Annual Review of Earth and Planetary Sciences - Volume 25, 1997
Volume 25, 1997
- Preface
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- Review Articles
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HYDROCHEMISTRY OF FORESTED CATCHMENTS1
Vol. 25 (1997), pp. 23–59More Less▪ Abstract“The song of a river ordinarily means the tune that waters play on rock, root, and rapid. …This song of the waters is audible to every ear, but there is other music in these hills, by no means audible to all. To hear even a few notes of it you must first live here for a long time, and you must know the speech of hills and rivers. Then on a still night, when the campfire is low and the Pleiades have climbed over rimrocks, sit quietly and listen for a wolf to howl, and think hard of everything you have seen and tried to understand. Then you may hear it—a vast pulsing harmony—its score inscribed on a thousand hills, its notes the lives and deaths of plants and animals, its rhythms spanning the seconds and the centuries.” Aldo Leopold, Song of the Gavilan [Reprinted in part from (Leopold (1940), by permission of The Wildlife Society.]
The pathways that water may take through a catchment and its reactions with organisms and soils are myriad and ever varying. A promising means to unraveling the mystery of watershed hydrochemistry is the study of “small” catchments, yet the hydrochemical function of even the smallest of catchments involves an amazingly intricate web of flowpaths and biogeochemical processes. Monitoring of catchments and comparison of their inputs to their outputs yields clues to their workings. Manipulation of catchments offers some means of “controlled” experimentation as to their nature. Modeling of catchment hydrochemical response attempts to put it all together. Every forested catchment is individual in its structure and hydrochemical response, yet a select, carefully studied few often are drafted to serve as representatives in assessments of responses to environmental influences or perturbations (e.g. acid rain). Many factors must be considered in such extrapolations. Studies of forested catchments often are driven by environmental concerns and thus fluctuate accordingly as to their location and intensity. Despite such fluctuations, the future of the field is clear and bright. Much has been learned as a result of recent studies, not only of what to think about catchment function but, more importantly, how to think about it.
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CHONDRULES
Vol. 25 (1997), pp. 61–83More Less▪ AbstractChondrules are ∼1-mm igneous droplets in primitive meteorites, and their abundance suggests widespread melting in the protoplanetary disk. Chondrules with relict unmelted grains or igneous rims record multi111ple melting events. There are two main types of chondrules, type I (FeO-poor and volatile-poor) and type II [FeO-rich and approximately chondritic (solar) in composition]. Type I chondrules in the unmetamorphosed chondrite Semarkona show evidence of evaporative loss with regard to the moderately volatile elements. Loss of S produces much of the FeNi metal in chondrules. Though the finest grained type I and II chondrules in Semarkona are both approximately chondritic in bulk composition, they differ in FeO content of olivine, indicating different precursors. Simulations suggest temperatures of chondrule formation of 1550–1900°C, with short (<1 min) heating times. Short-lived isotopes suggest that chondrules formed relatively late, and nebular shock waves are the current favorite heating mechanism. As chondrules were transported to the midplane more easily than fine dust or fluffy aggregates, they were probably important components in building planets.
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DEBRIS-FLOW MOBILIZATION FROM LANDSLIDES1
Vol. 25 (1997), pp. 85–138More Less▪ AbstractField observations, laboratory experiments, and theoretical analyses indicate that landslides mobilize to form debris flows by three processes: (a) widespread Coulomb failure within a sloping soil, rock, or sediment mass, (b) partial or complete liquefaction of the mass by high pore-fluid pressures, and (c) conversion of landslide translational energy to internal vibrational energy (i.e. granular temperature). These processes can operate independently, but in many circumstances they appear to operate simultaneously and synergistically. Early work on debris-flow mobilization described a similar interplay of processes but relied on mechanical models in which debris behavior was assumed to be fixed and governed by a Bingham or Bagnold rheology. In contrast, this review emphasizes models in which debris behavior evolves in response to changing pore pressures and granular temperatures. One-dimensional infinite-slope models provide insight by quantifying how pore pressures and granular temperatures can influence the transition from Coulomb failure to liquefaction. Analyses of multidimensional experiments reveal complications ignored in one-dimensional models and demonstrate that debris-flow mobilization may occur by at least two distinct modes in the field.
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THE EVOLUTION OF THE ALTIPLANO-PUNA PLATEAU OF THE CENTRAL ANDES
Vol. 25 (1997), pp. 139–174More Less▪ AbstractThe enigma of continental plateaus formed in the absence of continental collision is embodied by the Altiplano-Puna, which stretches for 1800 km along the Central Andes and attains a width of 350–400 km. The plateau correlates spatially and temporally with Andean arc magmatism, but it was uplifted primarily because of crustal thickening produced by horizontal shortening of a thermally softened lithosphere. Nonetheless, known shortening at the surface accounts for only 70–80% of the observed crustal thickening, suggesting that magmatic addition and other processes such as lithospheric thinning, upper mantle hydration, or tectonic underplating may contribute significantly to thickening. Uplift in the region of the Altiplano began around 25 Ma, coincident with increased convergence rate and inferred shallowing of subduction; uplift in the Puna commenced 5–10 million years later.
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BETA PICTORIS: An Early Solar System?
Vol. 25 (1997), pp. 175–219More Less▪ AbstractBeta Pictoris (βPic) is the best studied of the normal main-sequence stars surrounded by circumstellar dust disks. We review the status of βPic and its disk, and compare it with both the early and the present Solar System. The disk has very little gas and therefore is more evolved and older than the primordial solar nebulae, which persist for 1–10 Myr. We concentrate on the observed optical properties, spatial and size distribution, mineralogy, and physics of the dust component, all of which are similar, if not identical, to those of the interplanetary and cometary dust in the Solar System. The most important process in the disk is collisional fragmentation of orbiting solid bodies, leading to the eventual removal of micron-sized and smaller debris from the system by radiation pressure. Silicate dust and sand, as well as planetesimals (perhaps comets) are observed around the star in quantities that are orders of magnitude larger than those in the present Solar System, but are consistent with a young solar system in the clearing stage. Theory of the βPic disk indicates that its age must be <100 Myr, and its mass comparable with that of all solid bodies in our system. Several indirect arguments support the hypothetical existence of planet(s) in orbit around the star. Our current knowledge strongly suggests a positive answer to the title question.
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THERMODYNAMIC MODELS OF IGNEOUS PROCESSES
Vol. 25 (1997), pp. 221–241More Less▪ AbstractThermodynamic modeling alone cannot uniquely characterize the evolution path (T-P-t path) of a magmatic system, because the assumption of reaction reversibility precludes recovery of the history of that evolution from the final state that is preserved in the rock record. Nevertheless, as a tool for discriminating possible scenarios for magma evolution, such models are informative. This point is illustrated with two examples: The first involves modeling equilibrium and fractional crystallization of midocean ridge basalts. Attention is focused on the variation of intensive parameters (like oxygen fugacity) and heat output with crystallization, and how the latter can impact fluid dynamical modeling. The second example illustrates modeling mantle metling during closed-system adiabatic ascent. Here thermodynamic modeling leads to quantitative predictions of melt productivity, which may be used to interpret melt generation rates and chemical characteristics of lavas produced from volcanic centers.
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DETERMINATION OF THE COMPOSITION AND STATE OF ICY SURFACES IN THE OUTER SOLAR SYSTEM1
Vol. 25 (1997), pp. 243–277More Less▪ AbstractTelescopic data combined with data gathered by spacecraft has brought worlds as distant as Pluto and the Kuiper belt objects under increasingly close scrutiny. Of particular interest here is the progress that has been made in our understanding of the properties of the satellites of the giant planets. As such, the purpose of this chapter is to review the present understanding of the nature of icy surfaces in the outer solar system, the ongoing processes that affect the composition, distribution, and physical state of volatiles on icy surfaces, and new techniques for probing the mysteries of the origin and evolution of icy bodies in the Solar System.
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HYDROLOGICAL MODELING OF CONTINENTAL-SCALE BASINS
Vol. 25 (1997), pp. 279–300More Less▪ AbstractRecent increased interest in the role of the land surface in weather and climate, including impacts due to climate change, has resulted in land surface hydrologic models that incorporate processes which describe the exchange of water and energy at the Earth's surface. The development of a grid-based hydrological model with a full soil-vegetation-atmospheric-transfer (SVAT) land surface parameterization is summarized. The model is suitable both for simulating continental-scale river basins at high temporal and spatial resolutions and as the land surface parameterization in atmospheric general circulation models (AGCMs). Results for the Missouri River basin show the model can successfully simulate hydrological fluxes (e.g. streamflows and evaporation) for large catchments.
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GPS APPLICATIONS FOR GEODYNAMICS AND EARTHQUAKE STUDIES
Vol. 25 (1997), pp. 301–336More Less▪ AbstractGeodetic measurements obtained with the Global Positioning System (GPS) are increasingly more widely applied in geophysical studies. In this paper, we review the changes to the technology of GPS geodesy over the last five years that are responsible for this increased applicability. We survey geophysical investigations employing GPS to measure coseismic, postseismic, and interseismic deformation; plate motion and crustal deformation at plate boundaries; volcano deformation; and the deformation associated with glacial isostatic adjustment and its application to sea-level studies. We emphasize the use of GPS determinations for the modeling of this wide variety of geophysical phenomena. We also discuss the recent advent of permanent GPS networks for regional geophysical studies, as well as the possible future of GPS surveying in light of the recent advances.
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STRATIGRAPHIC RECORD OF THE EARLY MESOZOIC BREAKUP OF PANGEA IN THE LAURASIA-GONDWANA RIFT SYSTEM
Vol. 25 (1997), pp. 337–401More Less▪ AbstractRift basins of the Central Atlantic Margins (CAM) of North America and Morocco preserve largely continental sequences of sedimentary strata and less important minor basalt flows spanning much of the early Mesozoic. The best known is the Newark basin of New Jersey, New York, and Pennsylvania where an astronomically calibrated magnetic polarity time scale is developed.
Lacustrine cycles of Milankovitch origin are commonly present in CAM basins, with the period changing from 10 ky (paleoequator with coals), to 20 ky (4°–10°N), to perhaps 40 ky northward with evaporites. Cycles of ∼100 ky, 413 ky, and ∼2 my are also important.
Four mostly unconformity-bounded tectonostratigraphic sequences are present. The Anisian TS I is fluvial and eolian. TS II–TS IV (Late Triassic to Early Jurassic) consist of “tripartite” lacustrine sequences caused by extension pulses. The Newark basin accumulation rate history allows comparison with quantitative rift basin models.
The North American plate's slow northward drift resulted in a relative shift of climate, although the rapid humidification during the latest Triassic and Early Jurassic is associated with a sea-level rise. The Triassic-Jurassic mass extinction is of independent origin, plausibly impact related.
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SEDIMENT BACTERIA: Who's There, What Are They Doing, and What's New?
Vol. 25 (1997), pp. 403–434More Less▪ AbstractThe prokaryotes (bacteria) comprise the bulk of the biomass and chemical activity in sediments. They are well suited to their role as sediment chemists, as they are the right size and have the required metabolic versatility to oxidize the organic carbon in a variety of different ways. The characteristic vertical nutrient (electron donor and electron acceptor) profiles seen in sediments are produced as a result of microbial activities, with each nutrient a product or reactant of one or more metabolic groups. Thus, understanding the mechanisms by which the chemical environment of a sediment is generated and stabilized requires a knowledge of resident populations, something that has been very difficult to obtain, given the techniques available to microbiologists. However, the new approaches of molecular biology, which have added insights into the phylogenetic relationships of the prokaryotes, have also provided tools whereby sedimentary populations can be examined without the need for culturing the organisms. These techniques, in concert with new methods of microscopy, isolation of new metabolic groups, and the study of new ecosystems, suggest that there is much that will be learned about the microbiology of sedimentary environments in the coming years.
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THE ORIGIN AND EVOLUTION OF DINOSAURS
Vol. 25 (1997), pp. 435–489More Less▪ AbstractPhylogenetic studies and new fossil evidence have yielded fundamental insights into the pattern and timing of dinosaur evolution and the emergence of functionally modern birds. The dinosaurian radiation began in the Middle Triassic, significantly predating the global dominance of dinosaurs by the end of the period. The phylogenetic history of ornithischian and saurischian dinosaurs reveals evolutionary trends such as increasing body size. Adaptations to herbivory in dinosaurs were not tightly correlated with marked floral replacements. Dinosaurian biogeography during the era of continental breakup principally involved dispersal and regional extinction.
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Previous Volumes
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Volume 52 (2024)
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Volume 51 (2023)
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Volume 50 (2022)
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Volume 49 (2021)
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Volume 48 (2020)
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Volume 47 (2019)
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Volume 46 (2018)
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Volume 45 (2017)
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Volume 44 (2016)
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Volume 43 (2015)
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Volume 42 (2014)
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Volume 41 (2013)
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Volume 40 (2012)
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Volume 39 (2011)
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Volume 38 (2010)
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Volume 37 (2009)
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Volume 36 (2008)
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Volume 35 (2007)
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Volume 34 (2006)
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Volume 33 (2005)
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Volume 32 (2004)
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Volume 31 (2003)
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Volume 30 (2002)
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Volume 29 (2001)
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Volume 28 (2000)
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Volume 27 (1999)
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Volume 26 (1998)
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Volume 25 (1997)
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Volume 24 (1996)
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Volume 23 (1995)
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Volume 22 (1994)
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Volume 21 (1993)
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Volume 20 (1992)
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Volume 19 (1991)
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Volume 18 (1990)
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Volume 17 (1989)
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Volume 16 (1988)
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Volume 15 (1987)
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Volume 14 (1986)
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Volume 13 (1985)
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Volume 12 (1984)
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Volume 11 (1983)
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Volume 10 (1982)
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Volume 9 (1981)
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Volume 8 (1980)
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Volume 7 (1979)
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Volume 6 (1978)
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Volume 5 (1977)
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Volume 4 (1976)
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Volume 3 (1975)
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Volume 2 (1974)
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Volume 1 (1973)
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Volume 0 (1932)