )) for 146 United States (U.S.) Geological Survey 8‐digit hydrologic units located in the Colorado River Basin (CRB) are used to examine the temporal and spatial variability of the CRB water balance for water years 1901 through 2014 (a water year is the period from October 1 of one year through September 30 of the following year). Results indicate that the CRB can be divided into six subregions with similar temporal variability in monthly R . The water balance analyses indicated that approximately 75% of total water‐year R is generated by just one CRB subregion and that most of the R in the basin is derived from surplus ( S ) water generated during the months of October through April. Furthermore, the analyses show that temporal variability in S is largely controlled by the occurrence of negative atmospheric pressure anomalies over the northwestern conterminous U.S. (CONUS) and positive atmospheric pressure anomalies over the southeastern CONUS. This combination of atmospheric pressure anomalies results in an anomalous flow of moist air from the North Pacific Ocean into the CRB, particularly the Upper CRB. Additionally, the occurrence of extreme dry and wet periods in the CRB appears to be related to variability of the Atlantic Multidecadal Oscillation and the Pacific Decadal Oscillation.

Arizona, California, Colorado, Nevada, New Mexico,↗

USGS2017

Monitoring storm tide and flooding from Hurricane Matthew along the Atlantic coast of the United States, October 2016

Introduction Hurricane Matthew moved adjacent to the coasts of Florida, Georgia, South Carolina, and North Carolina. The hurricane made landfall once near McClellanville, South Carolina, on October 8, 2016, as a Category 1 hurricane on the Saffir-Simpson Hurricane Wind Scale. The U.S. Geological Survey (USGS) deployed a temporary monitoring network of storm-tide sensors at 284 sites along the Atlantic coast from Florida to North Carolina to record the timing, areal extent, and magnitude of hurricane storm tide and coastal flooding generated by Hurricane Matthew. Storm tide, as defined by the National Oceanic and Atmospheric Administration, is the water-level rise generated by a combination of storm surge and astronomical tide during a coastal storm. The deployment for Hurricane Matthew was the largest deployment of storm-tide sensors in USGS history and was completed as part of a coordinated Federal emergency response as outlined by the Stafford Act (Public Law 92–288, 42 U.S.C. 5121–5207) under a directed mission assignment by the Federal Emergency Management Agency. In total, 543 high-water marks (HWMs) also were collected after Hurricane Matthew, and this was the second largest HWM recovery effort in USGS history after Hurricane Sandy in 2012. During the hurricane, real-time water-level data collected at temporary rapid deployment gages (RDGs) and long-term USGS streamgage stations were relayed immediately for display on the USGS Flood Event Viewer ( https://stn.wim.usgs.gov/FEV/#MatthewOctober2016 ). These data provided emergency managers and responders with critical information for tracking flood-effected areas and directing assistance to effected communities. Data collected from this hurricane can be used to calibrate and evaluate the performance of storm-tide models for maximum and incremental water level and flood extent, and the site-specific effects of storm tide on natural and anthropogenic features of the environment.

Florida, Georgia, North Carolina, South Carolina↗

USGS2018

Analysis of multi-decadal wetland changes, and cumulative impact of multiple storms 1984 to 2017

Land-cover classification analysis using Landsat satellite imagery acquired between 1984 and 2017 quantified short- (post-Hurricane Sandy) and long-term wetland-change trends along the Maryland and Virginia coasts between Metompkin Bay, VA and Ocean City, MD. Although there are limited options for upland migration of wetlands in the study area, regression analysis showed that wetland area increased slightly between 1984 and 2011, indicating that marsh aggradation rates were sufficient to maintain wetland elevation relative to mean sea level. Following Hurricane Irene (August 2011), the Halloween Nor’Easter (October 2011), and Hurricane Sandy (October 2012), wetland area decreased by more than 7 km 2 compared with average pre-storm extents. We assume that Hurricane Sandy had the greatest impact due to the size and intensity of the storm. However, the cumulative effects of multiple storms within a short time period likely contributed to the greater observed losses in coastal wetlands relative to earlier periods. Five years after Hurricane Sandy, wetland area had not significantly recovered, but more time may be necessary to assess if the observed wetland losses will persist or if new growth within flooded marsh areas will be sufficient for the wetlands to recover to pre-storm extents. Comparisons of long-term and storm-driven wetland changes can lead to improved accuracy of habitat vulnerability models and greater understanding of potential impacts of future storms and SLR to coastal wetlands.

Wetlands Ecology and Management↗

USGS2015

Accuracy assessment of NOAA gridded daily reference evapotranspiration for the Texas High Plains

The National Oceanic and Atmospheric Administration (NOAA) provides daily reference evapotranspiration (ET ref ) maps for the contiguous United States using climatic data from North American Land Data Assimilation System (NLDAS). This data provides large-scale spatial representation of ET ref , which is essential for regional scale water resources management. Data used in the development of NOAA daily ET ref maps are derived from observations over surfaces that are different from short (grass — ET os ) or tall (alfalfa — ET rs ) reference crops, often in nonagricultural settings, which carries an unknown discrepancy between assumed and actual conditions. In this study, NOAA daily ET os and ET rs maps were evaluated for accuracy, using observed data from the Texas High Plains Evapotranspiration (TXHPET) network. Daily ET os , ET rs and the climatic data (air temperature, wind speed, and solar radiation) used for calculating ET ref were extracted from the NOAA maps for TXHPET locations and compared against ground measurements on reference grass surfaces. NOAA ET ref maps generally overestimated the TXHPET observations (1.4 and 2.2 mm/day ET os and ET rs , respectively), which may be attributed to errors in the NLDAS modeled air temperature and wind speed, to which reference ET ref is most sensitive. Therefore, a bias correction to NLDAS modeled air temperature and wind speed data, or adjustment to the resulting NOAA ET ref , may be needed to improve the accuracy of NOAA ET ref maps.

Texas↗

USGS2009

Gas hydrate drilling transect across northern Cascadia margin - IODP Expedition 311

A transect of four sites (U1325, U1326, U1327 and U1329) across the northern Cascadia margin was established during Integrated Ocean Drilling Program Expedition 311 to study the occurrence and formation of gas hydrate in accretionary complexes. In addition to the transect sites, a fifth site (U1328) was established at a cold vent with active fluid flow. The four transect sites represent different typical geological environments of gas hydrate occurrence across the northern Cascadia margin from the earliest occurrence on the westernmost first accreted ridge (Site U1326) to the eastward limit of the gas hydrate occurrence in shallower water (Site U1329). Expedition 311 complements previous gas hydrate studies along the Cascadia accretionary complex, especially ODP Leg 146 and Leg 204 by extending the aperture of the transect sampled and introducing new tools to systematically quantify the gas hydrate content of the sediments. Among the most significant findings of the expedition was the occurrence of up to 20 m thick sand-rich turbidite intervals with gas hydrate concentrations locally exceeding 50% of the pore space at Sites U1326 and U1327. Moreover, these anomalous gas hydrate intervals occur at unexpectedly shallow depths of 50-120 metres below seafloor, which is the opposite of what was expected from previous models of gas hydrate formation in accretionary complexes, where gas hydrate was predicted to be more concentrated near the base of the gas hydrate stability zone just above the bottom-simulating reflector. Gas hydrate appears to be mainly concentrated in turbidite sand layers. During Expedition 311, the visual correlation of gas hydrate with sand layers was clearly and repeatedly documented, strongly supporting the importance of grain size in controlling gas hydrate occurrence. The results from the transect sites provide evidence for a structurally complex, lithology-controlled gas hydrate environment on the northern Cascadia margin. Local shallow occurrences of high gas hydrate concentrations contradict the previous model of gas hydrate formation at an accretionary prism. However, long-lived fluid flow (part of the old model) is still required to explain the shallow high gas hydrate concentrations, although it is most likely not pervasive throughout the entire accretionary prism, but rather localized and focused by the tectonic processes. Differences in the fluid flow regime across all of the transect drill sites indicate site-specific and probably disconnected (compartmented) deeper fluid sources in the various parts of the accretionary prism. The data and future analyses will yield a better understanding of the geologic controls, evolution and ultimate fate of gas hydrate in an accretionary prism as an important contribution to the role of gas hydrate methane gas in slope stability and possibly in climate change. ?? The Geological Society of London 2009.

Geological Society Special Publication↗