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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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USGS2012

Geologic isolation of nuclear waste at high latitudes: the role of ice sheets

Geologic isolation of high-level nuclear waste from the biosphere requires special consideration in countries at high latitudes (>40°N) owing to the possibility of future episodes of continental glaciation (Talbot 1999). It is now widely recognized that Pleistocene continental glaciations have had a profound effect on rates of sediment erosion (Cuffey & Paterson 2010) and deformation including tectonic thrusting (Pedersen 2005) as well as groundwater flow (Person et al. 2007; Lemieux et al. 2008a,b,c). In addition, glacial mechanical loads may have generated anomalous, or fossil, pore pressures within certain clay-rich confining units (e.g. Vinard et al. 2001). Because high-level nuclear wastes must be isolated from the biosphere as long as 1 million years (McMurry et al. 2003), the likelihood of one or more continental ice sheets overrunning high-latitude sites must be considered.

Geofluids↗

USGS2012

Glaciation and regional groundwater flow in the Fennoscandian shield

Regional-scale groundwater flow modeling of the Fennoscandian shield suggests that groundwater flow can be strongly affected by future climate change and glaciation. We considered variable-density groundwater flow in a 1500-km-long and approximately 10-km-deep cross-section through southern Sweden. Groundwater flow and shield brine transport in the cross-sectional model were analyzed under projected surface conditions for the next 140 ka. Simulations suggest that blockage of recharge and discharge by low-permeability permafrost or cold-based ice causes sinking of brine and consequent freshening of near-surface water in areas of natural discharge. Although recharge of basal meltwater is limited by the requirement that water pressure at the base of the ice sheet not exceed the pressure exerted by the weight of the ice, warm-based ice with basal melting creates a potential for groundwater recharge rates much larger than those of present, ice-free conditions. In the simulations, regional-scale redistribution of recharged water by subsurface flow is minor over the duration of a glacial advance (approximately 10 ka). During glacial retreat, significant upward flow of groundwater may occur below the ice sheet owing to pressure release. If the mechanical loading efficiency of the rocks is high, both subsurface penetration of meltwater during glacial advance and up-flow during glacial retreat are reduced because of loading-induced pressure changes. The maximum rate of groundwater discharge in the simulations occurs at the receding ice margin, and some discharge occurs below incursive postglacial seas. Recharge of basal meltwater could decrease the concentration of dissolved solids significantly below present-day levels at depths of up to several kilometers and may bring oxygenated conditions to an otherwise reducing chemical environment for periods exceeding 10 ka.

Fennoscandian Shield↗

USGS2012

Book review: Earthquakes and water

It is really nice to see assembled in one place a discussion of the documented and hypothesized hydrologic effects of earthquakes. The book is divided into chapters focusing on particular hydrologic phenomena including liquefaction, mud volcanism, stream discharge increases, groundwater level, temperature and chemical changes, and geyser period changes. These hydrologic effects are inherently fascinating, and the large number of relevant publications in the past decade makes this summary a useful milepost. The book also covers hydrologic precursors and earthquake triggering by pore pressure. A natural need to limit the topics covered resulted in the omission of tsunamis and the vast literature on the role of fluids and pore pressure in frictional strength of faults. Regardless of whether research on earthquake-triggered hydrologic effects ultimately provides insight into the physics of earthquakes, the text provides welcome common ground for interdisciplinary collaborations between hydrologists and seismologists. Such collaborations continue to be crucial for investigating hypotheses about the role of fluids in earthquakes and slow slip. Review info: Earthquakes and Water. By Wang, C.-Y. and Manga, M., 2010. ISBN: 9783642008092, 218 pp.

Geofluids↗

USGS2012

Pyrite–sulfosalt reactions and semimetal fractionation in the Chinkuashih, Taiwan, copper–gold deposit: A 1 Ma paleo-fumarole

The mineralized fracture system that underlay paleo-fumarole field at Chinkuashih, Taiwan has been exposed by copper–gold mining to depths of about 550 m below the paleo-surface. Its mineralogy and systematic variations in metal and semimetal (Fe, Cu, As, Sb, Bi, Hg, Cd, Sn, Zn, Pb, Se, Te, Au, Ag) concentrations provide insights into the chemical responses of a magmatic-vapor phase as it expands through fracture arrays to the surface and discharges as fumaroles associated with more extensive solfatara. At Chinkuashih, following initial sealing of the fractures by silica-alunite alteration, brittle failure reestablished discharge from an underlying reservoir of magmatic vapor. Crystalline pyrite was deposited first in the fractures and was succeeded and replaced by ‘enargite’ (Cu 3 (As,Sb)S 4 ) as sulfosalt encrustations (‘sublimate’) on fracture surfaces and in extensional cracks. Subsequent recrystallization resulted in complex exsolution intergrowths with antimony fractionation to the evolving crystal–vapor interface. Heavy metal fractionation between sulfosalt and vapor enriched the vapor phase in heavy metals that subsequently precipitated as complex Bi–Hg–Sn sulfosalts in discrete areas (paleo-fumaroles) close to the paleo-surface in a manner analogous to modern-day fumaroles on active volcanoes such as Vulcano, Italy. As in similar paleo-fumaroles (e.g., El Indio, Chile and Lepanto, Philippines), the most characteristic reaction sequence is the partial replacement of the early pyrite by enargite and Fe-tennantite. It is proposed that this reaction tracks the decrease in the pressure of the underlying magmatic-vapor reservoir because of the sustained discharge of vapor to the surface.

Geofluids↗

USGS2018

Simulating the evolution of fluid underpressures in the Great Plains, by incorporation of tectonic uplift and tilting, with a groundwater flow model

Underpressures (subhydrostatic heads) in the Paleozoic units underlying the Great Plains of North America are a consequence of Cenozoic uplift of the area. Based on tectonostratigraphic data, we have developed a cumulative uplift history with superimposed periods of deposition and erosion for the Great Plains for the period from 40 Ma to the present. Uplift, deposition, and erosion on an 800 km geologic cross-section extending from northeast Colorado to eastern Kansas is represented in nine time-stepped geohydrologic models. Sequential solution of the two-dimensional diffusion equation reveals the evolution of hydraulic head and underpressure in a changing structural environment after 40 Ma, culminating in an approximate match with the measured present-day values. The modeled and measured hydraulic head values indicate that underpressures increase to the west. The 2 to 0 Ma model indicates that the present-day hydraulic head values of the Paleozoic units have not reached steady state. This result is significant because it indicates that present-day hydraulic heads are not at equilibrium, and underpressures will increase in the future. The pattern uncovered by the series of nine MODFLOW models is of increased underpressures with time. Overall, the models indicate that tectonic uplift explains the development of underpressures in the Great Plains.

Geofluids↗