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USGS2018

Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2015

This report continues the practice where the IAU Working Group on Cartographic Coordinates and Rotational Elements revises recommendations regarding those topics for the planets, satellites, minor planets, and comets approximately every three years. The Working Group has now become a “functional working group” of the IAU and its membership is open to anyone interested in participating. We describe the procedure for submitting questions about the recommendations given here or the application of these recommendations for creating a new or updated coordinate system for a given body. Regarding body orientation, the following bodies have been updated: Mercury, based on MESSENGER results; Mars, along with a refined longitude definition; Phobos; Deimos; (1) Ceres; (52) Europa; (243) Ida; (2867) Šteins; Neptune; (134340) Pluto and its satellite Charon; comets 9P/Tempel 1, 19P/Borrelly, 67P/Churyumov-Gerasimenko, and 103P/Hartley 2, noting that such information is valid only between specific epochs. The special challenges related to mapping 67P/Churyumov-Gerasimenko are also discussed. Approximate expressions for the Earth have been removed in order to avoid confusion, and the low precision series expression for the Moon’s orientation has been removed. The previously on-line only recommended orientation model for (4) Vesta is repeated with an explanation of how it was updated. Regarding body shape, text has been included to explain the expected uses of such information, and the relevance of the cited uncertainty information. The size of the Sun has been updated and notation added that the size and the ellipsoidal axes for the Earth and Jupiter have been recommended by an IAU Resolution. The distinction of a reference radius for a body (here, the Moon and Titan) is made between cartographic uses, and for orthoprojection and geophysical uses. The recommended radius for Mercury has been updated based on MESSENGER results. The recommended radius for Titan is returned to its previous value. Size information has been updated for 13 other Saturnian satellites and added for Aegaeon. The sizes of Pluto and Charon have been updated. Size information has been updated for (1) Ceres and given for (16) Psyche and (52) Europa. The size of (25143) Itokawa has been corrected. In addition, the discussion of terminology for the poles (hemispheres) of small bodies has been modified and a discussion on cardinal directions added. Although they continue to be used for planets and their satellites, it is assumed that the planetographic and planetocentric coordinate system definitions do not apply to small bodies. However, planetocentric and planetodetic latitudes and longitudes may be used on such bodies, following the right-hand rule. We repeat our previous recommendations that planning and efforts be made to make controlled cartographic products; newly recommend that common formulations should be used for orientation and size; continue to recommend that a community consensus be developed for the orientation models of Jupiter and Saturn; newly recommend that historical summaries of the coordinate systems for given bodies should be developed, and point out that for planets and satellites planetographic systems have generally been historically preferred over planetocentric systems, and that in cases when planetographic coordinates have been widely used in the past, there is no obvious advantage to switching to the use of planetocentric coordinates. The Working Group also requests community input on the question submitting process, posting of updates to the Working Group website, and on whether recommendations should be made regarding exoplanet coordinate systems.

Celestial Mechanics and Dynamical Astronomy↗

USGS2023

Bringing the Nature Futures Framework to life: Creating a set of illustrative narratives of nature futures

To halt further destruction of the biosphere, most people and societies around the globe need to transform their relationships with nature. The internationally agreed vision under the Convention of Biological Diversity—Living in harmony with nature—is that “By 2050, biodiversity is valued, conserved, restored and wisely used, maintaining ecosystem services, sustaining a healthy planet and delivering benefits essential for all people”. In this context, there are a variety of debates between alternative perspectives on how to achieve this vision. Yet, scenarios and models that are able to explore these debates in the context of “living in harmony with nature” have not been widely developed. To address this gap, the Nature Futures Framework has been developed to catalyse the development of new scenarios and models that embrace a plurality of perspectives on desirable futures for nature and people. In this paper, members of the IPBES task force on scenarios and models provide an example of how the Nature Futures Framework can be implemented for the development of illustrative narratives representing a diversity of desirable nature futures: information that can be used to assess and develop scenarios and models whilst acknowledging the underpinning value perspectives on nature. Here, the term illustrative reflects the multiple ways in which desired nature futures can be captured by these narratives. In addition, to explore the interdependence between narratives, and therefore their potential to be translated into scenarios and models, the six narratives developed here were assessed around three areas of the transformative change debate, specifically, (1) land sparing vs. land sharing, (2) Half Earth vs. Whole Earth conservation, and (3) green growth vs. post-growth economic development. The paper concludes with an assessment of how the Nature Futures Framework could be used to assist in developing and articulating transformative pathways towards desirable nature futures.

Sustainability Science↗

USGS2017

Assessment of critical minerals: Updated application of an early-warning screening methodology

Increasing reliance on non-renewable mineral resources reinforces the need for identifying potential supply constraints before they occur. The US National Science and Technology Council recently released a report that outlines a methodology for screening potentially critical minerals based on three indicators: supply risk ( R ), production growth ( G ), and market dynamics ( M ). This early-warning screening was initially applied to 78 minerals across the years 1996 to 2013 and identified a subset of minerals as “potentially critical” based on the geometric average of these indicators—designated as criticality potential ( C ). In this study, the screening methodology has been updated to include data for 2014, as well as to incorporate revisions and modifications to the data, where applicable. Overall, C declined in 2014 for the majority of minerals examined largely due to decreases in production concentration and price volatility. However, the results vary considerably across minerals, with some minerals, such as gallium, recording increases for all three indicators. In addition to assessing magnitudinal changes, this analysis also examines the significance of the change relative to historical variation for each mineral. For example, although mined nickel’s R declined modestly in 2014 in comparison to that of other minerals, it was by far the largest annual change recorded for mined nickel across all years examined and is attributable to Indonesia’s ban on the export of unprocessed minerals. Based on the 2014 results, 20 minerals with the highest C values have been identified for further study including the rare earths, gallium, germanium, rhodium, tantalum, and tungsten.

Mineral Economics↗

USGS1967

Petrology of eucrites, howardites and mesosiderites

The eucrite and howardite calcium-rich achondrites and many mesosiderites are considered as a coherent meteorite assemblage, their silicates consisting essentially of calciumpoor monoclinic and orthorhombic pyroxenes and calcium-rich plagioclase feldspar. The achondrites can be grouped according to their brecciated structure as follows: eucrites—unbrecciated and monomict brecciated achondrites; howardites—polymict brecciated achondrites. Many mesosiderites contain brecciated structures; they are distinguished from the achondrites by their large metallic fraction. The structure and composition of rock fragments in the breccias indicate a complicated sequence of events including magmatic differentiation, brecciation, recrystallization and refragmentation, and ejection from the parent body. Detailed mineralogical and chemical data suggest that the magmatic differentiation proceeded primarily by the separation of pyroxene from an ultrabasic parent material that had a much lower alkali content than ordinary chondrites. Magmatic crystallization took place in environments ranging from extrusive to deep-seated intrusive. Polymict breccias contain fragments with a wide variety of magmatic and recrystallization textures, which suggests that the breccias were formed either in very large or repeated fragmentation events. Monomict breccias contain fragments with a small range of similar magmatic textures, which suggests that these breccias were formed by small or single events. Petrographic evidence suggests that many of the breccias are impact breccias. Either in their original magmatic crystallization sites or in the sites of breccia accumulation, most of these meteorites apparently had a near-surface location prior to ejection from the parent body. Evidence obtained from eucrites, howardites and mesosiderites forms an important part of our understanding of the early evolution of the surface regions of their parent body. Chemical and oxidation conditions were different from those presently found in the Earth's crust and upper mantle, but the necessary conditions may have been present in the early history of the Earth. A lunar origin for eucrites, howardites and mesosiderites is proposed, but an asteroidal origin can not be presently excluded.

Geochimica et Cosmochimica Acta↗

USGS1975

A high 87Sr 86Sr mantle source for low alkali tholeiite, northern Great Basin

Olivine tholeiites, the youngest Tertiary units (about 8–11 m.y. old) at five widely spaced localities in northeastern Nevada, are geologically related to the basalts of the Snake River Plain, Idaho, to the north and are similar in major element and alkali chemistry to mid-ocean ridge basalts (MORB) and island arc tholeiites. The measured K (1250–3350 ppm), Rb (1·9–6·2 ppm) and Sr (140–240 ppm) concentrations overlap the range reported for MORB. Three of the five samples have low, unfractionated rare earth element (REE) patterns, the other two show moderate light-REE enrichment. Barium concentration is high and variable (100–780 ppm) and does not correlate with the other LIL elements. The rocks have 87 Sr / 86 Sr = 0·7052–0·7076, considerably higher than MORB (~0·702–0·703). These samples are chemically distinct (i.e. less alkalic) from the olivine tholeiites from the adjacent Snake River Plain, but their Sr isotopic compositions are similar. They contain Sr that is distinctly more radiogenic than the basalts from the adjacent Great Basin. About 10 b.y. would be required for the mean measured Rb/Sr (~ 0·02) of these samples to generate, in a closed system, the radiogenic Sr they contain. The low alkali content of these basalts makes crustal contamination an unlikely mechanism. If the magma is uncontaminated, the time-averaged Rb/Sr of the source material must have been ~0·04. A significant decrease in Rb/Sr of the source material (a factor 2̆) thus most probably occurred in the relatively recent (1̌0 9 yr) past. Such a decrease of Rb/Sr in the mantle could accompany alkali depletion produced by an episode of partial melting and magma extraction. In contrast, low 87 Sr 86 Sr "> 87Sr86Sr ratios indicate that the source material of the mid-ocean ridge basalts may have been depleted early in the Earth's history.

Geochimica et Cosmochimica Acta↗

USGS1979

Chemical composition of Mars

The composition of Mars has been calculated from the cosmochemical model of Ganapathy and Anders (1974) which assumes that planets and chondrites underwent the same 4 fractionation processes in the solar nebula. Because elements of similar volatility stay together in these processes, only 4 index elements (U, Fe, K and Tl or Ar 36 ) are needed to calculate the abundances of all 83 elements in the planet. The values chosen are U = 28 ppb , K = 62 ppm (based on K U = 2200 "> KU= 2200 from orbital γ-spectrometry and on thermal history calculations by Toksöz and Hsui (1978) Fe = 26.72% (from geophysical data), and Tl = 0.14 ppb (from the Ar 36 and Ar 40 abundances measured by Viking). The mantle of Mars is an iron-rich [ Mg /( Mg + Fe ) = 0.77] garnet wehrlite ( ρ = 3.52−3.54 g / cm 3 ), similar to McGetchin and Smyth's (1978) estimate but containing more Ca and Al. It is nearly identical to the bulk Moon composition of Morgan et al. (1978b). The core makes up 0.19 of the planet and contains 3.5% S—much less than estimated by other models. Volatiles have nearly Moon-like abundances, being depleted relative to the Earth by factors of 0.36 (K-group, T cond = 600–1300 K ) or 0.029 (Tl group, T cond < 600 K ). The water abundance corresponds to a 9 m layer, but could be higher by as much as a factor of 11. Comparison of model compositions for 5 differentiated planets (Earth, Venus, Mars, Moon, and eucrite parent body) suggests that volatile depletion correlates mainly with size rather than with radial distance from the Sun. However, the relatively high volatile content of shergottites and some chondrites shows that the correlation is not simple; other factors must also be involved.

Geochimica et Cosmochimica Acta↗

USGS1994

A precise 232Th-208Pb chronology of fine-grained monazite: Age of the Bayan Obo REE-Fe-Nb ore deposit, China

We have obtained precise Th-Pb internal isochron ages on monazite and bastnaesite for the world's largest known rare earth elements (REE)-Fe-Nb ore deposit, the Bayan Obo of Inner Mongolia, China. The monazite samples, collected from the carbonate-hosted ore zone, contain extremely small amounts of uranium (less than 10 ppm) but up to 0.7% ThO 2 . Previous estimates of the age of mineralization ranged from 1.8 to 0.255 Ga. Magnetic fractions of monazite and bastnaesite samples (<60-μm size) showed large ranges in 232 Th 204 Pb "> 232 Th 204 Pb values (900–400,000) and provided precise Th-Pb internal isochron ages for paragenetic monazite mineralization ranging from 555 to 398 Ma within a few percent error (0.8% for two samples). These results are the first indication that REE mineralization within the giant Bayan Obo ore deposit occurred over a long period of time. The initial lead isotopic compositions (low 206 Pb 204 Pb "> 206 Pb 204 Pb and high 208 Pb 204 Pb) "> 208 Pb 204 Pb) and large negative ϵ Nd values for Bayan Obo ore minerals indicate that the main source(s) for the ores was the lower crust which was depleted in uranium, but enriched in thorium and light rare earth elements for a long period of time. Zircon from a quartz monzonite, located 50 km south of the ore complex and thought to be related to Caledonian subduction, gave an age of 451 Ma, within the range of monazite ages. Textural relations together with the mineral ages favor an epigenetic rather than a syngenetic origin for the orebodies. REE mineralization started around 555 Ma (disseminated monazite in the West, the Main, and south of the East Orebody), but the main mineralization (banded ores) was related to the Caledonian subduction event ca. 474-400 Ma.

Bayan Obo, Kuanggou Fault↗

USGS1967

An operational theory of laser-radar selenodesy

A theory of the utilization of laser techniques for ranging from the Earth to the Moon for the purpose of providing control points on the lunar surface at which the figure of the Moon is measured to an accuracy at least an order of magnitude better than that of the present astrometric measurements is presented. This, in turn, increases the accuracy of the horizontal selenocentric coordinates of topographical features measured by present astrometric methods. The improvement in the vertical and horizontal coordinates of control points in the Apollo landing zone will aid in the analysis of Unmanned Lunar Orbiter photographs for the selection of Apollo landing sites. The present discussion proposes the means of obtaining the ground control upon which the Orbiter photogrammetry is to be fastened. In addition, a technique of combining Goldstone tracking data to show where the resulting lunar figure is positioned relative to the Moon's center of mass is presented. If corner reflectors are placed on the lunar surface, as suggested by many members of the scientific community, or on a lunar orbiting vehicle, one or more Earth-based laser ranging systems are essential. These reflectors will give enough enhancement in return signal to allow for an additional increase in range accuracy of one to two orders of magnitude. In addition to the primary data on the figure of the Moon, a number of other measurements of scientific importance are then readily obtainable. As far as the measurement of control points is concerned, however, the use of corner reflectors is not essential for the success of this project. Questions regarding the influence on the present shape of the Moon of the frozen tide, isostasy, and past impacts of large asteroids appear in large part answerable through the data which are indicated to be obtainable under the present theory.

Icarus↗

USGS1987

Nucleation and triggering of earthquake slip: Effect of periodic stresses

Results of stability analyses for spring and slider systems, with state variable constitutive properties, are applied to slip on embedded fault patches. Unstable slip may nucleate only if the slipping patch exceeds some minimum size. Subsequent to the onset of instability the earthquake slip may propagate well beyond the patch. It is proposed that the seismicity of a volume of the earth's crust is determined by the distribution of initial conditions on the population of fault patches that nucleate earthquake slip, and the loading history acting upon the volume. Patches with constitutive properties inferred from laboratory experiments are characterized by an interval of self-driven accelerating slip prior to instability, if initial stress exceeds a minimum threshold. This delayed instability of the patches provides an explanation for the occurrence of aftershocks and foreshocks including decay of earthquake rates by time −1 . A population of patches subjected to loading with a periodic component results in periodic variation of the rate of occurrence of instabilities. The change of the rate of seismicity for a sinusoidal load is proportional to the amplitude of the periodic stress component and inversely proportional to both the normal stress acting on the fault patches and the constitutive parameter, A 1 , that controls the direct velocity dependence of fault slip. Values of A 1 representative of laboratory experiments indicate that in a homogeneous crust, correlation of earthquake rates with earth tides should not be detectable at normal stresses in excess of about 8 MPa. Correlation of earthquakes with tides at higher normal stresses can be explained if there exist inhomogeneities that locally amplify the magnitude of the tidal stresses. Such amplification might occur near magma chambers or other soft inclusions in the crust and possibly near the ends of creeping fault segments if the creep or afterslip rates vary in response to tides. Observations of seismicity rate variations associated with seasonal fluctuations of reservoir levels appear to be consistent with the model.

Tectonophysics↗

USGS1992

The international seismological observing period in Africa

The International Seismological Observing Period (ISOP) is a specific time interval designated for enhanced international cooperation in the collection and dissemination of observatory measurements from the global seismographic network. The primary purpose of the ISOP is to strengthen the international infrastructure that supports current seismological practice and increase the cooperation among nations that operate seismological observatories. Measurements, reported by the existing global network and compiled by agencies such as the International Seismological Centre (ISC), are providing new information about earthquakes and the structure of the Earth of fundamental importance to the Earth sciences. However, these data represent but a small fraction of the information contained in the seismograms. One of the goals of the ISOP is to collect improved sets of data. In particular, the measurement and reporting of later-arriving phases, during a fixed ISOP period, from earthquakes selected for detailed observation by the cooperating stations will be encouraged. The use of advanced, digital instrumentation provides an unprecedented opportunity for enhancing the methods of seismogram interpretation and seismic parameter extraction, by the implementation of digital processing methods at seismic observatories worldwide. It must be ensured that this new information will be available to the entire seismological community. It is believed that this purpose is best served with an ISOP that promotes increased on-site processing at digital stations in Africa and elsewhere. Improvements in seismology require truly international cooperation and the educational aspects of seismological practice form one of the goals of the ISOP. Thus, workshops will be needed in Africa to train analysts in ISOP procedures and to introduce them to modern techniques and applications of the data. Participants will, thus, benefit from theoretical results and practical experience that are of direct relevance to their own work.

Tectonophysics↗

USGS1994

The Nd-, Sr- and Pb-isotopic character of lavas from Taal, Laguna de Bay and Arayat volcanoes, southwestern Luzon, Philippines: Implications for arc magma petrogenesis

Following the amalgamation of a collage of pre-Neogene terranes largely by strike-slip and convergence mechanisms to form the Philippine islands, volcanic chains, related to oppositely dipping subduction zones, developed along the eastern and western margins of the archipelago. There is ample field evidence that this volcanic activity, predominantly calc-alkaline in chemical character, had commenced by the Oligocene. Volcanoes resulting from subduction along the Manila-Negros trench in the west (e.g. Taal, Laguna de Bay and Arayat) form a high-angle linear array, trending away from the MORE field on Pb-isotopic covariation diagrams; have the highest Sr- and lowest Nd-isotopic compositions, of the two chains (but nevertheless plotting above bulk earth on the 87 Sr/ 86 Sr versus 143 Nd/ 144 Nd covariation diagram); and exhibit Sm/Nd and Rb/Sr values that are lower and higher, respectively, than the estimated values for bulk earth. While the Sm/Nd and Rb/Sr characteristics are common to both chains, volcanoes associated with the Philippine-East Luzon trench have Pb-isotopic compositions that fall in the Indian Ocean MORB field and that require time-integrated evolution in a high Th/U environment. They also have higher Nd- and lower Sr-isotopic ratios. The source materials of Philippine volcanoes, therefore, have undergone varied recent enrichments in LILE, as indicated by the decoupling of isotopic and elemental ratios. These enrichments, particularly for the western volcanoes, cannot be entirely due to small degrees of partial melting in the mantle wedge, considering that they were accompanied by elevations in radiogenic Pb. Elevated Pb ratios are best explained by the introduction of subducted, continentally derived sediments. The sedimentary component in the western volcanoes is probably the South China Sea sediments derived largely from Eurasia. That this component is not available in the Philippine-East Luzon trench is reflected by the fact that the eastern volcanoes have higher Nd- and lower Sr-isotopic ratios as well as less radiogenic common Pb.

southwestern Luzon↗

USGS1995

Abnormal chemical element concentrations in lichens of Isle Royale National Park

Lichens have been used for many years to monitor changes in deposited airborne chemical elements in many areas, but few studies have focused on areas suspected of experiencing slightly elevated pollution. Detection of subtle patterns of slightly elevated pollutants calls for developing several lines of evidence as opposed to single line studies used in heavily polluted areas. This study of two lichen species, Hypogymnia physodes and Evernia mesomorpha , in Isle Royale National Park, Michigan compares the concentrations and ranks of elements with the concentrations and ranks of the elements in the earth's crust, changes in element concentrations over a nine year period, and the geography of element concentrations in the park. S, Zn, Pb, Cd and Se were elevated in both species and higher in rank compared to the concentrations and ranks in the earth's crust. Toxic elements increased 123% in Hypogymnia and 62% in Evernia over 9 years, compared to increases of 45% and 59% for non-toxic elements in each species, respectively. Geographically, the lichens at certain localities with higher exposures experienced higher than average element concentrations. Finally, tissue concentrations of Mn, S and Se at some localities were above levels known to be either toxic or similar to those found in polluted areas. These four lines of evidence suggest that Isle Royale National Park is experiencing the onset of chronic air pollution stress from a number of sources.

Michigan↗

USGS1989

Chemistry and origin of minor and trace elements in vitrinite concentrates from a rank series from the eastern United States, England, and Australia

A rank series consisting of twelve vitrinite concentrates and companion whole-coal samples from mined coal beds in the eastern United States, England, and Australia were analyzed for C, H, N, O, ash, and 47 trace and minor elements by standard elemental, instrumental neutron activation analysis (INAA), and direct-current-arc spectrographic (DCAS) techniques. The reflectance of vitrinite, atomic H:C and O:C, and ash-free carbon data were used to determine ranks that range from high-volatile C bituminous coal to meta-anthracite. A van Krevelen (atomic H:C vs. O:C) diagram of the vitrinite concentrates shows a smooth curve having its lowest point at H:C = 0.18 and O:C = 0.01. This improves the van Krevelen diagram by the addition of our vitrinite concentrate from meta-anthracite from the Narragansett basin of New England. Boron content (400–450 ppm) in two Illinois basin vitrinite concentrates was about an order of magnitude higher than B contents in other concentrates analyzed. We attribute this to marine origin or hydrothermal activity. The alkaline-earth elements Ca, Mg and Ba (DCAS) have higher concentrations in our vitrinite concentrates from bituminous coals of the Appalachian basin, than they do in vitrinite concentrates from the marine-roofed bituminous coals of the Illinois basin; therefore, a nonmarine origin for these alkaline-earth elements is postulated for the Appalachian basin coals. An ion-exchange mechanism due to high concentrations of these elements as ions in diagenetic water, but probably not recent ground water, may be responsible for the relatively high values of these elements in Appalachian concentrates. Higher concentrations of Ni and Cr in one of the English vitrinite concentrates and of Zr in the Australian concentrate probably indicate organic association and detrital influence, respectively.

International Journal of Coal Geology↗

USGS1994

Deglaciation, lake levels, and meltwater discharge in the Lake Michigan basin

The deglacial history of the Lake Michigan basin, including discharge and routing of meltwater, is complex because of the interaction among (1) glacial retreats and re-advances in the basin (2) the timing of occupation and the isostatic adjustment of lake outlets and (3) the depositional and erosional processes that left evidence of past lake levels. In the southern part of the basin, a restricted area little affected by differential isostasy, new studies of onshore and offshore areas allow refinement of a lake-level history that has evolved over 100 years. Important new data include the recognition of two periods of influx of meltwater from Lake Agassiz into the basin and details of the highstands gleaned from sedimentological evidence. Major disagreements still persist concerning the exact timing and lake-level changes associated with the Algonquin phase, approximately 11,000 BP. A wide variety of independent data suggests that the Lake Michigan Lobe was thin, unstable, and subject to rapid advances and retreats. Consequently, lake-level changes were commonly abrupt and stable shorelines were short-lived. The long-held beliefs that the southern part of the basin was stable and separated from deformed northern areas by a hinge-line discontinuity are becoming difficult to maintain. Numerical modeling of the ice-earth system and empirical modeling of shoreline deformation are both consistent with observed shoreline tilting in the north and with the amount and pattern of modern deformation shown by lake-level gauges. New studies of subaerial lacustrine features suggest the presence of deformed shorelines higher than those originally ascribed to the supposed horizontal Glenwood level. Finally, the Lake Michigan region as a whole appears to behave in a similar manner to other areas, both local (other Great Lakes) and regional (U.S. east coast), that have experienced major isostatic changes. Detailed sedimentological and dating studies of field sites and additional development of geophysical models offer hope for reconciling the field data with our understanding of earth rheology. ?? 1995.

Lake Michigan Basin↗

USGS1995

Volcanic and structural evolution of Taupo Volcanic Zone, New Zealand: A review

The Taupo Volcanic Zone (TVZ) in the central North Island is the main focus of young volcanism in New Zealand. Andesitic activity started at c. 2 Ma, joined by voluminous rhyolitic (plus minor basaltic and dacitic) activity from c. 1.6 Ma. The TVZ is c. 300 km long (200 km on land) and up to 60 km wide, as defined by vent positions and caldera structural boundaries. The total volume of TVZ volcanic deposits is uncertain because a sub-volcanic basement has not been identified, but present data suggest bulk volumes of 15–20,000 km 3 , and that faulted metasediments form most of the immediate subvolcanic basement. Rhyolite (≥15,000 km 3 bulk volume, typically 70–77% SiO 2 ) is the dominant magma erupted in the TVZ (mostly as calderaforming ignimbrite eruptions), andesite is an order of magnitude less abundant, and basalt and dacite are minor in volume (< 100 km 3 each). The history of the TVZ is here divided into ‘old TVZ’ from 2.0 Ma to 0.34 Ma, and ‘young TVZ’ from 0.34 Ma onwards, separated by the Whakamaru eruptions, which obscured much of the evidence for older activity within the zone. The TVZ shows a pronounced segmentation into northeastern and southwestern andesite-dominated extremities with composite cones and no calderas, and a central 125-km-long rhyolite-dominated segment. Eight rhyolitic caldera centres have so far been identified in the central segment, of which two (Mangakino and Kapenga) are composite features, and more centres will probably be delineated as further data accumulate. These centres account for 34 inferred caldera-forming ignimbrite eruptions, in the c. 1.6-Ma lifetime of the central TVZ. The modern central TVZ is the most frequently active and productive silicic volcanic system on Earth, erupting rhyolite at c. 0.28 m 3 s −1 , and available information suggests this has been so for at least the past 0.34 Ma. The rhyolites show no major compositional changes with time, though the extent of magma chamber zonation may have changed with the incoming of rifting and crustal extension in the past c. 0.9 Ma. Within the central TVZ, non-rhyolitic compositions have been erupted apparently irregularly in time and space; in particular there is no evidence for a geographic separation of basalts from andesites. Between 0.9 and 0.34 Ma, a major episode of uplift affected areas around the TVZ, while at the same time the main focus of activity may have migrated eastwards within the TVZ accompanying rifting along the axis of the zone. The modern TVZ is rifting at rates between 7 and 18 mm a −1 and restoration of the thin (15km) ‘crust’ ( V p ≤ 6.1 km s −1 ) beneath the central TVZ to its pre-rifting thickness (25 km) implies that rifting at such rates may have begun only at c. 0.9 Ma. The TVZ is a rifted arc, but its longitudinally segmented nature, high thermal flux and voluminous rhyolitic volcanism make it unique on Earth.

Taupo Volcanic Field↗

USGS1990

Global data collection and the surveillance of active volcanoes

Data relay systems on existing earth-orbiting satellites provide an inexpensive way to collect environmental data from numerous remote sites around the world. This technology could be used effectively for fundamental monitoring of most of the world's active volcanoes. Such global monitoring would focus attention on the most dangerous volcanoes that are likely to significantly impact the geosphere and the biosphere.

Palaeogeography, Palaeoclimatology, Palaeoecology↗

USGS2007

The geochemistry of pesticides

The mid-1970s marked a major turning point in human history, for it was at that moment that the ability of the Earth’s ecosystems to absorb most of the biological impacts of human activities appears to have been exceeded by the magnitude of those impacts. This conclusion is based partly upon estimates of the rate of carbon dioxide emission during the combustion of fossil fuels, relative to the rate of its uptake by terrestrial ecosystems ( Loh, 2002 ). A very different threshold, however, had already been crossed several decades earlier with the birth of the modern chemical industry, which produced novel substances for which no such natural assimilative capacity existed. Among these new chemical compounds, none has posed a greater challenge to the planet’s ecosystems than synthetic pesticides, compounds that have been intentionally released into the hydrologic system in vast quantities—several hundred million pounds of active ingredient (a.i.) per year in the United States alone ( Donaldson et al. , 2002 )—for many decades. To gauge the extent to which we are currently able to assess the environmental implications of this new development in the Earth’s history, this chapter presents an overview of current understanding regarding the sources, transport, fate, and biological effects of pesticides, their transformation products, and selected adjuvants in the hydrologic system. (Adjuvants are the so-called inert ingredients included in commercial pesticide formulations to enhance the effectiveness of the active ingredients.)

Book chapter↗

USGS2021

Dating by cosmogenic nuclides

Since the 1990s, cosmogenic nuclides have revolutionized the study of Earth surface processes, particularly the understanding of rates and dates. These nuclides, including 3 He, 10 Be, 14 C, 21 Ne, 26 Al, and 36 Cl, enable dating of landforms and the measurement of erosion rates both at the scale of drainage basins and at specific locations on Earth's surface. Cosmogenic nuclides are produced at low rates (several to hundreds of atoms per gram per year) by the interaction of cosmic rays with elements both in the atmosphere and in surficial materials, including in rock and soil. Measuring nuclide concentrations requires elemental separation from source geologic material followed by counting of atoms using sensitive accelerator mass spectrometers. Because nuclide production rates have been quantified, the measured concentration of these nuclides can be interpreted as a near-surface residence time. Here, we review the systematics of commonly used cosmogenic nuclides, describe how they are extracted and measured, and then present case studies focusing on the most commonly measured cosmogenic nuclide, 10 Be. We present common applications such as dating surface features, including moraines and outcrops shaped by glaciation, the use of cosmogenic nuclides for inferring tectonic and erosion processes in drainage basins, and the use of these nuclides to trace sediment sources in drainage basins. When multiple nuclides are measured in one sample, they can be used to model burial and exposure histories in stratigraphic sections. We conclude by exploring what the future might bring in terms of measurements and applications.

Book chapter↗