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At least 811 records · Page 45Linked to original sources

USGS2004

Non-double-couple microearthquakes at Long Valley caldera, California, provide evidence for hydraulic fracturing

Most of 26 small (0.4≲ M ≲3.1) microearthquakes at Long Valley caldera in mid-1997, analyzed using data from a dense temporary network of 69 digital three-component seismometers, have significantly non-double-couple focal mechanisms, inconsistent with simple shear faulting. We determined their mechanisms by inverting P - and S -wave polarities and amplitude ratios using linear-programming methods, and tracing rays through a three-dimensional Earth model derived using tomography. More than 80% of the mechanisms have positive (volume increase) isotropic components and most have compensated linear-vector dipole components with outward-directed major dipoles. The simplest interpretation of these mechanisms is combined shear and extensional faulting with a volume-compensating process, such as rapid flow of water, steam, or CO 2 into opening tensile cracks. Source orientations of earthquakes in the south moat suggest extensional faulting on ESE-striking subvertical planes, an orientation consistent with planes defined by earthquake hypocenters. The focal mechanisms show that clearly defined hypocentral planes in different locations result from different source processes. One such plane in the eastern south moat is consistent with extensional faulting, while one near Casa Diablo Hot Springs reflects en echelon right-lateral shear faulting. Source orientations at Mammoth Mountain vary systematically with location, indicating that the volcano influences the local stress field. Events in a ‘spasmodic burst’ at Mammoth Mountain have practically identical mechanisms that indicate nearly pure compensated tensile failure and high fluid mobility. Five earthquakes had mechanisms involving small volume decreases, but these may not be significant. No mechanisms have volumetric moment fractions larger than that of a force dipole, but the reason for this fact is unknown.

California↗

USGS2016

Functional metagenomic selection of RubisCOs from uncultivated bacteria

Ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) is a critical yet severely inefficient enzyme that catalyses the fixation of virtually all of the carbon found on Earth. Here, we report a functional metagenomic selection that recovers physiologically active RubisCO molecules directly from uncultivated and largely unknown members of natural microbial communities. Selection is based on CO 2 -dependent growth in a host strain capable of expressing environmental deoxyribonucleic acid (DNA), precluding the need for pure cultures or screening of recombinant clones for enzymatic activity. Seventeen functional RubisCO-encoded sequences were selected using DNA extracted from soil and river autotrophic enrichments, a photosynthetic biofilm and a subsurface groundwater aquifer. Notably, three related form II RubisCOs were recovered which share high sequence similarity with metagenomic scaffolds from uncultivated members of the G allionellaceae family. One of the G allionellaceae RubisCOs was purified and shown to possess CO 2 /O 2 specificity typical of form II enzymes. X-ray crystallography determined that this enzyme is a hexamer, only the second form II multimer ever solved and the first RubisCO structure obtained from an uncultivated bacterium. Functional metagenomic selection leverages natural biological diversity and billions of years of evolution inherent in environmental communities, providing a new window into the discovery of CO 2 -fixing enzymes not previously characterized.

Environmental Microbiology↗

USGS2018

Geologic field-trip guide of volcaniclastic sediments from snow- and ice-capped volcanoes—Mount St. Helens, Washington, and Mount Hood, Oregon

This field guide for the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) Scientific Assembly 2017 focuses on volcaniclastic sediments from Mount St. Helens in Washington and Mount Hood in Oregon. The trip spends four days in the field and includes nine stops at each volcano. For completeness, this guidebook also includes sixteen optional stops in the Mount St. Helens area and three in the Mount Hood area. These two volcanoes provide excellent depositional records of the broad spectrum of volcanic hazards that involve the flow or fall of volcaniclastic particles. At the field-trip stops we will contrast and compare the different types of deposits—sediments that can be frustratingly difficult to distinguish from one another. Correct identification of deposit origin leads to a better understanding of hazards that can impact vulnerable communities at particular volcanoes. During this four-day field trip, we will spend two days in the Mount St. Helens area and two days near Mount Hood. On the first day, we will visit debris-avalanche and lahar deposits in the Toutle River valley in Washington. The second day will focus on pyroclastic density current, pyroclastic-fall, lahar, and volcano-fluvial deposits in the Lewis River drainage system near Mount St. Helens. On the third day, we will visit hyaloclastites, glacial tills, and other diamicts in the Hood River and Sandy River basins near Mount Hood. The fourth and final day will focus on distal lahar and volcano-fluvial deposits downstream of Mount Hood. What follows is an in-depth introduction to the deposits studied on this field trip. We provide criteria that are observable in the field to aid in differentiating between pyroclastic density current, pyroclastic-fall, debris-avalanche, lahar, water-flood, and glacial deposits. We also introduce the Holocene eruptive histories of Mount St. Helens and Mount Hood and discuss the processes responsible for deposit emplacement. Field-trip stops and features of interest along the route are described in detail in a road log that provides daily cumulative mileage.

Oregon, Washington↗

USGS1985

An estimate of hydrothermal fluid residence times and vent chimney growth rates based on 210Pb Pb ratios and mineralogic studies of sulfides dredged from the Juan de Fuca Ridge

The 210 PbPb ratios across two sulfide samples dredged from the Juan de Fuca Ridge are used to estimate the growth rate of the sulfide material and the residence time of the hydrothermal fluid within the oceanic crust from the onset of basalt alteration. 210 Pb is added to the hydrothermal fluid by two processes: (1) high-temperature alteration of basalt and (2) if the residence time of the fluid is on the order of the 22.3-year half-life of 210 Pb, by in-situ growth from 222 Rn ( Krishnaswami and Turekian, 1982 ). Stable lead is derived only from the alteration of basalt. The 210 Pb/Pb ratio across one sample was ∼ 0.5 dpm/10 −6 g Pb, and across the other it was ∼ 0.4 dpm/10 −6 g Pb. These values are quite close to the 238 UP/b ratios of basalts from the area, suggesting that the residence time of the hydrothermal fluid from the onset of basalt alteration is appreciably less than the mean life of 210 Pb, i.e., the time required for ingrowth from the radon. An apparent growth rate of 1.2 cm/yr is derived from the slope of the 210 Pb/Pb curve for one of the samples. This is consistent with its mineralogy and texture which suggest an accretionary pattern of development. There is no obvious sequential growth pattern, and virtually no gradient in 210 Pb/Pb across the second sample. This is consistent with alteration of the original 210 Pb/Pb distribution by extensive remobilization reactions which are inferred from the mineralogic and textural relationships of the sample.

Earth and Planetary Science Letters↗

USGS1994

Age and Sr isotopic composition of volcanic rocks in the Maricunga Belt, Chile: Implications for magma sources

K-Ar and 40 Ar/ 39 Ar dating of volcanic rocks from the Maricunga belt of north-central Chile indicate that igneous activity took place throughout most of Miocene time at various places in the 150 by 30 km belt. No migration patterns of volcanism appear in the Miocene rocks of the belt. Volcanic activity ceased by the end of the Miocene. All the Miocene volcanic rocks studied are calcic andesites to dacites with about 62% SiO 2 , 18% A1 2 O 3 , 4% Fe 2 O 3 (total), and 2% K 2 O. Initial 87 Sr/ 86 Sr (Sr i ) values fall into two groups, one of lower values around 0.7050 to the west and the other of higher values around 0.7060 to the east. It is postulated that the two Sr i groups reflect two adjoining coherent lower-crustal magma sources of possibly different age and subtly different composition that form part of the western edge of the South American craton.

Journal of South American Earth Sciences↗

USGS2019

Seismic velocity structure across the 2013 Craig, Alaska rupture from aftershock tomography: Implications for seismogenic conditions

The 2013 Craig, Alaska M W 7.5 earthquake ruptured along ∼150 km of the Queen Charlotte Fault (QCF), a right-lateral strike-slip plate boundary fault separating the Pacific and North American plates. Regional shear wave analyses suggest that the Craig earthquake rupturepropagated in the northward direction faster than the S-wave (supershear). Theoretical studies suggest that a bimaterial interface, such as that along the QCF, which separates oceanic and continental crust with differing elastic properties, can promote supershear rupture propagation. We deployed short-period ocean-bottom seismometers (OBS) as a part of a rapid-response effort less than four months after the Craig earthquake mainshock. During a 21-day period, 1,133 aftershocks were recorded by 8 OBS instruments. Aftershock spatial distribution indicates that the base of the seismogenic zone along the QCF approaches ∼25 km depth, consistent with a thermally-controlled fault rheology expected for igneous rocks at oceanic transform faults. The spatial distribution also provides supporting evidence for a previously hypothesized active strand of the QCF system within the Pacific Plate. Tomographic traveltime inversion for velocity structure indicates a low-velocity (V P and V S ) zone on the Pacific side of the plate boundary at 5–20 km depths, where NeogenePacific crust and upper mantle seismic velocities average ∼3–11% slower than the North American side, where the Paleozoic North American crust is seismically faster. Our results suggest that elastic properties along the studied portion of the QCF are different than those of a simple oceanic–continental plate boundary fault. In our study region, velocity structure across the QCF, while bimaterial, does not support faster material on the west side of the fault, which has been proposed as one possible explanation for northward supershear propagation during the Craig earthquake. Instead, we image low-velocity material on the west side of the fault. Explanations could include that part of the rupture was subshear, or that fault damage zone properties or fault smoothness are more important controls on supershear rupture than a bimaterial contrast.

Alaska↗

USGS2012

Basin and range crustal and upper mantle structure, northwest to central Nevada

We present an interpretation of the crustal and uppermost mantle structure of the Basin and Range of northwestern Nevada based on seismic refraction/wide‐angle reflection, near‐vertical reflection, and gravity data. In comparison to most previous estimates, we find that the crust is somewhat thicker (32–36 km versus 22–30 km), and the uppermost mantle velocity is somewhat higher (8.0 km/s versus 7.3–7.9 km/s). Along our transects, the crust is thinnest (32 km) in the Carson Sink‐Buena Vista Valley region and increases by 2–4 km to the west and east, respectively. There is considerable complexity throughout the crust where velocities range from of 2.5 km/s at the surface to 7.4 km/s in the lowermost crust. Variations in velocity and structure of the upper crustal layers reveal apparent basement velocity depressions (areas of lower velocities extending up to 10 km in depth) that underlie some surface ranges as well as the basins. The middle crust rises from about 20 km beneath central Nevada to within 12 km of the surface beneath the area of thinnest crust and is characterized by a modest (∼0.1 km/s) change in velocity and low‐velocity gradients. These midcrustal layers mark the onset of high crustal reflectivity and the apparent limiting depth to which Basin and Range faults can be traced in near‐vertical reflection profiles, suggesting that these midcrustal layers represent the transition between the brittle and ductile zones of the crust. The lower crust is more structurally complex, with layers thickening and thinning in a systematic manner with the upper crustal layers; generally, where there are velocity depressions in the upper crust, the lower crust is thickest and shallowest. The geometry of these lower crustal layers (derived from refraction modeling) coincides with changes in the crustal reflectivity, determined from the Consortium of Continental Reflection Profiling reflection data. The lower crustal layer is unusually high in velocity (7.4 km/s) and is likely the layer identified as mantle in some previous studies. We do not identify the 7.4 km/s layer as mantle because (1) there is an underlying layer with a velocity (8.0 km/s) that is more consistent with the worldwide average velocity for the upper mantle, and (2) the 7.4 km/s layer does not correspond to the “reflection” Moho. Gravity modeling and comparison to existing seismic models show a general consensus in many aspects with respect to crustal structure. This new model forms the basis for speculation on some of the processes associated with rifting of the Basin and Range Province. One such process, lithospheric magmatism, is inferred from the strong attenuation of transmitted seismic waves, which occurs at the same interface at which high‐amplitude, bright spot reflections originate. Unlike previous models, the overall structure and velocity of the crust and uppermost mantle of our new model are similar to other regions worldwide which have undergone high degrees of extension.

Nevada↗

USGS2012

Estimation of rod scale errors in geodetic leveling

Comparisons among repeated geodetic levelings have often been used for detecting and estimating residual rod scale errors in leveled heights. Individual rod-pair scale errors are estimated by a two-step procedure using a model based on either differences in heights, differences in section height differences, or differences in section tilts. It is shown that the estimated rod-pair scale errors derived from each model are identical only when the data are correctly weighted, and the mathematical correlations are accounted for in the model based on heights. Analyses based on simple regressions of changes in height versus height can easily lead to incorrect conclusions. We also show that the statistically estimated scale errors are not a simple function of height, height difference, or tilt. The models are valid only when terrain slope is constant over adjacent pairs of setups (i.e., smoothly varying terrain). In order to discriminate between rod scale errors and vertical displacements due to crustal motion, the individual rod-pairs should be used in more than one leveling, preferably in areas of contrasting tectonic activity. From an analysis of 37 separately calibrated rod-pairs used in 55 levelings in southern California, we found eight statistically significant coefficients that could be reasonably attributed to rod scale errors, only one of which was larger than the expected random error in the applied calibration-based scale correction. However, significant differences with other independent checks indicate that caution should be exercised before accepting these results as evidence of scale error. Further refinements of the technique are clearly needed if the results are to be routinely applied in practice.

Journal of Geophysical Research B: Solid Earth↗

USGS1997

Depth dependence of earthquake frequency-magnitude distributions in California: Implications for rupture initiation

Statistics of earthquakes in California show linear frequency-magnitude relationships in the range of M 2.0 to M 5.5 for various data sets. Assuming Gutenberg-Richter distributions, there is a systematic decrease in b value with increasing depth of earthquakes. We find consistent results for various data sets from northern and southern California that both include and exclude the larger aftershock sequences. We suggest that at shallow depth (∼0 to 6 km) conditions with more heterogeneous material properties and lower lithospheric stress prevail. Rupture initiations are more likely to stop before growing into large earthquakes, producing relatively more smaller earthquakes and consequently higher b values. These ideas help to explain the depth-dependent observations of foreshocks in the western United States. The higher occurrence rate of foreshocks preceding shallow earthquakes can be interpreted in terms of rupture initiations that are stopped before growing into the mainshock. At greater depth (9–15 km), any rupture initiation is more likely to continue growing into a larger event, so there are fewer foreshocks. If one assumes that frequency-magnitude statistics can be used to estimate probabilities of a small rupture initiation growing into a larger earthquake, then a small ( M 2) rupture initiation at 9 to 12 km depth is 18 times more likely to grow into a M 5.5 or larger event, compared to the same small rupture initiation at 0 to 3 km.

Journal of Geophysical Research B: Solid Earth↗

USGS1950

Populations and home range relationships of the box turtle, Terrapene c. carolina (Linnaeus)

SUMMARY: A population study of the box turtle (Terrapene c. carolina Linnaeus) was made during the years 1944 to 1947 at the Patuxent Research Refuge, Maryland. A thirty acre area in well drained bottomland forest on the flood plain of the Patuxent River was selected for intensive study. Similarly forested land extended in all directions from the study plot. Markers were established at eighty-three foot intervals over the study plot for reference in recording locality data. Individuals were marked by filing notches in the marginal scutes according to a code system. There were 2109 collections of study area turtles. Records of collecting sites and turtle behavior showed that in the bottomlands habitat cover is utilized extensively during the day as well as at night. Turtles not actively moving about are almost always found in or around brush piles, heaps of debris, and tangles of vines and briars. Gully banks and woods openings are used for sunning. Turtles are occasionally found in the mud or water of the gullies. The commonest type of night retreat is a cavity constructed by the turtle in leaves, debris, or earth. These cavities, termed 'forms,' may be used only once, but are sometimes used repeatedly, often at intervals of several days or more. Different turtles sometimes use the same form on successive nights. Weather conditions most favorable to turtle activity are high humidity, warm sunny days, and frequent rains. The most unfavorable influences are low temperatures and drought. On most summer days there are some active turtles but individual turtles are not active every day. Periods of activity are alternated with periods of quiet even in favorable weather. This behavior is most pronounced in early spring and late fall when inactive days are often more numerous than active ones. Adult turtles occupy specific home ranges which they maintain from year to year. The turtles living in the study plot retained their ranges even through a flood that completely covered the area. Maximum home range diameters were determined by measurements of the mapped ranges of individual turtles. The average range of adult males was 330 feet, adult females 370 feet. The difference between male and female ranges was not statistically significant. There was no evidence of defense of territory. Ranges of turtles of all ages and both sexes overlapped grossly. Turtles were frequently found near each other and no antagonistic behavior was observed. A trail-laying device was developed in order to follow individual travel routes. The trailer consists of a light weight housing fastened to the turtle's back. It contains a spool of white thread that unwinds as the turtle moves, thus marking its exact route. Turtles selected for this more detailed study were followed with trailers for a total of 456 turtle days. Maps illustrating their travels are shown. Normal movements within the home range are characterized by, (1) turns, doublings, detours, and criss-crossing paths completely covering the area, (2) interspersion of fairly direct traverses of the home range, (3) frequently repeated travels over certain paths or routes. Trailer records and mapped collection records both show that the maximum limits of the home range are ordinarily reached within a few days or weeks. This general procedure is varied by some turtles to include intensive coverage of only one portion of the range at a time. Some turtles have two home ranges and travel between them at infrequent intervals. One turtle showing this behavior was followed with a trailer for 161 days during 1946 and 1947. Trips outside the home range are made by some turtles. These include egg laying trips by females as well as trips of unexplained nature made by both males and females. Turtles from other areas occasionally occur as transients in the study plot. The size of the population was estimated on the basis of collections during on

Ecological Monographs↗

USGS1972

Site distribution of iron in staurolite

The Mössbauer spectrum of staurolite does not necessarily indicate that ferrous iron is distributed over both the tetrahedral Fe site and one or more of the octahedral sites, as previously thought. Two doublets are present in the spectrum, but their quadrupole spliting and isomer shift are more consistent with both being due to tetrahedrally coordinated ferrous iron. Smith's X-ray work has shown that cations in the Fe site actually assume several slightly different positions, and iron in each of these positions may give rise to a different Mössbauer doublet.

Earth and Planetary Science Letters↗

USGS2011

Simulations of historical and future trends in snowfall and groundwater recharge for basins draining to Long Island Sound

A regional watershed model was developed for watersheds contributing to Long Island Sound, including the Connecticut River basin. The study region covers approximately 40 900 km 2 , extending from a moderate coastal climate zone in the south to a mountainous northern New England climate zone dominated by snowmelt in the north. The input data indicate that precipitation and temperature have been increasing for the last 46 years (1961– 2006) across the region. Minimum temperature has increased more than maximum temperature over the same period (1961–2006). The model simulation indicates that there was an upward trend in groundwater recharge across most of the modeled region. However, trends in increasing precipitation and groundwater recharge are not significant at the 0.05 level if the drought of 1961–67 is removed from the time series. The trend in simulated snowfall is not significant across much of the region, although there is a significant downward trend in southeast Connecticut and in central Massachusetts. To simulate future trends, two input datasets, one assuming high carbon emissions and one assuming low carbon emissions, were developed from GCM forecasts. Under both of the carbon emission scenarios, simulations indicate that historical trends will continue, with increases in groundwater recharge over much of the region and substantial snowfall decreases across Massachusetts, Connecticut, southern Vermont, and southern New Hampshire. The increases in groundwater recharge and decreases in snowfall are most pronounced for the high emission scenario.

Connecticut, Massachusetts, New Hampshire, Rhode I↗

USGS1973

Lead concentration and isotopic composition in five peridotite inclusions of probable mantle origin

The lead content of five whole-rock peridotite inclusions (four lherzolites and one harzburgite) in alkali basalt ranges from 82 to 570 ppb (parts per billion). Approximately 30–60 ppb of this amount can be accounted for by analyzed major silicate minerals (olivine ≤ 10 ppb; enstatite 5–28 ppb; chrome diopside ∼400 ppb). Through a series of acid leaching experiments, the remainder of the lead is shown to be quite labile and to reside in either glassy or microcrystalline veinlets or accessory mineral phases, such as apatite and mica. The lead isotopic composition of the peridotites ( 206 Pb/ 204 Pb= 18.01–18.90; 207 Pb/ 204 Pb= 15.52–15.61; 208 Pb/ 204 Pb= 37.80–38.86) lies within the range of values defined by many modern volcanic rocks and, in particular, is essentially coextensive with the abyssal tholeiite field. In all but one instance, isotopic differences were found between the peridotite and its host alkali basalt. Two of the peridotites clearly demonstrated internal isotopic heterogeneity between leachable and residual fractions that could not simply be due to contamination by the host basalt. However, there is no evidence that these ultramafic rocks form some layer in the mantle with isotopic characteristics fundamentally different from those of the magma sources of volcanic rocks.

Earth and Planetary Science Letters↗

USGS2011

Partially melted granodiorite and related rocks ejected from Crater Lake caldera, Oregon

Blocks of medium-grained granodiorite to 4 m, and minor diabase, quartz diorite, granite, aplite and granophyre, are common in ejecta of the ∼6,900 yrBP calderaforming eruption of Mount Mazama. The blocks show degrees of melting from 0–50 vol%. Because very few have adhering juvenile magma, it is thought that the blocks are fragments of the Holocene magma chamber's walls. Primary crystallisation of granodiorite produced phenocrystic pl + hyp + aug + mt + il + ap + zc, followed by qz + hb + bt + alkali feldspar (af). Presence of fluid inclusions in all samples implies complete crystallisation before melting. Subsolidus exchange with meteoric hydrothermal fluids before melting is evident in δ 18 O values of −3·4+4·9‰ for quartz and plagioclase in partially melted granodiorites (fresh lavas from the region have δ 18 O values of +5·8−+7·0‰); δ 18 O values of unmelted granodiorites from preclimatic eruptive units suggest hydrothermal exchange began between ∼70 and 24 ka. Before eruption, the granitic rocks equilibrated at temperatures, estimated from Fe-Ti oxide compositions, of up to ∼1000°C for c. 10 2 –10 4 years at a minimum pressure of 100-180 MPa. Heating caused progressive breakdown or dissolution of hb, af, bt, and qz, so that samples with the highest melt fractions have residual pl + qz and new or re-equilibrated af + hyp + aug + mt + il in high-silica rhyolitic glass (75-77% SiO 2 ). Mineral compositions vary systematically with increasing temperature. Hornblende is absent in rocks with Fe-Ti oxide temperatures >870°C, and bt above 970°C. Oxygen isotope fractionation between qz, pl, and glass in partially fused granodiorite also is consistent with equilibration at T≥900°C (Δ 18 O qz.pl = +0·7 ± 0·5‰). Element partitioning between glass and crystals reflects the large fraction of refractory pl, re-equilibration of af and isolation or incomplete dissolution of accessory phases. Ba and REE contents of analysed glass separates can be successfully modelled by observed degrees of partial melting of granodiorite, but Rb, Sr and Sc concentrations cannot. Several samples have veins of microlite-free glass 1–5 mm thick that are compositionally and physically continuous with intergranular melt and which apparently formed after the climactic eruption began. Whole-rock H 2 O content, microprobe glass analysis sums near 100% and evidence for high temperature suggest liquids in the hotter samples were nearly anhydrous. The occurrence of similar granodiorite blocks at all azimuths around the 8 × 10 km caldera implies derivation from one pluton. Compositional similarity between granodiorite and pre-Mazama rhyodacites suggests that the pluton may have crystallised as recently as 0·4 Ma; compositional data preclude crystallisation from the Holocene chamber. The history of crystallisation, hydrothermal alteration, and remelting of the granitic rocks may be characteristic of shallow igneous systems in which the balance between hydrothermal cooling and magmatic input changes repeatedly over intervals of 10 4 -10 6 years.

Oregon↗

USGS2017

Geologic map of the northeast flank of Mauna Loa volcano, Island of Hawai'i, Hawaii

Summary Mauna Loa, the largest volcano on Earth, has erupted 33 times since written descriptions became available in 1832. Some eruptions were preceded by only brief seismic unrest, while others followed several months to a year of increased seismicity. The majority of the eruptions of Mauna Loa began in the summit area (>12,000-ft elevation; Lockwood and Lipman, 1987); yet the Northeast Rift Zone (NERZ) was the source of eight flank eruptions since 1843 (table 1). This zone extends from the 13,680-ft-high summit towards Hilo (population ~60,000), the second largest city in the State of Hawaii. Although most of the source vents are farther than 30 km away, the 1880 flow from one of the vents extends into Hilo, nearly reaching Hilo Bay. The city is built entirely on flows erupted from the NERZ, most older than that erupted in 1843. Once underway, Mauna Loa's eruptions can produce lava flows that reach the sea in less than 24 hours, severing roads and utilities in their path. For example, lava flows erupted from the Southwest Rift Zone (SWRZ) in 1950 advanced at an average rate of 9.3 km per hour, and all three lobes reached the ocean within approximately 24 hours (Finch and Macdonald, 1953). The flows near the eruptive vents must have traveled even faster. In terms of eruption frequency, pre-eruption warning, and rapid flow emplacement, Mauna Loa poses an enormous volcanic-hazard threat to the Island of Hawai‘i. By documenting past activity and by alerting the public and local government officials of our findings, we can anticipate the volcanic hazards and substantially mitigate the risks associated with an eruption of this massive edifice. From the geologic record, we can deduce several generalized facts about the geologic history of the NERZ. The middle to the uppermost section of the rift zone were more active in the past 4,000 years than the lower part, perhaps due to buttressing of the lower east rift zone by Mauna Kea and Kīlauea volcanoes. The historical flows that erupted on the north flank of the rift zone, which is more vulnerable to inundation, advanced toward Hilo. Lockwood (1990) noted that the vents of historical activity are migrating to the south. The volcano appears to have a self-regulating mechanism that evenly distributes long-term activity across its flanks. The geologic record also supports this notion; the time prior to the historical period (Age Group 1, orange units, pre-A.D. 1843–1,000 yr B.P.; see map sheet 2) is dominated by activity on the south side of the NERZ. The NERZ trends N. 65° E. and is about 40 km long and 2–4 km wide, narrowing at the summit caldera. It becomes diffuse (6–7 km wide) at its down-rift terminus, at the approximately 3,400-ft elevation. Its constructional crest is marked by low spatter ramparts and by spatter cones as high as 60 m. Subparallel eruptive fissures and ground cracks cut vent deposits and flows in and near the rift crest. Lava typically flows to the north, east, or south, depending on vent location relative to the rift crest. Encompassing 1,140 km 2 of the northeast flank of Mauna Loa from the 10,880-ft elevation to sea level, the map covers the area from Hilo to Volcano on the east and includes the rift zone from Puu Ulaula quadrangle in the southwest to Hilo in the northeast. The distribution of 105 eruptive units (flows)—separated into 15 age groups ranging from more than 30,000 years B.P. to A.D. 1984—are shown, as well as the relations of volcanic and surficial sedimentary deposits. This map incorporates previously reported work published in generalized small-scale maps (Lockwood and Lipman, 1987; Buchanan-Banks, 1993; Lockwood, 1995; and Wolfe and Morris, 1996).

Hawaii↗

USGS2017

Challenges in recovering resources from acid mine drainage

Metal recovery from mine waters and effluents is not a new approach but one that has occurred largely opportunistically over the last four millennia. Due to the need for low-cost resources and increasingly stringent environmental conditions, mine waters are being considered in a fresh light with a designed, deliberate approach to resource recovery often as part of a larger water treatment evaluation. Mine water chemistry is highly dependent on many factors including geology, ore deposit composition and mineralogy, mining methods, climate, site hydrology, and others. Mine waters are typically Ca-Mg-SO4±Al±Fe with a broad range in pH and metal content. The main issue in recovering components of these waters having potential economic value, such as base metals or rare earth elements, is the separation of these from more reactive metals such as Fe and Al. Broad categories of methods for separating and extracting substances from acidic mine drainage are chemical and biological. Chemical methods include solution, physicochemical, and electrochemical technologies. Advances in membrane techniques such as reverse osmosis have been substantial and the technique is both physical and chemical. Biological methods may be further divided into microbiological and macrobiological, but only the former is considered here as a recovery method, as the latter is typically used as a passive form of water treatment.

Conference Paper↗

USGS2014

Three-dimensional seismic velocity structure of Mauna Loa and Kilauea volcanoes in Hawaii from local seismic tomography

We present a new three-dimensional seismic velocity model of the crustal and upper mantle structure for Mauna Loa and Kilauea volcanoes in Hawaii. Our model is derived from the first-arrival times of the compressional and shear waves from about 53,000 events on and near the Island of Hawaii between 1992 and 2009 recorded by the Hawaiian Volcano Observatory stations. The V p model generally agrees with previous studies, showing high-velocity anomalies near the calderas and rift zones and low-velocity anomalies in the fault systems. The most significant difference from previous models is in V p / V s structure. The high- V p and high- V p / V s anomalies below Mauna Loa caldera are interpreted as mafic magmatic cumulates. The observed low- V p and high- V p / V s bodies in the Kaoiki seismic zone between 5 and 15 km depth are attributed to the underlying volcaniclastic sediments. The high- V p and moderate- to low- V p / V s anomalies beneath Kilauea caldera can be explained by a combination of different mafic compositions, likely to be olivine-rich gabbro and dunite. The systematically low- V p and low- V p / V s bodies in the southeast flank of Kilauea may be caused by the presence of volatiles. Another difference between this study and previous ones is the improved V p model resolution in deeper layers, owing to the inclusion of events with large epicentral distances. The new velocity model is used to relocate the seismicity of Mauna Loa and Kilauea for improved absolute locations and ultimately to develop a high-precision earthquake catalog using waveform cross-correlation data.

Hawaii↗

USGS2016

Lithospheric flexure under the Hawaiian volcanic load: Internal stresses and a broken plate revealed by earthquakes

Several lines of earthquake evidence indicate that the lithospheric plate is broken under the load of the island of Hawai`i, where the geometry of the lithosphere is circular with a central depression. The plate bends concave downward surrounding a stress-free hole, rather than bending concave upward as with past assumptions. Earthquake focal mechanisms show that the center of load stress and the weak hole is between the summits of Mauna Loa and Mauna Kea where the load is greatest. The earthquake gap at 21 km depth coincides with the predicted neutral plane of flexure where horizontal stress changes sign. Focal mechanism P axes below the neutral plane display a striking radial pattern pointing to the stress center. Earthquakes above the neutral plane in the north part of the island have opposite stress patterns; T axes tend to be radial. The M 6.2 Honomu and M 6.7 Kiholo main shocks (both at 39 km depth) are below the neutral plane and show radial compression, and the M 6.0 Kiholo aftershock above the neutral plane has tangential compression. Earthquakes deeper than 20 km define a donut of seismicity around the stress center where flexural bending is a maximum. The hole is interpreted as the soft center where the lithospheric plate is broken. Kilauea's deep conduit is seismically active because it is in the ring of maximum bending. A simplified two-dimensional stress model for a bending slab with a load at one end yields stress orientations that agree with earthquake stress axes and radial P axes below the neutral plane. A previous inversion of deep Hawaiian focal mechanisms found a circular solution around the stress center that agrees with the model. For horizontal faults, the shear stress within the bending slab matches the slip in the deep Kilauea seismic zone and enhances outward slip of active flanks.

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