On Selection of Analog Volcanoes     

Armando Rodado  Mark Bebbington  Alasdair Noble  Shane Cronin  Gill Jolly 《Mathematical Geosciences》2011,43(5):505-519

Estimating the occurrence probability of volcanic eruptions with VEI ??3 is challenging in several aspects, including data scarcity. A?suggested approach has been to use a simple model, where eruptions are assumed to follow a Poisson process, augmenting the data used to estimate the eruption onset rate with that from several analog volcanoes. In this model the eruption onset rate is a random variable that follows a gamma distribution, the parameters of which are estimated by an empirical Bayes analysis. The selection of analog volcanoes is an important step that needs to be explicitly considered in this model, as we show that the analysis is not always feasible due to the required over-dispersion in the resulting negative binomial distribution for the numbers of eruptions. We propose a modification to the method which allows for both over-dispersed and under-dispersed data, and permits analog volcanoes to be chosen on other grounds than mathematical tractability.  相似文献   

Towards a comprehensive distal andesitic tephrostratigraphic framework for New Zealand based on eruptions from Egmont volcano     

Phil Shane 《第四纪科学杂志》2005,20(1):45-57

The chronology and glass composition of 43 andesitic tephra layers in palaeolake sediments in northern New Zealand provide the basis for a fine‐resolution tephrostratigraphy of the interval 10–70 cal. ka. Their ages are constrained by 14 interbedded, (mostly) well‐dated rhyolitic tephra layers. The andesitic tephra have the potential to subdivide time intervals (1–5 kyr) bracketed by well known rhyolitic layers, including periods of rapid climate change such as the last glacial–interglacial transition and the Younger Dryas. The source of the distal andesitic tephra is identified as Egmont volcano (some 270 km S‐SW) on the basis of glass shard composition. The tephra contain high‐K₂O (3–6 wt%) andesitic‐dacitic (SiO₂ = 60–73 wt%) glass, with commonly heterogeneous shard populations (2–10 wt% SiO₂). Within stratigraphic intervals of < 10 kyr, individual tephra layers can be distinguished on the basis of their SiO₂ and K₂O contents, and variability in these contents can also be a distinguishing characteristic. The tephra record greatly extends the dated pyroclastic and geochemical record of Egmont volcano, and demonstrates that the volcano has frequently produced widely dispersed tephra over the last 70 kyr at a generally constant rate. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Chronological and palaeomagnetic constraints on widespread welded ignimbrites of the Taupo volcanic zone,New Zealand     

Tasha M. Black  Philip A. R. Shane  John A. Westgate  Paul C. Froggatt 《Bulletin of Volcanology》1996,58(2-3):226-238

 Large volume (100–1000 km³), widespread rhyolitic ignimbrites are the main products of the Taupo volcanic zone (TVZ) of New Zealand, one of the most active silicic volcanic regions on Earth. Several factors have made correlation and the eruptive history of the ignimbrites difficult to resolve, including limited exposure and chronological data, broadly similar lithologies and the lack of stratigraphic successions visible in the field. We have used the isothermal plateau fission track (ITPFT) method on glass shards from the non-welded basal zones to obtain new eruption ages for the widespread units: Ongatiti (1.25±0.12 Ma), Whakamaru group (0.34±0.03 Ma), Matahina (0.34±0.02 Ma), Chimp (0.33±0.02 Ma), Kaingaroa (0.31±0.01 Ma) and Mamaku (0.23±0.01 Ma) ignimbrites. These glasses show little evidence of geochemical alteration and allow the units to be fingerprinted for correlation. The glass ages we have obtained for the late Quaternary units provide an independent check on chronological data obtained from phenocryst phases. The ITPFT method is a useful dating approach for sanidine-poor eruptives which limit the application of ⁴⁰Ar/³⁹Ar. Errors as limited as 10–30 ka can be obtained from the weighted mean of several age determinations. The thermoremanent magnetic (TRM) direction recorded in the units provides a means of correlation over a wide area of the TVZ, because each ignimbrite can be distinguished by its unique record of palaeosecular variation. These data indicate that the four separately mapped members of the Whakamaru group represent the same phase of activity, occurring within a period of 100 years. The TRM data indicate that the widespread Ahuroa ignimbrite erupted during an excursion in Earth's magnetic field, perhaps associated with the Cobb Mountain subchron (ca. 1.2 Ma). The youngest widespread welded unit, Mamaku ignimbrite (ca. 0.23 Ma), also erupted during an excursion and may represent a southern hemisphere record of the Pringle Falls geomagnetic episode found in the western United States. The palaeomagnetic and ITPFT data for the widespread late Quaternary ignimbrites suggest a major period of caldera formation at 0.34–0.30 Ma. This interval represents the eruption of multiple units from the Whakamaru caldera, followed by the formation of the Okataina and Reporoa calderas in rapid succession. Received: 20 November 1995 / Accepted: 8 May 1996  相似文献   

Initial exploration results of the Collins epithermal Au-base metal prospect,Aceh, Indonesia     

Thomas Mulja  Shane Ebert  Lee A. Groat 《Resource Geology》2022,72(1):e12277

Interpretation of various exploration data, in particular geochemical prospecting, offers a powerful and rapid assessment of grass-root projects in a green-field terrain. Here, we present an example of the Collins epithermal prospect in Aceh Province, Indonesia. In this area, the Au+ base-metal-bearing sheeted quartz veins (individually mostly 2–4 cm wide), which are controlled by a 250 m wide by 800 m long NNE-trending structural corridor within Paleogene sandstone and volcanic rocks, are the product of two main stages of deposition. Stage I formed veins with a sliver of cryptocrystalline quartz wall zone followed by an inner zone of comb quartz with interstitial rhombic adularia that terminates in open space. Stage I or main-stage sulfide mineralization consisting of early galena + sphalerite and later chalcopyrite occurs with the quartz + adularia. Small amounts of galena also occur in the wall zone. Stage II mineralization brecciated Stage I veins and overprinted them with silicification characterized by vuggy texture. Mineralization associated with this episode consists of earlier chalcopyrite + sphalerite + tennantite–tetrahedrite and later, vug-filling Au–Ag alloy (Ag_0.37–0.41Au_0.62–0.59). The above mineralized veins are successively flanked by silicic selvages, an illite + chlorite + pyrite ± kaolinite zone and a chlorite + epidote + carbonate + pyrite zone. Local supergene alteration induced replacement of galena by plumbogummite and anglesite and chalcopyrite by covellite. Data from fluid inclusion microthermometry in quartz indicated that the inner zone of Stage I veins formed from fluids with a 2.3 wt% salinity (0.5–3.3 wt% NaCl equivalent), at 174°C (155–211°C). Combining these physico-chemical parameters with the mineral assemblage, the mineralization occurred under a reduced environment. Rock and soil assays indicate that elevated Au concentrations (up to 16.5 ppm over 1 m) occur along northeast-trending zones and show a strong correlation with Pb, while Cu (up to 2.58% over 1 m), Zn, As, Sb, and Mo anomalies lie mostly at the periphery. The high-grade mineralized veins correlate with moderate to high resistivity and chargeability zones, and the pseudosections of such geophysical signals are interpreted as reflecting coalesced or enlarged veins at depth, or inclined veins in other localities. The intermediate sulfidation affinity for Collins points to potential mineralization at depth as well as preservation of Au-rich and sulfide-poor zones in the less eroded areas.  相似文献   

Spatio-temporal hazard estimation in the Auckland Volcanic Field,New Zealand,with a new event-order model   总被引：1，自引：1，他引：0  

Mark S. Bebbington  Shane J. Cronin 《Bulletin of Volcanology》2011,73(1):55-72

The Auckland Volcanic Field (AVF) with 49 eruptive centres in the last c. 250 ka presents many challenges to our understanding of distributed volcanic field construction and evolution. We re-examine the age constraints within the AVF and perform a correlation exercise matching the well-dated record of tephras from cores distributed throughout the field to the most likely source volcanoes, using thickness and location information and a simple attenuation model. Combining this augmented age information with known stratigraphic constraints, we produce a new age-order algorithm for the field, with errors incorporated using a Monte Carlo procedure. Analysis of the new age model discounts earlier appreciations of spatio-temporal clustering in the AVF. Instead the spatial and temporal aspects appear independent; hence the location of the last eruption provides no information about the next location. The temporal hazard intensity in the field has been highly variable, with over 63% of its centres formed in a high-intensity period between 40 and 20 ka. Another, smaller, high-intensity period may have occurred at the field onset, while the latest event, at 504 ± 5 years B.P., erupted 50% of the entire field’s volume. This emphasises the lack of steady-state behaviour that characterises the AVF, which may also be the case in longer-lived fields with a lower dating resolution. Spatial hazard intensity in the AVF under the new age model shows a strong NE-SW structural control of volcanism that may reflect deep-seated crustal or subduction zone processes and matches the orientation of the Taupo Volcanic Zone to the south.  相似文献   

The surface of Mars,by Michael H. Carr     

Shane Byrne 《Meteoritics & planetary science》2007,42(12):2181-2182

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Impacts of volcanism on pre-European inhabitants of Taveuni, Fiji     

Shane J. Cronin  Vincent E. Neall 《Bulletin of Volcanology》2000,62(3):199-213

 Taveuni is a Fijian ocean-island volcano that sporadically erupted throughout the Holocene. The 437-km² island is an active monogenetic volcanic field with a constantly shifting locus of activity along a single apparent rift axis. Although the eruptions were not large ( ≤VEI 2), unexpected shifts in Taveuni volcanism had the potential to affect habitation sites. Since known human settlement of the Fiji Group (ca. 950–750 BC), there have been at least 58 eruptions on Taveuni. Up to 25 of these eruptions potentially affected pre-European inhabitants of the island and at least four former occupation sites are known to have been affected by volcanic products. Despite apparent earliest settlement of Taveuni post-dating other nearby islands by up to 600 years, volcanism probably did not hinder or stall settlement of Taveuni compared with neighbouring islands. However, a period of voluminous eruptions between 300 and 500 AD covered much of south Taveuni with lava and/or thick tephra, apparently causing abandonment of at least this portion of Taveuni until approximately 1100 AD. Most eruptions were not of catastrophic proportions and, due to their localised effects, re-settlement was rapid in marginal unaffected areas. Localised stories and a relict place name survive to describe former eruption locations and effects since approximately 120–320 AD. Knowledge of the impacts on Taveuni's past inhabitants forms the basis of volcanic disaster-mitigation strategies to minimise future effects on the current 14,500 residents. Received: 9 September 1999 / Accepted: 21 February 1999  相似文献   

Galaxy magnitudes     

Gerald E. Kron  C. D. Shane 《Astrophysics and Space Science》1976,39(2):401-407

Systematic corrections to the magnitudes of galaxies in the Zwicky and the Shapley-Ames catalogues have been determined and are tabulated here. The corrections are based on the photographic measures by Holmberg, published photoelectric measures, and 392 photoelectric measures by Kron and Shane. These latter are mostly in the fainter magnitude range. The corrections for Volume I of the Zwicky Catalogue differ substantially from those for Volumes II to VI.  相似文献   

Predicting the effects of shade on water temperature in small streams     

J. Christopher Rutherford  Shane Blackett  Colin Blackett  Laurel Saito  Robert J. Davies‐Colley 《新西兰海洋与淡水研究杂志》2013,47(5):707-721

A computer model for stream water temperature was developed, and tested in a small pasture stream near Hamilton, New Zealand. The model quantifies shading by riparian vegetation, hillsides, and stream banks using three coefficients: canopy angle, topography angle, and canopy shade factor. Shade was measured directly and found to vary significantly along the channel. Using the maximum measured shade, a close match was achieved between observed and predicted daily maximum and minimum water and bed sediment temperature. Model predictions of incoming and outgoing long‐wave radiation flux closely matched measurements, but there were unexplained discrepancies in short‐wave radiation flux. Model predictions indicate that moderate shade levels (c. 70%) may be sufficient in temperate climates to restore headwater pasture stream temperatures to 20°C, an estimate of the thermal tolerance for sensitive invertebrates.  相似文献   

Coleoptera and microbe biomass in Antarctic Dry Valley paleosols adjacent to the Inland Ice: Implications for Mars     

William C. Mahaney  Kris M. Hart  Shane S. O'Reilly  Christopher C.R. Allen  James M. Dohm  Ronald G.V. Hancock  Brian P. Kelleher  Michael W. Milner 《Planetary and Space Science》2012,60(1):386-398

Bulk paleosol samples collected from a Middle to Early Miocene moraine in the New Mountain area of the Dry Valleys, Antarctica, yielded Coleoptera exoskeletons and occasional endoskeletons showing considerable diagenetic effects along with several species of bacteria, all lodged in a dry-frozen but salt-rich horizon at shallow depth to the land surface. The till is at the older end of a chronologic sequence of glacial deposits, thought to have been deposited before the transition from wet-based to cold-based ice (～15 Ma), and hence, entirely weathered in contact with the subaerial atmosphere. It is possible, though not absolutely verifiable, that the skeletons date from this early stage of emplacement having undergone modifications whenever light snowmelt occurred or salt concentrations lowered the freezing temperature to maintain water as liquid. Correlation of the Coleoptera species with cultured bacteria in the sample and the likelihood of co-habitation with Beauveria bassiani found in two adjacent, although younger paleosols, leads to new questions about the antiquity of the Coleoptera and the source of N and glucose from chitinase derived from the insects. The skeletons in the 831 section may date close to the oldest preserved chitin (Oligocene) yet found on Earth. While harsh Martian conditions make it seemingly intolerable for complex, multicellular organisms such as insects to exist in the near-surface and subaerially, life within similar cold, dry paleosol microenvironments (Cryosols) of Antarctica point to life potential for the Red Planet, especially when considering the relatively diverse microbe (bacteria and fungi) population.  相似文献