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Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

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At least 1,369 records · Page 76Linked to original sources
USGS2011

Direction of unsaturated flow in a homogeneous and isotropic hillslope

The distribution of soil moisture in a homogeneous and isotropic hillslope is a transient, variably saturated physical process controlled by rainfall characteristics, hillslope geometry, and the hydrological properties of the hillslope materials. The major driving mechanisms for moisture movement are gravity and gradients in matric potential. The latter is solely controlled by gradients of moisture content. In a homogeneous and isotropic saturated hillslope, absent a gradient in moisture content and under the driving force of gravity with a constant pressure boundary at the slope surface, flow is always in the lateral downslope direction, under either transient or steady state conditions. However, under variably saturated conditions, both gravity and moisture content gradients drive fluid motion, leading to complex flow patterns. In general, the flow field near the ground surface is variably saturated and transient, and the direction of flow could be laterally downslope, laterally upslope, or vertically downward. Previous work has suggested that prevailing rainfall conditions are sufficient to completely control these flow regimes. This work, however, shows that under time-varying rainfall conditions, vertical, downslope, and upslope lateral flow can concurrently occur at different depths and locations within the hillslope. More importantly, we show that the state of wetting or drying in a hillslope defines the temporal and spatial regimes of flow and when and where laterally downslope and/or laterally upslope flow occurs.

Water Resources Research↗
USGS2011

Formation dynamics of subsurface hydrocarbon intrusions following the Deepwater Horizon blowout

Hydrocarbons released following the Deepwater Horizon (DH) blowout were found in deep, subsurface horizontal intrusions, yet there has been little discussion about how these intrusions formed. We have combined measured (or estimated) observations from the DH release with empirical relationships developed from previous lab experiments to identify the mechanisms responsible for intrusion formation and to characterize the DH plume. Results indicate that the intrusions originate from a stratification‐dominated multiphase plume characterized by multiple subsurface intrusions containing dissolved gas and oil along with small droplets of liquid oil. Unlike earlier lab measurements, where the potential density in ambient water decreased linearly with elevation, at the DH site it varied quadratically. We have modified our method for estimating intrusion elevation under these conditions and the resulting estimates agree with observations that the majority of the hydrocarbons were found between 800 and 1200 m.

Geophysical Research Letters↗
USGS2011

Exchange of Groundwater and Surface-Water Mediated by Permafrost Response to Seasonal and Long Term Air Temperature Variation

Permafrost dynamics impact hydrologic cycle processes by promoting or impeding groundwater and surface water exchange. Under seasonal and decadal air temperature variations, permafrost temperature changes control the exchanges between groundwater and surface water. A coupled heat transport and groundwater flow model, SUTRA, was modified to simulate groundwater flow and heat transport in the subsurface containing permafrost. The northern central Tibet Plateau was used as an example of model application. Modeling results show that in a yearly cycle, groundwater flow occurs in the active layer from May to October. Maximum groundwater discharge to the surface lags the maximum subsurface temperature by two months. Under an increasing air temperature scenario of 3?C per 100 years, over the initial 40-year period, the active layer thickness can increase by three-fold. Annual groundwater discharge to the surface can experience a similar three-fold increase in the same period. An implication of these modeling results is that with increased warming there will be more groundwater flow in the active layer and therefore increased groundwater discharge to rivers. However, this finding only holds if sufficient upgradient water is available to replenish the increased discharge. Otherwise, there will be an overall lowering of the water table in the recharge portion of the catchment.

Geophysical Research Letters↗
USGS2011

Constraints on the long‐period moment‐dip tradeoff for the Tohoku earthquake

Since the work of Kanamori and Given (1981), it has been recognized that shallow, pure dip‐slip earthquakes excite long‐period surface waves such that it is difficult to independently constrain the moment ( M 0 ) and the dip ( δ ) of the source mechanism, with only the product M 0 sin(2 δ ) being well constrained. Because of this, it is often assumed that the primary discrepancies between the moments of shallow, thrust earthquakes are due to this moment‐dip tradeoff. In this work, we quantify how severe this moment‐dip tradeoff is depending on the depth of the earthquake, the station distribution, the closeness of the mechanism to pure dip‐slip, and the quality of the data. We find that both long‐period Rayleigh and Love wave modes have moment‐dip resolving power even for shallow events, especially when stations are close to certain azimuths with respect to mechanism strike and when source depth is well determined. We apply these results to USGS W phase inversions of the recent M9.0 Tohoku, Japan earthquake and estimate the likely uncertainties in dip and moment associated with the moment‐ dip tradeoff. After discussing some of the important sources of moment and dip error, we suggest two methods for potentially improving this uncertainty.

Tohoku↗
USGS2011

Quantifying the influence of sea ice on ocean microseism using observations from the Bering Sea, Alaska

Microseism is potentially affected by all processes that alter ocean wave heights. Because strong sea ice prevents large ocean waves from forming, sea ice can therefore significantly affect microseism amplitudes. Here we show that this link between sea ice and microseism is not only a robust one but can be quantified. In particular, we show that 75–90% of the variability in microseism power in the Bering Sea can be predicted using a fairly crude model of microseism damping by sea ice. The success of this simple parameterization suggests that an even stronger link can be established between the mechanical strength of sea ice and microseism power, and that microseism can eventually be used to monitor the strength of sea ice, a quantity that is not as easily observed through other means.

Alaska↗
USGS2012

One hundred years of volcano monitoring in Hawaii

In 2012 the Hawaiian Volcano Observatory (HVO), the oldest of five volcano observatories in the United States, is commemorating the 100th anniversary of its founding. HVO's location, on the rim of Kilauea volcano (Figure 1)—one of the most active volcanoes on Earth—has provided an unprecedented opportunity over the past century to study processes associated with active volcanism and develop methods for hazards assessment and mitigation. The scientifically and societally important results that have come from 100 years of HVO's existence are the realization of one man's vision of the best way to protect humanity from natural disasters. That vision was a response to an unusually destructive decade that began the twentieth century, a decade that saw almost 200,000 people killed by the effects of earthquakes and volcanic eruptions.

Hawai'i↗
USGS2019

Induced seismicity reduces seismic hazard?

Earthquakes caused by human activities have been observed for decades. Often these are related to industrial activities pumping fluids into deep geologic formations, like with wastewater disposal. The simplest theory connecting these processes to earthquakes is straightforward: injection leads to fluid pressure changes that either reduce the strength of preexisting faults or generate new faults. In practice, the conditions that lead to induced earthquakes are not always clear in ways that can be generalized. Kao et al. (2018, https://doi.org/10.1029/2018GL079288) show how the distribution of induced earthquakes in Western Canada relate to natural rates of deformation in the crust. Using these new results, they discuss an intriguing paradox: induced seismicity can cause short-term increases in the seismic hazard that are followed by a period of reduced seismic hazard. Such hazard-reducing scenarios are plausible but hinge upon simplifying assumptions about how the crust stores and releases strain energy in the form of earthquakes.

Geophysical Research Letters↗
USGS2021

Coastal wetland resilience, accelerated sea-level rise, and the importance of timescale

Recent studies have produced conflicting results as to whether coastal wetlands can keep up with present‐day and future sea‐level rise. The stratigraphic record shows that threshold rates for coastal wetland submergence or retreat are lower than what instrumental records suggest, with wetland extent that shrinks considerably under high rates of sea‐level rise. These apparent conflicts can be reconciled by recognizing that many coastal wetlands still possess sufficient elevation capital to cope with sea‐level rise, and that processes like sediment compaction, ponding, and wave erosion require multidecadal or longer timescales to drive wetland loss that is in many cases inevitable.

AGU Advances↗
USGS2020

Step increase in eastern U.S. precipitation linked to Indian Ocean warming

A step increase in annual precipitation over the eastern U.S. in the early 1970’s commenced five decades of invigorated hydroclimate, with ongoing impacts on streamflow and water resources. Despite its far-reaching impacts, the dynamical origin of this change is unknown. Here, analyses of a century of atmospheric and oceanic data trace the dynamics to changes in the Indian Ocean. Spring and fall precipitation explain more than half the annual eastern-U.S. precipitation variance over the century, and changes in fall are predominantly responsible for the step increase. The driving mechanism is emergence of a pan-Pacific atmospheric wave emanating from deep convection over the warming Indian Ocean. Documentation of this fall teleconnection draws attention to projected anthropogenic increases in tropical oceanic heat content, and their potential impacts on hydroclimate of the midlatitudes.

Geophysical Research Letters↗
USGS2021

Airborne dust plumes lofted by dislodged ice blocks at Russell Crater, Mars

Linear dune gullies on poleward-facing Martian slopes are enigmatic. Formation by CO 2 -ice block or snow cornice falls has been proposed based on optical imagery of bright, high-albedo features inside gully channels. Because these features often resemble patchy frost residue rather than three-dimensional blocks, more evidence is needed to support the ice-block formation mechanism. Satellite imagery captured two simultaneous airborne plumes with in-channel sources at the Russell crater megadune, thrust up, and dispersed outward along the path of linear dune gullies. We use spectral data analyses, climatic analyses of bolometric temperatures, and thermal modeling to further develop the mechanistic framework for linear dune gully development. Basal sublimation and CO 2 gas venting likely cause CO 2 -ice-block detachment and falls from gully alcoves in southern early spring, accompanied by ice-block off-gassing and saltation of sands and coarse silts that are redeposited around gully channels, and lofting of sublimation lag (coarse dust/silt) into airborne plumes.

Geophysical Research Letters↗
USGS2023

Correction to “The March 1940 superstorm: Geoelectromagnetic hazards and impacts on American communication and power systems”

In Love et al. (2023), 5 estimated geopotentials on long lines for the March 1989 storm are incorrect. This was the result of incorrect calculation of line integrals. This error affects the two paragraphs of Section 11 and Figure 10 of that paper. The most significant impact of this error is that we overestimated the average ratio of the geopotentials measured the long lines during the March 1940 storm to the estimated geopotentials for the March 1989 storm. Instead of being a factor of 9 higher, the average ratio is only 9% higher. This means the inductive geoeffectiveness of the March 1940 storm was comparable to, or just slightly greater than, the geoeffectiveness of the March 1989 storm. Corrected paragraphs and a corrected figure are provided here.

Space Weather↗
USGS2012

Crustal magnetic anomalies

This Quadrennial Report departs in format from its predecessors. Earlier reports provided brief descriptions of the entire range of topics on “crustal magnetic anomalies.” Following guidelines established by the AGU, we instead focus our discussion on only a few selected topics. Our abbreviated list of references reflects this restricted focus. A more comprehensive bibliography can be obtained from the authors as noted subsequently. The past quadrennium was distinguished by a significant change in the scale and scope of crustal magnetic anomaly research. Advances in instrumentation, navigation, and data processing techniques resulted in increasing use of two-dimensional anomaly maps rather than profile data. Although maps are commonly used in aeromagnetic studies of continental areas, their use in the ocean basins has been limited until recently. The other important change has been a trend towards increased integration of magnetic anomaly data with gravity, seismic, geochemical, remote sensing, and geologic data to enhance the interpretation and reduce the ambiguity of magnetic field data.

Reviews of Geophysics↗
USGS1998

On the influence of biomass burning on the seasonal CO2 signal as observed at monitoring stations

We investigated the role of biomass burning in simulating the seasonal signal in both prognostic and diagnostic analyses. The prognostic analysis involved the High-Resolution Biosphere Model, a prognostic terrestrial biosphere model, and the coupled vegetation fire module, which together produce a prognostic data set of biomass burning. The diagnostic analysis involved the Simple Diagnostic Biosphere Model (SDBM) and the Hao and Liu [1994] diagnostic data set of biomass burning, which have been scaled to global 2 and 4 Pg C yr −1 , respectively. The monthly carbon exchange fields between the atmosphere and the biosphere with a spatial resolution of 0.5° × 0.5°, the seasonal atmosphere-ocean exchange fields, and the emissions from fossil fuels have been coupled to the three-dimensional atmospheric transport model TM2. We have chosen eight monitoring stations of the National Oceanic and Atmospheric Administration network to compare the predicted seasonal atmospheric CO 2 signals with those deduced from atmosphere-biosphere carbon exchange fluxes without any contribution from biomass burning. The prognostic analysis and the diagnostic analysis with global burning emissions of 4 Pg C yr −1 agree with respect to the change in the amplitude of the seasonal CO 2 concentration introduced through biomass burning. We find that the seasonal CO 2 signal at stations in higher northern latitudes (north of 30°N) is marginally influenced by biomass burning. For stations in tropical regions an increase in the CO 2 amplitude of more than 1 ppmv (up to 50% with respect to the observed trough to peak amplitude) has been calculated. Biomass burning at stations farther south accounts for an increase in the CO 2 amplitude of up to 59% (0.6 ppmv). A change in the phase of the seasonal CO 2 signal at tropical and southern stations has been shown to be strongly influenced by the onset of biomass burning in southern tropical Africa and America. Comparing simulated and observed seasonal CO 2 signals, we find higher discrepancies at southern tropical stations if biomass burning emissions are included. This is caused by the additional increase in the amplitude in the prognostic analysis and a phase shift in a diagnostic analysis. In contrast, at the northern tropical stations biomass burning tends to improve the estimates of the seasonal CO 2 signal in the prognostic analysis because of strengthening of the amplitude. Since the SDBM predicts the seasonal CO 2 signal reasonably well for the northern hemisphere tropical stations, no general improvement of the fit occurs if biomass burning emissions are considered.

Global Biogeochemical Cycles↗
USGS2012

Investigations at active volcanoes

The field of volcanology has expanded greatly in the years 1967–1970, and work on active volcanoes has kept pace with this expansion. I have restricted this summary and the accompanying bibliography to studies by U.S.‐based investigators of active or potentially active volcanoes. I have been immeasurably aided in writing this summary by communications from R. Citron of the Smithsonian Institution Center for Short‐Lived Phenomena, W. Melson and T. Simkin of the Smithsonian Institution, A. McBirney of the Center for Volcanology, University of Oregon, R.B. Forbes of the University of Alaska, and R.W. Decker of Dartmouth College.

Eos, Transactions, American Geophysical Union↗
USGS2012

Volcanism and massive sulfide formation at a sedimented spreading center, Escanaba Trough, Gorda Ridge, northeast Pacific Ocean

Seismic‐reflection profiles over the sediment‐filled Escanaba Trough at the southern Gorda Ridge reveal a series of volcanic centers that pierce the sediment. The volcanic edifices are 3 to 6 km in diameter and are spaced at 15 to 20 km intervals along the axis of the trough. The volcanic intrusions have uplifted the sediment as much as 100 m, and in places fresh basaltic flows are exposed at the sea floor. Unoxidized pyrrhotite‐rich massive‐sulfide samples were obtained from the flanks of one of these volcanic centers. The composition and form of the sulfide samples suggest significant interaction between hydrothermal fluids and sediment at depth, and deposition of sulfide within the sediment pile.

Geophysical Research Letters↗
USGS2014

Glacier‐measurements in the United States

It is doubtless known to many members of the Section of Hydrology that prior to the World War there existed an International Glacier Commission (la Commission Internationale des Glaciers) whose self‐appointed task it was to gather and publish the results of all available measurements showing the annual variations in length—advance or recession—of glaciers in different parts of the world. On this Commission the United States was represented by two men who made frequent contributions to the International record.

Eos, Transactions, American Geophysical Union↗
USGS2014

Activity of Parícutin volcano from December 1, 1946 to March 31, 1947 patterns

A record of the activity of Parícutin Volcano, Michoacán, Mexico, is shown in the diagram of eruptive characteristics, Figure 1, covering the period December 31, 1946 to March 31, 1947, and is supplemented by the maps of the areal extent of the lava flows, Figures 2 and 3. This continues the previous record for the period from September 18 to November 30, 1946 [Trans. Amer. Geophys. Union, v. 28, no. 4, pp. 567–572, 1947], and reference is made to that report for explanatory discussion of the diagram of eruptive characteristics and for general information concerning the methods of investigation. As shown in Figure 1, the periods of predominantly heavy pyroclastic eruption occurred December 16 to February 14 and March 15 to 28. The periods of greater effusion of lava occurred December 1 to 20 and January 22 to February 25.

Parícutin, Michoacán↗
USGS2014

Nonsteady flow to a well of constant drawdown in an extensive aquifer

A mathematical theory is given for the discharge of a well of constant drawdown, discharging as by natural flow from an effectively infinite aquifer of uniform transmissibility and uniform compressibility. This theory is based on the solution by L. P. Smith of the analogous problem in heat conduction. The mathematical function involved in the solution, which cannot be integrated directly, is evaluated by numerical integration. A table of its values is given for a wide range of its argument. This function is compared with other,asymptotic solutions, and simple, useful approximations are given. Two graphical methods are outlined for determining the coefficients of storage and transmissibility from variations in the rate of discharge of wells flowing at constant drawdown. Data from the Grand Junction, Colo., artesian basin are treated by these methods. In the Grand Junction artesian basin there are about 25 flowing wells ranging in depth from 600 to 1600 ft, most of which obtain water from the Entrada sandstone. A few of the wells obtain water from a sandstone in the overlying Morrison formation and a few tap the underlying Wingate sandstone. The procedure of the tests is outlined, and the “ink-well” mercury gage used to measure the artesian pressures is described. Recovery tests were run on the same wells after the discharge tests. Values of transmissibility obtained from the recovery tests check those obtained by means of the discharge tests.

Colorado↗